!,.,~
i
".'. 'i! 'i
KAISER ALUMINUM ELECTRICAL BUS CONDUCTORS TECHNICAL MANUAL
}
'.I
,::,,,';'
KAISER ALUMINUM ELECTRICAL BUS CONDUCTORS TECHNICAL MANUAL
FIRST EDITION
KAISER ALUMINUM & CHEMICAL SALES, INC. 919 North Michigan Avenue Chicago 11, Illinois
, y.
EDITORIAL ACKNOWLEDGEMENT Information presented in this book was compiled and written by Chester G. Sorflaten, Electrical Condnctor Sales, Kaiser Alnminum & Chemical Sales, Inc., as a company service to the Electrical Indnstry. Factual data have been obtained from numerous individuals and companies whose help and cooperation Kaiser Aluminuul gratefully recognize. In addition, acknowledgement is offered to the othel' personnel throughout this company and the complete staff of the Technical Publications Department whose combined efforts have made this book possible.
J. M.
AnLE,
Technical Editor
,.{
Copyright 1957
by Kaiser Aluminum & Chemical Sales, Inc.
TABLE OF CONTENTS Page
Page
SECTION I: General.
1-13
Dt . . 0 f~ R' e ermmation
.
27
dc
ALLOY CHARACTERISTICS AND PROPERTIES. .. Physical Properties : . . . . .. Electrical Properties . . , , .. Conductivity . . . . . . . . . . . . . . . . . .. Resistivity Thermal Properties of Aluminum Bus Conductors. . . .. Temperature Coefficient of Resistance. . . . . . . . . . .. , . . . . . . . . . . . . . . . . . .. Specific Heat ,............. Thermal Conductivity Effect of Heating on Tensile Strength. . . . . . . . . . . .. '" ,. '" . Creep Conosion Resistance General Classes of Bus Conductor Alloys. . . . . . . . . . .. Non-Heat-Treatable Bus Alloys .. ,. ... . .. . .... .. Temper Designation for Non-Heat-Treatable Bus Bar Alloys. . . . . . . . . . . . . . . . . . . . . . . . . .. Heat-Treatable Bus Alloys. . . . . . . . . . . . . . . . . . . .. Temper Designations for Heat-Treatable Bus Bar Alloys. . . . . . . . . . . . . . . . . . . . . . . . . ..
1 1 2 2 2 2 2 3 3 4 5 5 6 6 6 6
Problem No.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27 INDUCTIVE REACTANCE OF BUS CONDUCTORS. Solid Round and Round Tubular Bus Conductors. . . .. Inductive Reactance to a One-foot Radius. . . . . . . .. " Inductive Reactance Spacing Factor Geometric Mean Distance (GMD). . . . . . . . . . . . .. Inductive Reactance of Rectangular Bars. . . . . . . . . .. Graphical Solution Using Reactance Curves. . . . . .. Methods of Calculation. . . . . . . . . . . . . . . . . . . . . . .. Widely Spaced Conductors. . . . . . . . . . . . . . . . . . . .. Inductive Reactance of Square Tubular Conductors and Channels in Box Form. . . . . . . . . . . . . . . . . .. Method of Calculation. . . . . . . . . . . . . . . . . . . . . . . .. Graphical Solution Using Reactance Curves ..... " Problem No.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
8 8 8 9 9 9 9 10 10 10 10 11 11 11 11 12 12 12 12
MANUFACTURING PROCESS AND TOLERANCES .. Extruded Bar and Shapes. . . . . . . . . . . . . . . . . . . . . . . .. Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . .. Rolled Bar and Structural Shapes. . . . . . . . . . . . . . . . ..
12 13 13 13
35 35 35 38
BUS IMPEDANCE : Problem No.4 Voltage Drop-Vectorial Relationship. . . . . . . . . . . . .. '" , Problem No.5
39 39 39 40
CURRENT RATING OF BUS CONDUCTORS Current Rating of Round Conductors. . . . . . . . . . . . .. Heat Loss by Convection-Outdoor Rating Heat Loss by Convection-Indoor Rating. . . . . . . .. Heat Loss by Radiation. . . . . . . . . . . . . . . . . . . . . . .. Method of Calculation. . . . . . . . . . . . . . . . . . . . . . . .. Limitations of Round Conductors-Solid and Tubular Cunent Rating of Rectangular Bar. . . . . . . . . . . . . . . .. Effect of Width of Bar on its Cunent Rating. . . . . .. Effect of Bar Thickness on Current Rating. . . . . . . .. , Effect of Position on Cunent Rating Cunent Ratings of Multiple Bar Arrangements. . . . . .. Current Rating for Square Tubular Bus. . . . . . . . . . . .. Current Rating for Standard Channels and Angles. . .. Cunent Rating for Non-Standard Bus Shapes Conversion Factors .Effect of Bus Enclosures. . . . . . . . . . . . . . . . . . . . . . . .. Effect of Painting Bus Bars. . . . . . . . . . . . . . . . . . . . . ..
40 41 41 41 42 42 43 43 43 44 44 46 46 46 46 46 48 49
SECTION III: Mechanical Design SECTION II: Electrical Design
29 29 29 30 30 30 30 34 35
7
BUS CONDUCTOR SHAPES " Rectangular Bar . . . . . . . . . . . . . . . . . . . . . . . . . .. Edge Contours Alumimun Rectangular Bar Alloys. . . . . . . . . . . . . .. Alloy Selection . . . . . . .. Bending Properties . . . . . . . . . . . . . . . . . . . . . . . . . .. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Round Tubular Conductor. . . . . . . . . . . . . . . . . . . . . .. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . .. Alloys Bending Properties " Square Tubular Conductor. . . . . . . . . . . . . . . . . . . . . .. Electrical Characteristics . . . . . . . . . . . . . . . . . . . . .. Alloys : . . . . . . . . . . . . . . . . . . . . . . .. Channel and Angle Conductor. . . . . . . . . . . . . . . . . . .. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Alloys Fabrication Other Conductor Shapes. . . . . . . . . . . . . . . . . . . . . . . ..
15-49
D-C RESISTANCE OF BUS CONDUCTORS Calculation of D-C Resistance. . . . . . . . . . . . . . . . . . .. Problem No.!. " Temperature Conversion of D-C Resistance " Temperature Coefficient of Resistance (it)
15 16 16 16 17
A-C RESISTANCE OF BUS CONDUCTORS Skin Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Effect of Bus Shape and Size on A-C Resistance. . . . .. Rectangular Bars Tubular Conductors . . . . . . . . . . . . . . . . .. . . . . . . .. Channels and Angles Arranged in Box Form. . . . . .. Calculation of A-C Resistance Independent Variable . . . . . . . . . . . . . . . . . . . . . . . .. Shape Parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
18 20 20 20 21 23 23 23 27
~'
,.r·
51-72
SHORT CIRCUIT FORCES oN BUS CONDUCTORS. Lateral Forces , Value of k Short Circuit Cunent. . . . . . . . . . . . . . . . . . . . . . . .. Symmetrical Currents . . . . . . . . . . . . . . . . . . . . . . . .. Asymmetrical Currents . . . . . . . . . . . . . . . . . . . . . . .. '. . . . . . . . .. Effective Current NEMA Standards . . . . . . . . .. Calculation of Fault Current. . . . . . . . . . . . . . . . . . . . .. Calculation of Lateral Short Circuit Forces , Force between Two Conductors. . . . . . . . . . . . . . . .. Force on End Conductor of Three-Phase Bus Spaced Horizontally . . . . . . . . . . . . . . . . . . . . . . .. Force on Center Conductor of a Three-Phase , Bus with Flat Symmetrical Arrangement Forceon Each Conductor in a Multiple Bar Arrangement
51 51 52 52 52 52 54 54 55 56 56 56 56 58
\
Page
I
,!
, !.
Vibration and Resonance , Stress Factors Longitudinal Forces Torsional Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
59 59 60 61
BUS DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Clearances " Deflections of Bus Conductors Bare and Loaded " Bus Loading-Ice and Wind Ice Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. " Combined Ice and Wind Load Formulas for Deflection and Stress of Bus Conductors. Calculation of Deflection and Stress in a Typical Bus Installation " Expansion of Aluminum Bus Conductors " Calculation of Bus Expansion. . . . . . . . . . . . . . . . . .. Types of Expansion Joints. . . . . . . . . . . . . . . . . . . . .. Application of Expansion Joints " Methods of Support for Buses. . . . . . . . . . . . . . . . . . . .. Fixed Supports in Center Only " Fixed Supports at One End Only " Fixed Supports at Both Ends. . . . . . . . . . . . . . . . . .. Fixed Supports at Intermediate Points " Fixed Supports at!Center and Both Ends. . . . . . . . ..
61 61 62 63 63 63 65 65
SECTION IV: Joining Bus Conductors
69 70 70 71 72 72 72 72 72 72 72
73-103
PREPARING ALUMINUM CONTACT SURFACES Aluminum to Copper Joints , , . .. Silver Plated Contact Surfaces Other Methods of Surface Preparations
73 74 74 74
JOINT RESISTANCE Total Joint Resistance. . . . . . . . . . . . . . . . . . . . . . . . . .. Contact Resistance for a Uniformly Applied Pressure . . . . . . . . . . . . . . . . .. Metal Resistance in a Lapped Joint with Uniformly Applied Pressure Joint Resistance of Bolted Bus Bars , Effect of Overlap on Bolted Bus Bars. . . . . . . . . . ..
75 75 75 76 77 77
77 77 , 78
JOINT BOLTING PRESSURE Distribution of Applied Force in a Bolted Joint Bolting Methods
JOINT DESIGN , . . . . . . . . . . . . . . . . . . . . . . .. Heating in a Typical Bus Joint. Effect of Heating in a Bus Joint. Current Limitation per Bolt , '" , Design of a Lapped Joint" Multiple Bars per Phase , ,, Joint with Silver Plated Surfaces "
79 79 79 80 80 80 81
CLAMPING FORCES DEVELOPED BY BOLTS ..... Joint Stresses Developed by Bolted Clamping Forces.. Reducing Joint Stresses with Flat Washers ,. Strength Characteristics of Fasteners , . .. Aluminum Bolts Steel Bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
81 81 83 83 83 84
BELLEVILLE SPRING WASHERS. . . . . . . . . . . . . . .. Belleville Washer Design , , . . . .. Belleville Spring Materials and Finish Selection of a Belleville Washer , "
85 85 86 86
WELDING ALUMINUM BUS BAR Melting Point and Thermal Capacity .. ,
87 , .. 87
Page
Thermal Conductivity 87 Oxide Films , 88 Porosity 88 Thermal Expansion and Contraction. . . . . . . . . . . . . .. 88 Effects of Welding Heat on Bus Bar Properties. . . . . .. 88 Preparing Aluminum Bus Bar for Welding ..... " ... 89 Joint Design and Edge Preparation. . . . . . . . . . . . .. 89 Cleaning of Welding Surfaces , '" ., .. " 89 Preheat ' , . .90 Choice of Welding Method 90 Welding Methods for Aluminum Bus Bar. . . . . . . . . .. 90 Gas Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 90 Equipment for Gas Welding 90 90 Gas Flame Adjustment , Filler Rods , .. ,................. 91 Welding Flux , , .. , 91 Edge Preparation ahd Cleaning before Welding 91 Preheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93 Welding Procedure 93 Cleaning after Gas We1ding. . . . . . . . . . . . . . . . . . .. 93 Physical Properties of Gas Welded Work Hardened Alloys (EC & 1100) . . . . . . . . .. . . . . .. 93 Properties of Gas Welded, Heat-Treatable Alloys (6101, 6061, & 6063) , . . . . . . . . . . . . . . . .. 93 Metallic Arc Welding , '" . " .. 94 Equipment 94 Electrodes 94 Edge Preparation and Cleaning Before Welding 94 Preheating and Welding Procedure 95 Cleaning after Metallic Arc Welding. . . . . . . . . . . .. 96 Properties of Metal Arc Welds , .. ; . . .. 96 Tungsten-Inert-Gas Welding (TIG) 96 Equipment 96 Filler Rods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96 Gas Coverage 96 Edge Preparation and Cleaning before Welding , 96 Preheating and Welding Procedures. . . . . . . . . . . .. 98 Properties of TIG Welded Bus , '" 98 Metal-Inert-Gas Welding (MIG) 98 Equipment 98 Filler Wire , , 99 Gas Coverage 99 Edge Preparation and Cleaning before Welding. . .. 99 Preheating and Welding Procedures 100 Properties of MIG Welds 100 Carbon Arc Welding 100 Atomic Hydrogen Welding 101 Resistance Welding 101 Pressure Welding 101 Joining Aluminum to Copper by Welding 101 Joint Design 102 Silver Solder Coating the Copper Bar 102 Procedures ' ~ 102 Physical Properties of Aluminum to Copper MIG Welds " 102 Exothermic Welding 102
SECTION V: Accessories Welding Fittings Bolted Accessories Tee Connectors Expansion Connectors Stud Connectors Bus Supports' ' Couplers and Terminals
105-116 ,
, .105-107 107 108-109 110-111 , .. 112-113 114-115 116
SECTION VI: Tables and Specifications . . , .117-168
.
'I r. :1
FOREWORD
..
) ,~
The wide acceptance of aluminum and its alloys in the electrical industry rests basically upon its economy and abundance. Aluminum's physical characteristics, such as high conductivity and light weight, give it unique advantages in Plany electrical applications where other non-ferrous metals formerly served exclusively. While the use of EC grade aluminum as bus bar dates back to 1895, the application of alloy aluminum bus conductor has been more recent. The various alloys and tempers now available provide a full range of properties, both elech'ical and physical, to meet practically any requirement. Aluminum bus bar is readily employed in proposed designs of new electrical systems and equipment and, in most cases, with only minor changes it can also be designed into existing systems. The primmy purpose of this book is two-fold: (1) to illustrate, describe and classify the numerous aluminum bus bar shapes and alloys now available; and (2) to assist the reader in making the most advantageous utilization of aluminum for various electrical bus bar applications. The versatility of aluminum bus bar as a rigid conductor is evidenced in the countless small installations designed to carry a few hundred' amperes to the extremely large facilities distributing currents on the order of 60,000 amperes. The smaller installations include rectangular bar in bus duct which provides service to machinery and equipment in many industrial plants. The larger facilities, such as chemical and reduction plants, require massive sections of bus bars to cany the high process currents. Selection of the most suitable alloy to provide both conductance and strength for the proposed usage is covered in Section 1. All of the common shapes of bus conductor offered by producers are described in detail. Fabricating processes, such as extrusion and cold rolling, are outlined to compare surface finish, strength characteristics, and dimensional tolerances inJparted to the alloys processed by each fabricating method. Electrical bus condu:ctor design is discussed in detail in Section II, while Section III presents mechanical design infOlmation to prove the adequacy of the proposed installation when subjected to short circuit forces and vibrational stresses, with or without additional loads such as wind pressure and accumulations of ice in outdoor conductor installations. Section IV offers methods of joining aluminum bus . C:ollductor both mechanically and by fusion processes. Emphasis has been placed upon the proper surface preparation to give low resistance, stable electrical joints; recommended bolting techniques are indicated. Fusion welding by four principal methods, .i.e., gas, metal are, tungsten inert-gas, and metal ineli-gas is described for applications where permanent electrical joints are prefened. Each welding process is covered in detail, including such subjects as preheating, edge preparation, and a practical method of welding aluminum to copper. j" Accessories commonly used for joining, supporting, tapping, and terminating bus bar are illustrated in Section V. These illustrations show the wide variety of installation methods possible with such accessories. Line drawings in this section indicate recent developments in welding fittings for bus conductor. Special attention is directed to the numerous charts, graphs, line drawings, and other illustrations. All have been handled with care both to simplify and augment text material. Numerous tables on bus bar physical and electrical properties provide a ready reference for design and application studies. . A comprehensive table of contents is presented under each section heading. July 1, 1957
ALUMINUM BUS CONDUCTORS
ALLOY CHARACTERISTICS AND PROPERTIES
I
I
I
,
,.
ing characteristics. The 59 EC temper is intended for . The abundance of aluminum ores and the rapid severe forming operations such as edge bending. Its eXpansion of aluminum production capacity are two forming properties are thus comparable to EC-H12. iUlportant factors that assure the electrical industry of a continued reliable supply of aluminum bus bar ma- These replacement alloys have somewhat less conductivity than EC grade confluctors, but their physical terials.. The reduction facilities necessary to produce properties and lower cost offset this disadvantage for ll,luminum from aluminum oxide (alumina) depend ·.upon large quantities of electrical power. It requires many applications. :N>proximately 9 kw-hr of electrical energy to produce one pound of aluminum. Since the production costs of electrical power are inherently stable, the price of Physical Properties of Aluminum .aluminum should also be stable. This is reflected in Bus Conductors ,the historical price pattern of aluminum. The many applications for aluminum bus conduc. ' As a result of this stability, aluminum has become tor demand a number of alloys with varied physical . ',the most economical of all conductor materials, and properties in addition to good electrical characteristics. .. because of this, a more extensive use of aluminum bus To supply the designer with this flexibility, several conductor has developed. Such conductor is finding its aluminum bus bar alloys are available that will pro,,!, way into manufactured electrical equipment of all vide physical properties to meet the requirements of kinds where its use heretofore had been considered most applications. This range of properties provides , neither feasible nor economical. Accompanying this alloys with high tensile strength at only a slight sacri'gradual spread of aluminum bus conductor into many fice in ductility for applications requiring high strength electrical usages has been the demand for performance but limited bending or forming properties. More duccharacteristics other"than those available with EC tile alloys for extreme bending or forming require(electrical conductor) grade aluminum. This trend has led to the development of several tempers of. a new . ments are also available where moderate tensile strengths are satisfactory. The physical properties of high strength bus bar alloy. The chemical composition these commonly used aluminum bus conductor alloys of this alloy conforms to the Aluminum Association are shown in Table L designation of alloy 6101. Four tempers of this bus These aluminum alloys have common physical conductor alloy have been developed to providl'l miniproperties important in the mechanical design of a mum conductivities of 55, 56, .57, and 59 per cent bus bar installation. One imp0rtant property is unit . . . (lACS) and physical properties superior to the EC bus weight as measured by density in pounds per cubic bar tempers which the new alloy conductors are reinch. Although other metal additions are made to placing. Kaiser Aluminum has designated these alloys some of the bus bar alloys, theYi are so small that, for as follows: all practical purposes, density. can be considered as 55EC (6101-T6); identical in all of· these alloys. The specific gravity 56EC (6101-T62); will thereby be a constant also. These properties are 57EC (6101-T61); given as: 59EC (6101-HIll). Density-lbs. per cubic inch-0.09765; The high strength tempers-55 EC and 56 EC-are Specific Gravity -2.703. replacements for EC-H17 and are intended for applications where only limited forming properties are deThe modulus of elasticity for all bus bar alloys can sired. The lower strength EC-H12 and EC-H13 alloys also be considered to have the same value, can be replaced by 57 EC and 59 EC which are more E = 10 X 106 (psi). ductile than 55 EC and 56 EC to provide better form-
1
!
section I - general
TABLE .1 -
Alloy
PHYSICAL PROPERTIES OF ALUMINUM BUS CONDUCTOR ALLOYS
Minimum
Typical
Minimum
Typical
Typical Compressive Yield Strength (psi)
Yz
29,000
32,000
25,000
29,000
28,00.0
14
Vil- Yz
27,000
290 000
22,000
26,000
25,000
14
Thickness (Inches)
55 EC
Ys-
56EC 57 EC
Ys - 0.749 0.750 - 1.499 1.500 - 2.000
59EC
-
6061-T6
-
20,000 18,000 15,000 12,000 38,000
Vil- Yz
6063-T6
Ultimate Tensile Strength (psi)
30,000 33,000
Tensile Yield Strength (psi)
Elongation in 2 Inches (Per bent)
-
15,000 11,000 8,000
-
-
-
-
-
-
8,000
-
-
35
35,000
40,000
-
12
35,000
25,000
31,000
31,000
38,000
30,000
36,000'
36,000
10
12,000
10,000
35
-
45,000
-
12
6063-T83
0.050 - 0.150
EC-H12
Vil - 1
12,000
15,000
8,000
- % Ys- Yz
14,000
17,000
12,000
16,000
14,000
20
20,000
15,000
19,000
17,000
14
EC-H13
j~
EC-H17
-
EC-H111 EC-Hl12
Vil- Y2
lh - 1 1
- 1Yz
17,000 9,000
-
4,000
-
-
12,000 11,000 10,000
-
7,000 5,000 4,000
-
-
-
* * * *
-
*Elongation of these tempers will be equal to or greater than the elongation of EC-HI2.
Electrical Properties of Aluminum Bus Bar Alloys
TABLE 2 - PERCENTAGE VOLUME CONDUC· TIVITY (lACS) OF BUS CONDUCTOR ALLOYS AT 20 C
Conductivity-The selection of a bus conductor alloy for current carrying ability is based primarily on its electrical conductivity. In 1913, the International Annealed Copper Standard (lACS) was estabUshed based on annealed copper at 20 C and designating 100 per cent volume conductivity for a rod one meter in length and one square millimeter in cross section, having a resistance of 0.017241 ohm. This is the basis for establishing the percentage conductivity of other metals and their alloys. The percentage volume conductivity of these materials will be inversely proportional to the resistance of identical specimens at 20 C, e.g., the per cent conductivity of an EC (electrical conductor) grade aluminum wire one meter long and having the same one square millimeter cross section and a resistance of 0.028264 ohm at 20 C will have a per cent volume conductivity as follows: Per Cent Conductivity of EC 0.01724:1 100% - 0.028264 Per Cent Conductivity of EC = 61%. The per cent volume conductivity (lACS) for the common bus bar alloys is given in Table 2.
Thermal Properties of Bus Conductors
Resistivity-Resistivity is the reciprocal of conductivity and, like conductivity, is expressed on either a volume or a weight basis. Standard values for resistivity are also based on a temperature of 20 C. These values
Temperature Coefficient of Resistance-Standards for conductivity and resistivity are established for a tem.~ perature of 20 C, and d-c resistance calculations using these values will give resistance at 20 C. Conversi9n '
2
Bus Conductor Alloy
EC Grade (All Tempers) 55 EC 56 EC 57 EC 59 EC 6063-T6 6063-T83 6061-T6 1100 (Annealed) 1100 (Hard)
. . . . . . . . . .
Minimum
Typical
61 55 56 57 59 51
62 56 57 58 53 56 40 59 57
provide the basis for the calculation of. resistance of bus conductors according to formulas presented in the section on electrical characteristics. The resistivity of common bus conductor alloys is given in Table 3 in both units of volume and weight resistivity.
,i
general- section I
tABLE 3 -
RESISTIVITY (p) OF ALUMINUM BUS CONDUCTOR ALLOYS AT 20 C
. .
-
(Based on Minimum and Typical Conductivity Values)
'.
..
Maximum Values
~"'. : ,
EC Grade 610/0 Condue-
" :.
tivity
,,"
57 EC 570/0 Conductivity
56 EC 560/0 Conductivity
Typical Values
55 EC 55% Conductivity
6063-T6 51~ Con uctivity
EC Grade 62~ Con tlCtivity
1100 Annealed 59% Conductivity
55 EC, 56 EC 1100-Hard 57% Conductivity
Wef~~t Resistivity
6063-T6 53% Conductivity
6063-T83 56% Con duc·tivity
6061-T6 40% Conductivity
'.
,,'II ••
436.24 0.07640 ·¢!crohms-pound/feet' 15.65 ., ~Iuiis-pound/mile' .,. ¢~-gram fmeter' ..
466.85 0.08176 16.75
475.19 0.08322 17.05
483.83 0.08473 17.36
521.78 0.09138 18.72
429.20 0.07516 15.40
451.03 0.07899 16.18
466.85 0.08176 16.75
502.09 0.08793 18.01
475.19 0.08322 17.04
18.195 0.03025 1.191 14.29 3.025
18.520 0.03079 1.212 14.55 3.079
18.857 0.03135 1.234 14.81 3.135
20.336 0.03381 1.331 15.97 3.381
16.728 0.02781 1.095 13.14 2.781
17.578 0.02922 1.151 13.81 2.922
18.195 0.03025 1.191 14.29 3.025
19.568 0.03253 1.281 15.37 3.253
18.520 0.03079 1.212 14.55 3.079
665.27 0.1165 23.86
V:~~~e Resistivity ';ohms-cir mil/foot .... :Johms-sq rom/meter .. ·microhms-inch iIiicrohms--
17.002 0.02826 1.113 13.35 2.826
:tb other temperatures is often necessary, and the tem,iperature coefficient of resistance (a) is used for this, ,see Table 4. Generally, each metal has a unique doc ~esistance vs. temperature characteristic which is lin';ear in the range of temperatures usually encountered. .The temperature coefficient is derived from the slope · .bf the linear portion and indicates the amount of .' change in doc resistance per degree Centigrade of .temperature change. . A series of metals having like structure but different ·"chemical content exhibit a thermal coefficient of re· sistance which is proportional to their conductivity. .: Thus, alloying or work hardening effects on aluminum I and copper which alter conductivity, also change the ·; temperature coefficient of resistance correspondingly. · . This is expressed mathematically as follows: ~,
'~i"
'
'.
a20
= 66
X
10-6
A.20
(at 20 C).
\>1.; Where: a
is the temperature coefficient of resistance
25.928 0.04310 1.697 20.36 4.310
to raise its temperature a given amount. On an equal weight basis, aluminum has a higher specific heat than copper. EC aluminum is 0.214 cal/gmrC and copper 0.0921 cal/gmrC. On an equal doc resistance basis, the thermal capacities are approximately equal. This high thermal storage capacity enables aluminum bus to withstand high overloads and short circuit currents. Test results show that under short circuit conditions, the bum-off characteristics of equivalent sizes of aluminum and copper conductors are similar. Specific heat values for a number of aluminum bus conductor alloys are: Aluminum Alloys
EC Grade 6063 55 EC (6101) 56 EC (6101)
Specific Heat
0.214 cal/gmrC 0.23 callgmr C 0.23 cal/gmrC 0.23 cal/gmrC
A. is the per cent conductivity (lACS) at 20 C.
TABLE 4-THERMAL COEFFICIENT OF RESISTANCE (a) AT 20 C
Aluminum Alloy
EC 59EC · 57 EC 56EC 55 EC 6063-T6 '"
.. . . . . .
Per Cent Volume Conductivity (lACS)
Thermal Coefficient of Resistance at 20 C
61 minimum 59 minimum 57 minimum 56 minimum 55 minimum 53 typical
0.00403 .0.00389 0,00376 0.00370 0.00363 0.00350
A more complete table of thermal coefficients of resistance is given in the section on electrical charac-· teristics along with examples of resistance conversions to other temperatures, see page 17. Specific Heat-The specific heat of a bus conductor material is a measure of the thermal energy required
Thermal Conductivity-The thermal conductivity of a material is its ability to conduct or carry away heat from a high temperature area and distribute and dissipate it. On an equal weight basis, aluminum bus conductor has higher thermal conductance than both steel and copper. On an equivalent resistance basis, the thermal conductance is comparable for both aluminum and copper bus conductors.}'-·
THERMAL CONDUCTIVITY AT 20 C (WATTS/IN2 IIN/SECI °C) Material
ECAluminum 59 EC, 1100 Soft 57 EC, 1100 Hard 56 EC, 6063-T83 55EC 6063-T6 6061-T6
....
Watts/in' /in/sec/oC
5.9 5.7 5.5 5.4 5.3 5.1 3.9 3
r I
section I - general
I
I I
I ,!'
i
,
(,
, i'
1.1
"
i:
! Ii ji
:.;
'I "I
Effect of Heating on Tensile Strength-The generally accepted maximum continuous operating temperature limit for electrical bus conductor is 70 C. This maximum continuous operating temperature is established at an ambient temperature of 40 C with a conductor temperature rise above ambient of 30 C. These are the standard conditions used to e,stablish the continuous current ratings of bus conductors. These ratings are described in detail in the section on electrical characteristics, page 40. The effect of this 70 C temperature upon the physical properties of aluminum bus conductor is negligible. However, short time emergency conditions or high ambient conditions may cause conductor temperatures in excess of the normal 70 C operation, and the effects of heating' should be considered for such conditions. The effect of time at temperature on the hot and cold tensile' strengths of EC-Hl1 and 6063-T6 aluminum bus ,conductor is shown in Figs. 1 and 2. All alloys show a reduction in tensile strength at elevated tempera.wres. For EC-H17 alloy, tensile strength ranges from 20,000 psi at room temperature to approximately 10,000 psi at 200 C. Likewise, the tensile strength of alloy 6063-T6 falls upon heating, the extent depending upon the magnitude of the temperature as shown in Fig. 1. A similar behavior can be expected from 55 EC, 56 EC, 57 EC, and 59 EC.
These curves also show the effect of continued heating at elevated temperatures. The downward trend of the EC-H17 curves indicates progressive annealing. It is not significant until temperatures exceed 100 C where annealing just starts or proceeg.s very slowly. With rising temperature, the rate of an- . neal becomes progressively faster. At approximately 570 C, annealing is very rapid. Short time emergency overloads can be safely carried on EC aluminum bus conductor without seriously affecting its strength properties. At temperatures of approximately 150 C and below, the continued heating of 6063-T6 has the effect of artificially aging the alloy, and tensile strength.. may actually increase for a period of time before annealing is initiated. At temperatures exceeding 175 C, the continuous heating of 6063-T6 alloy produces an immediate reduction in tensile strength which is more pronounced than for EC-H17. The consequences of continued overheating of bus conductors must also be considered in bolted bus conductor joints where reduced clamping forces may result unless conservative methods of joining are used. These are described in the section on mechanical joining, see page 79. The cumulative effects of continued heating of aluminum bus conductors after they have cooled to
45000 , . . . . . - - - - , - - - - - - , - - - - - , - - - - - , . - - - - ,
45000 TENSILE STRENGTH AT ROOM TEMPERATURE AFTER HEATING
TENSILE STRENGTH AT ELEVATED TEMPERATURES
II
40oo01-----j----+----+----+----j
40000
35000 I - - - - - - - i - - - - / - - - - - t - - - - - + - - - - - j 65 C
35000
.1
6063 -T6
85 C
30000 r6:
,T6
3ססoo
v; <>.
150 C
~ 25000 ~--+--=1r::-i75~=t"'-'---=4---_l_-~~-l~ 25000
C>
Cl Z
z .... '" lU
lU
.... '"
II)
~
II)
20000
f----~----T~""'---+---,..,__---l
lU
v;
':=
w
lU
.... EC-+--~""-
15000
, I !
20000
E~
II)
z ....
Z
-H17
15000
-H17
10000 I---*-'-+~
10000
5000 1 - - - - 1 1 - - - - - + - - - - / - - - - - + - - - - 1
O'--_ _--' 0.1
1.0
--J.
--'--
10 100 HEATING PERIOD, HOURS
Fig. 1
--'-
1000
--'
10000
-+
5 0 0 0 1 - - - - 1 - - - - + - - - - + -_ _
1
O'-:-_ _-:'~--_:::_----'-----L--_:_:_:~ 0.1
1.0
10 100 HEATING PERIOD, HOURS
1000
10000
Fig. 2 Courtes!I Aluminum Co. of America
4 "i j
general - section I 6063-T6
EC-HI7
EC - H12
35000
32 C
30000
25000
10000
15000
32 C 10000
-
100 C
"-
ISO C
5000
200 C
200 C
o 10
100 TIME, HOURS
1000
10
100
1000
TIME, HOURS
Fig. 3 - Creep Characteristics of Bus Alloys
room temperature are shown in Fig. 2. These curves are similar to the curves showing tensile strength at elevated temperatures, Fig. 1, but at room temperatures, the cumulative effects of this heating show a more pronounced annealing. The curves also show a signi£cant gain in the tensile strength of- alloy 6063-T6 at room temperature due to arti£cial aging' at these elevated temperatures. Creep of Aluminum Bus Conductors-In some applications of aluminum bus conductor, high temperature and stress may be sufficient to cause a gradual plastic deformation of the metal. This is referred to as creep, and its rate is a function of both stress and temperature. Bolted bus conductor joints are particularly vulnerable to this phenomenon as bolting stresses may be high and current loadings produce a temperature rise that results in signi£cant rates of creep. The reliability of bolted joints can be affected by these higher rates of creep unless design measures are incorporated to prevent serious reduction in the pressure applied to the joint. This is discussed in the section on mechanical joining, see page 81. The curves shown in Fig. 3 indicate the creep characteristics for EC-HI2, EC-HI1, and 6063-T6 aluminum alloys. The EC aluminum alloys show less creep resistance than the heat-treatable alloys such as 6063-T6, 55 EC, 56 EC, and 57 EC. EC-HI2 bus conductor has less creep resistance than EC-H17 at low
10
100 1000 TIME, HOURS Cow'tesy Aluminum Co, of America,
temperatures, but this is reversed at the higher temperatures (at approximately 150 C and up) where the recrystallization of EC-HI7 is more rapid. Resistance to creep at room temperature of bus conductor alloys in order of increasing resistance is ECHIll, EC-HI2, EC-H1l2, EC-H13, EC-HI7, 57 EC, 56 EC, 55 EC, 6063-T6, and 6063-T83. The creep characteristics of 55 EC and 56 EC alloys are expected to be slightly lower tllan alloy 6063-T6.
Corrosion Resistance Aluminum owes its excellent resistance to corrosion to a thin, tightly adherent £lm of aluminum oxide that forms instantaneously when the metal is exposed to the atmosphere. This protective layer resists attack under many conditions of service. Under severe exposure, a heavier £lm may form. Thus, a corrosion process is likely to be self stopping before signi£cant attack has occurred. The service performance of aluminum bus bar will follow closely these general con./', cepts of the corrosion behavior of aluminum. The aluminum alloys EC, 6063, 55 EC, 56 Ee, 51 EC, and 59 EC are especially well suited for bus bar applications. Except for EC grade aluminum, these alloys are of tlle silicon-magnesium group with only small percentages of alloying elements added to increase their physical properties. These alloying elements make possible a group of aluminum alloys recognized 5
l.
C
section I - geneml
for superior corrosion resistance. Because of the higher aluminum content of EC, it will have a more uniform, naturally formed, protective oxide layer than other aluminum alloys. Consequently, EC may demonstrate slightly superior resistance to corrosion in more severe atmospheres. In view of the substantial metal sections used in bus bar applications, corrosion should present no problem under all normal conditions of service.
General Classes of Bus Conductor Alloys Aluminum bus conductor alloys fall into two general classes: 1. Non-heat-treatable alloys which achieve strength
through cold working; 2. Heat-treatable alloys that obtain their properties through heat treatment alone or in combination with cold working.
., , !
'1.,
I' i
Non-Beat-Treatable Bus Alloys-Where high conductivity is essential, EC aluminum is usually required. EC grade aluminum has a nominal purity in excess of 99.45 per cent aluminum. The many tempers of this alloy offer a range of physical properties with all tempers having a minimum conductivity of 61 per cent (lACS). The softer tempers of EC bus bar such as EC-H12 and EC-H13 are normally used where edge bending characteristics or other extreme forming propelties are desired. Often, the lower cost of these softer tempers determines the selection when strength is not an essential requirement. Commercially pure aluminum alloy-99 per cent aluminum-designated as alloy 1100 is sometimes used for bus conductors. Although its conductivity is somewhat less than that of EC grade aluminum, it may be more readily available in standard shapes where only small quantities are required. Alloy 1100 has 57 per cent conductivity in the full hard temper and 59 per cent in its softest temper. Other standard non-heat-treatable aluminum alloys may be used for bus conductor, but since conductivity is greatly affected by small amounts of alloying elements, they find only limited use for electrical purposes. Such alloys, however, may be more readily available in the standard shapes for small requirements. Or, if some other characteristic is desired, such as strength, ease of welding, brazing, or soldering, then their use may be preferable. Temper Designation for Non-Beat·Treatable Bus Bar Alloys-Several tempers, from soft to full hard, apply to the non-heat-treatable bus bar alloys. The temper designation follows the alloy designation, e.g., in the bus bar alloy EC-H17, the temper designation is H17 and is separated from the alloy designation by a hyphen.
6
The standard temper designations show two things: They identify the specific temper; They indicate how that temper is obtained. Tempering by cold rolling or cold drawing is indicated by the letter "H" followed by two digits, e.g., H12, H24, H36. The first digit indicates the manufacturing process used to obtain the temper, i.e.: I-indicates that the bus bar is hardened by cold working the material after annealing, such as by cold rolling or drawing; 2-indicates that the material is first cold worked to a higher temper than desired and then partially annealed to the desired temper; 3-indicates that the material is cold worked after annealing and then stabilized. Stabilizing is a low temperature treatment-IOO F-400 F-and is usually confined to alloys containing magnesium as the principal alloying agent. The second digit of the temper designation indicates the degree of hardness or temper, e.g., the following designations have tempers indicated by their second digit: HI2-~hard;
Hi4-~hard;
HI6-%ohard; HiS-full hard; Hi~-extra hard-usually reserved for EC drawn wire. EC bus bar tempers depart from the standard tempers in two instances where intermediate tempers have been found desirable for bus bar applications. These intermediate tempers are designated as: EC-HI3-properties between % and liz hard; EC-H17-usually designated as the hard temper for EC bus bar. Two other letter designations are used for indicating temper. These are designated "0" and "F." "0" indicates material that is fully annealed or dead
soft; "F" indicates the "as fabricated" condition where the process does not control the temper. Heat-Treatable Bus Alloys-A number of heat-treatable alloys are available for bus conductor. Those used most frequently are as follows: Alloy
6063-T6 6063-T83 55 EC (6101-T6) 56 EC (6101-T62) 57EC (6101-T61) 59 EC (6101-Hll1) 6061-T6
Principal Alloying Elements
magnesium and silicon; magnesium and silicon; magnesium and silicon; magnesium and silicon; magnesium and'silicon; magnesium and silicon; magnesium, silicon, chromium, and copper.
These alloys are all of the magnesium-silicon group with 6061 having small amounts of chromium and
geneml- section I I
~
65
I
I 111111
I IIIIII
I
I 111111
I
-- --. '~
I III III
cu.
"- ". TI.
60
~ 0.01
I
I 1I1III
0.1
I
I I I 1111
1.0
I
I I 11111
10.0
ADDED ElEMENT, PER CENT
Fig. 4
i ,,'
I 11111
I
I IIIII
NI.
-.......
51.
50
\
I 111111
I
55
\
I
1111111
'\
:'-ZN.
\
I
I J J '"I
M~
65
\MG.
0.001
I
copper added to impart greater strength. The addition . of alloying elements to aluminum adversely affects the conductivity of all aluminum alloys. However, the strength and superior creep performance imparted to them and the ease of fabricating these alloys into bus conductor gives them a decided economic advantage over the EC bus bar tempers. The addition of magnesium and silicon in the proper proportions, along with other impurities, depresses the conductivity. A close control of such additions, plus a similar control of the amounts of other impurities permits ~aintenance of conductivity at an adequately high level. Certain impurities have a greater effect on conductivity than others, and the chemical content of these undesirable elements must be established at low levels. The curves in Figs. 4 and 5 show comparatively the effect of adding small quantities of several elements on the conductivity of pure aluminum. Among those having the greatest effect on conductivity are vanadium, titanium, chromium, and manganese. Small traces of these elements in quantities of 0.01 to 0.1 per cent have a pronounced effect on conductivity. Elements such as copper, iron, silver, magnesium, and silicon have slightly less effect when present in this percentage, but have noticeable effect when percentages exceed 0.1. Even less effect on conductivity is produced by such impurities as zinc, nickel, gold, and gallium. Concentrations up to one per cent have only a small effect, while greater percentages depress conductivity appreciably. Some of the alloying elements added to aluminum form inter-metallic compounds. Of principal impor-
I
0.001
I 111111
0.01
I
I 111'11
I
I 111111
0.1 1.0 ADDED ELEMENT, PER CENT
I
I 111111
10.0
Fig. 5
tance in bus bar alloys is the combination of magnesium and silicon into tlle compound magnesium silicide (Mg2 Si). This inter-metallic compound has less effect on the conductivity of a bus conductor than the total effect these elements would produce individually. The proportions of magnesium and silicon added to bus conductor alloys is made in the proper ratio to produce Mg 2 Si. The addition of silicon is usually slightly in excess of these requirements so that the bus conductor will have a small free silicon content rather than. a free magnesium content, sihce the latter has a greater effect in depressing the conductivity of the , alloy. Boron is sometimes intentionally added to electrical conductor materials to improve their conductivity. This element does not directly increase conductivity but achieves this effect by its tendency to precipitate other elements from their solid solution state in these aluminum alloys. In particular,Jboron helps to precipitate titanium, since this element depresses conductivity when present in very small percentages. Temper Designations for Heat·Treatable Bus Bar Alloys-The stable tempers resulting from various heat treatments applied to heat-treatable aluminum alloys are designated by tlle letter "T"followed by a single digit oi· several digits which indicate the particular heat treating method or combination of methods, e.g.: T3-indicates the material has been solution heat treated and then cold worked;
7
section I - general
T4-indicates the material has been solution heat treated only; T5-indicates the material has been artillcially aged only-precipitation heat b'eatment; T6-indicates the material has been solution heat treated, then artillcially aged; T8-indicates the material has been solution heat treated, cold worked, and then artificially aged. Added numbers to designations denote a modification of these standards. Letter designations such as "W," "0," and "F" also apply to heat-treatable alloys.
·
W-indicates the unstable condition of the material following solution heat treatment; O-indicates material that is fully annealed or dead soft; F-indicates the "as fabricated" condition where no control of temper is made during the process.
I
,. 'I ,
;
" ii "
I
['/'
"',
.,
Solution heat 'freatment is a high temperature treatment ranging approximately from 900 to 975 F. At this temperature, certain alloying elements go into solution or dissolve in the solid metal. The materials are then quenched, usually in cold water, to retain
these alloying elements in solid solution. The material after quenching has relatively low physical properties.. This is not a stable condition, however, as these elements are not as soluble at room temperature. Immediately after quenching, these alloying elements begin . to precipitate from the solid solution. This precipitation produces extremely small grains of the alloying ,elements in the solid metal, and the strength at room temperature increases as this precipitation or aging continues. The rate of precipitation or natural aging varies with different alloys. In alloy 2024-T4, precipitation progresses rapidly and uniformly at room temperature and is virtually complete at the end of four days at which time maximum physical properties are attained. Precipitation heat treatment or artificial aging at relatively low temperatures is necessary in some alloys to develop their maximum physical properties. In these alloys, the natural aging process is not sufficient to"i develop maximum physical properties. A low tempera~ .1 ture treatment ·for a specified time accelerates the precipitation process. The extent of this precipitation is controlled by the length of time and the temperature. This will vary for the different alloys.
:'1
I'
BUS CONDUCTOR SHAPES
I
,
,i j
"
Rectangular Bar The most common form of aluminum bus conductor is rectangular bar. It presents large exposed surfaces for heat dissipation. Several bars can be paralleled with a small air space between each bar to build up a bus of high current capacity. The many flat exposed surfaces, both internal and external, readily provide for the dissipation of generated heat. The capacity of such a bus is theoretically unlimited when carrying direct current since the current is distributed uniformly in an isolated d-c conductor. However, when used to carry alternating current, special arrangements must be resorted to on high capacity installations to maintain a more uniforIn distribution of current. Rectangular bar can be more easily jollied than other shapes of bus conductor. The broad flat surfaces are bolted together without special fittings and also to standard equipment terminals. Welding, brazing, and soldering rectangular bar are easily accomplished where these methods of joining are preferred. Rectangular bar is more rigid in the direction of its larger dimension; supports must be closely spaced where loads or short circuit forces are perpendicular to the flat surfaces of the bar. , Electrical applications for rectangular bus conductor are extensive. It is used in many fabricated products such as bus duct, switchboards, panelboards, metal clad switch gear, equipment terminals, and other similar electrical products. It is also used extensively for
8
high capacity d-c buses, in generating stations, substations, and many industrial and commercial plants where it may be fabricated and installed on the job. Rectangular bar is the most versatile of all conductor shapes because it can be easily formed in 90 degree flat bends and readily joined and attached to wall supports and building structures. Edge Contours-Various standard edge contours are available with rectangular bar. These contours are specified by ASTM Specification B236* for EC rectangular bar. Sketches with a description of the standard tolerances applying to each are shown. Square Corners-Bar finished with commercially square corners will have a maximum permissible corner radius as follows: lh2 inch radius for . bar 78 to 1 inch inclusive in thickness, ~6 inch radius for bar over 1 inch in thickness. Rounded Corners-Bar finished with corners rounded to a quarter circle will have the following corner radius: %2 inch radius for bar 78 to %6 inch inclusive, l!J.6 inch radius for bar over ~16 to 1 inch inclusive in thickness, 78 inch radius for bar over 1 inch in thickness.
CJ
CJ
* Complete specification on page 149.
geneml- section I
Rounded Edge-Bar finished with rounded edges will have a radius of curvature approximately 1~ times the thickness of the bar for bar % inch and over in thickness. The tolerance on the radius shall be ~ the thickness of the bar. Fttll Rounded Edge-Bar finished with full rounded edge will have a uniform round edge with a radius of curvature approximately one half the thickness of the bar, but in no case will the radius exceed lh the thickness by more than 25 per cent. Sawed Edge-A rough surfaced edge showing saw marks and very slight or no deformation of the corners. The sawing operation leaves a slight burr on the corners which is generally not completely removed and which may necessitate care in handling.
Aluminum Rectangular Bar Alloys-Rectangular bar is produced in several bus conductor alloys and in many tempers of EC grade aluminum from annealed to full hard, depending upon the physical properties desired and the degree of fmming or bending necessary. The alloys most commonly used for rectangular bar are: ConductivityAlloy Per Cent (lACS) EC-H111 61-62 61-62 EC-H1l2 EC-H12 61-62 61-62 EC-H13 EC-H17 61-62 55-56 55EC 56-57 56EC 57-58 57EC 59EC 59-60 57-59 1100
and EC-H13 which it replaces. Its forming and bending characteristics approach these Ee tempers. 3. 59 EC is the most ductile of the alloy rectangular bars and is intended to be used for severe forming or bending operations such as edge bending. It is comparable to EC-HI2 for this use. The EC-HIll and EC-H1l2 rectangular bar alloys are designations for the "as fabricated" condition of EC grade aluminum. EC-H1ll is the designation for an "as extruded" bar, and EC-H112 is the designation for rectangular bar sawed to required widths from hot rolled EC plate.
Bending Properties-The bending properties of rectangular bar often detelmine the selection of a bus alloy and temper. Certain applications may require the bar to make both edge and flat bends. The physical properties and dimensional shape of the bar are factors which govern its bending properties. Bending properties are described as follows: 1. Edge bending requirements for EC-Hlll, ECH1l2, EC-HI2, and EC-HI3 rectangular bar 4 inches or less in width are established by ASTM Specification B236-"Aluminum Bars for Electrical Purposes." No edge bending requirements have been established for EC-HI7. Of the rectangular heat-h'eatable alloy bars, only the lower tensile sh'ength materials are recommended for edge bending. Alloy 59 EC is the most ductile in this class and is preferred for edge bending applications. Alloy 56 EC is not recommended for edge bending and alloy 57 EC for only very limited edge bending. 2. For flat bending, the following EC alloys can be bent 90 degrees aTOund a radius equal to its thickness without cracking or evidence of sliversEC-HIlI; EC-H1l2; EC-HI2; EC-HI3. See ASTM Specification B236. EC-HI7 requires a slightly larger flat bending radius. A 2t radius is suggested for this alloy. Flat bends for aluminum alloy bus conductor are governed by the following:
FLAT BEND RADIUS
Alloy Selection-Alloys for aluminum rectangular bar have a considerable range of electrical and physical properties. This versatility gives the designer wide latitude in adapting aluminum rectangular bus conductor to the requirements of a particular application. In many instances, several alloys may be used for the same application. Where conductivity can be saCl-ificed, lower cost alloys may be substituted. For example: 1. 55 EC and 56 EC are lower cost alloys, have lower
conductivity, but higher strength than, EC-H17 which they often replace; 2. 57 EC is a lower cost alloy, has lower conductivity, ' but higher strength characteristics than EC-H12
Alloy 55EC 56EC 57EC 59EC
TIlickness, t (Inches)
0-0.499 0-0.499 0-0.499 0.500-0.749 All Thicknesses
Bend Radius
2t It It
2t It
Specifications-A specification for EC aluminum rectangular bus bar has been tentatively issued by ASTM . (American Society for Testing Materials) and is designated as ASTM B236 "Aluminum Bars for Electrical Purposes," (Bus Bars). This specification covers only EC grade aluminum bars in all tempers. It is reprinted on page 149.
9
section I - general
ROlmd Tubular Conductor ROUild hlbular conductors are used primarily in outdoor sub-stations and switching structures where long spans between supports are required. They are also used for generator phase bus. The inherent rigidity of a tubular shape in all directions resists lateral forces such as wind loads; vertical loads that include its own dead weight and accumulated ice formations; and in addition to these loads, the forces due to short circuit currents. The light weight of an aluminum hlbular shape provides a minimum bare deflection, thus presenting visually a straight uniform appearance. Tubular conductors are generally manufactured in Iron Pipe Sizes (IPS). Physical and electrical characteristics for both the standard IPS and the extra heavy pipe sizes are given on pages 126 and 127. Fittings for these IPS conductors are standard and can be obtained from accessory manufacturers for coupling lengths together, for making connections and terminals, Fig. 6, and for expansion joints and supports. The practice of welding joints in hlbular conductor is gaining in acceptance and general use. A properly welded joint has the advantage of being a pelmanent connection and as reliable as the conductor itself, Fig. 7.
I i
I: •j
t
Electrical Characteristics-A round hlbular shape is the most efficient electrical shape for an a-c bus conductor. Alternating current is distributed more unifonnly in tubing than in other shapes, hence it has the lowest skin effect of commonly used bus conductors. Its current rating is limited, however, in comparison with rectangular bar conductor because of the smaller ratio of smface area to volume for the dissipation of heat. The internal cooling of tubular conductors by forced air or circulating liquid coolants finds very limited application. , Due to skin effect, optimum w'all thickness for all sizes of EC aluminum tubular conductors carrying 60 cycle alternating current is approximately 11!J.6 inch; for aluminum alloy 6063-T6, the optimum wall thickness is approximately 0.8 fuch for all diameters. Conductor wall thicknesses greater than these add nothing to the current carrying capacity. This means that only a limited range of wall thicknesses is available for tube of given diameter and conductivity which results in a limited range of available alternating current ratings for each diameter tubular conductor. Further details are given on page 22.
a
I'
, I
r
"
,
. ..
; ~
Alloys-Strength is usually the primary requirement of a hlbular conductor used for long span construction. Hence, the higher sb'ength alloys such as 6063T6, 56 EC, and 57 EC are generally used for this application although conductivity is somewhat lower than for the EC grade conductors. These alloy con10
ductors are heat treated to improve their physical properties, and hence, are lower in cost than the EC tempers which require cold drawing. Tubular con-
Fig. 6 - Bolted Construction
Fig. 7 - Welded Construction
ductors can be fabricated from many aluminum alloys. The required physical and elecb'ical properties, along with cost, will determine the most suitable alloy for the application. Bending Properties-Satisfactory 90 degree bends and offsets can be made with tubular conductors, thus eliminating many fittings. Bends are made without elaborate equipment except for short radius bends. The curve shown in Fig. 8 gives the conditions for satisfactory bends with tubular conductors of alloys 6063-T6, 6063-TS3, 56 EC, and 57 EC. The EC tempers can also be bent Field bending is shown in Fig, 9.
geneml- section I
Skin effect resistance ratios are slightly greater than for round tubular conductor of the same wall thickness and diameter. Electrically, it is a very efficient conductor shape. The optimum wall thickness of square tubing, due to skin effect, is approximately the same as for round tubular conductor ·of the same material. Wall thicknesses greater than this value are not practical because alternating current ratings are not increased. A small range of alternating current ratings can be obtained for a given size tube by varying the wall thickness below the optimum value.
16
~18
f--
II
AREA No.1
uJ 12 Z'" uJ::>
~
~
!
Z~
,
!
1/
uJO
4
6 ~
2
'"
/
/
V
/
V
/
/ I
V
'/
ffiV5
u
/
I
ZD
i
./V
./
AREA No.3
V
4:;;;: "'4:
-uJ 6 ~o
II·
/
"'...00 10 ::>uJ "'''' -...OuJ 8
I
VAREA No.2
-
o ~.
V
/1
14
./V
/
1/
r/ V
V
_~~o,
AREA No.4
/
\
V
tR . .- TK
~'-~
/
'£. V
AREA No, 5
o
20
40
60
RATIO,
80
lOa.
120
140
OUTSIDE DIAMETER OF TUBE THICKNESS OF TUBE WALL =
160
180
200
0.0.
TK
Fig. 8 Area No. I-No Mandrel or Wiper Die Area No.2-Plug Mandrel and Wiper Die Area No.3-One Ball Mandrel Area No. 4- Two Ball Mandrel and Wiper Die Area No..5-Nat'Practical
Alloys-The high short circuit strength requirements of a square tubular bus usually require a heat-treatable, high strength alloy. Alloys 6063-T6 and 57 EC are generally used for this purpose. The cost and difficulty of drawing EC grade aluminum and the limited strength after drawing usually preclude the use of EC grade aluminum for square tubular conductor.
Channel and Angle Conductor Channels and angles used for bus conductors can either be rolled, extruded, or formed. These shapes may conform to the standard structural channel or angle section used in the steel indusby or they may be of special design for electrical applications. Where they are used for a-c buses, they are usually arranged to form a hollow square to provide an efficient elecb'ical configuration having a low skin effect resistance ratio. This is illusb'ated in Fig. 10.
T
..
l[JIO Courtesy Tal Bending Equip., Inc.
Fig. 9 - Field Bending
Square Tubular Conductor Square tubular conductors are used for applications reqt.Jiring high current carrying capacity and greater rigidity to resist extremely high short circuit forces. They are .used primarily for generator phase bus and for high capacity station bus. Courtesy General Electric Co.
I.
Electrical Characteristics-The current carrying capacity of square tubular conductor, like round tubing, is limited because of the smaller amount of exposed surface area for the dissipation of generated heat. To ventilate the interior surfaces, large holes are sometimes provided in the top and bottom surfaces to supply additional internal cooling by convectiop. air currents.
Fig. 10
The channel alTangements shown approximate square tubular conductor in both electrical characteristics and rigidity with the added advantage of providing cooling for the interior surfaces by convection. Current carrying capacity is thereby increased over an equivalent section of conventional square tubular con11
( I
I
;P-'=
section I - general
ductor. Where space is limited, such as in isolated phase bus, the special channels shown can be used to advantage. This is shown diagrammatically in the two equivalent sections, Fig. 10. The 5 inch special channel shapes arranged in box form have the same rating as the 7 inch standard channels. * In most cases, the size of the housing for isolated phase bus need not be increased when special aluminum channel sections are used.
!
I, ~
I
I I
il II' f
11'
,!, ;1] 1-. Ii
, .1
,
'I I.
:i1'1. i i'{ "j. ~ ,
\: )t
Applications-Standard channel conductor is used primarily for long span construction where a high current rating is desired and structural rigidity is necessary to withstand high short circuit forces. These sections can be used to advantage in outdoor substations and switching stations where a greater current capacity is desired than can be obtained with round or square tubular conductors. Channel bus conductor is also used in many low voltage, high current industrial applications for both a-c and d-c service. Typical of these applications is service to large rotating equipment, induction furnaces, rectifiers, and other mill installations having unusual current needs. It is also employed as bus conductor in industrial sub-stations and for bus ties between sub-stations or large electrical installations. Alloys-High current ratings, high short circuit forces, and long spans usually require high strength, heattreatable alloys such as 6063-T6 and 57 EC. Where even higher strength is desired and some conductivity can be sacrificed, 6061-T6 alloy may be used. For maximum conductivity, EC grade aluminum is preferred; however, the lower physical properties of EC aluminum must be considered in the design of supports, span lengths, and distances between buses. Usually the harder tempers of EC aluminum or a heattreatable alloy are most suited for a high capacity bus because of strength requirements..
t
~~ I
I
Ii 1
I
:1
II I:!: I' ~
t'
Other Conductor Shapes Special designs requiring non-standard shapes of bus conductor are readily fabricated from a number of aluminum alloys. These shapes, Fig. 11, may be produced by the extrusion process where a relatively
Fig. 11
simple extrusion die is required and the conductor thus produced will have close dimensional tolerances. The alloy selected will be governed by the physical and electrical properties required for the application and by cost consideration.
MANUFACTURING PROCESS AND TOLERANCES
!J, )
Fabrication-The broad flat surfaces of ch~umel and angle sections are used to advantage in joining sections of bus together. Flat plates may be bolted to both the inside and outside surfaces in either a straight splice or for making 90 degree angle bends. Prefabricated bus such as isolated phase bus is usually joined in this manner by bolting the prefabricated sections together in the field. Where standard channels and angles are fabricated on the job such as in an outdoor sub-station, these conductors are sometimes joined by welding. This method of joining is economical, particularly for the larger installations. Both methods of joining, either bolting or welding, give reliable elecbical joints when properly made.
.1
The methods of producing aluminum bus conductor generally fall into two classes: 1. Extruded bar and shapes; 2. Rolled bar and structural sections. Other methods are used to a limited extent for producing bus conductor. Among these is the casting method for producing large sections for high capacity bus. Bus conductor is also formed into various bus shapes from rolled aluminum sheet or plate. Drawn bus conductor is usually produced by one of the two basic methods of production indicated above and is an
* "Application of
Alumi.num Charulel Conductors for Station Bus," AlEE TECHNICAL PAPER 52-295, by E. J. Casey and N. Swerdlow, September, 1952.
12
added operation to achieve either strength, contoured edges, or dimensional tolerance. Each of the two general methods of production listed has its advantages and limitations, and discussion will be confined to these methods. The process used by the manufacturer in producing bus conductor should be the one that can most economically produce the quantity and the quality desired in the finished product. All of these basic production methods produce high quality bus conductor. The electrical properties of the conductor are not affected by the process used. The surface finish will be slightly different-each process producing its own inherent surface characteristics. Dimensional tolerances can be held to close
geneml- section I
limits with extruded or rolled bus bar. Cast bus bar has relatively larger tolerances.
Extruded Bar and Shapes The extrusion process is one of the most versatile used in producing bus conductor. All bus conductor alloys, both non-heat-treatable and heat-treatable, can be extruded into practically any shape desired. The process is particularly economical for the heat-treatable alloys which achieve strength through a heat treatment following the extrusion process. The nonheat-treatable alloys on the other hand, such as EC aluminum, must be cold worked to refine the grain structure and thereby impart greater strength to the "as extruded" material. This is done by cold drawing operations following the extrusion process in which the conductor is pulled through a die or series of dies, each being slightly smaller than the preceding one. The number of drawing operations required will depend on the amount of cold reduction necessary to produce the temper desired. The drawing operation is also limited by the shape of the section. Usually only the simple shapes such as rectangular bar, round bar, and round or square tubular sections lend themselves to a drawing operation. Irregular shapes create die design problems, and it is usually advisable to either extrude these shapes in a heat-treatable alloy, or as in the caSe of a standard structural section, it may be produced by cold rolling in rolling mill equipment.
Tolerances-Standard tolerances for aluminum extruded shapes and extruded rod and bar have been established by the Aluminum Association and applicable ASTM specifications. Aluminum Association tolerances are shown on pages 141 and 143 and are applicable to the average section. Column two tolerances in
the table on page 141 apply to all solid metal dimensions such as the thickness and width dimensions of rectangular bars and to all dimensions where 75 per cent or more of the dimension is solid metal. Standard tolerances for solid round bar and aluminum pipe are given on pages 124 and 126, respectively. The ASTM tolerances for EC aluminum rectangular bar in all tempers are shown on page 149.
Rolled Bar and Structural Shapes The production of rolled sections requires large rolling mill equipment which is not as flexible as the extrusion process. This generally limits the hot rolled and cold rolled bus conductor sections to standard structural shapes and flat or round bars. Edge contours on rectangular bar, other than square corners, are usually applied in separate edge rolling or drawing operations. The rolling process does offer advantages in processing wrought conductor alloys such as EC grade aluminum in rectangular or round bars and the standard structural shapes because cold working increases the temper of the material, imparting improved physical properties. Several tempers can be produced depending upon the degree of l~eduction in the rolling process. Hot rolled bus conductor is generally limited to rectangular bar which is sawed or sheared to width from hot rolled plate. In this form, it is designated as EC-H1l2. Although EC grade aluminum plate is commonly employed to produce hot rolled rectangular bar, commercially ptu'e almninum, 99 per cent aluminum which is designated as alloy llOO, can also be used. While dimensional tolerances can be closely controlled by cold rolling, greater dimensional accuracy and contoured edges usually require a drawing operation following cold or hot rolling..
Xl
t:
('l
13
-
--.~
---
-.
..= , ...
-'-'~~.,_
v
ELECTRICAL DESIGN OF BUS CONDUCTORS D-C RESISTANCE OF BUS CONDUCTORS
a
In long homogeneous conductor carrying a continuous current, the current is distributed through its cross section equally. The resistance is given by the formula:
R dc =
p
volume resistivity and weight resistivity corresponding to the per cent conductivity (lACS) at 20 C of aluminum and the various aluminum alloys used for bus conductor. For the per cent conductivity, (lACS), at 20 C of the various bus conductor alloys, see the table below.
L A ohms (at temperature, t)
in which R dc is the direct current resistance and p isthe volume resistivity of the conductor material, L is the length, and A is the cross sectional area, all at temperature, t. . This may also be written in terms of the weight resistivity, in which case it becomes:
R dc
= P WL
CONDUCTIVITY OF BUS BAR MATERIALS (Per Cent Conductivity (lACS) at 20 C) Material
EC (All Tempers) 1100-0
Minimum
Typical
61
62 59 57
1100-HIB
ohms (at temperature, t).
59EC 57EC 56EC 55EC 6063-T6 6063-T83 6061-T6 HD Copper
Here, p is the weight resistivity of the conductor material at temperature, t, and W is the weight of the conductor material ill either pounds or grams per unit of length consistent with the units of p. R dc is the d-c resistance at temperature, t. With these two formulas, the d-c resistance of a conductor can be calculated when the value of p is in any standard units. This means, however, that where p is given in ohms-cir mil/foot, the unit of area should be in circular mils and the length, L, should be in feet, or where p. is given as the weight resistivity in microhms-poundjfeetz, the weight, W, should be indi; cated in pounds per foot and the length, L, should be given in feet. The 'various values for p are shown in Table 1. This table lists the common units for both
59 57
•• .j'
i·
58 57 56 53 56 40 98
56 55
51
.,
Minimum conductivity is established by ASTM or company standards' and represents a guaranteed minimum conductivity for the respective alloy when purchased according to the governing specification. Typical conductivity values are not guaranteed. They are the representative values obtained from daily
TABLE 1 - RESISTIVITY (p) AT 2.0 C FOR BUS CONDUCTOR MATERIALS J"
% Conductivjty (lACS) at 20 C Aluminum Alloys Units Weight Resistivity
40%
Copper
51%
53%
55%
56%
57%
59%
60%
521.78 0.09138 18.72
502.09 0.08793 18.01
483.83 0.08473 17.36
475.19 0.08322 17.05
466.85 0.08176 16.75
451.03 0.07899 16.18
443.51 0.07767 15.91
20.336 0.03381 15.97 3.381
19.568 0.03253 15.37 3.253
18.857 0.03135 14.81 3.135
18.520 0.03079 14.55 3.079
·18.195 0.03025 14.29 3.025
17.578. 0.02922 13.81 2.922
17.285 0.02874 13.58 '2.q74
I /
61%
62.%.
98%
436.24 0.07640 15.65 .
429.20 0.07516 15.40
893.06 0.1564 32.03
*
Ohms·pound/mile" ... Ohms-gram/meter' Microhms-pound/feet'
665.27 0.1165 23.86
\
Volume Resistivity Ohms-cjr. mil./ft..... Ohms-mm' /meter .... Microhms-sq. in,fft... Microhms~cm. .......
*A
,
25.928 0.04310 20.36 4.310
?
i
~
....
. 17.002 0.02826 13.35 ~. 2.1126 ,,'
16.728 0.02781 13.14 2.2!l1 .
10.583 0.01759 8.31? I 059'
density of 2.703 is tak~n for ,aluminum far can'ductivity values 40-62 per: cent. A density of 8.89 is takeJ' for 98 per cent conductivity copper.
~.' -, ~
r!~ .-
I .70
(?
~
...
/« f
(.~
':?
I:{ / •
/. 16J. '
l- / S
/. / 3
///
·/oe;;;.-
. . ;.IJ
section II - electrical design
D = 1250 mils; A = (1250) 2 = 1,562,500 circular mils; L = 1 foot (unit of length) ; P = 17.002 ohms-cir mil/foot at 20 C (for 61 per cent lACS); ,
production mllS. Typical values will exceed the guaranteed minimum conductivity by a margin which allows for a small variance in the composition or manufachlring process.
L
Calculation of D·C Resistance
Rae=PA;
To illustrate the application of the d-c tesistance fonnulas to the calculation of d-c resistance for common aluminum bus bars, refer to the following problem.
R de
Required: The d-c resistance at 20 C of the following bus bars in microhms per foot: A. Flat rectangular bus bar 4 inches X % inch of EC grade aluminum; B. A I1f4 inch solid round EC bus of 61 per cent conductivity (lACS); C. A 1 112 inch standard IPS extmded almninum tubular bus of alloy 6063-T6 with a typical conductivity of 53 per cent (lACS); D. Extruded aluminum alloy channel bus-4 inches-2.16 lb.-of alloy 6063-T6. Solution: I-A. The d-c resistance of a4 inch X lf4 inch flat rectangular bus bar of EC grade aluminum in microluns per foot at 20 C is calculated as follows: A = 4 inches X % inch = 1 square inch cross sectional area; L = 1 foot (unit of length) ; p = 13.35 microhms per square inch per foot at 20 C (for 61 per cent lACS);
" II'
k ,I I;
,j
,I
Rae
i
,!
, I
L
,j
1
I
= 13.35 microhms
per
foot at 20 C.
;i
I
I-B. The d-c resistance of a 11;4 inch solid round bus of EC grade aluminum of 61 per cent conductivity in microhms per foot at 20 C is calculated as follows:
!:
!I it
"
Laboratory Tests Being Made on Aluminum Bus Conductor
16
The d-c resistance of a 1% inch IPS extruded aluminum alloy tubular bus of 6063-T6 with a typical conductivity of 53 per cent (lACS) is calculated in microluns per foot as follows:
= 0.939
pounds per foot (table on page 126); L = 1 foot; P = 18.01 microhms-lb/feet 2 at 20 C (for' 53 per cent lACS) ; L Rae=PW; W
I ;
I
R de
=
1 18.01 X 0.939
= 19.2 microhms per
foot at 20 C. ' I-D. The d-c resistance of a 4 inch-2.16 lb. extruded channel section of aluminum alloy 6063-T6 in microhms per foot is calculated as follows: A
= 1.84 square inches
(cross sectional area), see page 132; L = 1 foot (unit of length); P 15.37 microluns per square inch per foot at 20 C (for 53 per cent lACS) ;
=
R de
= 15.37 X 1.~4 =8.35 microhms per foot at 20 C.
= P A:;
Rae = 13.35 X
6
ohms per foot at 20 C; = 10.88 microhms per foot at 20 C. l~C.
PROBLEM NO. 1
1 = 17.002 X 1,562500 = 10.88 X 10,
Temperature Conversion of D·C Resistance The heating or coolin b of an aluminum conductor produces a d-c resistance change which is linear
electrical design - section II
f· :
within the normal operating temperatures of the conductor. Graphically, this is shown in Fig. 1. The projection of the linear portion of the curve to the horizontal axis denoting zero doc resistance establishes a theoretical "temperature of inferred zero resistance." This "temperature of inferred ·zero resistance" will be a characteristic of each bus conductor material having a given percentage conductivity (lACS). To convert d-c resistance values from any temperature, such as the standard 20 C temperature, to another temperature within the normal operating limits where the above curve is linear, the following can be used: R tl = R t [1 + at (t, - t)]. Where: R tl is the doc resistance desired at a temperature, t , (in degrees C);
20 C as conductivity, resistivity, and basic resistance values are standardized at this temperature. In Table 2, the value of a is established for other operating temperatures. Care should be taken in the substihItion of a in the foregoing doc resistance conversion formula that its value and the known resistance are both for the same temperahlre. Due to skin effect and other inductive phenomena, a-c resistance does not follow the same linear relationship of temperature versus resistance that the doc resistance follows for the normal operating temperatures. To arrive at the a-c resistance at any value of temperahIre, the doc resistance should first be corrected to the temperatme desired, using the d-c resistance conversion formula. The a-c resistance can then be calculated for that temperature by methods shown in succeeding pages.
R t is the known d-c resistance at a temperature, t (in degrees C); at is the tempel~atme coefficient of resistance at temperature, t; (t , -.,. t) is the change in temperature in degrees C. ;,.
Temperature Coefficient of Resistance (a) The temperature coefficient of resistance represents the change in doc resistance per degree C. Its value will vary with the material, its percentage conductivity, and the temperature. The standard temperature coefficient of resistance is given for a temperature of
Temp. dcg. C. 0 10 20 25
o
·r
TEMPERATU RE
Fig. 1
TABLE 2 -.TEMPERATURE COEFFICIENTS OF RESISTANCE (a) FOR BUS CONDUCTORS 'MATERIALS' O( PERCENTAGE CONPUCTlVITY (lACS) 40% Condo
51% Cond.1 53% Cond.1 55% Condo
0.00279 ·0.00271 0.00264
0.00361 0.00349 0.00337
"il.6026i
ii:'Oo33I
0.00376 0.00363 0.00350 0.00344
I
0.00391 0.00377 0.00363
'D.Do'357
56% Condo
57% Condo
59% Condo
60% Condo
0.00400 0.00384 0.00370 0.00363
0.00407 0.00391 0.00376 0.00369
0.00422 0.00405 0.00389 0.00382
0.00430 0.00412 0.00396
0.00257 0.00251 0.00245 0.00239
0.00326 0.00316 0.00306 0.00297
0.00338 0.00327 0.00317 0.00307
0.00350 0.00338 0.00327 0.00317 __ _ _••:;0
0.00357 0.00345 0.00333 0.00322
0.00362 0.00350 0.00338 0.00327
0.00374 0.00361 0.00348 0.00337
0.00381 0.00367 0.00354 0.00342
70 80 90 100
0.00233 0.00228 0.00223 0.00218
0.00288 0.00280 0.00273 0.00265
0.00298 0.00289 0.00281 0.00273
- 0.00307 0.00298 0.00289 0.00281
0.00312 0.00303 0.00294 0.00285
0.00316 0.00307 0.00298 0.00289
0.00326 0.00315 0.00306 0.00297
0.00331 0.00320 0.00310 0.00301
Materials Aoolicable
6061-T6
Min. 6063-T6
1
Typical 6063-T6
Min.. 55 EC
atl
65ltTB~
Min. 57 EC
Typical 1100 Annealed
J
~
= desired thermal coefficient of resistance
62% Condo 98% Condo 0.00445 0.00426 0.00409 0.00401
0.00417 0.00400 0.00385
0.00387..... '0.00373 0.00360 0.00347
0.00393 0.00378 0.00364 0.00351
0.00371 0.00357 0.00345 0.00334
0.00335 0.00325 .0.00314 0J)!l30~
0.00340 0.00328 0.00318 0.00308
0.00323 0.00313 0.00303 0.00294
Typical EC-All Tempers
Represen.. tative Value for Commercial Copper Bus Bar
0.00438 0.00420 0.00403 0.00395
ii:'iiii38ii
30 40 50 60
Min. 56EC
61"fo Condo
M;" EC-All Tempers
Q.'6O'378
= known value of thermal coefficient of resistance = temperature in degrees C of known value of coefficient of resistance t, = temperature in degrees C at which desired coefficient is wanted.
at t
section IT - electTical design
A·C RESISTANCE OF BUS CONDUCTORS
When a conductor is used to carry alternating current, its resistance is apparently increased over its d-c value by several factors. This increase over the d-c resistance may be the result of one or more phenomena, each contributing an increment of resistance to the total a-c resistance of the conductor. The design of an a-c bus installation is influenced by such factors as skin effect and proximity which act independently of each other to increase d-c resistance. Losses due to induced circulating currents and hysteresis have a related effect on conductor a-c resistance in that both are incurred by the magnetic field of the bus conductor. In the over-all design of a bus conductor for a-c installations, thought should be given to all factors that contribute to a-c resistance. The major factors are: 'I. Skin effect This phenomenon is the tendency of current to concentrate more in the outer layers of the conductor thus apparently increasing the d-c resistance due to less efficient dist:ribution of the current in the conductor. The alternating current frequency, the conductor cross sectional shape, and its d-c resistance are factors that influence the magnitude of skin effect.
ij
2. Proximity effect This is the influence of nearby current carrying conductors on the current distribution in a conductor. When the current in two closely spaced conductors is opposite in direction at any instant, the current will be crowded toward the facing sides. When the current is in the same direction, it will be crowded toward the outer sides. This is shown diagrammatically.
II
:\ d 'j ,I I
,I:-
CURRENTS IN OPPOSITE DIRECTIONS
I I
00
jt
I: " i;'
Ii I~
Current Crowded Toward Facing Sides
I'
I;
Current Crowded Toward Outer Faces
The extent to which proximity increases d-c resistance depends upon the closeness of the spacing. The curves in Fig. 2 show the effect of proximity on the current rating of 55 EC rectangular conductors when spaced on 18 inch and 4 inch centers. Although a slight additional reduction in current rating at 4 inches is due to mutual heating, the majority is due to proximity. The 18 inch spacing may be considered as adequate for most
I: "
i!
,"
CURRENTS IN SAME DIRECTION
"
18
installations to reduce proximity to a negligible amount. 3. Mutual heating effects Mutual heating may be linked closely to proximity, but where proximity effect is the influence of the magnetic field of one conductor on a nearby conductor, mutual heating is due only to the interference of one conductor on the heat dissipation of the other. Close spacing, however, is not always indicative of mutual heating. On closely spaced, vertically arranged rectangular bars, the "chimney effect" created may actually aid in heat dissipation. Usually, however, closely spaced buses concentrate the heat produced by elements of the circuit and convection cannot dissipate this heat as effectively as it can when a greater separation is maintained. Less efficient cooling causes a more rapid temperature rise in the conductor and thereby reduces the current that can be carried for a given temperature rise. This phenomenon does not affect the RRac ratio of the bus. An equal degree of de
heating on either an a-c or d-c bus will produce like heating effects. 4. Induced circulating currents Induced circulating currents in nearby metallic parts require energy which must be supplied from the inducing circuit. This loss is accounted for by an additional component of resistance. The magnitude of this loss is a function of the distance to adjacent metal parts, the magnitude of the current flowing, and the resistivity of the metal part. Where such heating effects become excessive, e.g., in a common enclosure for a 3 phase bus installation, such as segregated phase or isolated phase bus, it may be necessary to make individual housings for each phase. 5. Hysteresis losses Hysteresis losses or magnetic heating is associated with the losses caused by induced circulating currents in that both are a result of the magnetic field of the conductor. This additional loss is also accounted for by an additional component of resistance. Where excessive heating is produced in nearby building steel, it may be necessary to band the steel sh'ucture with low resistance sh'aps or interpose an amortisseur grid between the bus and the steel to be protected. Losses in adjacent building steel will also be reduced by the presence of high circulating currents in metallic enclosures which separate the bus from building steel, as these circulating currents set up fields directly opposed to the conductor fields, thereby reducing the net effect. *
* "Temperature Rise
and Losses in Solid Structural Steel," O. R. Schurig and H. P. Kuehni, Journal AIEE, May 1926, pp. 446-453.
electrical design - section II
EFFECT OF CONDUCTOR SPACING ON CURRENT RATING 6101 Aluminum Bus at Spacings of 4" and 18"
6"xy"" RECTANGULAR BARS
V
V 3000
Current ratings are for bars arranged vertically and based on a 30 C temperature rise over 40 C
V
/
V
ambient in still but unconfined air.
/ V>
V
w
2000
...
:lj 2500
V
3"xlh" RECTANGULAR BARS
~'"
~ I-
u
()~:7 e;,~
...
V.I¥ <:;~tS-~'0
zw
'"'"
17
...... I.........
~
II
V 1000
/
VV
o
'0
V
...-
I
/
I I IV 1500 VI
~
~'/
/
...
~./'
;:,
u
rjA;t¢°
'";:,'"
.
S
e;
zw
V V
~
...
V
./' 1500
.~
S
1/ V> w
i?-0/
~
/ /
/V
V 500
1006 2
1
. 1
3
2
'"
NUMBER OF BARS PER PHASE
3000
2500
3
4
NUMBER OF BARS PER PHASE
5"x'4" RECTANGULAR BARS
4"x lh" RECTANGULAR BARS
V
V V
/
/
2000 V> w
0
o~
...'" ...zS w
w
'"'"
-"
"~ ...y . I~\~
~
/
1500
;:,
u
/
...
)
0 '0
II
V
/
/'
V v
2500
--
v
V> w
l - I--
....'"w ~ ...
e;,~!>"
.it
~'~
'"
V
'"
0
o~
e:;~~
b/
,'I>
2000
V
.
;:,
7
u
...
V
)
o
"v
'0
V
,.
'\~9-
....
,/
!.e;,~p
1/ / " 1/
17
1500
1000 r/
1/
VV jV
IlJ 1000
500 1
2 3 NUMBER OF BARS PER PHASE
2
1
4
3
NUMBER OF BARS PER PHASE
Fig. 2
'" •••. ;.
',. ~'"
t
e ••
-Ii'·
X
.. J
section II - electrical design
6. Losses due to corona Cowna discharge from a high voltage conductor or equipment is due to the gaseous discharges in the air in its immediate vicinity. This discharge represents an energy loss which also adds to the value of a-c resistance. The magnitude of corona loss is a function of a. Voltage of the bus; b. The diameter of the conductor; c. Irregular smfaces such as bolt heads, sharp projections, or rough spots and dirt on the conductor sUlface; d. The humidity of the atmosphere; e. The atmospheric density. Corona losses may be minimized by eliminating all sharp irregularities on the conductor installation such as bolt heads or other sharp projections and by keeping the conductor clean and free from rough abrasions. Where these factors unavoidably exist, electrostatic shields can be used as a cover to minimize cororiildischarge.
!
r i
i
JI
i
~
I[ (
Skin Effect
1,: ( ,
~i ,
II"',
,"
Ii
':111
': :,
.1
, •
," j I
*
Of the factors that contribute to the a-c resistance of a bus conductor, skin effect is generally the most important. At any particular a-c frequency, skin effect is an inherent characteristic of the cross sectional shape and resistivity of the bus itself and can be evaluated independent of the electrical design of the circuit. Skin effect is caused by the internal magnetic flux in the bus conductor. More of this internal flux links the center of the conductor than the surface, thereby inducing a greater reactive voltage drop, Ix, at the center of the conductor than near the surface. The total voltage drop for any given length of conductor will be the same, whether measured near the center, as V e, or near the sUlface, V., Fig. 3.
H, !
"
I
,',
r
"
I
,I
I
I
i/,
I I
,j
n
Ve =lcR+jlcX c
II :1
"
I I
=~=============~=========~=~
I
I
I
I
,j
Vs=lsR+j'sX s
:'
I:
I:
\
===========================?=~ \
:
\
I:
; ;: iI I
II II,Ii I:
\: "
l"
IiI . i.
I' : Ii
.,!
"
Effect of Bus Shape and Size on A·C Resistance Rectangular Bars-High current requirements often demand that a bus be built up in laminated form using several rectangular bars of smaller capacity. The arrangement of these rectangular conductors, when grouped to form a large a-c bus, i,s important to utilize the cross section of metal efficiently. Several methods are used to reduce skin effect, some of which can be enumerated as follows: 1. Ananging the conductors of a bus to produce a void at the center of the group to reduce the effect of internal flux; 2. Interlacing or paired-phase arrangements of parallel bars; 3. Installing iron magnetic loops or balancers to increase the reactance in bars carrying higher currents. (Not practical for most installations.) The necessity of incorporating one of the above methods to a bus composed of a number of rectangular bars will be apparent from Fig. 5 showing one phase of a typical bus bar system. This illustration shows the division of current between the 10 indi-
1020
225
350 513
249
342 257
677
480
9" TO 1ST BAR OF RETURN
=
of Electric Power Transmission," L. F. Woodruff, Published by John Wiley & Sons, Inc,
I:
Bus conductors have a unUOlm resistivity throughout; hence, in order to maintain a lower resistance drop at the center of the conductor, the current density in this portion of the conductor must be lower than at the surface. This greater concentration of current at the surface is termed "skin effect," and in the large low resistance sections usually encountered in bus bar, its magnitude can be appreciable at 60 cps. Special arrangements and designs are necessary for large, low resistance a-c buses to effectively reduce skin effect.
728
Since the inductive reactance at the center, lexe, is greater than the surface reactance drop, I.x., the resistance drop at the center must be smaller than the resistance drop, lsr, at the surface in order to produce the same voltage drop at the center that appears across any other filament parallel to the conductor axis as shown in the diagram, i.e., /Yel /y.I. Vectorially, this is shown in Fig. 4.
I,X,
Fig. 4
Fig. 3
* "Principles ;1
V,
20
Fig. 5 '" '" "Current Carrying Capacity of Hollow Conductors," H, W. Pabst, The ELECTRIC JOURNAL, July, 1931.
.1;>0
elect1'ical deSign - section II
vidual rectangular bars comprising the bus. These bars are arranged vertically with each bar separated by a small air space. The internal flux greatly increases the reactance in the center bars, causing reduced currents and a slight shift in phase relationship between the currents in the individual bars. Vectorially, the addition of these individual currents gives a total current of 4380 amperes, although the algebraic sum of the currents is 4849 amperes. This is shown in Fig. 6.
728
513
480
677
what superior to the hollow square arrangement as all bus surfaces are adequately exposed to dissipate heat, and the internal flux, although producing greater current densities in the outer edges of the bars, gives high current ratings for multiple bar arrangements. The interlacing of bars, or paired-phase arrangements, offers an excellent solution to the unequal distribution of currents in low voltage systems. Low voltage bus duct of low reactance design makes use of these arrangements to almost completely nullify proximity and skin effects. The arrangements of bars, Figs. 8 and 9, illustrate these types of design.
C:==:::::JI A1 C:==:::::JI Bl
Fig. 6"
'--
Proximity effect causes the non-symmetrical division of current in the bars. The relatively small spacing to the return bus and the high current causes a pronounced concentration of current in the facing bars and much less current in the outside bars.
B
-II Cl
A
C:==:::JI A2 C:==:::JI B2 '--
....IIC2
'--
....IIA3
C:==:::JI B3 C==:::JIC3
Modified Hollow Square Arrangement
Hollow Square Arrangement Fig. 7
Various hollow square arrangements of multiple rectangular bars have been used to reduce skin effect. Two common arrangements are indicated in Fig. 7. Both arrangements essentially produce a void at the center of the group of conductors. The hollow square arrangement gives a low skin effect resistance ratio-the resulting shape being similar to a square tubular conductor. Current density will be slightly greater at the corners of this arrangement. The disadvantage of this arrangement is the necessity of spacing supports closer than for square tubing and box channel shapes. The reduced surface exposure for the dissipation of heat also limits the current carrying capacity, but it is obviously better than a closed square tubular conductor. The modified hollow square arrangement is some* "Current Carrying Capacity of Hollow Conductors," H. W. Pabst, The ELECTRIC JOURNAL, July, 1931.
Interlaced Bars
C Paired Phase Arrangement
Fig. 8
Fig. 9
The paired-phase arrangement, Fig. 9*, produces uniform current density because of the ahnost complete neutralization of the magnetic fields. Currents tend to divide evenly in all bars under conditions of unbalanced load apd even for single phase loads. In each pair of bars, the currents tend to be nearly equal in magnitude and opposite in phase, e.g., the currents in A1 and B2 , A 2 and C 1 , and B 1 and C 2 , as shown vectorially-are nearly opposite in phase relation and nearly equal in magnitude. The total phase current in each of the three phases-A, B, and Cdivide into two components-A 1 and A 2 , B1 and B2, C 1 and C 2-each pair tending to be nearly equal in magnitude and differing in pha,~e angle by nearly 60 degrees. It is important that ~terphase ties be made at all intermediate load connections; otherwise, the system impedance will be affected; currents will not divide equally between pairs of bars, and higher temperature rises will be encountered in the more heaVily loaded pair of bars. . Tubular Conductors-A tubular conductor provides the most efficient cross section for an electrical conductor when considering skin effect because the center of the conductor is hollow where current densities " "Current Distribution in Paired-Phase Bus Bars Under Unbalanced Load Conditions." J. B. Cataldo and N. Shaclanan, A.I.E.E. Transactions Paper 54-329, October. 1954.
21
·-------~··------.--·~·--~··-.·I'-~......,...
..
·__
" ,
.~
_r- •• ~ •••_•• _
~.
..
':;"; ~..::..' . '
section II - electrical design
EFFECT OF WALL THICKNESS ON ELECTRICAL CHARACTERISTICS OF A 3 INCH O.D. ROUND ALUMINUM TUBE OF ALLOY 6063·T6 2
o
2.0
jT 7!
~ Rae
C
Rdc
"./
--~
~
/' ,/ /"
/.
15 1.5
·1 !I
/
f!
!
I
'II ! . I
/
(
;
i
/
/
Ii
11
II;j
u
·1'
o o .... '"w a..
1 11 ,
I
~
o u '"
10 1.0
U
,
~ Vl
~
w
'
Z
if I
I'
i.
""
'.
t Il
t ." ",
"
"
II
~ f-"""
\,
,;
5
Z
:'\:
'""-
o
:
..........
.....
0
Rae AT
..........
~
...~
70 C
..........
0
z
i"""'-- ..........
1500
<{
"""- r- ~
Rdc AT
'"...
70 C
z
1400
w
'"::>'" Vl
1300
a..
U 0
'" .2
.3
.4
.5
.6 .7 WALL THICKNESS,
.8
Fig. 10
22
1600
;::
.9
1.0
1.1
1.2
1.3
1.4
1.5
t (INCHES) Current ratings are based on a 30 C temperature rise over a 40 C ambient temperature in still but unconfined air.
"j: l' ~I );
.1
1700
u u
1/
Ii
"~
1800
0
/
:i I~ L
;1
...w ...'"0u
u
,: '
I
1900
~
0.8"
/ 1/
I J:"
'I
<{
'"a..w
c
/ ","
2000
....'"
::>
J
. ~1"~
<{
w ::>
I
/
2100
~
I ~~
I Wi ",
I I I I I I
K
I
'"
w
'"a..w
lac
I
~; .'
r
r;;
I
/
';
,II
I
V-
V
I~ J
i' f'
I I
/'
I:
i
~'
.j
V
l/
/ ./
/'
\
Vl
W
~
-
\ \
~
"
/
~
,Vl
~/
,
\ \
;::-
i ~
I
V
~
i,
ti
r
/
R
,;
il
Rae Rdc
1200
electrical design - section II
normally would be smaller. A round tubular conductor is slightly more efficient than a square tubular conductor as currents will tend to be slightly greater at the corners of square tubing. The magnitude of skin effect increases with wall thickness in a round tubular conductor as shown
internal ventilation. As a result, standard shapes make an efficient bus conductor in the arrangements indicated and are used where high current ratings are desired.
by the RR ae curve in Fig. 10. For thin tubes, skin effect
Calculation of A-C Resistance
lie
conductor. The Rae curve, Fig. 10, shows this variation R rle for a 3 inch outside diameter tube of aluminum alloy 6063- T6 which has a typical conductivity of 53 per cent (lACS). The d-c resistance at 70 C as indicated in Fig. 10 is a function of wall thickness. When the d-c resistance values are multiplied by corresponding
The calculation of the a-c resistance of a conductor is based on the determination of the apparent increase in the d-c resistance of the conductor due to skin effect only, since this is the principal component that influences d-c resistance. For any given cross sectional shape, its d-c resistance, and the frequency of the circuit, skin effect can be evaluated independent of the conductor material and the parameters of the circuit. To find a-c resistance, the "skin effect resistance
. t ance ra t'10,"R va1ues a f t1le "k':ff s m e ect reS1S Ifae ,a curve
ratio," RR ae , is first determined. This ratio is a multiply-
is negligible and increases with wall thickness until it is a maximum where the tube becomes a solid round
(Ie
dc
giving a-c resistance is obtained. This a-c resistance curve, Rae, shows that a-c resistance becomes a minimum with a wall thickness of approximately 0.8 inch and increases slightly when the wall thickness is increased beyond this point. The current rating of this 3 inch diameter tube is also greatest at a wall thickness of 0.8 inch where a-c resistance is at a minimum as shown by the curve, lac. These curves are typical for all diameters of tubing having a conductivity of 53 per cent (lACS at 20 C). A-c resistance will be a minimum and the current rating a maximum at approximately 0.8 inch wall thickness for all diameters. Other materials will produce similar characteristics, but these optimum. characteristics will occur at a different wall thickness. Copper tubing (98 per cent conductivity lACS), has a minimum a-c resistance and maximum current rating when the wall thickness is approximately 0.5 inch and EC aluminum tubing (61 per cent conductivity lACS) at approximately 0.7 inch wall thickness. The effect of high conductivity of the material is to concentrate the current nearer the surface of the conductor. This means that a lower conductivity material fares better, with regard to skin effect; a given cross section is better utilized with current more uniformly distributed. It is sometimes possible to design a conductor of aluminum with the same outside diameter as one of copper, both with the same a-c resistance per foot. As a consequence, the same size fittings can be used. *
Channels and Angles Arranged in Box Form-These shapes arranged in box fonn, shown on page 11, approximate square tubular conductor in configuration. The web or leg thickness of standard sections is usually within the optimum limits where skin effect is at a low value. In addition, such shapes provide for
* "Aluminum in Heavy Current Conductors," 'VilJiam Paper 55-261, April 20, 1955.
Deans, AlEE Trans
ing factor that is used to modify the d-c resistance to obtain a-c resistance at the same temperature, e.g., Rac
=R
de
Rae R dc
X-.
The magnitude of the skin effect resistance ratio,
Rae' can b e determme : d convemen . tl y f rom curves:., R dc The following curves are used in this text as the basis for determining. skin effect for the common shapes of conductor, Fig. 11, page 24, skin effect in isolated rectangular bus conductors; Fig. 12, page 25, skin effect in isolated round wires and tubes; and Fig. 13, page 26, skin effect in isolated square tubular conductors. . Independent V ariable-The conductor shapes in Figs. 11, 12, and 13 have a common independent variable 'which is the abcissa on these graphs. The value of this independent variable is dependent upon the circuit frequency and the d-c resistance of the conductor at a given temperature, t. If the a-c resistance is desired at any other temperature, the d-c resistance must be converted to that temperature before the independent variable is calculated. The d-ch'esistance temperature conversion is shown on page 17. With the d-c resistance converted to the desired temperature, the calculation of tlle independent variable is then made by the following:
Where: Rde is the resistance in microhms per foot; is the frequency in cycles per second.
f
This establishes one coordinate for determining from
* "Electrical Coils and Conductors," H. B.
Dwight, McGraw-Hill Book Co.
23
lilillliililiililllll~
~
__..- ~._.~ . ~~=--.- ~
__.
section II - electrical design
CURVES FOR SKIN EFFECT OF ISOLATED FLAT RECTANGULAR CONDUCTORS I. 5
v
I
v
/ fl ~
1.4 I - - -
r---
/
t
~
~
I
I-
w.
/
I
II
/
J
)
If /
I I I 7 11 17
iJ ....
'.1
"-
~J
J /
./
J J
VhF! II
'0
J /f
I I 1 I /V II '/
1.3
II'
I
-$')
}
V
J
If
7
.../
7 J
/
/ VI /
If 'I iJlf
1.2
Ii / If V 'I
,j
J
J
j
'j
IJv
1.1
).
v
1/ /v 1.0
,.,.
ji ¥
\.
i ,;; !.
20
40
60
80
~ fx10 3
100
120
H. B. Dwight, "Elech'ical Coils and Conductors," McGraw-Hill Book Co.
.", l::
o
IN MICROHMS PER FOOT
j:
~
l----"V Rdc
L"
il:
/
Fig. 11
24
140
160
180
electrical design - section II
CURVES FOR SKIN EFFECT OF ISOLATED ROUND ROD AND TUBULAR CONDUCTORS 2. 1
2.0
t~
1.9
! - f--
1.8
ii;'
i'"
e
0
!:2
o· 0
'"
""'Ii "'t:I ~
-
-
'"""
0
1.7
t/ d' tid tid
O.~5
0
'"
0
::J
0.40
tid
1.6
I
o'
0.35
!:!
o'
0.30
!2 O' 0.
0
C::i
~
1.5
O'
&
O'
1.4
~
O'
~
O'
1.3
r;:,~ 1.2 Cl~
J;;P'
,1° 1.1
_0.0'1.
\/0.-
I,
tid-om 1.0
o
50
100
150
200
V
250
300
350
400
f•lO,
Rdc
Rdc
IN MICROHMS PER FOOT.
H. B. Dwight, "Electrical Coils and Conductors," McGraw-Hill Book Co.
Fig. 12
25
section II - electrical design
CURVES FOR SKIN EFFECT OF ISOLATED SQUARE ROD AND SQUARE TUBULAR CONDUCTORS
2.1
2.0
1.9
1
1.8
iI,
:11
,j:
"I: ~~ I,
1.7
'P
'i iii
J i,
1.6
Ii
~
I,
~
;,:
1.5 " J
t
.. I[
".
f
I
I
1.4 :
!
r " [
I
i
1.3
,;'I' ::
o
Ii
i;
I:: I..
1.2
i' I
II:
I:r, "
.1
I~ ,
1.1
I
I: t:
1.0
It;;
i~ ".
o
50
I {.i, .j
i:
150
200 r e 2 5 0 f,,103
Rdc
1
300
Rdc IN MICROHMS PER FOOT
Fig. 13
Ii
IIf: .
100
H. B. Dw;ghl, "Electrical Coils and Conductors," McGraw-Hill Book Co.
26
.J;
.
i:\
3.$0
400
450
electrical design - section II
curves the skin effect resistance ratio of the particular conductor section. The other parameter is a function of the conductor shape or physical dimensions, and its detelmination will be considered in the following paragraphs for the common bus conductor shapes.
curve representing the ratio ~
=
0.5 is the limitin
9
case for a solid square conductor. These curves may be used without appreciable error on channel bus conductors arranged in box form and also for angle conductors arranged in box form, Fig. 15.
Shape Parameter-The shape parameter is different for all of the foregoing conductor sections and is extremely variable because of the innumerable combinations of conductor dimensions. The graphical method provides for this variation by offering a family of curves to cover the practical range of bus conductors.
Rectangular Bar-The shape parameter for rectangular bar is the ratio of conductor width, W, to conductor thickness, t, in the same units of measure. The condition where Wit = 1 is the limiting case for a solid square conductor. Where several rectangular bar conductors are grouped together with a small separation between bars, a larger rectangular section is formed. The over-all dimensions of this section may be used with little error to establish the Wit ratio. For example, the Wit ratio for four rectangular conductors each G inches X Y4 inch spaced % inch apart will be as indicated in Fig. 14.
Fig. 15
The
dt ratio for the boxed channel arrangement
will be the ratio of the channel web thickness to the average outside dimension formed by the channels. For the boxed angle arrangement, the
~ ratio is the
ratio of the leg thickness to the average outside dimension formed by the two angles. These dimensions are listed on pages 133 and 135 for the standard clamps usually used as supports and spacers.
W
T=
6 1%
.. f Rac D elerlnluallOn 0 -R dc
= 3.425
With the independent variable calculated as described above and the shape parameter determined from the physical dimensions of the conductor, the Rae "k' . t ance ra t'10" can b e d etelmme . d '-R s m e ff ect reSlS de
Fig. 14
Solid Round and Tubular Conductors-The shape parameter for round tubular conductors is the ratio of the wall thickness of the tube to its outside diameter,
{Z, both in the same units of measure. The limit-
ing case
where~ = 0.5 is the curve for a solid round
conductor.
Square Tubula1' Conductors-The shape parameter for a square tubular conductor is the ratio of the wall thickness to its outside square dimension, _t. The
.
d
from the appropriate graph for the conductor shape. The shape parameter determines the proper curve from the family of shape curves and the independent variable establishes a point on this curve for which a ...:l ·(j)n t I1e or dinate sca Ie. · Rae correspon dmg - ra t"10 IS reaUj R dc To determine a-c resistance, the d-c resistance is multiplied by this ratio. This gives the a-c resistance at the same temperature, R ac = -Roc X Rde· Rdc To illustrate the calculation of the a-c resistance of aluminum bus bar, sample calculation is presented for several common conductor shapes.
a
PROBLEM NO. 2 Required: The 60 cps a-c resistance at 70 C in microhms per foot for the various bus conductor shapes illustrated in Problem No.1 on page 16.
27
section II - elect1'ical design
A. Rectangular EC aluminum bus bar 4 inches X % inch with a d-c resistance of 13.35 microhms per foot at 20 C; B. 1114 inch solid round EC aluminum bus bar with a d-c resistance of 10.88 microruns per foot at 20 C; C. Ph inch IPS tubular bus bar of alloy 6063-T6 with a doc resistance of 19.2 microhms per foot at 20 C; D. Two extruded channels 4 inches-2.16 lb. of 6063-T6 alloy arranged in box form with a d-c resistance of 8.35 microhms per foot at 20 C.
= 1.061
Rae
R de
and the a-c resistance is Rae
=r X
Rae
= 1.061
Rae
2-C.
,I
=
= =
t/fXT03 d and \/~mustbe calculated. These
[1 + a20 (70 - 20) J 13.35 [1 + (0.00403) (50)] 16.04 microhms perfoot at 70 C. R ae20
are given ~s follows for 11;2 inch standard IPS tubing:
t
~f
Rae
3
Rae
= 1.060
and the a-c resistance at 70 C is
R
Rae10
Rae = -R de
R ae10
= 1.060 X 16.04 = 17.00 microhms perfootat70 C.
de10
The a-c resistance at 60 cps of 1% inch solid round EC aluminum bus bar at 70 C is calculated as follows by determining first its d-c resistance at 70 C:
=
[1 + a20 (70 - 20) J [1 + (0.00403) (50)J 13.07 microhms per foot at 70 C. R
= 10.88
=
The skin effect resistance ratio for solid round conductor is obtained from Fig. 12 0.50 and by using the curve where tid calculating the parameter:
=
~f X
3
10 =
R de
From Fig. 12, the skin effect resistance ratio is:
28
_
-
= 22.57 microhms per foot at 70 C.
The skin effect resistance ratio from Fig. 12 for all practical purposes, is unity and the a-c resistance is equal to the d-c resistance for 11;2 inch IPS tubing. The approximate skin effect resistance ratios for the standard IPS conductors of 6063-T6 alloy at a temperature of 70 C are given in the table on page 127. This table shows that the skin effect resistance ratio at 60 cps for bus conductors operating at 70 C is approximately unity for all sizes up to 3 inches standard IPS and up to and including 1 inch IPS in the extra heavy sizes.
Then, the skin effect resistance ratio from Fig. 11 is approximately
R ae10
10 3
= 0.076
Rae R = 1.000 and Rae = R de de
10 =
X
X
Rae
-t = % -4 = 16
2-B.
0.145
d = 1.900
W
Rae Rae
= R de20 [1 + azo (70 - 20) J = 19.2 [1 + (0.00350) (50)J = 22.57 microruns per foot at 70 C.
To find the skin effect resistance ratio from Fig. 12 on page 25, values for the factors
The skin effect resistance ratio for rectangular bus bar is given in Fig. 11 on page 24. For a 4 inch X 14 inch bus bar, the coordinates that establish the skin effect resistance ratio are calculated as follows:
~f X
= 13.87 microhms
The a-c resistance at 60 cps of 1112 inch IPS tubular bus is calculated by determining first its d-c resistance at 70 C: R de70
The 60 cps a-c resistance of 4 inch X % inch rectangular EC bus bar at 70 C is calculated as follows by determining first the d-c resistance at 70 C: R aC10
X 13.07
per foot at 70 C. -
Solution:
2-A.
R de
2-D.
The 60 cps a-c resistance in microhms per foot at 70 C for two channels of aluminum alloy 6063-T6 arranged in box form, each channel 4 inches-2.16 lb. with a d-c resistance of 8.35 microhms per foot at 20 C, is obtained by converting the d-c resistance at 20 C to 70 C and then obtaining the skin effect resistance ratio from Fig. 13. The d-c resistance of a single channel at 70 C will be: R dc10
= R,!e2o [1 + a~o (t t)] = 8.35 [1 + (0.00350) (50)J 1 -
= 9.82 microhms per foot at 70 C or
= 4.91 microhms per foot at 70 C for two channels.
elect1'ical design - section II
and
The corresponding skin effect resistance ratio from Fig. 13 is:
-R-- must be obtained. These factors ~ are calculated as follows:
Rae 1.045. R de The a-c resistance'is calculated as follows:
To use Fig. 13, the coordinates
~
X103
=
de
£= 0.~47 =
0.0618
Rae
Rae = -R X
R
de
de
~f X 103 = Rile
60,000
= 1.045 X 4.91
= 111.
= 5.13 microhms per foot at 70 C.
4.91
INDUCTIVE REACTANCE OF BUS CONDUCTORS The total inductive reactance, then, is the algebraic sum of these two parts:
The inductive reactance for various bus conductor shapes is obtained by different means. For solid round and round tubular bus, established formulas for inductive reactance may be used or reactance values may be obtained from tables for the standard sizes. For rectangular bus bars and for channel bus arranged in box form, the most convenient method of determining 60 cps inductive reactance is from curves giving reactance in terms of conductor spacing or equivalent spacing. These 60 cps reactance values can be converted to any other frequency by multiplying the 60 cps value by a ratio of the two frequencies, e.g., where X 60 is the 60 cps reactance and the reactance, Xr, is wanted at another frequency, f, it is obtained by the relation:
X r = X so
xL.
60 The methods of determining reactance for various bus conductor shapes are illustrated in Problem No.3 on page 38.
XL
XLI
that due to the flux out to a radius of one foot from the center of the conductor; .
2.
tha! due to the remaining flux beyond the onefoot radius and extending to the retum conductor or neutral.
XLi'
XL2'
1 = 0.88191 f Log lo GMR (microhms perfoot).
Where: GMR is given in feet; f is given in cycles per second.
.
The GMR term is the geometric mean radius of the conductor. It is a mathematical relationship expressing the radius of an infinitely thin tube whose inductance, carrying the same current, is equal to that of the conductor. The GMR for non-magnetic solid round or tubular conductors can be determined from their physical din1ensions. For these conductors, the GMR is expressed by the following relations: 1. Solid Round Conductor GMR = 0.7788 l' (in feet when radius, r, is in feet) 2. Tubular Conductor j .• 1\4
LnGMR=Lnr 1 _ 4
=
1.
+ XL2'
Inductive Reactance to a One-Foot Radius-The
The inductive reactance for a round conductor is given by the fOlmula: GMD XL 0.88191 f Log io GMR For convenience in calculating and tabulating inductive reactance, this formula is usually written in two terms. These terms separate inductive reactance into two parts:
XLi
fOlmula applying to inductive reactance due to the flux within a radius of one foot of the center of the conductor is:
Solid. Round and Round Tubular Bus Conductors
(mierolmls per foot, eonduetor to neutral) .
=
-1'1 2 1'2 2 +1'2 4. (%+Ln:i.) l'
(1'1 2
-
1'22)2
2
Where: 1'1 is the outside radius of the tube; 1'2 is the inside radius of the tube; Ln is the natural logarithm.
Values of inductive reactance for a one-foot spacing have been established for each standard size of solid round and round tubular conductor by the above 1'elations. ThIs portion of the total inductive reactance is a function of the GMR of the conductor at any given frequency and is a constant for each standard size.
29
"
......
'
' ..t _.., . . .1.'.,,1 ..
I
'.
section II - electrical design
The GMR values for both the standard pipe sizes of tubular bus and the extra heavy IPS series are shown on page 127. The values of GMR for standard sizes of solid rOlU1d bus conductor are given on page 125. This table also lists the inductive reactance at 60 cps for a one-foot spacing using the standard values of GMR given in these tables.
can be calculated for various conductor arrangements, as illustrated in Fig. 16. The general formula for the GMD of a conductor in any three-phase configuration is given by the following expression: GMD
= \o/A X B X C
Where:
Inductive Reactance Spacing Factor-The portion of inductive reactance due to the remaining flux beyond the one-foot radius from the conductor and extending to the return circuit or neuh'al is: XL2
= 0:88191 f Log
10
GMD (microhms per foot).
A, B, and C are the distances between the three conductors.
The calculation of the GMD for various standard arrangements and spacings is given in the following examples:
Where:
1. Symmetrical Triangular Spacing of 10 Feet GMD = A B C = 10 feet;
= =
tis the frequency in cycles per second. The values obtained from this formula are usually called "spacing factqr( and are algebraically added to the values of inductive reactance for a one-foot spacing to get the total inductive reactance. These "spacing factors," as their name indicates, are a function of the total distance between conductors where only one return conductor is involved or, more generally, the GMD (geometric mean distance between conductors) or equivalent spacing where several con-' ductors comprise the circuit. The spacing factors for conductor spacings of 1 to 251 inches are given on page 137. These spacings are based on the total separation between conductors and not from one foot outward.
Geometric Mean Distance (GMD )-The GMD is dependent upon the conductor spacing and arrangement. For a single-phase installation, the GMD is merely the physical spacing between conductors in feet. For a three-phase configuration, the equivalent spacing
= =
2. Right Triangulal' Spacing where A C 10 Feet GMD 1. 123A = 1.123 X 10 11.23 feet;
=
=
3. Unequal Triangular Spacing where A = 10 Feet, B 12 Feet, C 15 Feet GMD = \0/ 10 X 12 X 15 = 12.16 feet;
=
=
4. Symmetrical Flat Spacing A
GMD = 1.26A
= 1.26 X
10
= B = 10 Feet = 12.6 feet;
5. Non-symmetrical Flat Spacing where A = 10 Feet, B = 12 Feet, C = 22 Feet GMD
= \0/ 10 X. 12 X 22 = 13.82 feet.
Once the GMD or equivalent spacing has been detennined, the inductive reactance due to this spacing may be determined from convenient tables of inductive reactance spacing factors which list values of inductive reactance corresponding to various spacings or equivalent spacings (GMD) as determined by the above formulas.
Inductive Reactance of Rectangular Bars
Af\.
L~ Symmetrical triangular spacing GMD=
Unequal triangular spacing GMD= iYAXBxC
Right triangular spacing A C GMD = 1.123 A
=
A=B=C
Ii ,.
Unsymmetrical Bat spacing GMD iY A X B X C
Symmetrical flat spacing
A=B GMD
= 1.26 A
=
Fig. 16
30
Graphical Solution Using Reactance Curves-The inductive reactance of rectangular bars usually cannot be calculated by the methods used for round conductors. The reactance of a circuit comprised of two rectangular bars can generally be determined more expediently by curves than by a rigid mathematical treahnent of the problem. The reactance curves * in Figs. 17 and 18, establish the 60 cps inductive reactance of a circuit comprised of two bars for a wide range of spacings and conductor dimensions. Inductive reactance obtained by these curves is based only upon the physical dimensions and arrangement of the conductors. Fig. 17 should be used for closely spaced conductors and Fig. 18 for widely spaced conductors. Where a conductor is composed of several bars grouped together with a small air space between bars, the over-all dimensions of the group can be used for
* H.
B. Dwight, "Reactance Values for Rectangular Conductors," ELECTRIC JOURNAL, June, 1919.
electrical design - section 11
INDUCTIVE REACTANCE AT 60 CPS OF CLOSELY SPACED RECTM~GULAR CONDUCTORS
55
50
~/
-"
./ ./
45
~~
/
40
~~ / ~~ V ~~
oo ....
~ 35 OJ>
/
~ J:
o
~
'"
u
~ 30
~ ~V
/. ~ ~
I
en
.,:
o
.'0
~V
V
A-
.......!. -0
~ =5
/J ~~
v
~ 7d A
.... 25
« w
/I; II
U
z
« ....
t=O",-
u ~ 20
~ ~I t
'"
w
> ;::
If/;/
u
::> Cl
I
~ 15
.
"
-lAr-
B- 2
T-
"A -1
10
W
l~l--s--;1~
A_v: 8- 2
/iJ ~
I
5
IC
R
I
t=115
~ =1/10
/ o
-
8
8 -
//; I"r-..
/
~V
./
I 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 S
1.1
1.2
1.3
1.4
A+B Fig. 17 H. B. Dwight, "Electric JOUl'llal," Vol. 16, June 1919, Pages 255~256
1.5
1.6
1.7
1.8
1.9
2.0
I. '
.,.
section II - electrical design
INDUCTIVE REACTANCE AT 60 CPS OF WIDELY SPACED RECTANGULAR CONDUCTORS 95
90
85
C 0 u.
""w
80
0..
II)
::E :r
,
0
e; 75
(
I.....
~
I
.,; .,; 70
0 a
'0
...< w
65
V
Z
<{ l-
V
<{
w
""w
60
> u ;:) c 55
;::
z
II
i ,.i: I'
ii ~
50
'i:
c:;:;
:1'
-
r-T
"!I
i~ . -~ ~i
"d
0
l
2
3
"
5
6 S
A+B
7
or
8
9
10
GMO
A+B
. s NOTE: Use Graph and Fonnula only when - - b is greater than 2.
a+
APPROXIMATE FORMULA: GMD X so 52.9 Log1o a + b + 34.5 (rnicrohms per foot of conductor)
=
Conventional Arrangement GMD
Flat Arrangement For symmetrical flat spacings shown above (see page 30 for GMD of other conductor configurations)
= 1.26 S.
Fig. 18 H. B. Dwight, "Electric Journal," Vol. 16, June 1919, Pages 255-256
32
11
12
electrical design - section II
a rough approximation of reactance by considering the group as a single bar. This is shown in Fig. 19. Where a greater separation exists between bars, this rough approximation should not be made. When the bars comprising a conductor are widely spaced as in a hollow square arrangement, these bars may be
:::;
::
~d---1
-S:---I
assumes an equal division of current between bars and neglects proximity and skin effect. The error due to this assumption is usually not large for a frequency of 60 cps as resistance is affected to a far greater degree than inductance by an unequal distribution of current in the conductor cross section.
Fig. 19
grouped as illustrated in Fig. 20, to give a close approximation for reactance calculations. The determination of reactance by these methods
-r--.
1.1 1 1.10
5',-,
I
.............r-.,Lo
-
1.09
~
---
-
1.08 1.07 5
I I I --1 ~S
j
1.12
1.06
GMD
~ ~
~
" --
~ 0.70
""" '" - '" """
-
0,65
1.04
.............
.............
~
-
~
r---...
~
1.02 0.40 0.30
L- 0.10
0.00
0.99
o
0.1
~~
" ""'" " I"'" ......
~
.........
,
i'......
r-- r--. I'-.. I'....... ~ ~ ........... ~ ~ r-I--.. r-- r---.... ~ ~~~ r-- r-.... r-- I -- r---- -......: r--. r=::: ~~ :'-.. r---...:::: :S:::: ~ r-:: t--- --.: ::-:::: t:S ~ ~ -.::::: ::-:::: r-- ~ ~ ~
?r
1.00
S
-- ---
0.55 0.50
1.01
.............
r--: ~
0.60 1.03
I~T
r--......
.............
0.75 1.05
,0
Fig. 20
II---..
1.13
c
8
A
:::::
It1"-
-
U
0.2
0.3
0.5
0.4
0.6
0.7
0.8
0.9
""
1.0
Fig. 21
0t.
"Engineering Calculations Inductance and Reactance f01' Rectangular Bar Conductors," O. R. Schurig, General Electric Reoiew, Vo . 36, No.5, May 1933. Curves plotted from tables calculated by F. W. Grover.
33
section II - electrical design I
Methods of Calculation-The calculation of inductive reactance and voltage drop is often necessary for conductor arrangements other than two rectangular bars. Such arrangements as the multiple bars per phase, 5.4
5.0 4.6
3.8
~
.~
1\ \
4.2
3.4
1\
GMD 3.0
LL-
II-
I-
~S-1
\
S
i=O 1\ ./
l-
II-
TO 0.1
~
2.6
'\..
'\
2.2
SEE CHART BELOW FOR VALUES IN DOTTED AREA
i'..
"
1.8
~=0.2
1.4
~
/'
-..::::::
....
-
I
I
-~-
I-
- -
I
1.0 0.05
I
0.08 0.10
0.15
0.2
0.3
0.4 0.5 0.6
0.8 1.0
S B
1.34
111111111 I I I I I III 1
I
1.32 1.30
A
.~
1.28 1.26
1.24
~ ~.S-1
1.22 A , -fB=O TO 0.1_
f-
1.20
I....
t- ~-02, • f- B -
l\
1.12
1\1
1.10 1.08
\1
1\1
1.06
"
1.02
0.8 1.0
1.5 S
2
3
4
5
6
8 10
B
Fig. 22*
* "Engineering
Calculation of Inductance and Reactance for Rectangular Bar Conductors," O. R. Schurig, GENERAL ELECTRIC REVIEW, Vol. 36. No.5, May, 1933. Curves plotted from tables calculated by F. W.
34
L
21 [Ln 2GMR 1 = 1000
1
GMRJ (Microhenries). + -1-
(2)
The term GMR is the self geometrical mean distance in cm of all points within the area of the conductor cross section and 1 is, the length of the bar in cm. The value of GMR for a rectangular section is given below, when a and b are the dimensions of the bar in cm.
GMR
= 0.2235 (a + b)
(Centimeters)
The mutual inductance between a pair of straight, parallel rectangular bars is indicated by the relation:
GMD] (Microhenries). (3) + ~l-
= LA + M AB -
MAO - M.w ( Microhenries for group A) .
(4)
Where:
......... ["'0.,
0.3 0.4 0.5 0.6
Grover.
L t = L - M. The calculation of the self inductance, L, of a straight rectangular bar, neglecting the return conductor is given by the relation:
L TA
1.00
(1)
The total inductance, L t , in the above expression, is the difference between the self-inductance, L, of the conductor and the mutual inductance, M, between two conductors of the circuit. The total inductance, L t , of each conductor of a circuit composed of two bars is expressed by the relation:
I""
1.04
(microhms per foot)
where the GMD is the geometrical mean distance in cm of the two conductor areas from each other and 1 is the length of the bars in em. The GMD can be determined from the curves in Fig. 21 for conductors in an edgewise position or from Fig. 22 for a facing position. The spacing between bars, s, is given in cm. The useful application of these formulas will be apparent from the reactance calculations of the circuit shown in Fig. 20. The two conductors per phase in this illustration result from the grouping of the eight bars per phase into two groups of four bars each, The inductance of group A, designated by L TA , is given by the relation:
1.18
1.14
= 27T f L t
21 [Ln 2 1 -1 M = 1000 GMD
GMD
S 1.16
X
f-
A
1\ \
Fig. 20, and three-phase configurations sometimes require the more fundamental calculations of self and mutual inductance. * The 60 cps inductive reactance values shown on the curves,in Figs. 17 and 18 express the total reactance, X, of the conductor,
LA is the self inductance of group A; MAB is the mutual inductance of the circuit comprising groups A and B; MAO is the mutual inductance of the circuit comprising groups A and C; M.w is the mutual inductance of the circuit comprising groups A and D.
electrical design - section II
By adding the quantity of LA - LA mula and grouping terms, it becomes:
L TA = (LA - MAO)
+ (LA -
( Microhenries for group A).
= 0 to
the for-
M4D ) - (LA - MAE)
The total inductance of group A is thus the algebraic sum of the inductance values for the three branches indicated and the total reactance of group A will be:
XTA = 27T f L TA = (X AO + X AD - X AS ) ( Microhenries for conductor group A).
The individual reactances can be determined from the curves in Figs. 17 and 18 or the self inductance and the mutual inductances may be calculated by formulas (2) and (3) and the values substituted in relation (4) to obtain the total inductance of group A. The inductance and inductive reactance of group B is calculated in a similar mamler. Widely Spaced Conductors-Where the value of s a + b is less than 2, the reactan~e should be deter-
mined either by the curves in Fig. 17 or by calculation. For widely spaced conductors where the value of s a + b is greater than 2, the 60 cps reactance can be
formulas and graphs advanced by these authors express reactance for widely spaced, thin, square tubes and assume a uniform distribution of current throughout the cross section. Commercial aluminum tubing having a wall thickness up to its optimum value, page 22, will have reactance values that closely approach the reactance of a thin hollow square tube. Method of Calculation-The reactance for widely spaced, thin, square tubes may be calculated approximately by the formula below: X
= 0.88216 f [ Log
+ 0.235 + 0.0108 ~
10 :
J.
Where: "s" is the spacing between centers in the same units as the square tube dimension "a," Fig. 23.
Approximate corrections to the reactance found by this formula have been advanced by the authors to correct for the thickness of the tubing and for round comers usually present on commercial tubing. These corrections are evaluated by the curves in Figs. 24 and 25 and are added as corrections to the calculated value.
determined graphically from Fig. 18 or by the approxi-
.
s
mate formula below. For ratios of --b greater than
a+
2, this will give 60 cps reactance within 1 per cent accuracy. X so
= 52.9 Log
10
GMD +b
a
+ 34.5
(Microhms per foot per conductor).
Graphical Solution Using Reactance Curves-A more expedient method of determining inductive reactance for a frequency of 60 cps is by means of the curve shown in Fig. 23. This curve expresses 60 cps s reactance for various ratios of - for two thin, square a . tubes. Corrections should be made to the 60 cps re-
Where:
a, b, and GMD are in the same units.
II
70
For two conductors widely spaced, the GMD is equal to the spacing, s. For three widely spaced conductors, the GMD can be determined from the relation GMD
= iY A X
B X C.
Where: A, B, and C are the spacings between conductors. See page 30 for the value of GMD for the more common conductor arrangements.
~,,v
III
w
U
~ 60 o >0
~
0 50
o"-
"""-w U'l40
/
~ J:
Inductive Reactance of Square Tubular Conductors and Channels in Box Form The inductive reactance of square tubular conductors can be determined approximately by the formulas an~graphs advanced by Dwight and Wang.* The
* "Reactance of Square Tubular Bus Bars," H. B. Dwight and T. K. Wang, AlEE Transactions. 1938. Vol. 57.
/
o u '"
~ 30
20 1
/
/
V
V
V
V
V
V
rCl
~,~
I I I III
2
3
4 RATIO
5
6
7
8
sic
Fig. 23 - Reactance of Thin Square Tubes
10 12 14
I
=
section II - electrical design
actance determined from this curve to correct for the wall thickness of the tube and for round comers usually present on commercial tubing. The curves in Figs. 24 and 25 provide the approximate corrections which are added to the reactance obtained from the curve in Fig. 23. 3.0
I
I
{OJ
2.5
~a==i
II)
w
U
>u 2.0 o-0
II
.... -<
....
o o u..
1.5
'"c..w II)
/
~
:z:
o
~ 1.0 ~
0.5
o
I
V o
/ V
V
/
V
0.05
0.10 RATIO
0.15
0.20
0.25
t/a H. B. Dwight and T. K. Wang
Fig. 24 - Correction for Wall Thiclmess 1.5
proximated by these methods using the average length of the sides of the double channel arrangement for the · . W +d d nnenSlOn, a, 0 f a thin square tub e, e.g., a = --2-' see Fig. 27. Reactance should be corrected for channel thickness. The 60 cps reactance of standard channel sections arranged in box form and separated by standard spacers and spacer supports is expressed by the curves in Fig. 27. These curves give the inductive reactance for standard channels with depths of 3 inches to 10 inches for conductor spacings up to 100 inches. For spacings over 100 inches, the reactance for a 12 inch spacing should be taken from the curves and a spacing factor from the table on page 137 added to this reactance to obtain the total inductive reactance per conductor. The reactance of double channel conductors arranged in box form can be determined by a more rigorous mathematical formula developed by Siegel and Higgins. * The mathematical solution presented by these authors, however, verifies the close approximation obtained with the Dwight and Wang formulas and the curves presented. Reactance determinations by these methods assumes a uniform distribution of current in the cross section of the two channels. However, measurements reported by O. R. Schurig * have shown that, for closely spaced buses in a three-phase flat arrangement, the outside channels may carry substantially less current than the inside channels, This is due essentially to the fact that the two channels have a di1Ierent phase spacing from other conductors in the circuit and the flux linking each of the two channels in box arrangement will be different. This unequal division of current in a typical three-phase closely spaced double channel bus arrangement is shown in Fig. 26,
,.-----.------.--------,---~--...,
lJ lJ r
II)
w
U >-
u
~ 1.0 .
.... -<
....
f--12"
o ou..
I·
12"
1570
I
6"-4.48# ALUMINUM CHANNELS
'"w
~ 0.5 f-----+------..~-I-----+----_\
Fig. 26 - Division of Current in 3 Phase Channel Bus
~
:z:
o u '" ~
0 1 - o ~
o
J.......
0.1
J_
0.2 RATIO
_'__
0.3
_l
'0.4
ria H. B. Dwight and T. K. Wang
·~ .
Fig. 25 - Correction for Round Comers
The calculation of inductive reactance for double channel conductors arranged in box form can be ap-
36
Equations have been advanced by Siegel and Higgins ** for determining the magnitude of this unequal distribution of current in the outside channels of a three-phase double channel bus, Where closely spaced, high current, double channel arrangements are used for 60 cps installations, the concentration of cur-
* ''Equations for the Inductance and Short-Circuit Forces of Buses Com-
prised of Double Channel Conductors," C. M. Siegel and T. J. Higgins, AlEE Traosactions, Vol. 71, January, 1952. **"Equations for Determioing Current Distribution Among the Conductors of Buses Comprised of Double Channel Conductors," C. M. Siegel and T, J. Higgins, AIEE Traosactions Paper 54-467, October, 1954.
electrical design - section II
REACTANCE CURVES AT 60 CPS FOR DOUBLE·CHANNEL CONDUCTORS ARRANGED IN BOX FORM 9(1
II
J
V V ~~
I I
I
V ~~
I I
~w-1
80
'-,T
,-J
----...
I-
0 0 .... 0-
60
I
, I
I
I
.50
II
0 -0
I
l-
«
J
u
U
40
> ;::
II
u
::::l 0
/
36
V I A
/ If
1/ tf
I
V kf
1/ A
20
VII / ~
Iwl.!ft.
STANDARD CHANNelS'
y~'"
V
3"_1.73#~ Lbs.
r;'
I
1/
V
~
l--:::::.;;::b::b::::~l/
5"-3.10~?:::....-::::~V
....... 1/
6"-4.48#::=:':::::% j
V
~
/ VVVV V V / 7 /: ~V; V / /
~~/
VVA I i
1/
A
A
II
/
V
....... 1.---"
8,,~.80~.%'
3
V
-
.
:
..... ~
I I I II
i
.
4
V
I
II
~c:V 0
~ ~ II
/j 'V0
/<7 r/?71f 1/
10"_10.05#
7
/~
J
~
:lfl /iIjil
1/ kr~ ~ l/ ~ ~~II II
4"_1.85#~:/-':l/-":~~V
7"-5.10#
II
k1 V 1I
4"-2.16#--:;VV-::;V ~
6"-3.63# 7"_5.96#
It"
~A/ 1/ /
II
~
d
IJ
I
'/
~
1/
y/ I/~~ ~ /
w
""w
tI
I
vi
z « I« w
I
I
I
~
1/
'I
/~ ~
/ V V I~ 'I~V / / # kf ~ IJV 1I 11 bI V LJ II l,I 1/ / V ~/ V V l! / ~1/ ~ IIV 1/ !J 1/
I
I
...:
II .J ~
1
~
0 u "" ~
U
/
d
70
""w l'"
IJ ~
5
6
7
8
9
10
12
15
20
30
40
50
60
70
8090100
CONDUCTOR SPACING (D) OR EQUIVALENT SPACING (GMD) (INCHES)
* SIZE
IS DESIGNATED BY THE. DEPTH OF THE CHANNEL AND THE WEIGHT PER FOOT
Fig. 27
37
.... _r.---
section II - electrical design
with an unsymmetrical h-iangular spacing of 10 feet, 12 feet, and 15 feet will be as follows. The inductive reactance for a onefoot spacing is obtained from the table on page 125; its value is;
rent in one channel of an outside pair may cause overheating on normal loads. This would be particularly true where the current rating of the double channel arrangement is closely approached. PROBLEM NO. 3 This problem will illush'ate methods of determining inductive reactance for various shapes of bus conductor.
XLI
The inductive reactance spacing factor is found by calculating the GMD or equivalent spacing. This value will be:
Required: The 60 cps inductive reactance in microhms per foot for a three-phase installation of the following shapes of conductors; A. Rectangular bus bar 4 inches X 1;4 inch arranged with flat surfaces vertical and spaced with a 10 inch flat symmetrical spacing; B. 11;4 inch solid round bus conductor with an unsymmetrical h"iangular spacing of 10, 12, and 15 feet; C. 1 % inch IPS tubular bus bar with a symmeh-ical flat spacing of 10 feet; D. A three-phase installation of channel bus conductor-each phase consisting of two 4 inch-2.16 lb. channels arranged in box form. These phases are arranged in an unsymmeh"ical flat spacing of 12, 15, and 27 feet. Solution: 3-A.
GMD
XL2 == 57.4 microhms per foot. The total inductive reactance, then, is equal to the algebraic sum, of the two above reactance values. XL
The 60 cps inductive reactance for' a three-phase symmetrical flat spacing of 10 feet for 1 Y2 inch IPS tubular bus bar is determined as follows. The inductive reactance, due to a one-foot spacing, is determined from the table on page 127. Its value is: XLI == 59.51 microhms per foot. The inductive reactance spacing factor for a 10 foot symmetrical flat spacing is found by calculating the GMD as follows: GMD
a+
inductive reactance is obtained from the curves in Fig. 18 or the formula for widely spaced conductors. The GMD for a flat symmeh-ical spacing of 10 inches is;
XL2
For the conventional arrangement of bars shown in Fig. 18, the inductive reactance in microhms per foot is a function of
XL
GMD==~==296 %+4 ..
a+b
~!
'"
For this value, the inductive reactance from Fig. 18 will be XL == 59.4 micmhms per foot to neutral. 3-B.
38
The inductive reactance for a 1 % inch solid round, three-phase 60 cps installation
== XLI + X L2 == 59.51 + 58.2 == 117.71 microhms per foot (or:e phase to neutral).
GMD
a+
== 58.2 microhms per foot.
The total inductive reactance will be the sum of these two reactance values:
(10)
of the bar as indicated for the conventional arrangement.
10 == 12.6
feet or 12 feet 7 inches.
The inductive reactance spacing factor corresponding to this value of GMD is obtained from the table on page 137. For a total spacing of 12 feet 7 inches, this value is:
Since the value of~b is greater than 2,
--b' where a and b are the dimensions
== 1.26A == 1.26 X ==
+ 74
== 1.26A == (1.26) == 12.6 inches.
~,
i'.
""'';
3-C.
s 10 - - b == - 4 11 == 2.35
GMD
== XLI + X L2 == 73.66 + 57.4 == 131.06 micmhms per foot (one phase to neutral) .
a+
+
== '{Y1O X 12 XIS == 12.16 or == 12 feet 2 inches.
From the table on page 137, the inductive reactance spacing factor corresponding to a total spacing of 12 feet 2 inches is:
The inductive reactance for a 60 cps, three-phase, symmetrical flat configuration with a 10 inch spacing for a vertical arrangement of one 4 inch X 1;4 inch rectangular bar per phase is determined as follows. The method of calculation will s depend on the value of --b
a
== 73.66 micmhms per foot.
3-D.
The inductive reactance per phase for two 4 inch-2.16 lb. channels arranged in box form is found as follows for a 60 cps threephase unsymmetrical flat spacing of 12, 15, and 27 feet. The inductive reactance for the two channels alTanged in box form is determined from Fig. 27 where reactance in microhms per foot at 60 cps is given as a function of conductor spacing or equivalent spacing in inches. The equivalent spacing or GMD for this installation is:
elect1'ical design - section Il
CUD
=
=
XLI = 39.0 micl'ohms per foot. The spacing factor corresponding to 16 feet 11 inches from the table on page 137 is: XL2 = 65.0 microhms per foot. The total inductive reactance, then, will be the algebraic sum of XLI and XL2 or
V'12 X 15 X 27 16.93 feet = 16 feet 11 inches (203 inches).
Referring to Fig. 27, the reactance corresponding to this value of spacing is -beyond the scale shown with these reactance curves, hence, the detelwination will necessarily involve the use of spacing factors given in the table on page 137 for this installation.
XL
=
XLI
+ XL2
= 39.0 + 65.0
= 104.0 microhms per foot
The reactance for a 12-inch spacing, according to Fig. 27, will be:
(one phase to neutral).
BUS IMPEDANCE The impedance of a bus conductor is obtained from the fundamental impedance formula and is expressed in the same units as the a-c resistance and reactance:
Z
= V R2 + X2
rnicrohms pel' foot.
I
I\
The impedance angle is given by the relation: ¢
= tan-
I
X R'
The application of the above impedance fOlIDulas to the rectangular bus conductors in Problems 2 and 3 is given in Problem No.4, using the a-c resistance and reactance values calculated in part A of these problems.
PROBLEM NO. 4 The impedance and impedance angle, ¢, is required for the following 60 cps three-phase bus bar installation for which the a-c resistance at 70 C was calculated in problem 2 and the inductive reactance in problem 3. The three 4 inch X V4 inch EC aluminum rectangular bars in the referenced problems have a 60 cps resistance of 17.00 microhms per foot at 70 C and an inductive reactance of 59.4 microhms per foot. The impedance and impedance angle will be: i
I I,
I
I
I
Z
= V (17.00)2 + (59.4)2
= 61.8 micl'Ohms pel' foot 59.4 ) = tan- 3 49 4 = tan- ( 17.00 'I' . ¢ = 74 degrees, 2 minutes. ,I.
I
--
I
Voltage Drop-Vectorial Relationship Contraly to a d-c bus bar installation, the resistance drop (IR) in an a-c bus installation is not usually a significant part of the total voltage drop. The reactance drop (IX) in an a-c installation is usually the larger factor, Vectorially, the relationship between these voltage drops, the phase current, and the sending-end and
Fig. 28 - Vector Diagram for Single Phase Circuit
receiving-end voltages is given in Fig. 28 for one phase of an a-c system. Where:
IR IX
= resistance voltage drop; = reactance voltage drop;
Es
= sending-end voltage;
E,-
:::>:
receiving-end voltage;
= a-c phase current; = impedance angle; e = power factor angle;
I ¢
IZ = impedance voltage drop. The magnitude of the sending-end voltage for a given load and load power factor angle, e, is obtained by the following formulas:
39
section II - electrical design
E s == \I (E,. cos ()
+ IR)2 +
(Ersin ()
+ IX)2
cos () = 0.9
() = 25.83 degrees
( Generated voltage to neutral)
,/3E. == (Generated voltage phase to phase).
= 0.4359 IR = (728) (17.00 X 10-
sin ()
PROBLEM NO. 5 The application of these formulas to a typical bus installation is offered in the following problem using the resistance, reactance, and impedance values calculated in previous problems.
IX
Required:
=
Solution: With 440 volts available at the load, the sending-end voltage is desired to determine if the installation is within the 2 per cent voltage drop required. watts 1- \13 X volts X pf 500,000 1== (\13) (440) (0.9)
== 728 amperes
(100)
= (728)
(59.4 X 10-6 ) (100) = 4.32 volts
IZ = (728) (61.8 X 10-6 ) (100) == 4.50 volts
It is required to supply rated power to a 440
volt, three-phase, 60 cps load of 500 kw at 0.9 power factor lagging without exceeding a 2 per cent voltage drop. The bus consists of one 1/4 inch X 4 inch EC aluminum bar per phase in a run 100 feet long. The elecb:ical characteristics of this installation have been illustrated in part A of Problems 2, 3, and 4, as follows: a-c resistance, R == 17.00 microhms per foot at 70 C; reactance, X = 59.4 microhms per foot; impedance, Z = 61.8 microhms per foot at 70 C; impedance angle, ep 74 deg., 2 min.
6)
== 1.24 volts
Er .
\13
+ 11)2 +(Ersin + 1x)2 11[(254.0) (0.9) + 1.24)2 + [(254.0)
E s == V (E r cos
=
= 44~ = 254.0 volts (line to neuhal)
(J
(J
(0.4359)
+ 4.32)"
= 257.0 volts to neutral at switchboard E8 Es
== (257.0) \13 = 445.1 volts (line to line) -
E r =445.1- 440
== 5.1 volts (actual voltage difference) A 2 per cent voltage drop required for this installation would be: (440) (0.02) ==8.8volts. The actual voltage difference of 5.1 volts is lower than the 8.8 volts that represents 2 per cent voltage drop so that the installation meets the requirements for voltage drop. The current carrying capacity of a 4 inch X 1/4 inch bar arranged vertically is listed as 1000 amps for a 30 C rise over ambient when installed in still, but unconRned air, so that this installation also meets the requirements for current rating.
CURRENT RATING OF BUS CONDUCTORS In the majority of bus conductor installations, temperature rise of the conductor is the limiting factor. Since bus conductor runs are usually short, voltage drop and energy loss are usually not important factors. This is particularly true on high voltage installations. However, at the a-c distribution voltage level and on low voltage d-c bus where very high currents are encountered, voltage drop and power loss may be important factors. Industrial a-c bus runs utilizing voltages less than 600 volts fall in this latter class. For any given surface condition, i.e., fixed emissivity, the temperature rise of a bus conductor is affected by the magnitude of the current flowing and the resistance of the bus bar. These two factors govern the amount of heat generated within the bus conductor 40
and are directly responsible for increasing the temperature above its surroundings. This generated heat within the conductor is dissipated by two means-the radiation of heat to other bodies located nearby and by air currents which become heated and carry away heat either through natural convection currents, as in a closed room, or by forced air circulation such as a light breeze or wind in an outdoor installation. The difference in the latter two quantities, i.e., the loss due to natural convection air currents or the heat loss by forced air circulation, determines the indoor and outdoor current ratings respectively of bus conductors. Temperature limits for a bus conductor must be established such that continuous operation is possible with a reasonable factor of safety for the bus itself
electl'ical design - section II
and for equipment connected to the terminals of the Where: bus. Where equipment ratings are based on a 30 or J2R represents the heat generated in the conductor 35 C rise, the bus rating is usually limited to the same in watts per unit of length; temperature rise. The bus and the connecting leads to W, and We represent, respectively, the heat loss by this equipment, then, will not operate at a higher temradiation and convection in watts per unit of perature and conduct heat into the equipment, thereby surface area; raising its normal operating temperature. A represents the surface area per unit of length of The physical properties of rolled or drawn prodthe conductor. .ucts, i.e., tensile strength and yield strength, may be The above formula solved for the current, I, gives: sacrificed by excessive heating, and temperature limits should be established with due regard to the thermal I(W, + We) A properties shown on page 4. Expansion lengthwise of 1= '\j Rae amperes. the bus conductors may also become a problem on long bus iuns. Expansion fittings and flexible connecWhen the a-c resistance, Rae, is given in microhms tions are used to compensate for elongation of the bus per foot, the heat losses W, and Weare given in watts members so that strains are not imposed on supporting per square inch of surface area, and the diameter of insulators and equipment terminals. The reliability of the conductor, in inches, replaces the surface area per electrical connections to bus conductors may also be foot, A, I then becomes: affected by high current densities and excessive heating. This is discussed in the section on the joining of 37.7 (W, + We) D X lOG 1= R amperes. bus conductors. ae . To determine the current rating of a bus conductor, it is necessary to establish an ambient air temperature and a maximum safe continuous conductor operating ""'Heat Loss by Convection-Outdoor Rating-The temperature. These temperatures determine the perheat loss due to convection air currents is based on a missible temperature rise over ambient. The continuminimum value of wind velocity which is generally ous current that is required to produce equilibrium at taken as 2 feet per second. This is from 5 to 10 times this established temperature rise is the nominal curthe estimated velocity of air currents due to ·free conrent rating of the conductor. Usual procedure is to use vection, but is a low value for usual outdoor wrnd velocities. Heat loss by outdQOf convection currents is: a 40 C ambient air temperature and a maximum safe continuous operating temperature of 70 C which 0.0128 V PV M . means that a 30 C temperature rise is the limiting We watts per square mch, T aO.123 IjD condition. Once the temperature limits have been established, Where: other variables that affect the current rating must also P absolute air pressure be taken into account. Such variables as wind velocity, (P = l.0 for atmospheric air pressure); emissivity of the conductor surface, atmospheric pressure, the effect .of sunlight, and bus enclosures should V = cross-wind velocity in feet per second; be considered. M = te~perature rise of the conductor above ambient in degrees C; . T a = T +2 To is the average ab soIute temperature 10 Current Rating of Round Conductors
~
=
=
The Schurig and Frick * method of calculating the degrees Kelvin betl'veen conductor and air current carrying capacity of round conductors is gentemperatures; erally accepted as the method which approximates D = the conductor diameter in inches. field conditions and gives proper weight to the above factors. The effect of sunlight in raising conductor v'Heat Loss by Convection-Indoor Rating-The intemperature has been found to be small on loaded door ratmg of a bus conductor is considerably lower conductors and is neglected in this method of calthan the outdoor rating because the heat loss due to culation. . natural convection air currents is lower. Thus, the This method essentially balances the heat generwatts dissipated from a cylindrical conductor indoors ated in the conductor by I2R losses against the heat -free convection-for any temperature rise and any loss by convection and radiation. The general formula ambient air temperature is: for the steady-state condition is: 17.5 X 10-G T aO.754 M VI>
We =
* "Heating and Current Carrying Capacities of Bare Conductors for Outdoor
Service," Schurig and Frick, GENERAL ELECTRIC REVIEW, VoL 33, No.3, March, 1930.
D Ln
[0.0031 T aO.941 Do.s1 f:"t O•27
+1
]
watts per square inch.
41
section II - electl"ical design
For the standard conditions of 30 C temperature rise over a 40 C ambient air temperature at atmospheric pressure, this becomes: 0.01805
We ==
D Log10
watts pe1' square inch.
[0.298] DO.81 + 1
When D is more than 3 inches, an approximate relation for the convection heat loss indoors is:
We
0.14 = DO.19 watts per square inch, approxima.tely.
W _ 0.0128 e -
yW t"t' y'D
Ta,0.123
.
Where: P = atmospheres (air pressure) usually taken as
1; V == cross-wind velocity-2 feet/second; == temperature rise-30 C above an ambient of 40 C; Ta, == average absolute temperature of conductor and ambient temperatures; t"t
== 70; 40 + 273 == 328 K; Heat Loss by Radiation-The radiation heat loss, W n for both indoor and outdoor installations can be calculated as:
W 7 == 36.8e
[C~O Y- (1~~0 y]
watts per square inch. Where: e is the surface emissivity constant-usually given as 0.35 for indoor installations and as 0.5 for outdoor bus with average tarnished metal surface, Black non-metallic surfaces have greater emissivity and 0.9 is generally used; T is the absolute temperature of the conductor in degrees Kelvin; To is the absolute temperature of the surroundings in degrees Kelvin-usually taken as absolute air temperature.
In the case of outdoor installations, bus conductors are subject to more corrosive conditions and the degree of surface tarnish will have an influence on its ability to radiate heat to surrounding objects. This factor is taken into consideration by the term e which represents the emissivity of the surface of the conductor. For outdoor installations, e is generally taken as 0.5; while for indoor bus conductors, the average emissivity has been found to be approximately 0.35, Bus conductors are sometimes painted with a flat nonmetallic paint to increase their emissivity. This is discussed on page 49.
.~
Method of Calculation-The indoor and outdoor current ratings for a 1 ~ inch IPS extruded bus conductor of alloy 6063-T6 are determined as follows for a 30 C temperature rise over 40 C ambient air temperature:
=
Diameter D 1.900 inches; A-C resistance at 70 C = 22.57 microhms per foot; Emissivity e 0.35 for indoor rating; 0.5 for outdoor rating.
,1,1
; I;· . IR':
=
Outdoor Rating The outdoor rating for this conductor is calculated as follows: 42
W- (0.0128) y(l) (2) (30) . (328)0.123'11.9
e-
'
= 0.1931 watts per square inch;
C~O)' - C~~O)']
W 7 = 36.8e [ watts per square inch. 'Where:
T == 70 + 273 = 343 K, conductor temperature in degrees K; To == 40 + 273 == 313 K, temperature of . surroundings usually taken as ambient air temperature in degrees K; e == 0.5 for outdoor installation; W,. == (36.8) (0.5) [(0.343)4 - (0.313)4]; == 0.0781 watts per square inch; We
+ W == 0.1931 +
0.2712 watts per
0,0781 square inch;
7
!( 37.7) 1= '\j
(0.2712) (1.9) lOG 22.57
= 927.8 amperes or 930 amperes. Indoor Rating W _ e-
0.01805 [0.298 D Log10 D 081
+1
0.01805 0.298 1.9 Log10 [ 1.90.81
]
+1
]
= 0.1341 watts per square inch W 7 = 36.8e
[(l~OY - C~~O)']
= (36.8) (0.35) (0.00424) = 0.0546 watts per square inch
electrical design - section II
We
+ W r = 0,1341 + 0.0546 = 0.1887 watts per square inch 1
=
/37.7 (We
+ Wr )
'\j
D
X
106
Rae
/(37.7) (0.1887) (1.9) 106 - '\j 22.57 _
=
770 amperes
Limitations of Round Conductors-Solid and Tubular-Round bus conductors do not have the disadvantage of requiring orientation with respect to convection air currents for dissipating l"R heat losses. This advantage is offset by the limited amount of exposed surface area on a round conductor. In tubular conductors, the internal surface does not contribute to the dissipation of heat unless methods are provided for circulating a cooling medium. This is not practical for most installations. A small variation in the cunent rating of a tubular conductor can be achieved by varying the wall thickness up to its optimum value, page 22. Wall thicknesses greater than optimum do not add to its current canying capacity. The efficiency of a tubular conductor with a given outside diameter can only be improved by changing the denominator of the efficiency formula, i.e., by lowering the a-c or d-c resistance by increasing the wall thickness up to its optimum value, as surface area remains constant. This is shown by the following relation:
that a rectangular bar of given dimensions and material will have one current rating when arranged with its width vertically and another rating when its width is arranged horizontally. Other intermediate ratings will depend upon the angle the flat sides of the bar make with the horizontal or vertical position. Rectangular bar lacks the symmetry of a round conductor; hence, the dimensions of a rectangular bar-its width and thickness-also affect CUlTent rating in addition to the orientation. Each is discussed in detail. Effect of Width of Bar on Its Current Rating-Since the exposed surface area is more a Mlction of the width of the bar than the tIlickness, changing the width of a bar increases surface area and enhances its ability to dissipate heat. The most efficient rectangular conductor is one that has the highest ratio of exposed surface area to a-c resistance or to d-c resistance for direct cun-ent applications. This is expressed simply as: . exposed surface area/unit of length E ffi Ctency = . /um ' t 0 f lengt}~ reStstance Changing the width of a rectangular bar increases efficiency by affecting favorably both the numerator and denominator in the efficiency formula. The exposed sUlface area is increased and a-c resistance is decreased, both of which increase the efficiency of the bar. Table 3 gives current ratings of various sizes of bar to show the effect of varying tile width of a bar rather than its thickness.
Current Rating of Rectangular Bar The alternating cunent rating and the direct current rating of an aluminum rectangular bar with its width arranged either vertically or horizontally is available from tables for standard design conditions, pages 118 and 119. It is apparent from these tables
I I
,j
~i
I
I/,~
( J
I
Effie' exposed surface area wncy = a-cor d-c resistance . It is impractical to design for maximum efficiency in most instances as this will require a large diameter tube to increase surface area, with a thin wall to give a maximum of surface area per unit of cross section. The design and selection of a tubular conductor is often dictated by the cost of the accessories used to support, tap, and join the lengths together. From filn accessory cost standpoint, good design will usually indicate that an aluminum tube with a wall thickness approaching optimum, see page 22, will allow the replacement of a standard copper IPS conductor with the same outside diameter aluminum tube. Solid round aluminum conductors are practical up to approximately 2 inches in diameter for a-c applications while any size is suitable for d-c operation, see page 125.
I j I
I'
TABLE 3-CURRENT RATINGS (Rectangular EC Aluminum Bar, Arranged Vertically)
Size
A-C Current Rating * (Amperes)
3X ~ 4 X 14 3X %
775 990 955
f
Cross Sec- Surface Area Current tional Area Per Foot Density (Square (Square (Amperes Per Inches) Inches) Square Inch)
%
1
IVa
78
1033
102
990 849
81
* 30 C temperature rise over 40 C ambient in still but unconfined air.
The 60 cps alternating current rating of a 3 X ~ inch rectangular bar arranged vertically is shown to be 775 amperes. The most desirable shape for a replacement bar in order to increase tile current rating to approximately 1,000 amperes would be to select a bar of increased width rather than thickness. The tabulation shows that a 4 X ~ inch bar has a current rating of 990 amperes and a cross sectional area of one square inch. An increase in the thickness of tile original bar to % inch, with the width remaining at 3 inches would provide a ba~. with greater cross sec43
section II - electrical design
tional area-tVa square inches, while sluface area is increased by only 3 square inches, thus giving a rating of 955 amperes. The use of a 4 X 14 inch bar for the required rating provides a significant increase in surface area-24 square inches per foot, and yet only increases cross sectional area from % to 1 square inch. It is not practical in most installations to pursue the ultimate in efficiency as space limitations often dictate conductor dimensions. A wide thin rectangular conductor, although quite efficient, is obviously not suitable in modem installations. Some degree of latitude in design, however, may be used to take advantage of a slight increase in the width of a rectangular bar. In multiple bar installations, somewhat greater efficiency may be obtained by using more bars of reduced thickness to provide more total surface area between laminations.
Effect of Bar Thickness on Current Rating-From an efficiency standpoint, a change in the thickness of a rectangular bar is not as effective as a change in width as only the resistance is changed without appreciably affecting the amount of exposed surface area. In the efficiency formula, this means that a change in thickness affects primarily the denominator. Since the thickness, t, of the bar is proportional to the cross sectional area, A, for a constant width, W; and the d-c resistance is inversely proportional to cross sectional area:
Wt 1 = A 1 Wt 2 A 2
=R
2
R1
and t 1 t2
=R
2
•
R1
Two bars of the same material, having identical widths, but slightly different thicknesses, possess nearly the same exposed surface area for heat dissipation. These two bars will necessarily generate and dissipate nearly equal amounts of heat to maintain like operating temperatures. This means the J2R losses will be approximately the same for each bar, i.e.:
11 12 =
/2'
\iT = 1.41.
A comparison of the actual current ratings of two bars of equal widtll but with a thickness ratio of 2 to 1, shows a close correlation of the above ratio to the actual ratio of their direct current ratings, e.g., EC aluminum bar, 8 inches 2720 amperes d-c; EC aluminum bar, 8 inches 1920 amperes d-c;
11 2720 12 = 1920
X ~~
inch-
X ~~
inch- .
= 1.417.
A comparison of their alternating cun-ent ratings will show a slightly different ratio due to the influence of skin effect. The actual ratio of the a-c ratings of these bars is 1.34.
Effect of Position on Current Rating-The effect of position on the current rating of a rectangular bar is very pronounced. Where the long flat sides of a bar are arranged vertically, the convection air currents pass upward along the sides of the bar and thereby efficiently canoy away the heat generated by the J2R losses. The horizontal anangement of a rectangular bar prevents the rising convection air currents from contacting the large flat surfaces of the bar which present the greatest exposed area for natural ventilation. The curves in Fig. 29 show the difference in the current rating of a single bar when arranged both vertically and horizontally. 2000 , - - - - - - - , . . - - - - - , . - - - - . . - - - - , - - - - ,
1600 I------il----+----+~,L:.._=..-l"'::::;;..-----l
11 2 R 1 = 12 2 R 2 • Where: 11 2 R 1 is the heat generated in one bar; 12 2 R 2 is the heat generated in the other. A ratio of the currents in the two bars will be:
." 1200. UJ
'" "" ~ UJ
800 ~~~~f=-----+----I----+-~----j
11 2 R 2 11 /R 2 12 2 =R 1 and 7;= VR 1 ' By substitution, the relation between bar thickness and current rating will be approximately,
400
1-----1I--'---+----t---+----j
OL_ _-L_ _-.L 3x!4
5xv..
--L-_ _--L_ _----'
6xv..
7xv..
SIZE OF BARS
The relation between two bars of equal width, where one bar is twice the thickness of the other, will be approximately 44
Fig. 29 - Effect of Position on Rating NOTE: Ratings are for 30 C rise over 40 C ambient temperature in still but unconfined air.
electrical design - section II
ALTERNATING CURRENT RATING AT 60 CPS*
OF MULTIPLE COPPER AND EC ALUMINUM RECTANGULAR BARS 7000
6000
1f.I "x6" BARS-..........
t---..
5000
o z
~ ~ 4000
"l
w
DVl7 ic
","-
w::E
:t «
o
3000
u
0
VB
2000
~
~
G&H
0
N___
0
5000
R
Q
p
o
o
.~
4000
4;
'"
(M
::E
3000 ~ ::>
"-
""z w -
1f.I"x4" BARS
c.. :::E :::E::>
J
2000
F
4; -' 4;
C---< ~
u
w
A
1000
o
V
V ~ "" /0 ~
;::'"
N
I,.--"
1000
s:
0 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CD
n
16
:r
NUMBER OF BARS
III ~
n',
!!!.:
ARRANGEMENT OF BARS
I
A
II
B
I I I
c
"I I
E
III II
r
I II
I I
F
/II
I
G
"I
II
f--",,-j
H
II I
II
0
I
II
I
I II I
/I
J
1111
/I
I
II
/'
/I /I /I II
I
N
I:,;;~
II II
Il'!L
III' III /I
J
/I II
p
II II
II II II
II
II
I I
I M,
II II
I
"'II "'II III III III
II II /I
f--18"~
"
Q
"' "'
'"
""
1/11
""
"II
R
~.;
l' J iJ
""
/1/1
f--",,-i
I'J'~ "i
I
I"
1/1
*
inch. Large spacings between bars are 2% inches.
Fig. 30
fi
1
.
1
j' Ii•if ~
;f'
) r.
1/l u If i" " §nu j
l'r
'"
/III
i:,J
/III
;1
:/
'I'
t" (I
IJ
j: , I:: '
!
:'"
iiI' i~
* For a 30 C temperature rise over 40 C ambient in still but unconfined air. Ratings are for single phase in the multiple arrangements shown above. NOTE: Small spacings between bars are
~
,
1111 K
oti'
I
I
I /I"
0
0 CD ur
i
I'
1:1" : I: I! I' "
'
(IT
,45
'! ,f
,I
"
fl
;, :~
..__.__ ~_JUJ1: '
section II - electrical design
Current Ratings of Multiple Bar Arrangements A great deal of experimental work has been done in determining the current ratings of copper rectangular bus bars in the many' arrangements being used. These values can be used to determine the current rating of aluminum rectangular bars where the same number and size of aluminum bars are arranged as the copper installation. These copper ratings, however, must be reduced by the conversion factors shown in the table on page 47. These factors will be accurate for d-c conversions and conservative for alternating current ratings. Where a more exact alternating current rating is desired, the direct current rating should be modified to correct for the skin effect resistance ratios of the buses. For example, if the d-c rating of a copper rectangular bar is given as 2000 amperes and the d-c rating is desired for an identical bar in EC aluminum, the conversion factor from the table for the copper bar in terms of the EC aluminum bar at 70 C is 1.273, using EC aluminum as the base value of 1.000. The EC aluminum rating then at 70 C is as follows: 2000 1.273
= 1570 amperes for EC aluminum.
If the d-c rating is desired for the same construction in 55 EC aluminum bar, this is determined from the conversion factor of 0.958 in the same table which gives: 1570 X 0.958
= 1500 amperes for 55 EC aluminum.
To facilitate this conversion for the 60 cps ratings of 4 X lf4 inch and 6 X lf4 inch rectangular bars, the published curves * of copper ratings are reprinted as Fig. 30, with a scale added for the ampere rating of EC aluminum bars. The 60 cps ratings for EC aluminum bars can be converted approximately to other aluminum alloys by the d-c conversion factors in Table 4. Such values will be conservative for aluminum alloys of lower conductivity. Standard replacement sizes of aluminum bars have been designated by Underwriters Laboratories Inc. in their "Standard for Dead-Front Switchboards." These sizes are shown to the right.
Current Rating for Square Tubular Bus The current ratings for square tubular bus are indicated on page 136. Where a ventilated square tubular bus is used, these current ratings can be increased by 15 to 20 per cent. Ventilation is obtained by drilling holes in the top and bottom surface of the square tube to allow convection air currents to pass through the interior section of the bus. These holes are staggered
* "Current
Carrying Capacity of Bus Bars," H. W. Pabst, ELECTRICAL WORLD. September 21, 1929.
46
for maximum effect at intervals of approximately 4 inches. Holes normally are Ilf4 inch diameter for the 3 inch square hlbe and range in size to 1% inch for the 6 inch square tube.
Current Rating for Standard Channels and Angles The current ratings for standard channel shapes arranged in box form are shown on page 133; the current ratings for angles arranged in box -form are also indicated, page 135. The current ratings for standard channel shapes not listed are best determined experi~ mentally.
Current Rating for Non-Standard Bus Shapes The current rating of non-standard shapes should be determined experimentally where an accurate determination is required.
Conversion Factors Many tables give the resistance and current rating of a bus conductor in terms of a particular material or alloy with its conductivity based on the International Annealed Copper Standard (lACS) at 20 C. It is often desirable to know the characteristics of an identical conductor when fabricated of another metal or alloy when only its conductivity is specified. Conversion factors may be used to convert standard values such as the resistance and current rating of one metal to the other without starting from basic values. These values apply only to a given conductor size and shape, i.e., a conductor of equal dimensions and cross sectional area, see Table 4. This table of conversion factors applies essentially to the d-c constants of a given size and shape conductor. In many cases, the direct current rating is of sufficient accuracy that it can be substituted for the BUS BAR CURRENT RATINGS FOR DEAD-FRONT SWITCHBOARDS * Bus Bar Rating in Amperes
225
400 600 800 1000
Minimum Dimensions of Bus Bars in Inches Copper
~by
%
lf4 by IVz Y4 by2 Y4 by3 Y4 by4
Aluminum
Y4 by % Y4 by 2 Y4 by3 Y4 by4 lf4 by 6 or two Y4 by 3
A minimum tolerance of five per cent in the cross sectional area is allowed for rounding and shaping a bus bar. A bus bar having other dimensions may also be acceptable if it has not less than the cross sectional area specified in the table and has equivalent rigidity.
* Underwriters boards."
Laboratories "Standard for Dead-Front Switch-
electrical design - section II
TABLE 4 - CONVERSION FACTORS FOR IDENTICAL SHAPES BUT DIFFERENT CONDUCTOR MATERIALS (EC Aluminum -
55 EC Minimum
6063-T6 Mini- 6063-T6 Typical 6061-T6 mum
Bus Conductor Material
Per Cent Conductivity (lACS) ..... 40 Equivalent Conductance at 20 C ...... 0.656 Equivalent d-c Resistance at 20 C ...... 1.525 Equivalent d-c Resistance at 70 C* . .... 1.437 Equivalent d-c Rating 0.834 at 70 C. '" .. Equivalent d-c Voltage Drop at 70 C ...... 1. L98
* Resistance
61 Per Cent Conductivity -
51
55
53
as a Base)
56 EC 6063-T83 1100-H18 1100-0
56
57
59
EC
61
Hard Drawn Annealed Copper Copper MiniMinimum mum
98
99
lACS
100
0.836
0.869
0.902
0.918
0.934
0.967
1.000
1.607
1.623
1.639
1.196
1.151
1.109
1.089
1.070
1.034
1.000
0.622
0.616
0.610
1.170
1.126
1.089
1.074
1.060
1.028
1.000
0.618
0.613
0.607
0.925
0.943
0.958
0.965
0.971
0.986
1.000
1.273
1.278
1.283
1.082
1.062
1.043
1.036
1.029
1.014
1.000
0.787
0.783
0.779
oCD
III
aQ' :::I
values calculated for 70 C temperatures by using the following temperature coefficients of resistance:
6063-T6 ................... . 0.00350
..................... 1100-HI8 ..................
55 EC
1100-0 .................... 0.00389
606l-T6 ................... . 0.00264
••••••
0
••••••••••••••
0.00363
57 EC
..................... ........................
0.00376 0.00376
56 EC .................... . 0.00370
59 EC
0.00389
6063-T83
EC
0.00403
•••
0
•••••••••••••••
0.00370
alternating current rating. This is true where the skin effect resistance ratio of the two materials investigated is veIY low or nearly the same and where proximity can be ignored. Where a more accurate equivalent alternating current rating is desired, the d-c rating obtained by the conversion factors in the table must be corrected to allow for the difference in the skin effect resistance ratios of the two conductors. For the standard shapes, the a-c resistance can be determined easily by obtaining first the d-c resistance value at 70 C for each conductor and then multiplying this value by the respective skin effect resistance ratio for each conductor as obtained from the following curves: 1. Round conductors-solid or tubular, page 25; 2. Square conductors-solid or tubular, page 26; '·3. Rectangular conductors, page 24.
Copper- 98 per cent conductivity ......... 0.00385 Copper- 99 per cent conductivity ..... , ... 0.00389 Copper-lOO per cent conductivity
1 -
2
IR2~c
'\j R lac •
....... 0.00393
Where: I 1 is the altemating current rating desired for conductor 1; R lac is the a-c resistance of conductor 1; I 2 is the known altemating current rating of conductor 2; R 2ac is the a-c resistance of conductor 2. The following example illustrates the calculation of the altemating current rating of a 55 EC rectangular bar having a conductivity of 55 per cent using the current ratings of an EC aluminum rectangular bar of the same shape but with a conductivity of 61 per cent. The equivalent values in Table 4 are used to simplify this conversion. These charaCteristics apply to a 3 X ¥4 inch EC aluminum bar with current ratings given for a vertical arrangement.
With these data, the altemating current rating, I 1 , can be determined by the following ratio: I - I
.
Material
Size (Inches)
EC Aluminum 3 X
¥4
Current CarryD-C Resistance ing Capacity ( Microhms at 70 C Per Foot) (Amperes) 20 C 70 C D-C 60 cps
17.81
21.40
780 760 47
_==Uf'
section II - electrical design
The conversion of the a-c rating of the above EC aluminum bar to the rating of a 55 EC rectangular bar of the same shape is given as follows. The d-c resistance at 70 C for 55 EC aluminum alloy bar, using the conversion factor 1.089 from the table is: R de70 = 21.40 X 1.089 = 23.30 microhms per foot at 70 C. To determine precisely the equivalent a-c values, the skin effect resistance ratios should be calculated and used to correct the d-c resistance values. The skin R effect resistance ratio, Rae, for a 3 X Y4 inch EC de
aluminmn bar is determined from the following calculated values and the curves on page 24.
/f
'\I
X
Rc/e7o
W
Rae de
/60,000 V 21.40
The skin effect resistance ratio,
R Rae,
for a 3 X ~
inch bar of 55 EC is obtained from the curves on page 24 after calculating these values:
dC70
/60,000 = 50.8
'\j 23.30
.
.
-R = 1.036 (from page 24).
jl
The a-c resistance at 70 C for 55 EC aluminum alloy will be: RaC70 = 23.30 X 1.036 = 24.14 microhms per foot. The equivalent alternating current rating of the 55 EC bar may be found from the formula below where R lae and R 2ae are the a-c resistances of the two bars:
"
11 =12
I'"
f_
"I
,
"
:. 1. , i'L~' ,J"
.i
I ' .I": • "
i
"'
I I,
J: j (/I
1':1 I,
1 1'1: 1 ,
I
1
, I"
'
;,
I
" "1 . ;11;'
~l':d'n,
= 1.084.
This compares with a skin effect resistance ratio of 1.041 for an EC aluminum bar of the same shape and 1.036 for a bar of 55 EC aluminum alloy. The d-c resistance of the copper bar using the conversion factor in the table for d-c resistance at 70 Cis: R de - cu = (0.618) (21.40) = 13.22 microhms per foot. R The a-c resistance, using the Rae ratio, will be:
= (13.22) (1.084) = 14.33 mierohms per
~
=
/2228 760V24:14
= (760)
/14.33
155
(0.961)
= lei< '\j 24.14 =leu X 0.771 for a-c conversion.
This compares with the direct current conversion factor of 0.753 as calculated below from values in the table: leu
lEO
lae
= 730 amperes.
The conversion factor for the alternating current rating is 0.961. This compares with the tabulated value of 0.958 for the conversion of the d-c rating. These factors are so nearly equal that for many applications, 48
The conversion factor applying to the 60 cps current rating of 55 EC will be calculated from its a-c resistance at 70 C, calculated above as R ae55 = 24.14 microhms per foot:
R2ae
-R
The a-c rating, then, of the 55 EC bar is:
I
74 6.
foot.
de
1. " , 1 ;,;
de
Rae-au
Rae
I
,I.
Rae
-R
/4
I"
=
de
W 3 -t =v=12
L' "
3
/60,000
'\j 13.22
The skin effect resistance ratio for the copper bar corresponding to the above is:
rle
10
103
W T= 12.
= 1.041 (from page 24).
/f X V R
X
V Rde20
.
The a-c resistance at 70 C for the EC aluminum bar is: R aC70 = 21.40 X 1.041 = 22.28 microhms per foot.
,
/f
= 529
3 ~ =12
T= -R
3
10 =
the d-c values could be used with sufficient accuracy where an approximate value for the alternating current rating is desired. When the change in the conductivity of the two bars is small, the difference in the a-c and d-c conversion factors will also be small. When the materials have a considerable difference in conductivity, skin effect will have a greater influence on the a-c resistance of the higher conductivity material. For example, assume a conversion factor is desired for converting the a-c rating of a copper bar with 98 per cent conductivity to the rating for a 55 EC aluminum bar with 55 per cent conductivity. For the size just calculated, the skin effect resistance ratio for an iden- , tical size copper bar can be obtained by using the curves on page 24 with the following values:
155
155
= 1.273
155
and lEO = 0.958 0.958 leu 1.273 = leu X 0.753 for d-c conversion.
=
Effect of Bus Enclosures Current ratings for indoor bus bar installations are based on a given temperature rise over ambient in
elect1'ical design - section II
still but unconfined air. These ratings apply to installations in a large enclosed room without circulating air, in which the volume of air is sufficient to prevent the heat generated by the bus from having an appreciable effect on the room temperature. Cooling is affected by natural convection air currents and by radiation. Where the bus bars are installed in an enclosure, the heat generated is also dissipated by radiation directly to the inside walls of the housing and by convection air currents. The small volume of air in the enclosure rapidly increases in temperature as it recirculates in this confined space. The temperature rise of this trapped air will depend upon tlle amount of heat it can transfer to the housing before it is recirculated. There exists, therefore, a series of temperature gradients in a bus enclosure, i.e., from the bus bars to the enclosed air, from the enclosed air to the walls of the enclosure, and from the walls of the enclosure to the surrounding air. This process of heat transfer from a small bus enclosure slows up the cooling process, and a de-rating factor is necessary to prevent tlle bus from exceeding its upper temperature limits. The magnitude of the de-rating required when a bus is enclosed in a nonmagnetic housing such as aluminum is variable and will depend on several factors, such as the size of the housing, the quantity of heat generated by the bus, and the relation between the radiation and convection heat losses of the conductor. High current, laminated, rectangular bus bars with Hat sides vertical are cooled principally by convection air currents and depend to a high degree on "chimney effect" for cooling, i.e., the updraft between laminations. Such arrangements will require a more drastic de-rating when installed in a confined housing since convection cooling represents a greater than normal avenue for heat dissipation. The current carrying capacity of enclosed buses in non-magnetic housings can only be discussed in general terms because of the variable factors noted above. De-rating factors for three phase bus arrangements in a compartmented 24 K,V. enclosure each 30Y2 X 32~ inches-have been presented. * For these conditions, the following approximate ratio applies:
Rating in Non-Magnetic Housing do . In or Current Ratmg
= 75 per cent.
A ratio of only 60 to 65 per cent applies for high current, laminated bus bars that depend upon convection air currents as the principal cooling medium. '" "Carrying Capacities of Enclosed Buses" by A. P. Fugal, ELECTRICAL WORLD, March 19, 1932.
Non-magnetic housings are preferred over magnetic housings for a-c bus bar enclosures, particularly for high current installations and installations where the bus is in close proximity to the walls of the enclosure. Alternating current induces eddy currents in the enclosure walls and, in magnetic material, causes additional hysteresis losses, both of which raise the temperature of the housing. Non-magnetic housings eliminate the losses due to hysteresis. Oftentimes a further de-rating is necessary where magnetic enclosures are used. * The relationship between the current ratings in these two types of housing was found to be approximately as follows:
Rating in Magnetic Enclosure 5 R' . N on- Magnetzc . E nclosure = 8 per cent. atmg m This percentage will valY depending upon the proximity of the conductor to the walls of the enclosure and tlle magnitude of the current in the conductor. Common practice is to limit bus bars carrying alternating currents to 1200 amperes when they are instaUed in a magnetic housing. For higher current ratings, a non-magnetic enclosure is usually required. A common enclosure for a three-phase bus installation, such as generator phase bus, usually requires a non-magnetic aluminum housing to minimize heating. In these common enclosures, the heat generated by the combined three-phase circulating currents induced in the covers of the enclosure limit the rating of enclosed bus. When current ratings are 6000 amperes and over, it is common practice to isolate each phase in an individual non-magnetic aluminum enClosure.
Effect of Painting Bus Bars Painting the surface of an aluminum bus bar is done to increase the amount of heat loss by radiation. New aluminum surfaces have a relatively low emissivity which is improved in time upon exposure to the atmosphere. Outdoor weathered bus bar having average tarnished surfaces is usually considered to have an emissivity of 0.5 and indoor bus to have a slightly lower value, taken generally as 0.35 for average conditions. This compares with the value of 1.00 for the ideal black body. For indoor applications, the current rating of a bus bar can be increased appreciably by painting it with a Hat, non-metallic paint of any color. Increases in current rating up to 25 per cent have been attained by the use of some types of Bat paint. A particularly effective application for painted bus bar is isolated phase bus.
MECHANICAL DESIGN SHORT CIRCUIT FORCES ON BUS CONDUCTORS
The mechanical design of bus conductors and their supports must include provisions for resisting the electromagnetic forces due to short circuit currents. These forces, which are exerted on the conductors during short circuit conditions, are in tum transmitted.') to the insulator supports. Bo~h conductors and su?) ports must be designed to wIthstand these short Cll'cuit forces in addition to the natural loading of the bus conductor. The lateral forces of attraction or repulsion exerted on bus conductors during short circuit produce several force components acting on the insulator supports. These are: Lateral forces exerted on these supports at right angles to the axis of the bus conductors; Longitudinal forces which deflect the insulator supports in the direction of the axis of the bus due to the greater bus deflection tending to pull the supports toward the center of the span; Torsional forces exerted on the insulator at the end supports when the bus swings laterally due to short circuit lateral forces.
Where: The currents i 1 and iz are the maximum direct currents or either (1) the instantaneous peak values of the altematmg current or (2) the maximum RMS asymmetrical alternating current; D is the separation between conductors in inches; k is the shape factor of the bus conductor. It is sometimes desirable to state this force in terms of absolute units for convenience in deriving equations for certam shapes of conductor, as:
F
2 k i iz = -D-(Dynes per centimeter of bus length). 1
A r : : L E Of TORSIONAL ROTATION
)(
TORSIONAL fORCE LONGITUDINAL FORCE
LATERAL fORCE
Such forces, Fig. 1, are illustrated in a typical outdoor bus installation.
Lateral Forces
,
,.,'I ,"
:
~~
it.
The direction of the lateral short circuit forces acting on two bus conductors will be one of repulsion when the currents in the two conductors are in opposite direction. When the currents are in the same direction in the two conductors, the force will be one of attraction. Such a condition exists, for example, in a bus conductor composed of two channels arranged in box form. The proximity of the two channels requires the addition of spacer clamps at short intervals along the conductor to maintain a separation during short circuits. These spacer clamps also add rigidity to lateral movement of the bus conductor. Calculation of this lateral short circuit force between conductors utilizes the basic short circuit formula. This formula gives the force between conductors in pounds per foot length of bus conductor: F
=
5.4 k i 1 i z 10-7 D
(Pounds per foot length).
Fig. 1 - Short Circuit Forces
Mter the solution has been obtained from this fundamental relation, the units of measure can be converted to the standard units of pounds and inches by simple conversion factors. *
* prised "Equatio;'s for the Inductance and ShRrt Circui~ Forces of Buses. C,?mof Double Channel Conductors, C. M. SIegel and T. J. Hlggms, AlEE Trans, Vol. 71, January, 1952, pp. 522-531.
!\ "
51
=
section III - mechanical design
Value of k-The value of k in the foregoing equations is determined from the physical shape and arrangement of the bus conductor. It is commonly referred to as the shape factor. For the common shapes of bus conductor, the value of k will be as follows:
( 1.75 or 1.8)
X
I EMS
RMS current (lst half cycle ); i"
2. Round tubular conductors and symmetrical square
tubular conductors for all practical purposes will have a value of k equal to unity. The value of k for non-symmetrical rectangular tubular conductors can be calculated.** However, for the practical spacings used for rectangular tubular conductor, the value of k can usually be taken as unity. 3. The equations for short circuit forces for double
channel and sb'uctural shapes of bus bar have been advanced by Siegel and Higgins and by Higgins. *** In these equations, forces are determined from fundamental formulas. Short Circuit Current-The short circuit current that will produce the maximum electromagnetic force is the maximum d-c fault current or the maximum peak instantaneous value of alternating current. For most design applications, the maximum value of the short circuit force is desired. However, to determine this force, peak currents often must be' calculated in terms of other current values. For example, the ratings of some equipment are based on the root mean square (RMS) symmetrical short circuit current values. To differentiate between the various currents, the symbols below are used to designate current values described in the following paragraphs. i' = instantaneous peak symmetrical current; ( I
I RMS = 'I,
i
z'1 ,
y2 symmetrical RMS current;
= instantaneous peak asymmetrical current (i = 2i/ );
* Fonnulas for the Geometric Mean Distances of Rectangular Areas ** ***
52
and of Line Segments," T. J. Higgins, JOURNAL OF APPLIED PHYSICS, April, 1943, Vol. 14. "Fonnulas for Calculating Short Circuit Stresses for Bus Supports for Rectangular Tubular Conductors," T. J. Higgins, ELECTRICAL ENGINEERING, August, 1942, Vol. 61, pp. 578-580. "Formulas for Calculating Short Circuit Forces Between Conductors of Structural Shape," T. J. Higgins, ELECTRICAL ENGINEERING, October, 1943, Vol. 62, pp. 659-663. "Equations for the Inductance and Short Circuit Forces of Buses Comprised of Double Channel Conductors," C. M. Siegel and T. J. Higgins, ELECTRICAL ENGINEERING, Oct., 1943, Vol. 62, pp. 659-663.
= average peak asymmetrical current, see page 60;
=1.25i'.
1. For rectangular bars the value of k may be deter-
mined by equations advanced by Higgins * from the bus bar dimensions and spacing. However, graphical solutions are more practical for the usual rectangular bus conductor applications and offer, in addition, a visual comparison of the values of k for different shapes and arrangements of rectangular bar. The value of k in terms of the ratio of conductor dimensions and spacing is shown in Fig. 2. It will be noted that where the long sides of the rectangular bars are perpendicular to the plane of the axes, k will be less than unity. If the short sides are perpendicular to the plane of axes, k will be greater than unity.
= maximum asymmetrical
Symmetrical Currents-When it is desirable to use the RMS values of current in calculating short circuit forces, a multiplying factor is necessary to correct RMS values to instantaneous peak current values in the formula. Symmetrical RMS values are denoted by the value of T in Fig. 3. Th~peak instantaneous symmetrical current, i', in terms of the symmetrical RMS current is:
i' =
y2 I EMS
and I EMS = 0.707 i' .
A symmetrical a-c short circuit current results when the fault is initiated at the instant of peak voltage. The current is symmetrical about its axis and no d-c transient exists for this short circuit condition. Instantaneous peak current is represented in Fig. 3 on page 54 by the crest value, B, of the symmetrical CUlTent.
Asymmetrical Currents-The condition for a symmetrical fault current is seldom attained in actual practice; an asymmetrical fault is the general rule since the probability of the fault being initiated at the instant of peak voltage is very small. When the fault is initiated at zero voltage, a maxinrum asymmetrical condition exists and the alternating current wave is fully offset from its axis. This gives a momentary peak current, i, in the first half cycle which decays rapidly as shown in the sketch, Fig. 3. This peak current reaches a value designated by point A, and represents the maximum possible fault condition. This maximum short circuit disturbance usually governs the design and selection of electrical equipment such as bus conductor and bus conductor supports. Normally, the severity of the fault CUlTent will range in magnitude between a symmetrical fault current and a maximum asymmetrical fault current, depending upon the point on the voltage wave in which the fault is initiated. For this reason, the maximum asymmetrical RMS current is sometimes used in place of maximum peak current particularly where dampmg is present in the system. This maximum asymmetrical current is composed of two parts: 1. A d-c decaying component;
2. A sustained a-c componE;nt. The diagram, Fig. 3, shows these current components for an asymmetrical fault condition.
mechanical design - section III
SHAPE FACTOR, k, FOR RECTANGULAR CONDUCTORS 1..4
1. 3 ' .
~~
I A-
~-O A B
I\.
\.
1. 2
I'.. I'\.
"- "......
"
......
1. 1~ ~A""""
5
r-...
r-....
r-.
r-.
I - 1-8=2
1t-
l-
'-""r- +-
f-
1.O
_A B
1-....
--
l...l...-
l-I--
-- --
I-
V
v
~A - .5, / L..-
~
t-t- +-
1
0.9 I-
t-
-
1--1-
I~--
--
.... _I_f.--
I...-
L..-
L..l-
I/
A
~I..
V 1/
00.7 8·=·25 J w :>
/
II 1/
f7 I-~
A--j
....
~.
0.6
1. SINGLE BARS PER PHASE I ....
1/
~
~
1.7
1/
r7
V"
L..-
I.....
O. 8
i 1/
i
0.5
/
I1-'1--''-1--
~I -I
1-11-1~I-
r-A-J
/
~~~ ~~~I
1/
J
II 1/
I-
·0.3 1-1- l - " 8 =0
I I
~
2. MULTIPLE BARS PER PHASE
1/ 0.4
f--
~S r-Tl
J
!-.~ =.1
rJ~ l-
s
l-
IS
-j
~s-'I
J / II
I
IT 0.1
-,.
1
I I
II
o 0.2
0.4
0.6
0.8
1.0
I I I I I I I I I I I I I I I I I Tl I I I I I II I I I 1.4 1.2
1-11-11-11-11-11-11-1-'II-~
1-1I-~
1-1I-~ I-~
1-11-11-11-11-11-11-11-11-11-1-
I I I I I I I I I I I I I I II I I
1.6
1.8
2.0
S-A A+B H. B. Dwight, "Electrical Coils and Conductors," McGraw-Hill Book Co.
Fig. 2
53
section III - mechanical design A
n:--Tl"~~Ir""""r-i:----"--~~_B --T
Fig. 3 - Short Circuit Current* I)
Where: AB is a curve passing through maxima peak cur-
II
'Ii I
'j
,
-I
L ~ j'
_il i: )1 . :,1 T.- ;:',';,
rent values; EF is a curve passing through minima peak current values; DC is the d-c component midway between curves AB and EF and represents the offset of the a-c current due to the d-c component; ST is a curve of the RMS values of the alternating current component only; RT is a curve of the RMS values of the alternating and direct currents. The theoretical maximum asymmetrical peak current as shown by the value at A on curve AB will be a maximum in the first one-half cycle. For conservative bus design, this value will be used to determine the maximum electromagnetic force produced by an asymmetrical short circuit. This maximum instantaneous peak asymmetrical value of current, i, as represented by the conditions in the first one-half cycle will be twice the normal symmetrical peak current, i = 2i', and in terms of the symmetrical RMS current as represented by the value, T, on the curve, ST, it becomes:
,I, .'
i = 2i'
>11[,J_
= 2 (y2I
RMs )
= 2.828 [RbiS Maximum peak asymmetrical
, ,1
amperes.
Effective Current-It is sometimes desirable to use the effective value of current rather than maximum peak current in the calculation of electromagnetic forces. This effective value of current is represented by the curve, RT, and its value at any instant is the
* A.
G. Darling, "Short-Circuit Calculating Procedure for Low-Voltage A-C Systems," AlEE Transactions, 1941. Vol. 60.
54
square root of the sum of the squares of the RMS value of alternating current represented by the curve, ST, and the instantaneous direct current represented by curve, DC. The maximum asymmetrical RMS value of the total short circuit current is represented by the value, R, on the curve, RT, and is sometimes taken as 1.75 or 1.8 times the value of the RMS symmetrical current value. Where these values of current are used to determine short circuit forces, it is well to investigate the system for possible vibration resonance and determine the proper stress factor to apply to the ' system, page 59.
:,i
.,
.
'.i
NEMA Standards The National Electrical Manufacturers Association ( NEMA) standards for Power Switching Equipment, Publication No. SG6-1954, has established conservative standards for the calculation of electromagnetic forces between two current carrying conductors. The basis of this calculation is the fundamental formula for short circuit forces using instantaneous peak current values to establish the maximum force. This standard recognizes the fact that the forces thus calculated are, in most cases, higher than those that actually occur. This, however, tends to compensate for the possibility of increased force due to resonant vibration since this factor is not taken into consideration. The standard force formula shown gives the force in pounds per foot of conductor:
F=M
5.4 i 2 X 10-7
D
The value of i in this formula is taken as maximum asymmetrical peak current and is used in conjunction with a multiplier, M. When maximum peak current is substituted, M 1 for a d-c fault or a single-phase
=
~
;
.'.\
'1 'j
mechanical design - section III
fault on either a single-phase or a three-phase circuit. Often it is desirable to use RMS current values either symmetrical or asymmetrical. Where these current values are available, they can be used in the formula with a corresponding value of M from the following table. The multiplier, M, acts not only as a correction for peak current but also corrects for the maximum force in a' three-phase fault, taken as 0.866 the value of a single-phase fault. This maximum force occurs on the center conductor of a flat symmetrically spaced arrangement, page 57. MULTIPLYING FACTORS Current Used
Circuit
Multiplying Factor, M
Current
1.00
1.0
1 phase a-c or Maximum peak 1.00 1 phase of 3 phase
1.0
Maximum peak
d-c
1 phase a-c or 1 phase of RMS asymmetrical 3 phase
1.63
(1.63)2 or
2.66
1 phase a-c or 1 phase of RMS 3 phase' symmetrical
2.82
(2.82)2 or
8.0
0.866 X (l)2
0.866
** 3 phase a-c ** 3 phase a-c
3 phase a-c
**
Maximum peak 1.00
, RMS asymmetrical
I 1.63
0.866 X (1.63)2
2.3
2.82
0.866 X (2.82)2
6.9
RMS symmetrical
r.;.
Relation to Peak
*
* NEMA "Standard for Power Switching Equipment," 1954. ** For the center bus of a flat symmetrically spaced bus.
Publication SG6-
Calculation of Fault Current
,. '.,
The calculation of actual short circuit current usually involves the use of symmetrical components, except where the three-phase short circuit is considered. For high voltage installations where resistance is small compared to reactance, the circuit resistance can usually be neglected and calculations based on reactance values alone. On low voltage installations, this is not always true, but in cases where circuits are comprised of h'ansformers, generators, and reactors, the value of reactance may be sufficiently greater than the resistance so that the reactance alone may be used without introducing too great an error.t An investigation of the relative magnitudes of resistance and reactance in a circuit will reveal whether reactance values alone can be used or whether a more accurate det61mination is advisable, using impedance values. In determining the total impedance on low t "Calculation of Fault Currents
voltage circuits, all small impedances become important and such components of circuit impedance as bus bars and their connections, disconnects, switches, and current transformers should all be considered in the total. Since the severity of the short circuit force on a bus conductor and its supports is dependent upon the magnitude of the fault current, the mechanical design of a bus installation should be based on a maximum fault condition. For most conditions, a three-phase fault may be used as an indication of maximum fault current for design purposes. This will be conservative for line to line faults in which the current magnitude is approximately 86 per cent of the three-phase value. For line to ground faults, the current may be greater or may be less than the three-phase fault current, depending upon the fault location in the circuit or the magnitude of the ground resistance. The three-phase fault current is of such a magnitude that it can often be used to represent line to ground fault conditions. Many bus installations connected to transformer secondaries are designed to withstand the maximum fault current output of the three-phase transformer bank. The calculation of this fault current is based on sustained primary voltage and the amount of power on the primary side. The formula for the greatest symmetrical three-phase short circuit current on the secondary side is:
in Industrial Plants," Raymond C. R. Schulze, ELECTRICAL ENGINEERING, June, 1941,pp. 271-279.
Where: KVA
X 100 =KVAy3X X1000 amperes. E XZ
= rating of three-phase transformer or trans-
former bank; E = secondary voltage of h'ansfOlmer or transformer bank; Z = per cent impedance of transformer or transformer bank. For example, assume a three-phase transformer bank with a capacity of 45,000 KVA. The voltage of the bank is 66,000/13,200 volts and the per cent impedance of the transformer bank is 10 per cent. The maximum three-phase secondalY short circuit current is· desired assuming sustained primary voltage and capacity available on the primary side.
KVA = 45,000 Secondary Voltage, E = 13,200 volts Per cent impedance of bank, Z 10 per cent
=
I = KVA X 1000 X 100 \/3 X Ex Z 45,000 X 1000 X 100 - 1.732 X 13,200 X 10
= 19,700 RMS amperes (three-phase symmetrical short circuit current).
55
=
section III - mechanical design
The vector sum of the two forces will vary in magnitude depending upon the angular displacement of the short circuit currents from the reference axis. A plot of the cosine functions through 180 electrical degrees will give one complete cycle of the functions. This is shown in Fig. 5. The total force, F A, which is the vector sum of the individual forces on bar, A, is equal to their numerical sum in this case since the forces are in the same direction. This total force becomes:
Calculation of Lateral Short Circuit Forces Force Between Two Conductors-The calculation of the electromagnetic short circuit force between two conductors involves the substitution of the proper values for the shape factor, k; the separation, D, in inches; and the short circuit currents, i 1 and i z, in the formula on page 5l. Where more than two conductors are involved, the short circuit force on anyone of the conductors is the vector sum of the forces between this conductor and each of the other conductors comprising the circuit. Force on End Conductor of Three-Phase Bus Spaced Horizontally-The total three-phase short circuit force on the end bar of a three-phase bus arranged with a horizontal symmetrical spacing of D inches as shown in Fig. 4 would be as follows. Using the vector relationship indicated for the three-phase symmetrical short circuit currents, equations can be written for the forces between any two bars. The total force on the outside bar, A, will be the vector sum of the forces between bars A and Band between A and C. These forces are:
z
F.!
AS
= F. w
5.4 k iAiB X 10D 54 k X 10-7
= . 2D = 5.4 k iAie X D
(
~
( iA COS a i e COS
,,, ,• ••
o -% ::l c..
-Y2
'"
Q)
cos a cos f3
+ cos a2cos OJ
«
0 in
cos a COS fJ
[
z o
w
7
X
;:: u
z
54 k X 10-7 F,IB=' D (iAcosaiBcosp)
7
= F + F,1O = 5.4 ki DX 10-
-%
,.
"
"
'.
~
v·- "-._,
,'Aoo /o%~ "
#
",,
1500-~
120"
\
\\ ,,
"1--..., ~./
,
'.
" 1
V
1\
\\
, ,• . .. '
,,
MAX: AT 165' (.0;768)
(J )
-1
10-7 ( cos a cos (J ) 2'
.-~.-
•••.• cos.I. cos,9
- - _ y, COsrJ..
COS I)
- - - VECTOR SUM OF COSINE FUNCTIONS
o[ oB
oC
"!II, 1 I
:I
REFERENCE
'f
!
Fig. 5 - Value of Cosine Functions
The sum of the cosine functions in this formula is a maximmn at 165 degrees, with a value of 0.768 as graphically shown. For a symmetrical three-phase fault, where i A is ie, the maximum force on the outside conductor of a symmetrical flat arrangement with a spacing of D inches will be 0.768 times the value for a single-phase fault of the same magnitude. The formula, then, for the force on the outside conductor of three symmetrically spaced conductors in a flat arrangement for a three-phase fault is:
= =
FA
(0.768) (5.4) ki z X 10-7 D
=
(lbs. per foot of conductor).
Fig. 4
56
.'1 1
Force on Center Conductor of a Three-Phase Bus with Flat Symmetrical Arrangement-The force on the center conductor of the same three-phase symmetrical flat arrangement of bus conductors will be the vector sum of the forces F I3A and F 130 which are given by the equations:
::l
mechanical design - section III
54 k X 10-1 F BA = ' D ( iB 7
= 5.4 kiniD X 10A
F no
=
5.4 k
X
D
f3 iA
COS
10-1
(i B
(
X
COS
symmetrically spaced conductors in a flat arrangement for a three-phase symmetricalfault will be:
(l')
cos f3 cos (l'
)
FB
= (0.866) 5.4D ki
'1 (
cos f3 cos
8)
2
z o
;::
u
-< ......'"
Yz
/
-<
o
[cos f3
COS
(l' -
-'h
cos f3 cos 8] z
(lbs. per foot force on the center conductor) .
The variable cosine functions which determine the magnitude of the forces F BA and F BO with respect to angular displacement are shown in Fig. 6 along with their vector sum which determines the variation and magnitude of the total force F B on the center conductor. This force will be a maximum at 75 degrees to the reference axis as shown with a magnitude of 0.866 times the single phase value for a fault of like intensity. The maximum force on the center conductor of three
"",''\.
/
10-1
(lbs. perfoot).
Q
'"
~ :l;
-%
'"
,
/7
,,/j
/
~".
60·
AT 75·
(0.866)
\
-
II/~
1
X
.........
/'
+ (- FBO)
= 5.4 k i D X 10-
® MA~.
.
These forces will be applied from opposite sides of the center so that the forces of attraction to one outside conductor will be added to the forces of repulsion of the other outside conductor. The maximum force for a three-phase symmetrical fault on the center conductor will be the vector sum of F BA and F BO or F B = F BA
X
f3 i o COS 8)
COS
1 = 5.4 kinioD X 10- X
2
•• •
.. . ..
90·
'\\
\
\\
\
\
120·
/'/
~ 150:1
180·
.•. I' •• ...
A
\, ./' ..'.
,.\KS I
,I
"'
-1 ________ COS! cos "_._._ cos (J COS 9 _ _ _ VECTOR SUM OF COSINE FUNCTIONS
Fig. 6 - Value of Cosine Functions
Interlaced Bars Feeding Electric Furnaces
57
section III - mechanical design
Force on Each Conductor in a Multiple Bar Arrangement-The same vector addition of the individual forces may be applied to any multiple arrangement of conductors. The total short circuit force on each conductor for a symmetrical flat spacing of six bars is derived in the same manner. For an interlaced bus arrangement of two bars per phase, Fig. 7, the short circuit force for any single bar is calculated as the vector sum of all the individual forces exerted between it and each of the other bars.
F 01.41
FORCES ON C l 5.4 k 10-1 • = 2D (~Ol cos 0 iAl cos a)
F 01Bl
= 5.4 kD 10-
' F 01A2
= 5.4 Dk 10-
1
k 10= 5.4 2D
1
F 01B2
F 0102
k 10= 5.4 3D
1
•
(to l cos 0 iBl cos (3) (.
~Ol
1
cos
()
•
~A2
cos a
)
•
(~Ol cos () i B2 cos (3) .
(to l cos () i02 cos 0)
0,8
0.4
f----\---+----++---+----+-'~_+__t--___l
0.2 f - - + - t - - - f - + - - - t - - - - + - - + + - t - - - - - i
Fig. 7 - Interlaced Bars
O!---o\'-i,....+-+---....--..".--...p--...-j
Assuming the vector rotation in Fig. 7, the forces on bars AI, Bl , and Cl are calculated as follows.
-0.2
f---~--hl\---+---+----''r-I-I---__t-~---l
'j 'I :1
'_1
FORCES ON Al
F AlBl
=
5.4 k 10-1 (.
~Al
D
F AlGI = 5.4k1O-1(. 2D ~Al
F AIB2
=
F AlG2
k 10= 5.4 5D
1
- 0.4 I--+-t--\---+---t--JI-.---tlt---t-----i •
~Bl COS
(3
a
~Ol COS
.
0)
COS
•
~A2
cos a
"
'"
"!
F BIA1
=
= 5.4 Dk 10-
1
F BlOl
k 10= 5.4 2D
1
F BIA2
k 10= 54. 3D
7
F BlB2
F B102 =
58
D
- 0 . 8 1 - - - + - - - - + 81 M A X , ' - - - + - - 76°-0.78
COS
a iB!
COS
(tAl COS
a i02
COS ())
•
•
(3)
•
(~Bl cos
/3
~Al cos a)
(i Bl cos
/3
i Ol cos ())
(iBl
- 0.6 1->"'-------t----\-t---+-i'-------1--->t__t--___l
)
FORC,ES ON B 1 5.4 k 10-1
1i
)
cos a
k 10-1 ,(. F AIA2 = 5.4 3D ~Al cos a 5.4 k 10-1 • 4D (ZAI
'i
cos (3 i A2
COS
a)
(i BI cos (3 iB2 cos (3)
54 k 10-1 . 4D (iBl cos
/3
i 02 cos ()
0°
30°
60°
90°
120°150°
180°
Fig. 8 - Vector Sum of Cosine Functions
The total vector sum of the forces on bars AI, B l , and C1 will vary with the angular values of the cosine functions. This total will vary sinusoidally as shown in Fig. 8, which gives the vector summation of these cosine functions for 180 electrical degrees. A maximum value occurs for each bar as follows. On: Bar Al at 162 degrees-vector sum 0.72 (maximum value); Bar Bl at 76 degrees-vector sum 0.78 (maximum value); Bar Cl at 95 degrees-vector sum 0.63 (maximum value).
j :j
mechanical design - section III
The equations for the maximum total force on these bars for a three-phase symmetrical fault current with the bars arranged as in Fig. 7, assuming currents divide equally between the bars of each phase, will be: F Al =
(0.72) 5.4 ki 2 D
= (0.78) 5.4Dki
2
FBI
= (0.63) 5.4Dki
2
F 01
X
10-7
X
10-7
X
10-7
(1bs. perfoot on A,). (lbs. per foot on BI)' (1bs. per foot on CI)'
Vibration and Resonance Vibration in a system of bus bars subjected to a-c short circuit currents may be attributed to the frequency of the components of current resulting from the short circuit. The system frequency contributes the fundamental frequency to which the bus bars are subjected. The first harmonic of the fundamental frequency may also be present as a result of the combination of two sine waves of double fundamental frequency as was noted for a three-phase fault shown in the graphs on page 58. For asymmetrical faults, a doc uni-directional component of force is also present. This is a variable force with a rate of decay depending upon its decrement factor. A bus conductor ipstallation will have a natural period of vibration depending upon the span length, rigidity of supports, degree of damping, and elasticity of its members. The conductor supports will also have a natural period of vibration. The frequency or frequencies at which this assembly vibrates is a combi~ nation of the natural frequency of the conductors to which the force is applied and the supports which provide the reaction to such motion. The calculation
of this period of vibration has been advanced by several authors. * The conditions for vibration are increased by the proximity of the conductors, short span lengths between supports, the inflexibility of the supports, and the rigidity of bus bar members. Resonance may be established. when the conductors and their supports vibrate in harmony with the electromagnetic short circuit forces. The conditions for resonant vibration are most favorable when the natural period of vibration of the conductor and its supports is equal to, or nearly equal to, the fundamental frequency or double fundamental frequency. This resonance may produce a significant increase in the normal short circuit stresses in a bus bar. In some cases, stresses may be many times greater than normal and it is desirable to change the natural period of vibration of the system by varying design conditions. Such variations as the following are effective in changing the frequency of vibration: Increase span lengths between supports to reduce natural frequencies; Provide flexible SUPPOlts so that more of the initial energy will be absorbed in the movement of the conductor and supports. In installations where bus bars are designed to swing laterally with the short circuit forces, extremely large short circuit currents can be encountered with little or no damage; The flexibility of a conductor will affect its natural period of vibration. Greater flexibility will decrease its natural period of vibration.
Stress Factors (p)-Where a bus bar system vibrates at or near a resonant frequency, it is sometimes necessary to assess a stress factor which, when multiplied by the force as calculated from the standard short circuit formula, gives the approximate increased force, P, due to resonance. It is: P
= P X F (lbs. per support).
Where: p is the stress factor; F is the force as calculated from the electromagnetic force formula for the span adjacent to the support. For doc short circuits, the initial force is suddenly applied to the supports with an impact that gives a higher initial force than the sustained short circuit force. The stress factor for this condition would theoretically be two. Actual determinations of these impact forces may show this stress factor to be slightly in excess of two or somewhat less than two, depending upon how much inherent damping is present in the system.
* "Short-Cut Method of Calculating Stresses in Bus Conductors," W. Specht, Flexible Supports ReduceVibriiffon
GENERAL ELECTRIC REVJEW, Vol. 31, No.8, August, 1928. "Sb-esses in Bus Supports," R. Tanberg, THE ELECTRICAL JOURNAL, Vol. 24, No. 10, October, 1927, pp_ 517-525. "Mechanical Stresses in Bus Bar Supports During Short Circuits," O. R. Schurig and M. F. Sayre, ALEE Trans., Vol. 60, pp. 478-486, Apr., 1925.
59
section III - mechanical design
For the usual outdoor installations of bus bar, under 66 KV, flexibility is inherent due to the long spans. This usually provides enough damping so that the initial movement of the conductor and its supports absorbs a part of the initial energy, A stress factor of one can usually be taken for these installations. On higher voltages (66 KV and up), considerable damping is usually present due to the length and flexibility of the bus and the height of the insulator stack. Short circuit forces calculated by the accepted methods outlined may be more conservative than is required since the natural frequencies of the bus assembly may be so low that allowances for resonant vibration are unnecessary. Where such a condition exists, a more realistic substitution of average asymmetrical peak current rather than the maximum asymmetrical peak current may give forces which are closer to actual effective values. Tests on long span high voltage conductors show that short circuit force calculated by standard methods is very conservative. * The effective force that deflects the insulator and causes insulator failure is in close agreement with the force calculated by the accepted formula using the average asymmetrical peak current instead of the maximum asymmetrical peak value, It is assumed that the initial electromagnetic forces acting on a long tubular bus act as a series of successive forces which are used initially to bend and deflect the bus and to initiate movement of the insulators from rest. The initial peak current in the first half' cycle of an asymmetrical fault is, therefore, not fully effective in this case because of its short duration and the inherent damping in the system. Such force is approximated if the average peak current of an asymmetrical fault from inception to steady state is used in the fundamental force formula. This may be taken as 1.25 times the symmetrical peak current or in terms of symmetrical RMS current, it will be: iff = 1.25 X
y2 X I RMs
= 1.77IRMs • Where:
I RMs is the symmetrical RMS current.
I
i~,
This value substituted in the standard force formula will give the "effective force" on the insulators and bus in a high voltage long span tubular bus installation. The use of average peak asymmetrical current instead of maximum peak asymmetrical current gives a factor of 1.77 times symmetrical RMS current. This value is in close agreement with the factors applied to symmetrical RMS current values (1.75 to 1.8) to obtain the maximum asymmetrical RMS value of the total current, see page 54. " "Behavior of High Voltage Buses and Insulators During Short Circuits," R. M. Milton and Fred Chambers, AlEE Trans. 55-11, February 16, 1955.
60
Longitudinal Forces The lateral deflection of a bus conductor and its supports during short circuit conditions creates an accompanying longitudinal deflection of the bus supports. The greater the lateral deflection of the bus, the greater will be this force tending to pull the insulator supports together. This longitudinal force will vary from a minimum at the center of the bus system to a maximum at the end support. The design of the bus installation, then, should consider the magnitude of these longitudinal forces on the end support and the support next to the end where they are the grtlatest. The calculation of longitudinal forces is beyond the scope of this manual, but methods have been advanced by several authors to determine mathematically its value. * AXIS OF CONDUCTOR
_1_
2F
SUPPORTNEXT TO END
R2
= V (2F)2 + P22
Fig, 9
Although the longitudinal force, P, is less on the span next to the end, the lateral force, F, is approximately twice that of the end support for equal spans, The resultant force, then, will be greatest on the support next to the end unless there is considerable flexibility in the bus conductor. This is shown in Fig. 9. The maximum total cantilever force exerted on the insulator is the vector sum of the lateral and longitudinal forces and is calculated as R 1 and R 2 for the end span and the span next to the end, respectively. To reduce the longitudinal forces in a bus installation, several design factors may be considered. They are as follows: Increase the stiffness of the bus conductor in the direction of the lateral forces; Decrease the length of the span between supports; Decrease the number of continuous spans. The first two factors limit the lateral deflection of the bus and the third reduces the magnitude of the longitudinal force at the end support. For rectangular bar and structural shapes, the arrangement of conductors with their axis of greatest stiffness perpendicular to the direction of short circuit force will limit deflection
* "Stresses
in Bus Supports," R. Tanberg, THE ELECTRIC JOURNAL, Vol. 14, No. 10, pp. 517-525. "Short-Cut Methods of Calculating Stresses in Bus Structures," W. Specht, GENERAL ELECTRIC REVIEW, Vol. 31, No.8, August, 1928, pp. 413-418. "Practical Calculation of Short-Circuit Stresses in Supports for Straight, Parallel Bar Conductors," 0, R. Schurig and C. W. Frick, GENERAL ELECTRIC REVIEW, Vol. 29, No.8, August, 1926, pp. 534-544.
mechanical design - section III
and, thereby, reduce the longitudinal force. Increasing the stiffness of the bar and decreasing span lengths will also change the natural frequency of vibration of the bus conductor and its supports. Where these factors increase the possibility of resonant vibration, a condition more serious may result because resonant vibration may increase lateral force to a far greater degree than they reduce the longitudinal force.
Torsional Forces Torsional forces are encountered in the end supports of a bus conductor installation. These forces are due to the twisting of the insulator support by the lateral swing of the bus bar during short circuit and
may be of serious proportions where the conductors are extremely flexible, and the late)'al movement is great. Since torsional stresses are a function of the lateral movement of the bus, they may be reduced by increasing the bus rigidity to lateral movement or by making the end support relatively free to rotate within limits. A slip fit support may also aid by allowing the bus to rotate slightiy within the retaining clamp. Where it is necessary to weld the bus in tile span, it is wise to reinforce the weld so that bending does not accompany the lateral movement of tile bus and tilereby increase the torsional force. Welds should not be placed in the center section of the bus where bending moments are high and may result in greater lateral deflections and permanent set.
BUS DESIGN Bus supports are designed for a cantilever sh'ess which is measured in inch-pounds, one inch from the base of the support. The total force acting on tilis support is the combined effect of the lateral and longitudinal forces imposed by electromagnetic short circuit conditions. In systems where considerable damping is inherent or short circuit forces relatively light, a small safety factor may be included in the design for these supports. Increased safety factors should be included where tile magnitude of tillS total stress is high and conservative design is anticipated. In outdoor installations, provisions should be made for the complete drainage of water that may collect on or within tile bus conductor shape. On a tubular bus, a small drainage hole in mid-span on the bottom will drain tile conductor. Such shapes as channel and I-beam sections should be arranged so that they drain naturally and do not allow water to stand in any depression. This water not only causes an increase in the dead load of the conductor but may initiate corrosion of tile conductor. Wind induced vibration in long span tubular conductors has been experienced in isolated cases under certain conditions. In most cases resonant vibration can be eliminated by threading a length of aluminum or ACSR conductor into the tube where it lays loosely and acts as a damper. This simple, effective method of dealing with wind induced vibration has become standard practice in tubular installations because of its simplicity and ease of installation.
Clearances Minimum standard clearances have been established between live parts of bus conductors such as switchboard circuits and other applications of rigid bus conductors. Tables 1, 2, 3 and 4 indicate acceptable clearances for various applications. The spacing of out-
door buses is based on design experience and physical size of equipment, and will vary with the voltage and application.
TABLE I-STANDARD FOR
SWITCHBOARD SPACING * Minimum Spacing in Inches Between Live Parts of Opposite Polarity
Voltage Involved
Minimum Spacing in Inches Through Air and Over Surface Between Live Metal Parts and Grounded Metal Parts
Over Through Surface Air
~
125 or less 126 to 250 251 to 600
2
* Underwriters'
Laboratories "Standard for Dead Front Switch-
%
1~
~
~
::Sl /4
1
1
boards."
i
TABLE 2 - MINIMUM CLEARANCES FOR SWITCHBOARDS* ~~'~~~:~eo~js~~~es~~~~e
Striking Distances when
Ri~?~rrS~rS~~I~~e:nd
of Insulating Panels
Between
Part~
of 0EPosite Po arity
% ~
%
1 114 1% 2Y2 3
Between Live Parts and Ground
~~
% ~
%
1~
1% 2Y2 3
Between Parts
of 0r-posite Po arity
Voltage Class**
Up to 50 125 250 600 750 1,500 2,500 3,500
Between Live Parts and Ground
~
:yg
~
%
% % %
1112
2 2Y2
~ ~
%
1~
!:(
2
;. ·1,.'
2~
i ; ;:
*Westinghouse Switchboard Data Book. **For intermediate voltages, it is advisable to use the distances given for the next higher voltage class. Note: For switchboard circuits connected to systems above 150 kva capacity, the distances between parts of opposite polarity should be increased from lh to 1 inch.
I'III !
i .J
61 "
r ,
.1
iL \
j"
-
section III - mechanical design
TABLE 3 -MINIMUM CLEARANCE IN INCHES BETWEEN LIVE PARTS OR BARE CONDUCTORS IN AIR*
Deflection of Bus Conductors Bare and Loaded In designing, the deflection of a bus between its SUppOltS should be considered for both the bare or unloaded condition and for ice and wind loads added to its dead load. It should have a small unloaded or bare deflection so that it visually appears to be reasonably straight;
The bus, when subjected to ice and wind loads, should not be stressed above safe limits nor should it sag excessively.
The unloaded deflection is important from an appearance standpoint. A visible amount of sag in a bare conductor would present an unsightly appearance. The same bus, when loaded with ice, would not present an objectionable appearance because of a slightly greater deflection. It is often desirable in designing . long span buses to formulate a rule which will govern the maximum tolerable unloaded deflection of the bus. This rule, e,g., can be a constant ratio expressing the relation of deflection to span length or it can be a rule which establishes maximum deflection as a function of bus diameter or physical size. The maximum bare deflection of a long span tubular bus is limited by some designers to one diameter of the bus while others prefer to designate the maximum unloaded deflection as a certain fraction of the span length. Conservative design limits the dead load deflection to 1/150 or 1/200 of the span length, while less conservative design to 1/80 of the span length. To gain a straight or level appearance, bus con-
TABLE 4 -
Indoors Phase to Phase
Outdoors
To Ground
3Yz
2Yz
4 7
5Yz
3%
'1' ,I Of
J
I
I
d
!
;:
1
6 6 6 12
6 6 6 9
8Yz 12 16
25,000 37,000 50,000
17 24 32
13 18 23
30 36 45
23 28 34
73,000 88,000 110,000
44 52 64
,32
54 63
41 47
132,000 154,000
77 89
56 65
76 89
57 67
187,000 220,000
106 124
78 90
,
if It I",- . g.
n I.'
q
38 47
* Westinghouse Switchboard Data Book. ** For intermediate voltages, use distances
given for next higher voltage. Note: The above table is for rigid conductors only when supported clear of surface. For flexible conductors, increase clearances given by twice the maximum sag. Smaller spacings may be used for standard apparatus when all parts are shaped to minimize electrostatic stresses.
ductors are sometimes formed with a slight bow equal to the normal unloaded deflection. When this bus it>
STANDARD CLEARANCES AND PHASE SPACINGS* Centerline Spacing 2 Inch Rod Gap, 60-Cycle Dry (Inches)
Minimum Safe Clearance to Ground (Inches)
Hook and Gang Disk Switches and Bus Supports (Inches)
Nominal System Voltage
Apparatus Voltage Rating
Dry
Wet
6,900 13,200 22,000
7,200 14,400 23,000
60 85 110
40 55 75
4.2 7.6 10.7
6.0 8.0 11.0
18 24 30
36 36 48
33,000 44,000 66,000
34,500 46,000 69,000
145 170 235
100 125 180
14.1 16.9 23.7
14.0 17.5 24.0
36 48 60
60 84
110,000 132,000 154,000 220,000
115,000 138,000 161,000 230,000
385
285
39.5
84
120
485 660
380 560
50.1 68.6
39.0 45.0 51.0 71.0
108 156
168 216
* Standard
i .1
To Ground
11 16 21
E~uivalent
i
Phase to Phase
Up to 3,500 4,500 7,500 15,000
Insulator 60-Cycle Flashovers (Kilovolts)
:i
**
Voltage Class
Horn-Gap Switches (Inches)
72
clearances and phase spacings as adopted by the NEMA and based on the joint EEl - NEMA preferred system voltage and also using AlEE standards as a basis. Standard Handbook for Electrical Engineers.
62
mechanical design - section III
then installed with the bow upward, the bare deflection neutralizes the upward bow and the bus conductor is straight or level between supports. The unloaded deflection is not usually the governing factor in a bus installation, particularly where heavy ice formations are encountered and high wind velocities add to the load imposed on the bus. These loads, along with shOlt circuit forces, add to the stress in the outer fibres of the bus conductor and should be limited to values that provide an adequate factor of safety. For most applications, it is satisfactOly to base the maximum fibre stress on a certain percentage of the yield strength or by reducing the yield strength by a £Xed amount. For the bus materials commonly used, the following yield sh'engths and suggested working stresses may be used as a guide in bus design. DESIGN STRESSES
,
Bus Material
EC-H17 EC-H13 55EC 56EC 57EC 59EC' 6063-T6 6063-T83 6061-T6 Drawn Copper Iron Pipe
Yield Strength (psi)
Thickness (Inches)
Up to Vz Up to % Up to Vz Up to Vz Upto%
Suggested Working Stress ( psi)
15,000 12,000 25,000 22,000 15,000 8,000 25,000 30,000 35,000 28,000
Up to Vz 0.050-0.150
10,000 8,000 15,000 13,000· 10,000 6,000 15,000 20,000 25,000 18,000 24,000
Ice Loading-Ice loads are assumed to be of uniform radial thickness on tubular conductors and of uniform thickness on all exterior smfaces of bus conductors such as channel or angle arrangements in box form. A factor of 57 pounds per cubic foot is commonly used to determine ice weight. Typical examples of ice loading are shown for channel bus and tubular or solid round bus.
r1 F
Tf:::::::':':::':':::::::::::::::::'::::
I 1:;: ; N +
...;}
ll", 2
(A
[(A
F X t = cross sectional area of ice on two flanges of one channel;
+ 2t) t =
cross sectional area of ice on outside web of one channel;
+ 2t) t + 2 Pt] = cross sectional area of ice on one channel;
2 [(A
+ 2t) t + 2 Ft]
X
12
= cubic inches of ice on two channels per foot of length;
Bus Loading-Ice and Wind Bus loadings are usually calculated for a given set of conditions depending upon geographic location and experience with ice and wind conditions. These must mst be determined before bus loads are calculated. Tables, pages 128-131, give bus deflections and stresses for bare or unloaded tubular bus conductors and for loadings of Vz inch ice, liz inch ice with 8 pounds of wind, and for 1 inch of ice. t
weight of ice = 1.244 t (D
X
::.:.:.:.:.:.:.:.:.:.:.:.:.:.:.'.'.:.:.
+ t)
lbsJft.
0.792 t [A
+ 2t + 2F] = weight of ice in lbs/ft on two channels.
Wind Loads-Wind loads are calculated for an assumed crosswind velocity acting on the projected area of the bus conductor. The projected area of an iced conductor is the over-all velucal dimension which includes the height of the conductor plus the top and bottom thickness of ice. The relationship between wind pressure in pounds per square foot of projected area and the actual wind velocity in miles per hour is shown in Fig. 10. The wind pressure on a cylindrical surface such as a tubular conductor will vary slightly from that on a flat surface such as a channel bus. This difference is shown by the two curves in Fig. 10 representing both types of bus conductors. The mathematical relationship for wind pressure and actual wind velocity is given by the following formulas:
63
:j
.," "
section III - mechanical design
WIND PRESSURE VS. WIND VELOCITY I
I
60
I
I I II
55
I
IT J
I ,I
I II
50 I
I
I I
45
I I
I
J
I
I
t--=
I
I
'I
40
I
u..
II
V)
l:l::
w c..
I
J
d 35
II
J
II
vi a:l
I
-' W
l:l::
:::>
:
c..
~
ct. J 4.JI vJ
tJl
l:l::
Z
I 'I
ct.J
V) V)
W
0
II
,
30
~
~~I
~F
25
"',:SJ
"J S,
PI .::s,
ll.:
~/
I
20
1/
I J
I 15
,
/
/
J
/
./ )
/
10
1/
J
/ ~
1/
/
~ ~
~
5
/
~
/
,/
___17 1:;;0' 17
o
..... 20
1."
40
60
80
100
120
WIND VELOCITY (MILES PER HOUR) Fig. 10
64
140
160
180
mechanical design - section III
Cylindrical smfaces- P
= 0.0025 V a
Flat surfaces-
= 0.0042 V a2lbs. per square
pI
2
lbs. persquam foot of protected area; foot of protected area.
Where:
Va is the actual wind v~locity, in miles per hour. Combined Ice and Wind Load-The combined loading on a conductor is calculated by the vector addition of all conductor loads. Graphically this is represented below. RESULTANT LOAD, (w r ) 10,.= V (w b +wi)2+W1/
lbs. per foot
BARE WEIGHT, (w b ) lbs. per foot (from tables)
Formulas for Deflection and Stress of Bus Conductors The calculation of bus deflection and stress is often necessary where tables do not give the required data. Tables, pages 128-131, list deflections and stress for standard IPS and extra heavy IPS tubular bus conductors since these shapes are used considerably for both indoor and outdoor installations. The deflection and stre'~ses for other shapes of conductors can be calculated from the standard beam formulas on page 66. The formulas for uniformly distributed loads have identical variable parameters but the constant in each formula is different. Hence, a simple ratio exists between these relations which permits deflections calculated by one formula to be easily converted where another formula applies. The values given in Tables, pages 128-131, for uniform loading can thus be converted from deflections for simply supported beams to deflections for other methods of support by the following conversion ratios. These conversion ratios do not apply where concentrated loads are applied. CONVERSION RATIOS (Using a simply supported beam as the base)
ICE WEIGHT, (10.) Solid Round or Tubular 10. = 1.244t(D
+ t)lbs./ft.
Two Channels (box form ) Wi O.79Zt [A +Zt+Zf] lbs./ft.
=
WIND LOAD, (w p ) Solid Round or Tubular D+2t w p = P X 1 2 lbs./ft. Two Channels (box form) , A+2t 10 p P X-- lbs./ft. 1Z
=
Where: W
r
= Resultant load in pounds per foot
Wi
= Bare conductor wt. in pounds per foot = Ice Weight in pounds per foot
Wp
= Wind load in pounds per foot
D
= Outside diameter of a tubular conduc-
Wb
tor in inches A = Channel depth in inches t = Ice thickness in inches P = Wind pressure in pounds per square foot of projected area (round surface) pI = Wind pressure in pounds per square foot of projected area (flat surface)
Method of Support
Deflection Formula
5WV
Conversion Ratios
Simply supported beam
D
= 384EI
Beam £Xed at both ends
D
= 384EI
Beam £Xed at one end and simply supported at other end Cantilever beam
D
= l85EI
2/5
WV D=8EI
9.6
WV WV
1 1/5
r
By means ()f these ratios, the deflections for a simply supported bus can be used to determine the deflection for a bus uniformly loaded but supported differently by using the above ratios as multiplying factors. For example, the center spans of a continuous bus may be considered as a beam £Xed at both ends. Mid-span deflection for a beam thus supported is 1/5 of the value listed for the same span simply supported. The end span of a continuous bus can be treated like a beam £Xed at one end and simply supported at the other end. The deflection for this span will be 2/5 of the deflection for the same span simply supported. The formulas and diagrams that apply to the common loadings on bus conductor spans are given on the following pages. For moments of inertia of common bus sections, along with common relations applying to all sections, see page 68.
65
!
i
I
Ir
II :' 1 " . ".!
!:/,,:, 0,
iI ;/1
Y
I, ~
section III - mechanical design
FORMULAS AND DIAGRAMS FOR STATIC BUS CONDUCTOR LOADS SIMPLY SUPPORTED BEAMS
CONCENTRATED LOAD NEAR ONE END (One Span-Ends Not Fixed) WcA -L-
=
UNIFORMLY DISTRIBUTED LOAD (One Span-Ends Not Fixed)
J¥"1"1~,,,~-+ :-
(max.ifA>B)
) = -WeB L - (max.ifB>A
I SHEA: DIAGRAM RlmTrm
I
I
= WC: X
M
W AB - _e_
1u...u...u...L.IIIIIIIIIIIIIIIIR2
-
IT
I
D
FS W
=2'
D
W.,(L-X) 2L
R 2
L
I -.L
l 2
WL
=8
M
~M
+ 2B)
V 3A (A 27 ElL
WeAB (A
"'a"
i
(if X
, I I I fSL ~-;-Wcma"=AB MOMENT DIAGRAM
I
SHEAR IDIAGRAM
M.,
,
W(L-2X)
I
+ 2B)
8fS
I,W"-=T
MOMENT DIAGRAM
, I
I
5WL3
D"la"
= 384 El .,
BEAM FIXED AT BOTH ENDS
UNIFORMLY DISTRIBUTED LOAD (Beam Continuous Over Both Supports)
CONCENTRATED LOAD NEAR ONE END (Beam Continuous Over Both Supports) J
1 - .-
-
-
I
I 1 M2 M
1
~ I W
~~
= WekL (1 - k)2, = W ek 2L (1 - k), M1>M or M2 ,
= R1X -M1,
rrmm rutlllllllllllllllR2
G
= 1+2k
1M
H
I
W ema..
_~gl
.
,
I I
~"
-I
D
V.,
=
=
K'l
SHEAR Rl DIAGRAM
R2 (L - X) - M 2,
.i [
W 2L (L-2X)
=
W
k<0.5~~g;g~g]~~
=2
if if k<0.5:: if k<0.5 if XkL
= ~ ( 6X _
L _
kL
M
=24'
M1
=12"
,-
=3-2;; if k<0.5 kL(l-k)2' 2 W ek 2 L3 (1 - k)3 if k<0.5 3 El (3 - 2k)2 '
_ 12fS W ma.,- L WL3
D ma.,
= 384El
g
=
0.211 L
I
,l:
.;~
CANTILEVER BEAM
'.;
UNIFORMLY DISTRIBUTED LOAD (Beam Continuous Over One Support)
CONCENTRATED LOAD NEAR ONE END (Beam Continuous Over One Support)
I
I
We
D~g~~ R\ W I
IIII111111
I
IDIIJJJ
I
r~ ..L~
MOMENT DIAGRAM
I i
:
J
L----1 l~lllll~ I
.
~2.r. ~ ~ !
R
=W e
M.,
=WeX =WeL
M
l
R
I
r -1'
fS
WL3
= 3El
=y
R
=W WX2
= 2L M
MOMENT DIAGRAM ~
I M I-i.
WX
V.,
X
Wemax=T, D ma.,
)
WL
! \ !
6~2
WL
L
D11IailJ
I
=
We (1 - 3k 2 + 2k 3 ) W ek 2 (3 - 2k) = 2W ek 2 L (1 - k)2, if k<0.5
M., M.,
.
M,
M
I
~;1
Rl
Rl R2
---------I.
\
WL
=-22fS
W",a"=T WL3
D"la".= 8El
mechanical design - section III BEAM FIXED AT BOTH ENDS
UNIFORMLY DISTRIBUTED LOAD (Beam Continuous Over One End and Supported at Other End)
R1
-
5W -S-
Rz
-
-B-
3W
W (3L - SX) SL
V" ~
I
M
= 0.07WL
M1
WL - S
M" E g
_WX(3L-4X)
8L 3L =s 3L =4
w
CONCENTRATED LOAD AT ANY POINT (Beam Continuous Over One End and Supported at Other End)
rx~
L
D
~ ! I I I
SHEAR DIAGRAM
Rl~
I
.
' --errrrrnI
6!1Tl1111
'IR
[[Jfui+
jf]--G~T
=
DIAGRAM
= total uniform loading of beam in pounds; = concentrated load in pounds;
= bare weight of beam in pounds per foot; Wi weight of ice load in pounds per foot; wp wind load on conductor in pounds per foot; Wr resultant load in pounds per foot; R reaction in pounds at the support; V = vertical shear in pounds; V" vertical shear at x in pounds; M bending moment in inch-pounds; M" bending moment at x in inch-pounds; f bending sh'ess on exh'eme fibre in pounds per square inch; I = moment of inertia of beam in inches 4 ; S = section modulus of beam in inches 3 ; E modulus of elasticity in pounds per square inch; D deflection in inches; L = length of span in inches; k distance from end to load or support divided by span in inches; g distance from end to nearest point of zero moment in inches; h distance from end to point of maximum deflection in inches; < less than; > greater than. Wb
= = = =
= = = =
= =
= = = =
=
I
~~~:~ I A1111IIII1JJbJ M ~~~g~
h
W We
I IIIIIIIIII! R
II
•
I
Description of Symbols
III I I II IIII I
'SHEAR DIAGRAM
R2
= 00422 L WV D",a" = ISS El 8fS W",a,,=y
.
M
Mx Mx G
H H
Wek (3 - k 2 )
2
We (2 - 3k + k 3 ) 2 WekL (2 - 3k + k 3 ) 2 Max. '(1.74 WeL) WekL (1- k Z ) 2 = R2 X, = RzX - We (X - kL),
if k = 0.366
if XkL
2L - (3 - k Z ) _ L (1 + k Z ) - (3 - k Z ) ,
if k
=L~2~k'
if k>Oo414
2fS W",a" = kL (2 - 3k + k 3 )' 2fS W",ax = kL (1 _ k Z ),
D
D D ma"
if kOo414
_ WekV (1-k 2 )3 3 (3 - k 2 ) Z El ' W kV (k -1)2 e . 6El 0.0098 WeV El
if k
~ 2 +k k
if k
ELEMENTS OF SECTIONS Material
Modulus of Elasticity, E (psi)
Aluminum
10 X lOG 16 X lOG
Copper Iron Pipe
27 X lOG 67
section III - meehamea . I d estgn . MOMENT OF INERTIA
RECTANGLE
CIRCLE
It
A =bd d
x III
1
Tn
"2
r----
_ bds
-1"2
-6 d V12
=
7T
----
f
= 0.288675 d
X I 11
S
I--b~
7T
-1-----11
d
d4 64
=4
ds
'TT 1,3
7T -
'TT
7T
rd
1~
2
1'
=2'
_
11
d2
=~ =
d
s _ bds 11
A
J
r4
1
.
-""3]2=4 d
l'
1'11=4'=2 TUBE
A =
'TT
(d 2
EQUAL ANGLE
dIS)
-
4
A =t(b+e)
d
x
"2
III :=
'TT
(d
4
X _ b 2 + et -2(b+c)
d/)
-
64
s
=
'TT
(d
d1
-
4
= Vd
2
+d
1
y
=X
III
= t (b -
)
32d
11
T11
4
x) 3 + bx s - a (x
t)3
3
2
. , .:-:I
I
4
.
.,
, .....
CHANNEL
I-BEAM
m n
.
.:'!
A = dt+2a (m+n)
A
= dt + a
X = d/2 Y = b/2
X
= d/2 bSn
y
(m + '11)
+ ct2 + a (m32
n) (b
+ 2t)
A
III
bd s
_
a
8 (m - n) (e 12
4
4
-
e
)
COMMON RELATIONS
I =Ar2
! I
'!
II
Where:
!
1
l'
= Radius of Gyration'mme , h es
:
n
= fibre Distance from eenter l'me 0 f gravity to extreme in inches.
f
The moment of inertia , I l' ab out an axis parallel to the
68
axis of th e sectlon ' and at a",- distance from it is given bneutral y t h e expression:
= 1+ AZ2
b earn The momentflexure of resistane resisting Mr e to th' e mtemal stresses of a forces producing bending ,must be equal to the external M1'-M I S ma,,= f n=f
mechanical design - section III
Calculation of Deflection and Stress in a . Typical Bus Installation The following typical bus installation will illustrate the application of beam formulas to determine maximum deflection and fibre stress in each span.
This deflection is smaller than one tube diameter 1
and is approximately 250 of the span length. This bare deflection can be considered conservative design. Maximum loaded deflection with Y2 inch radial ice:
WV D = 185EI Where: w,. Wb + Wi
=
= 1.262 + 1.788 = 3.05lbs. per foot
W SPAN 1
SPAN 2
SPAN 3
SPAN 4
Fig. 11 - Four Span Bus
=J:2 =
3.05
X
360
12 =
. 91.5lbs.-total umfonn load
(91.5) (360)3 (185) (10 X 10~) (0.6657)
D
The deflection and maximum fibre stress is desired for a 2 inch IPS extruded aluminum alloy tubular bus of 6063-T6 with span lengths as indicated in Fig. 11, with an assumed unifOlw ice loading of ~ inch in radial thickness. Short circuit forces and wind loads are not considered. Where these additional loads are applied to the bus, the resultant vector sum of all loads should be determined for the uniform conductor loading.
wrL
Maximum fibre sh'ess,
.
= 3.47 mches
f:
Mc
f =T Where: - WL M- 8 d
Beam Loading:
2.375
c = 2" = -2- = 1.188 inches
Ice weight: Wi
Where:
= 1.244 t (d + t) lbs. per foot.
WL
t = ~ inch ice d = 2.375 inches, (a.D. of 2 inch IPS pipe) Wi
= (1.244) ( lh ) (2.375 = 1.788 lbs. per foot.
(91.5) (360) (1.188) (8) (0.6657)
= 7,348 psi. The allowable working stress for this alloy is 15,000 psi so. that an adequate factor of safety is included in the design.
+ 0.5)
Bare weight: Wb
c
f = -8- x y=
= 1.262 lbs. per foot-bare conductor weight fronL tables.
Spans (2) and (3 )-fixed both ends. Bare deflection:
WV
Span (1), beam fixed one end, simply supported other end. Bare deflection:
WV D = 185EI
D
= ~84EI
Since the span length and loading are the same as span (1), the deflection can be calculated from a ratio of the constants in their respective deflection formulas. Hence, Maximum bare deflection:
Where:
185
L = 30
12 = 360 inches Wb = 1.2621bs. per foot, bare weight WbL 360 W = 12 = 1.262 X 12 = 37.86 lbs. E = 10 X lOG psi I = 0.6657 inches\ from table, page 126 X
(37.86) (360)3
.D
.
= 185 (10 X lOG) (0.6657) = 1.43 mches.
D = 384
X
1.43 = 0.69 inches, bare deflection.
Maximum loaded deflection: 185 D = 384 X 3.47 = 1.67 inches, loaded deflection. Maximum sh'ess, f:
f
-
-
Mc I
69
section III - mechanical design
Where:
Where:
lif (for R 2 and R4 )
M=
M
WL M=T+We L
WL
WL
=12 (for R
WLc
3)
WLc 10 I at supports R 2 and R 4
_ (36.60) (144) (1.188) (12) (144) (1.188) (2) (0.6657) + (0.6657)
=
(91.5) (360) (1.188) 10 (0.6657)
= 4703 + 3084
=
WLc 12 I at support R 3
f =
= 5878 psi at supports R and R 2
f
_ (91.5) (360) (1.188) 12 (0.6657)
4
4899 psi at SUpp01t
R3
Span (4), cantilever beam uniformly distributed load, W, and a concentrated load, We, at extreme end. Beam constants:
=
Wb 1.262lbs. per foot, bare weight L = 12 X 12 = 144 inches WbL 144 W 12 1.262 X 12 15.14lbs.,' total bare wetght W c = 12 pounds.
=
=
=
Bare deflection, with bare weight and concentrated load at free end: WV
D
WcLc
f =2T+-l-
WeV
=8El + 3El
= 7787 psi Expansion of Aluminum Bus Conductors Changes in conductor temperature due either to operating conditions or to seasonal temperatures affect the total length of a continuous bus. A temperature rise will increase the over-all length of the bus while a fall in temperahrre will decrease its length. On long conductor runs with rigid tap-offs to equipment, some provision is often necessary to prevent damage to the terminals of equipment connected to the bus and to prevent overstressing of bus supports. Flexible couplings between sections of the bus, sliding bus supports, and flexible tap connections are used to provide for the free expansion and contraction of the bus and, thereby, protect the bus, bus supports, and equipment terminals. Calculation of Bus Expansion-The amount of expansion or contraction of a bus is dependent upon its length, the temperature change, and its coefficient of thermal expansion. For the materials commonly used for bus conductor, the following coefficients of thermal expansion apply:
(15.14) (144)3 (12) (144)3 6 ( 8) (10 X 10 ) (0.6657) + (3) (10 X 106 ) (0.6657)
= 0.849 + 1.794 = 2.643 inches. Loaded deflection, uniformly distributed ice load plus £Xed load, We: WV D = 8El
W
WeV + 3El
L (Wb + Wi )12
= = 36.60 lbs.
=
+ 1.794
= 2.052 + 1.794 = 3.846 inches. Maximum fibre stress, f:
70
= Mc I
Material
Inch/Inch/ Degree F
Inch/Inch/ Degree C
Aluminum Copper Steel
12.8 X 10-6 9.4 X 10-6 6.4 X 10-6
23.0 X 10-6 16.9 X 10-6 U.5 X 10-6
The total expansion lengthwise of a continuous bus can be calculated, thus: t:>.l LC (t 2 - t 1 ) inches. Where: t:>.l change in length of the conductor in inches; L = length of continuous conductor run in inches; C = thermal coefficient of expansion in inch/inch/ degree F or inch/inchjdegree C; t1 starting temperature in degrees F or C; t 2 = final temperahlre in degrees F or C.
=
144 (1.262 + 1.788) 12
(36.60) (144)3 D = (8) (10 X 106 ) (0.6657)
f
Coefficient of Thermal Expansion
=
=
For a 30 C temperature rise, a 100 foot section of continuous aluminum bus will have an increase in length as follows:
mechanical design - section III
=
=
L 100 x 12 1200 inches C = 23 X 10-6 inch/inch/degree C (tz - t 1 ) = 30 C III = (1200) (23 X 10-6 ) (30) = 0.83 inch increase in length. Types of Expansion Joints-To compensate for this change in length with temperature, various types of expansion joints are used. A common form of expansion joint consists of thin sheets of aluminum laminations usually 0.010 to 0.016 inch thick. These sheets are soldered together at the ends where connections are made to the bus, or the ends can be welded to an aluminum plate, see Fig. 12. These expansion joints take up little room, are neat in appearance, and properly designed, give reliable performance. They can be bolted to both the inside and outside of square tubular conductors and the web surfaces of box channel arrangements. Also they may be inserted between laminations of a bus built up of several rectangular bars. Indoor applications are best suited for this type of expansion joint and for bus runs where a moderate amount of movement due to expansion and contraction is anticipated.
Flexible braid is often used for expansion joints and flexible connections. It is extensively applied where expansion produces considerable movement; hence, it can be used for long spans and in applications subject to considerable change in temperature. Braid is more bulky than the laminated sheet expansion joint and is commonly used for outdoor installations and in equipment where clearances are not critical. When flexible braid is installed on the inside surfaces of a box channel arrangement, the ends of the channels are sometimes staggered to provide more space for the flexible braided connections. These flexible braids may be applied in a number of ways such as bolting directly to the ends of the bus where flat surfaces present themselves or in expansion £ttings which incorporate flexible braid as the means of providing electrical continuity between the mechanical parts, and in bus expansion supports that serve the dual purpose of support and expansion joint with electrical continuity provided by flexible braids. Such joints are illustrated in the section on accessories, page 105, and below.
LAMIN'ATIONS SOLDERED TOGETHER' AT ENDS ONLY
Courtesy Velta
Sta~
Eleo. Vivo
I !
II
Courtesy I-T-E Circuit Breaker Co.
Fig. 12
Cou~tesy
Burndy Corp.
71
section III - mechanical design
Application of Expansion Joints-On short runs where the duty is not severe and only nonnal temperature variations are encountered, expansion joints are not ordinarily used. This applies to short straight runs of rectangular bar that are less than 75 feet in length. Small changes in the length of the bus are usually compensated for by a slight lateral movement of the bus between supports and a slight movement of the supports. Structural shapes of bus conductor are usually more rigid, and it may be desirable to incorporate an expansion joint in a short run of bus, particularly where it connected to rigid tenninals at both ends. Where possible, it is desirable to make a rigid support near the center of a short run and allow free expansion and contraction at the ends by the use of sliding support fittings. Typical methods of supporting bus conductors are illustrated below. These sketches show expansion joints combined with a support, but this combination may be a sliding or fixed support with an adjacent expansion joint.
Methods of Support for Buses TAP
-....H~TE SLIDE
SLIDE
2
FIXED
* H
E
SLIDE
SLIDE
Fixed Supports in Center Only-This method of support is applicable to a bus length up to approximately 75 feet and is a common method on short runs to eliminate expansion joints. Tap travel longitudinally will depend upon the tap distance from the center fixed support.
extreme end depending upon the length of bus; in most cases, a flexible tap will be required. This practice should be confined to a relatively short run where tap movement must be held to a minimum. TAP
~)---rtir-----:';t?----'R~-~ FIXED
SLIDE
EXPANSION SUPPORT
SLIDE
FIXED
F,ixed Supports at Both Ends-Where rigid connections are made to both ends of a bus run this method is applicable. One intennediate expansio~ joint is used where the bus run is of moderate length and taps are not located at too great a distance from the fixed ends. The center expansion joint also may be a support as shown in the sketch. TAP
H
SLIDE
rz!1---iZ? FIXED
EXPANSION SUPPORT
rz!1----,.-,He-FIXED
SLIDE
Fixed Supports at Intermediate Points-This method of support is similar to the bus with fixed supports at both ends but with additional slide supports on either end of the bus. Much longer runs are, therefore, possible. Without rigid end supports, torsional strains on these supports caused by lateral movement of a flexible bus on short circuit may be slightly less. Tap mov~ment will be slight near the fixed supports. Connections located near the expansion joint may require flexible taps.
TAP
7!-----;'H~---,..H..-------rH~T---H~ FIXED
SLIDE
SLIDE
SLIDE
SLIDE
Fixed Supports at One End Only-Where one end must be fixed, this method of support applies. Rigid connections to equipment are usually made at the fixed end. Taps will have considerable travel near the
* "Basic Principles
to Support Alunlinum and Copper Buses" M. Bl'enner ELECTRICAL WORLD, July 27, 1953, PP. 118-119.' ,
EXPANSION SUPPORT
FIXED
Fixed Supports at Center and Both Ends-This method applies to long bus nmS. With fixed supports at the ends, rigid connections to equipment may be mad~ at both ends of the bus. Intermediate slide supports can be used although not shown. The expansion joint may also be a point of support as illustrated.
JOINING BUS CONDUCTORS Aluminum bus conductor is commonly joined by several methods. The simplest and most widely used is overlapping the bus and bolting the sections together. The advantage of this method is its simplicity and flexibility, allowing field assembly and disassembly of component parts. Other joining practices such as welding, brazing, and soldering require skill and special equipment. Such joints, however, may be more stable for the materials are united in a bond that eliminates the variable contact resistance between bars. The variable nature of contact resistance affects joint efficiency, and standard practices must be followed to make reliable, efficient bolted bus bar joints.
The efficiency of a bolted joint is usually gaged in terms of its resistance. A joint is considered to have 100 per cent efficiency when the resistance of the joint is equal to an equivalent length of conductor used to make up the joint. The overlapped section is the length of the joint. The factors which determine high joint efficiency are those that initially produce the lowest possible joint resistance. The most important of these factors are the method of preparation of the contact surfaces and the application of sufficiently high clamping force to the joint.
PREPARING ALUMINUM CONTACT SURFACES The oxide film on an aluminum conductor is not a good conductor of electricity and must be removed from the contact surfaces before making an electrical joint. Since oxidation takes place almost immediately on a chemically clean surface of aluminum when exposed to the ahnosphere, a means should be provided to prevent the immediate re-oxidation of the mating surface after the oxide is removed. The following joining procedure provides for the removal of the oxide film and prevents re-oxidation while the joint is being made. The areas to be joined should first be cleaned of any dirt or foreign material and a grease-like sealing paste or compound applied to the smfaces to be joined. These surfaces are then abraded through this paste by using one of the following methods: Brushing with a suitable fiberglas brush; Abrading with emery cloth or emery paper; Wire brushing; Draw filing; Abrading with steel wool. Excellent smface preparation can be obtained with the first three methods of smface treatment, while the latter two give good results. A fiberglas brush produces a satin finish with the depth of scratches quite uniform, leaving numerous microscopic peaks and valleys. Wire brushes produce a slightly less uniform smface with deeper scratches.
After abrading through the sealing paste, the contact surfaces are joined together, either by clamps or with bolts. The excess paste will extrude from the joint where it can be wiped off. The sealing paste provides an important joint function. Electrical contact is made between coincident peaks on the two mating surfaces. The pressure applied to the bus bar joint causes these high points to Hatten or defOlTIl. This deformation is not complete, leaving a considerable amount of voids between the Hattened current carrying areas. The function of a sealing paste is to penetrate into these voids and make the joint gas tight and moisture proof. Deteriorating inHuences are thus kept from the joint surfaces, and oxidation is prevented. There are many excellent sealing pastes or compounds for making reliable electrical joints. These materials may be classed as electrical "contact aids" and ordinarily may be of two types: 1. Sealing pastes-These serve only to seal the pre-
pared joint surfaces from air and moisture. Examples are neuh'al greases, heavy bodied jells, extensible films, etc.; 2. Sealing paste and contact aid-This type incorpo-
rates a metallic particle suspended in a heavy bodied sealing paste, or it may contain a mild chemical in a sealing paste to remove the aluminum oxide film.
73
section IV - ioining
Many of these contact aids are available under brand names in various kinds of containers and dispensers. They are available in bulk form for paddle application and in collapsible tubes for direct application. Sealing pastes are also available in pressurized containers for spraying. The effectiveness of a joint contact aid can be gaged by its desirable properties. These may be listed as follows: High temperature stability-The joint compound should not drip or leach out when subjected to high temperatures. A measure of the high temperature stability is the drop point of the material; Low temperature stability-The material should be able to withstand low temperatures and vibration without cracking; Stable consistency-The paste should not evaporate or harden with service; Other properties-The material should be easily applied, non-inflammable, non-toxic, and non-staining.
Aluminum to Copper Joints Where aluminum bus bar is joined to copper bus bar, the same surface preparation should be made as indicated above. For indoor installations, protection against galvanic corrosion is generally not important, but for outdoor applications, it may be necessary to protect the joint with a covering or "cover-all" that will exclude air and moisture. Molded on plastic covers, self sealing hand applied mastic compounds, tape, and sprayed or brushed on paint and films are used. Generally, a liberal application of a suitable compound will give satisfactory protection.
Silver Plated Contact Surfaces A high degree of efficiency is attained in a bolted electrical joint where the aluminum contact surfaces are silver plated. This is achieved because of the high conductivity of silver and the fact that silver oxide and silver sulphide will conduct electricity. Both also tend to revert back to the metallic silver state upon heating; hence, silver plated contact surfaces need little or no preparation before joining, and the resistance of the joint will remain relatively stable over a long period of time for all normal conditions of loading. The contact resistance of a silver plated electrical joint is independent of the thickness of the silver plating but is dependent upon the bond to the parent material. A thin silver plating will produce as low a contact resistance as a heavier plating. It is advisable, however, to plate the contact surfaces with at least the commercial plating thickness as this will eliminate porosity of the deposit and thereby better protect the base metal and other preparatory platings applied to
74
the bars. A plating thickness of 0.0002 inch has been found satisfactory to withstand a great number of repeated contact operations such as plug-in bus duct. The silver plating process lends itself to production methods in which the quality of the plating and the uniformity of the deposits can be closely controlled. A recommended process for silver plating, which is easily adapted to production methods, is given on page 160. Small quantities of aluminum bus bar can be silver plated in many of the job shops experienced in silver plating aluminum. It is sometimes desirable to mask portions of the bar where silver plating is not necessary or where bending operations will be performed. Masking tapes or quick drying films can be applied to the areas where silver deposition is not wanted. By this procedure, silver deposits are made where required for electrical contact purposes. Where it is desirable to silver plate the electrical contact surfaces of small quantities of eus bar, a portable brush plating device can be used. This device produces high quality silver deposits for electrical contact purposes where plating thickness is not an important factor. It has the advantage that it may be used for emergencies, for small quantities of bar, and for field applications. A very selective silver deposit can be made on the aluminum contact surfaces without the necessity of masking the material. Any intermediate area can be silver plated on one or both sides and limited to portions of the conductor where actual .contact is to be made. The effectiveness of silver plated contacts in producing a permanent low resistance joint is recognized in the rating of electrical equipment. Where the terminals are silver plated, such equipment will have higher recognized operating temperatures than equipment with unplated terminals.
Other Methods of Surface Preparations Standards also recognize the use of other metallic contact materials besides silver for preparing the contact surfaces of aluminum. The Underwriter's Laboratories, Inc., in their "Standard for Busways and Associated Fittings," specify tin and cadmium as alternate metals. Cadmium is usually applied to aluminum by the electroplating process and may be advisable in some corrosive installations because its galvanic potential in certain environments is closer to aluminum than other metals. Where it is used in corrosive atmospheres, a plating thickness considerably greater than the commercial plating thickness should be used. * The application of tin to an aluminum contact surface can be done by electroplating or by hot flowing tin onto the aluminum contact surfaces. Hot tinning can be accomplished either by the use of suitable '" "Evaluation of Test pata in Determining Minimum Design Requirements for Aluminum to Copper Connectors," D. C. Hubbard and R. W. Kunkle, AlEE Tech. Paper 54-39, November, 1953.
ioining - section N
fluxes presently On the market or by the newly developed procedure of ultra-sonic tinning. In the latter process, the oxides are removed by ultra-sonic vibrations, and the tin is hot flowed onto the oxide free contact surface. Since it is necessary to heat the bars during tinning, the temper of cold worked or heat treated aluminum materials may be sacrificed and lower physical properties result. Hot tinning of bus bar contact surfaces, therefore, has some limitations in its application. Tinned contact sUlfaces are used in applications where assembly and disassembly of the joint will be encountered as no surface preparation is necessary for clean tinned contact surfaces.
Friction tinning of bus sUlfaces shows great promise for electrical applications. This method requires no flux. It is easily accomplished by abrading the surface of the aluminum bar through a molten globule of tin or a tin-zinc solder. Solders with a lead content are not recommended. The abrasion removes the oxide film, leaving a chemically clean aluminum surface for the solder bond. Fiberglas blUshes have proven to be excellent abrading devices and are available for preparing small quantities of bar by manual abrading methods. Development of automatic devices for friction tinning the ends and intermediate areas of bus bars on a production scale are now being investigated.
JOINT RESISTANCE Total Joint Resistance The total joint resistance of two lapped rectangular bus bars is composed of two parts-the contact resistance at the interface of the mated bars and the volumetric resistance of the metal in the overlapped section, Fig. 1, considering the j oint to be devoid of any contact resistance. The sum of these two components gives total joint resistance.
ship was uniformly applied to the external surfaces of the bars, giving a uniform pressure over the entire contact surface. This relation is expressed as follows and is applicable for the range of pressures used in bus conductor joints. RPll=C Where: R is the contact resistance in ohms or microhms; P is the total pressure in pounds; n is an exponent whose value will range from OAto 1.0; C is a constant.
iLl
Fig. 1
Where the pressure is uniformly applied, contact resistance is uniform across the- interface and contact area can be measured in terms of the total square inches of overlap area, such as multiplying the width of the bar by the length of overlap. This condition is produced, for example, by clamping the two lapped bars in a hydraulic press. Contact Resistance for a Uniformly Applied Pressure-The contact resistance between two lapped bars, Fig. 2, is the resistance at the contact interface. This resistance will be affected by the total applied force and the condition or preparation of the contact surface prior to joining. The contact resistance of such a joint has been established by a general formula as a function of pressure. * The pressure used to determine this relation-
* JOURNAL, "Electrical Contact of Bus Bar Joints," C. L. Denault, THE ELECTRIC July 1933.
I
_--.--_ _--1-1--------r~
iT
Fig. 2
Where a bus bar is prepared by abrading the contact sUlfaces with emery through a particular sealing paste such as NO-OX-ID, the above becomes approximately: RpO.724 = 1620. Where: R is given in microhms per square inch; P is the pressure in pounds per square inch. The formula applies only to surfaces prepared in this manner using this type of sealing paste. For silver plated contact surfaces mated with a uniformly applied pressure, the expression that approximates this surface preparation is: RpO.778 = 155. 75
section N - joining
Where: R is given in microhms per square inch; P is given in pounds per square inch. The contact resistance for these conditions of preparation is shown in the curves in Fig. 3. 8000
\.
600.0
\.
I'\. 1\
4000 3000
\.
I\.
'"
RP
~
II)
=155 "'" \.
0.0778
13 1000
'"c..
800
ti z
600
~
8
RP
tvt
=162b\
0.724
Resistance R L of the solid joint in Fig. 1:
\
Q) II Q)SILVER PLATED CONTACT ISURF~CES WITH NO COMPOUND
400
L R=p-.
\.
e::.
w
Resistance of equal length of a single bar:
\
1\
5i 2000
CD
RL
ABRAI~ED
300
©JoJJT ISUFHE .! THROUGH NO-OX·ID "A" SPECIAL
200
100 0.1
0.2
0.3 0.4
tact resistance, the effect of different lengths of overlap is shown in Fig. 4. The ratio of the resistance of this solid lapped joint to the resistance of an equal length of single bar is called the streamline or distortion factor. The value of this streamline factor is given in terms of the ratio Lit, where L is the length of overlap and t is the thickness of the bar. The resistance of the solid joint indicated in Fig. 1 in terms of the resistance of a single bar of length, L, and width, tv, is offered by the expressions below, which show the application of the streamline factor, e.
0.6 0.8 1.0
2.0
3.0 4.0
6.0 8.0
CONTACT RESISTANCE (MICROHMS PER SQ. INCH)
Fig. 3
Metal Resistance in a Lapped Joint with Uniformly Applied Pressure-Where the clamping force is uniformly applied to the external surfaces of two lapped bars, the effect of different lengths of overlap can also be determined. The effective overlap in this case will be the actual length of overlap, L, as shown in Fig. 2. Assuming the joint to be solid metal without con-
Generally, small amounts of overlap are not used and hence are not too important, except that they illustrate the value of the streamline factor. A length of overlap eqlial to or greater than eight to ten times the thickness of the bar is often considered adequate. For these commonly used lengths of overlap, the streamline factor approaches the value of 0.5 which means that the resistance of the solid joint approaches liz the resistance of a single bar of equal length. In many instances, the length of overlap is made equal to the width of the bar where the width is greater than eight to ten times the thickness: In bolting two' Hat rectangular bars together, the factor that generally determines the length of overlap is the spacing and arrangement of the bolts or the size of the clamp where one is used.
2.0
I--l
1.8 w
I
= e X R = e (p ~t ).
I
(OJ
,-
1.6
...'"o
t
~1.4
u..
w ~1.2
~ 1.0 ~
Fig. 5
,
1\
lJ)
.8
1"'-
""
.6 .4
o
2
l~_-=====CDJ~_-----==::(TI)===~
'-
3
---%1
4 5 6 VALUES OF L/ t
Fig. 4
7
8
9
10
76
------ % 1 - -
*
* ins. Copper W. Melsom and H. C. Booth, "The Efficiency of Overlappiog Joiots and Alumioum Bushar Conductors," JOURNAL IEE (G.B.), Vol. 60. No. 312. Aug. 1922.
Tt
Fig. 6
joining - section IV
Joint Resistance of Bolted Bus Bars Where bars are lapped and bolted as in Figs. 5 and 6, contact resistance and the metallic resistance due to different lengths of overlap are difficult to determine because current is not uniformly distributed across the contact interface. In a typical bolted joint, the current is concentrated more heavily around each bolt hole where pressure is high and contact resistance low. Current density is less in areas remote from the bolts, and these areas add little to the cun-ent canying capacity of the joint. This affects the volumetric resistance of the metal comprising the joint and also affects the contact resistance. Effect of Overlap on Bolted Bus Bars-The effectiveness of a length of overlap where only a single bolt is used is illustrated in Fig. 5. In this case, the effective overlap is not a great deal more than the diameter of the washer used. The effective overlapping area where two bolts are used, Fig. 6, indicates that the
effective length of overlap is approximately equal to the distance between the bolts plus the diameter of one washer. The latter arrangement is prefen-ed, for the bus bar in the region between bolts will divide the current How. Tests show that bolts placed near the ends of the overlapped section tend to decrease the streamline factor. Also, the heat generated in the length of bar between bolts will be considerably lower than in an equivalent length of single conductor. In a bolted joint, it is difficult to determine contact resistance in terms of pressure per square inch of contact area because the pressure is not uniformly distributed. The concentration of pressure around the bolt produces an area of low contact resistance in the immediate vicinity of the bolt hole. The area between bolt holes and the area near the edges of the bus bar have a much greater contact resistance. The magnitude of applied bolt force and more particularly the distribution of this applied force to the bus bars are important in determining the pattern of contact resistance and its effect on the life of the joint.
JOINT BOLTING PRESSURE One of the important factors in establishing a low resistance bus bar joint and maintaining this low resistance is the use of sufficient pressure well distributed. The initial contacts between coincident peaks on the mating surfaces can be considered as a number of small paralleled conductors. As pressure is applied, more of these peaks are brought into contact, and they Hatten into larg,er contact areas, thereby paralleling a multitude of electrical paths between the bars. To join two conductors efficiently, it is desirable to establish
Fig. 7 - Concentration of Pressme Around Bolt Holes
a maximum of these contact areas and to distribute them as uniformly as possible. This distribution will depend upon the surface preparation and the method of applying the clamping force.
Distribution of Applied Force in a Bolted Joint When force is applied by a bolt, Fig. 5, the contact area is concentrated more heavily around the bolt hole where pressure is highest. In such a joint, pressure can be considered as graduated in a series of concentric annular areas with the pressure decreasing in intensity as the distance from the edge of the bolt hole increases. The pattern of this pressure variation is shown in Fig. 7. Since pressure is highest around the bolt hole, the bus bar material in this area is forced into more intimate contact and all surface irregularities are flattened until the material is almost completely solid metal-tometal contact with little voids. From this high pressure and good metal-to-metal contact in the vicinity of the bolt hole, pressures are gradually reduced as tlle distance from the hole increases and the resulting metal-to-metal bond is less complete. At points remote from the bolt hole, little pressure may be exerted, and contact resistance in these areas will be higher. The pattern of pressure distribution around each individual bolt is important in a bus bar joint in order to maintain the low initial resistance indefinitely. This distribution of contact area in two typical. bolting de77
i !
section IV - joining MAXIMUM PRESSURE ELASTIC LIMIT OF CONDUCTOR MATERIAL
ELASTIC lIMI,.'\OF CONDUCTOR MATERIAL
MAXIMUM PRESSURE -----:::::::;;<>P Vi
in
0..
1£_11
w·
""
:;)
en en w
"" 0..
I
I
r ---;I----"l=;.:;z='!-.
0
0
~I~~~"'----~
~LAPPED BARS---+-HOlE+lAPPED BARS~
I
I
I I
I I
rvtxX"X''"V'"'''7V~h~-----l"TT7'~rv---;T"7.."...,..,~1
I I I I I
I
I
I
I
0..
W
""
:;)
en en w
"" 0..
0
I
I
I
I
LAPPED BARS-r- HOLE -I-lAPPED BARS-l
I
I
I i : I I
I I
I
I
I
I I
1
I
Fig. 8 - Poor Pressure Distribution Fig. 9 - Improved Pressure Distribution
signs is indicated in Figs. 8 and 9. The pressure distribution for an extreme condition is shown in Fig. 8. This would be typical where no washers are used under the head or nut of the bolt or where a very thin washer is used. The material in the immediate vicinity of the bolt hole may be stressed to the point where the bus material flows and the localized distortion at this point will tend, in time, to stabilize at a value near the elastic limit of the bus bar material. This high localized pressure near the bolt hole is subject to a high rate of creep when current loadings increase bus temperatures. A more desirable pressure distribution will result where thick, large diameter washers are used with each individual bolt. This is shown in Fig. 9. These washers, in effect, serve to distribute the applied bolt pressure more uniformly to the surface of the bus bar. The resulting pressure curves will be somewhat as indicated in the pressure diagram of Fig. 9. Such a joint will have more stable operating characteristics and longer life because localized portions of the bar near the bolt hole are not as highly stressed and are, therefore, not as subject to creep when the temperature of the joint increases. Where the pressure can be considered to be uniformly applied, design stresses on the total lapped area of 800 psi to 1,200 psi can be used for the EC aluminum tempers. Joints in the higher strength alloy bus bars such as 55 EC and 56 EC can be designed with pressures up to 2,000 psi.
78
Bolting Methods Two methods are generally accepted as producing reliable bolted bus bar joints. These methods are described as Method I and Method II. Method I makes use of an aluminum bolt and nut combined with thick washers. Method II uses a steel or bronze bolt and requires the use of a Belleville spring washer to maintain a uniform clamping force. This Belleville spring washer compensates for pressure variations due to the difference in the coefficients of expansion of the bolts and the aluminum bars. Both methods will produce reliable joints with proper surface preparation. Where
STEEL NUT METHOD I
METHOD II
Fig. 10
Fig. 11
Recommended Bolting Methods
it is desirable to use bolts % inch in diameter or smaller, Method II is generally used. Either method
joining - section IV
will produce excellent electrical joints where larger bolt sizes are used, that is, over % inch in diameter. These methods are shown in Figs. 10 and 11. Where two bars are joined as in Method I, the use of thick washers under the head and nut of the bolt produces a uniform pressure on the bars. By using an aluminum bolt, the thermal expansion of the bus bar and the bolt will be the same. Consequently, when current loadings increase the temperature of the joint assembly, the applied bolting force will remain constant. In fact, with steel washers, the pressure may slightly decrease because the washers will not expand as much as the aluminum bolt. This is a desirable characteristic since creep rates are increased considerably with a temperature rise, and a small reduction in pressure will tend to lower the creep rate slightly. When this joint is exposed to outdoor ahnospheric conditions, some provisions should be made to protect the steel washers from corrosion. In locations where ahnospheric corrosion is not severe, galvanizing or heavy platings of tin or cadmium may provide sufficient protection for the steel parts. In the more highly corrosive atmospheres, a stainless steel washer will be more reliable. Stainless steel type 316 is recommended. The use of steel bolts and flat washers is not generally recommended for bolting aluminum bus bars.
A satisfactory joint can be made with steel bolts, but this method of joining should only be applied to the higher strength bus bar materials, such as 55 EC and 56 EC, where current loading conditions are conservative and thicker than standard flat washers are used. Silver plating the contact surfaces will make such joints more reliable. Aluminum joints are also commonly made with Belleville spring washers and steel bolts. This is jofuing Method II. Since the steel bolts have a much lower coefficient of thermal expansion than the aluminum bars, provisions must be made to compensate for variations in joint pressure with temperature. Belleville spring washers provide this compensation. These spring washers are not usually required when aluminum bars are joined with aluminum bolts since both have the same thermal coefficient of expansion. On joints subjected to heavy loading or high temperatme operation, Belleville washers or a pressure plate may be used with aluminum bolts to effectively distribute the applied force and to reduce the possibility of excessive creep. Their use on the softer tempers of aluminum bus bar and buses composed of many laminations may give more reliability under these adverse operating conditions. Belleville washers should be used as shown in Fig. 11.
JOINT DESIGN The effect of multiple bolts in a bus bar joint is to provide a number of parallel paths for current flow. The current carrying capacity of a joint can thus be thought of in terms of the number of amperes per fastener and the total current as the product of tlle number of fasteners times the currentper fastener. In the design of a bus bar joint, it is desirable to limit the PR heat loss to a value not exceeding the heat loss in the parent conductor. A joint so designed will have 100 per cent efficiency. This condition, however, is not indicative of the life of the joint.
Heating in a Typical Bus Joint In a bolted joint, heat is produced from two sources-the resistivity of the metal comprising the joint and that generated at the contact interface due to the contact resistance of the joint. The heat generated due to tlle resistivity of the bus bar material is more or less uniformly generated in tlle lapped bars. The heat generated at the contact interface, however, is localized and will be greater in the vicinity of the bolt holes where resistance is low and the current density is high. The heat generated at the contact interface must be dissipated by conduction to the adjoining bus material and then dissipated by radiation
and convection to tlle atmosphere. Where more heat is generated at the contact intedace than can be effectively dissipated, a hot spot temperature rise will occur. To reduce this, it is desirable to provide a sufficient number of fasteners to limit the current per fastener and thereby reduce the current density and resultant heating at the contact interface around each bolt. This will assure a lower temperature rise as the smaller quantity of heat generated will be more readily conducted from the contact intedace. Effect of Heating in a Bus Joint-In a bolted joint, a hot spot temperature rise originates in an area where joint pressure is highest. When this pressure is concenh'ated around the bolt hole, tlle bus material is relatively free to flow in toward the bolt, and the elevated temperature automatically produces a higher rate of creep. This produces a gradual metal flow or migration from the high temperature, high pressme areas and leads to a reduction in the total clamping force applied to the bars. Sacrificing a portion of this clamping force then acts to increase joint resistance slightly and thereby initiate a slow but progressive failure. A conservatively designed joint prevents localized overheating at the interfaces and consequently protects against a loss in the applied clamping force.
79
section IV -'- ioining
This phenomenon is independent of the bolt and washer materials composing the joint. Where the bolt materials are different than the bus bar and their coefficients of thermal expansion are different, the joint pressure may also increase with temperahue. This condition exists where steel bolts are used to join aluminum bars. The effect of this high pressure is to add another increment to the rate of creep and further increase the metal flow from these high temperature, high pressure regions. Compensating Belleville springs are used to maintain pressure where creep would cause excessive loss in joint pressure.
e.g., a rectangular bar rated at 1000 amperes will require the following number of ¥Z inch diameter bolts: 1000 . 300 = 3.3 or 4 bolts (% inch in diameter). Good joint design should provide for the adequate distribution of the applied pressure for the greatest reliability and service life. The amount of overlap should
Fig. 12
Current Limitation Per Bolt To lessen hot spot temperahue rises, a conservative limit should be placed on the maximum current per bolt. This current rating per bolt will depend upon the following factors: The method of preparation of the contact surfaces; The effective distribution of the clamping force developed by each fastener; The size of the bolt and its tightening torque. Where only a sealing paste is used and the contact surfaces are abraded through this paste, conservative current ratings should be established per fastener according to its size and the clamping force it develops. Method I or Method II (Figs. 10 and 11) should be used to effectively distribute the applied pressure. A suggested current rating for each fastener in a lapped joint of two rectangular bars made by the above procedure is shown in the following table: Bolt Diameter less than ¥Z"
¥Z" %"
%" ,~
Amperes per Bolt * 225 300 375 ... /6." .450
These limitations apply only where aluminnm surfaces are prepared by abrading through a sealing paste.
The lower limit of 225 amperes per bolt applies in the smaller bolt sizes where bolting force is lower, and thinner smaller diameter. washers produce a more highly concentrated pressure on a small annular area. The rating for larger bolts becomes progressively greater because clamping force is somewhat greater. In addition this force is not usually as highly concentrated arolmd the bolt hole for annular areas increase with bolt diameter.
Design of a Lapped Joint The design of a lapped joint of the two bus bars shown in Fig. 12 will depend upon the current rating of the individual bar. Knowing the current rating of the bar, the number of fasteners can be determined,
80
be such that four bolts can be symmetrically spaced, giving a length of overlap at least eight times the thickness of the bar.
Multiple Bars Per Phase Combining bars to produce a bus of many laminations, using abraded surfaces and sealing paste, may require a modification of the amperes per bolt basis. The additional internal bars have only the edges exposed for dissipating 12R heat generated at the contact interfaces as opposed to a lapped joint of two bars that present one broad flat surface on either side of the lapped section for heat dissipation, Fig. 13. However, a compensating factor is the better distribution of clamping force applied to the internal bars.
Fig. 13
For this arrangement, current rating may be established on the basis of amperes per bolt per pair of bars. Thus, in Fig. 13, the rating would be based on two bolts and two pair of bars thus providing 2 X 2 or 4 current paths although one additional mated contact surface will be present per bolt in such a multiple arrangement. Many of the laminated buses are designed for wery high direct ClUTent operation. The number of bolts required for such duty would be excessive when surface preparation consists of abrading through a sealing paste and ratings are based on amperes per bolt per pair of bars. For these installations, it is wise to consider surface preparations that give a lower contact resistance such as silver plating. Sealing pastes that incorporate a contact aid may also be considered. Field silver plating can be accomplished with portable, battery operated silver plating devices where it is desirable to fabricate the bus on the job.
joining - section N
Joint with Silver Plated Surfaces Silver plated aluminum bus conductors have characteristics similar to silver plated copper, and the bolting patterns used for silvered copper bars can be applied to like sizes of silver plated aluminum bars.
This means that fewer bolts are necessary. The same bolting techniques described as Method I and Method II should be used, i.e., either steel bolts and Belleville spring washers or aluminum bolts and thick flat washers should be employed.
CLAMPING FORCES DEVELOPED BY BOLTS Before a joint can be designed properly, it is desirable to know the bolt clamping force. Since this is a function of the bolt size, the efficiency of the threads, and the tightening torque, these relations should be considered in the joint design. The curves in Fig. 14 show the approximate relation between the clamping force of a bolt and the applied tightening torque for a number of sizes of steel bolts with no intentional lubrication. Hot dipped galvanized bolts have erratic clamping force versus torque characteristics, and the clamping force values indicated should be reduced by at least 20 per cent for these bolts. At the higher tightening torques, hot dipped galvanized bolts may become even less efficient. Bolts that are electroplated with zinc, cadmium, or tin exhibit slightly higher clamping forces than indicated in Fig. 14 so tllat clamping force values from these curves will be conservative for plated fasteners. Unlubricated bolts, botll aluminum and steel, have similar tightening characteristics, but seizing or galling takes place at a lower value of torque with unlubricated aluminum bolts. When seizing takes place, the linear relations in Fig. 14 do not hold, and the curves level off quickly, giving little added clamping force for increased tightening torques. Both types of bolts should be lubricated when installed to insure high clamping forces at the higher torque values. Many lubricants give exceptionally low coefficients of friction, and these lubricants, when applied to the threads and bearing faces of botll aluminum and steel bolts, may produce slightly higher clamping forces than indicated in the curves. The sealing paste, NOOX-ID, grade XX, has relatively good lubricating qualities and is generally used for the dual purpose of jaM sealing paste and bolt lubricant. The clamping force values indicated by the curves in Fig. 14 can be used where NO-OX-ID or other comparable grease is used on the threads and bearing faces of the fastener. It is apparent from Fig. 14 that the diameter of a bolt has considerable influence on tlle clamping force it will develop. For example, a %6 inch diameter bolt will develop approximately twice as much force as a % inch bolt for the same tightening torque because the effective lever arm in these sizes has approximately 1:2 ratio and the tightening force a 2:1 ratio. The lever ann in tllis case is the distance from the center of the bolt to the mean radius of the bolt thread. For equal applied torques, tlle effective tightening force
at the mean radius of a %6 inch bolt will be approximately twice that of a % inch bolt. Hence, torques for % inch bolts will be double those for %6 inch bolts for equal clamping forces.
Joint Stresses Developed hy Bolted Clamping Forces Once the bolt material and size have been determined, and the tightening torque established, the impOltant design consideration is distribution of the clamping force. The effect of this force on both the contact inteIface and the extemal smfaces of the bars is important. The external surfaces are subjected to the bearing pressm:es of the bolt. These surfaces may be more highly stressed tl1an the contact interface and subject to a higher rate of creep. The area under the head of the bolt and the nut is an important consideration in tllis case. Without interposed washers, Fig. 8, extremely high contact pressures are created between bars in the immediate vicinity of the bolt hole. Even greater pressures are exerted externally on the bars and on tlle bearing surfaces of the fastener, see Table 1. Stress on tlle bearing face of all bolt sizes shown is in excess of 20,000 psi. High rates of creep can be expected for the softer bus materials at this stress, see page 5. This stress can be considered stable for only the higher strength aluminum alloys. The ASA heavy series of cap screws proTABLE I -
BOLT BEARING PRESSURES
g(f\\\~:\~~~~
Ud WASHUfAU,
Size
D
Diameter
Diameter of Bearing Face
and Thread (per inch)
0/16- 18 %-16 lh-13
%-11
%-10
(inches)
lh
%6 % 10/16 Pis
Approxi.
Area of
Nominal
mate
Bearing Face*
Tightening Torque
Clamping
Stress on Bearing
Force**
(in-lbs.)
(lbs.)
Face***
200 300 550 1000 2000
2,850 3,675 5,600 8,200 12,000
(sq. inches)
0.1196 0.1381 0.2454 0.3835 0.5522
* For ASA regular series) capscrews. ** The clamping force values shown are only approximate values cated steel bolts. *** This stress assumes complete utilization of the bearing face.
(psi)
23,800 26,600 22j800 21,400 21,700 for unlubri·
81
section IV - ioining
BOLT CLAMPING FORCE VS. TIGHTENING TORQUE FOR UNLUBRICATED STEEL BOLTS*
6000
5000
e:J 4000
"" ou.. C> Z
;;: ::E
< U I-
~
3000
2000
1000
o
100
m
~
~
~
~
~
m
~
I~
TIGHTENING TORQUE (INCH-lBS.)
Fig. 14
* Normally co=ereial bolts will have a slight residual oil film which produces 82
a lubricating effect. These curves are representative for such conditions.
joining - section IV
vide considerably more bearing area and are desired for bus bar joints. The pressure exerted by the fastener on the bus bar is of greater concern than the stress on the bearing face of the fastener because the bus bar alloy is more ductile than the bolt material and bearing stress should be lower. Washers are generally required under the head and nut of all bolts to achieve a low stable bearing stress on bus bar joints.
Reducing Joint Stresses with Flat W ashers-The selection of a flat washer is usually limited to standard stock sizes. Bus bar joints, however, may require special, thicker designs to provide the assurance of a reliable joint. Thick cast washers may provide the rigidity necessary in the larger bolt sizes. Generally, the thicker the washer material, the more resistant this washer will be to bending. The thick washer, in effect, acts as a rigid member to distribute the applied pressure from the small bearing surface of the fastener to a large area of bus bar under the washer. The distribution of this pressure will be somewhat as indicated in Fig. 9 with a slightly greater pressure near tlle bolt hole and a lesser pressure applied near the outer circumference. The thicker this washer, the more unifOrn1 will be this distribution of pressure. These washers should be designed to closely fit the shank of the bolt. This is particularly true where aluminwn bolts are used. Where the inside diameter of the washer provides excessive bolt clearance, the bearing faces of the fasteners are not completely utilized. As a result, tllese bearing surfaces may be so highly stressed that tlley will be unable to maintain the clamping force originally developed because of flow or creep of the material. Where a thick standard washer is too large in diameter to advantageously space tlle bolts in a joint, special thick washers of a desired diameter should be used.
Strength Characteristics of Fasteners One important consideration in tlle selection of a bolt is its strength characteristics. Both the strength of a bolt in tension and its resistance to shear when tightened should be considered in its selection. The resistance of bolts to shearing when tightened is lower for aluminum than steel and generally precludes the use of aluminum bolts % inch in diameter and under for joining bus bars. This means that for many applications where % inch diameter and smaller bolts are required, steel bolts will be preferred. Bronze bolts can also be used in many applications, with due consideration given to corrosion protection. The strength of a bolt in torsional shear varies as the third power of the root diameter of the bolt thread, so that only a small increase in the diameter
of a bolt greatly increases its strength in shear. Grade 1 and grade 2 steel bolts in sizes under % inch will generally fail in shear at the root diameter before the tensile strength of the bolt is reached. These grades in sizes % inch and larger become more resistant to shear. Tensile limitations govern the use of these sizes.
Aluminum Bolts-From an ultimate tensile strength standpoint, 2024-T4 aluminum bolts compare favorably with the same size grade 2 low carbon steel bolts. The physical propelties of 2024-T4 aluminum alloy are given in the table below. Bolts fabricated from this alloy are generally used for bolting aluminum bus conductors and give satisfactory performance for sizes YJ.6 inch and larger. PHYSICAL PROPERTIES OF 2024-T4 ALUMINUM BOLTS * Bolt Material
Tensile Strength (psi)
Yield Strength (psi)
Ultimate Shearing Strength (psi)
Hardness Brinell 10/500
2024-T4
62,000
. 40,000
37,000
120
* Cold Headed Cap Screws. Elastic proof loads have not been established for 2024-T4 aluminum alloy bolts, but a conservative value for the elastic proof stress may be taken as 50 per cent of the ultimate tensile strengtll. Bolts of 2024-T4 aluminum alloy using this value will have a stress of 31,000 psi. This is 56-60 per cent of the proof load stress for grade 2, low carbon steel bolts of the same size and threading. Clamping force for this stress will be attained at various tightening torques, depending upon the type of lubricant used. Unlubricated bolts will follow the curves in Fig. 14 for low values of torque only and quickly level off, giving diminishing returns for the higher torque values. Anodized aluminum bolts must also be lubricated to prevent early seizure of the metal bearing areas. Lubrication of these bearing areas will give clamping forces as indicated in Fig. 14. The manufacturers recommended maximum torque values should be followed for the types of lubrication specified. APPROXIMATE LOADS FOR 31,000 PSI TENSILE STRESS Bolt Load for 31,000 psi Tensile Stress
Bolt Size (Inch)
NCThread
% % % %
2,400 4,390 6,990 10,350
NFThread
2,720 4,950 7,920 11,540
83
section N - ioining
The following method of detennining optimum tightening torque has been found to be satisfactory: Tighten several samples of a particular size to failure under the same conditions of ultimate use; Take the lowest value of torque required to produce failure; Multiply this value by 70 or 80 per cent to get optimum torque for this size fastener. For pennanent joints, the value of 80 per cent generally applies; the value of 70 per cent is more applicable to joints subject to disassembly. Aluminum bolts of alloy 2024-T4 are less resistant to shearing when torqued than like sizes of either grade 1 or grade 2 steel bolts. However, only a slight increase in the diameter of an aluminum alloy bolt is required for it to be more resistant to failure by shearing than a given steel bolt. A grade 2, % inch-16 steel bolt, e.g., can be replaced by either a %6 inch-13 or a %6 inch-20 aluminum bolt of alloy 2024-T4. Both aluminum sizes will shear at higher values of torque than the smaller steel bolt. Aluminum bolts are preferred in many cases for joining aluminum bus bars as their use eliminates problems due to differences in expansion which are present when dissimilar materials are combined in a joint. These aluminum bolts are usually provided with a surface treatment or finish to prevent the threads from seizing. Although the principal function of this treatment is to prevent seizing, protection from corrosion is also afforded by treatments such as anodizing. These bolts should be lubricated when installed. Steel Bolts-The strength and hardness of the commercially available grades of steel bolts are given in Table 2. The elastic proof load of a steel bolt is the specified load it must withstand without sustaining a pennanent elongation of more than 0.0005 inches. It is intended that no elongation should take place and the 0.0005 inch limit is intended to compensate for errors in measurement. Elastic proof loads for the above grades of bolts are indicated in Table 3. Where carbon steel bolts are used in a bus bar joint, they usually require protective coatings such as cadmium, tin, or zinc. Stainless steel bolts can be used where a longer service life is desired. In highly corrosive areas where galvanized coatings and protective platings are short lived, stainless steel bolts are recommended. Where bolts are coated with protective metallic coatings, these coatings should be applied in sufficient thickness to adequately protect the steel bolt from rusting. Zinc and cadmium electroplatings on steel fasteners employed in joining aluminum bus bar are specified in ASTM standards A164 and A165, pages 163 and 166. The use of plated or galvanized steel bolts makes an aluminum joint susceptible to galvanic
84
action, but the greater mass of the aluminum bar usually leads to only superficial attack of the conductor in even the highly corrosive areas.
TABLE 2-TENSILE STRENGTH, PROOF LOAD, AND HARDNESS OF GRADE 2 AND GRADE 5 STEEL BOLTS * Minimum Tensile Grade, Description,
and Size
Strength (psi)
Grade 2 ** Low Carbon Steel Bolts-6 inches in length and under Up to Y2 inch .. 69,000 Y2 to % inch ... 64,000 Over 6 inches in length. All diameters ........... 55,000 Grade 5 *** Medium Carbon Steel- Quenched and Tempered Bolts Up to % inch .. 120,000 Over % to 1 inch 115,000
Hardness
Proof Load (psi)
Brinell
Rockwell
55,000 52,000
241 max. 241 max.
B100 max. B100 max.
207 max.
B95 max.
241-302 235-302
C23-C32 C22-C32
-
85,000 78,000
* "Physical Requirements for Bolts, Capscrews, Studs, and Nuts," SAE STANDARD. ** Grade 2-Cold headed, low carbon, steel bolts, stress relieved or hot forged bolts heat treated where necessary to meet requirements. Proof
load values apply only to hexagon head bolts and studs.
*** Grade 5-Minimum tempering temperature 800 F.
TABLE 3-PROOF LOADS AND MINIMUM TENSILE STRENGTH OF STEEL BOLTS *
Grade Grade 2 Low Carbon Steel Bolts***
Bolt (inches)
Diameter
% %0
%
0/16
Y2
0/10
% %
Grade 5 Medium Carbon Steel BoltsQuenched and Tempered
%
%0
%
0/10
Y2
0/10
% %
Coarse Thread Elastic Minimum Proof Tensile Load Strength** (lbs.) (lbs.)
Elastic Prool Load (lbs.)
Fine Thread Tensile Strength** (lbs. )
1,750 2,850 4,250 5,850
2,200 3,600 5,350 7,300
2,000 3,200 4,800 6,500
2,500 4,000 6,050 8,150
7,800 9,450 11,750 17,350
9,750 11,600 14,450 21,300
8,800 10,500 13,300 19,350
11,000 12,950 16,350 23,850
2,700 4,450 6,550 9,000
3,800 6,250 9,250 12,700
3,050 4,900 7,450 10,050
4,350 6,950 10,500 14,200
12,050 15,450 19,150 28,400
17,000 21,800 27,050 40,100
13,550 17,200 21,700 31,650
19,150 24,300 30,650 44,700
Minimum
* "Physical Requirements for Bolts, Capscrews, Studs, and Nuts," SAE STANDARD. ** Also proof load for nuts. *** Proolloads shown apply only to hexagon head bolts and studs.
ioining - section IV
BELLEVILLE SPRING VVASHERS By using Belleville spring washers, satisfactory joints can be made using steel or bronze bolts. These washers automatically provide a more uniform clamping force by compensating for the differences in expansion and contraction over the range of temperatures encountered in bus bar applications. This automatic adjustment is usually required when steel or bronze bolts are used. The magnitude of this difference is apparent from an inspection of the thermal coefficients of expansion of the materials commonly used for bus conductor and fasteners. These coefficients are given below: Aluminum Copper Steel
current at tlle contact surface. Heating thus is minimized around the bolt hole where the bus material is relatively free to How.
ELASTIC LIMIT OF CONDUCTOR MATERIAL AVERAGE
i II,alr""'
12.8 X 10-6 inch/inch/degrees F; 9.4 X 10-6 inch/inch/degrees F; 6.4 X 10-6 inch/inch/degrees F.
When aluminum bars are joined using steel bolts, the joint is comprised of two materials having a wide· difference in thermal coefficients of expansion. This represents an undesirable condition from an operating standpoint. When the temperature of the joint assembly increases due to loading of the circuit, the steel bolts expand at only one half the rate of the aluminum bars. As a result, this temperature rise is accompanied (~by an increase in the clamping force applied to the bars. These factors-temperature rise and higher I, clamping force-combine to increase the creep or How of metal from the regions of high pressure and thereby slightly relieve the bolting force applied to the joint. When the joint cools, the aluminum contracts more than the steel leaving the joint with less clamping force and lower pressures. Repetition of this cycle can lead to progressive failure as loss in pressure is usually accompanied by an increase in joint resistance causing overheating and more loss in pressure. Further, since the bolts are not a part of the current carrying circuit, they are heated principally by the conduction of heat from the bus bars to the bolts and hence, will often run cooler than the bus bars themselves. This is particularly hue on short circuits or heavy loads of short duration where the bus bars may heat up rapidly with the steel bolts remaining relatively cool until sufficient time has elapsed for heat to be conducted into the bolt material. This time lag, coupled with the lower coefficient of expansion of the steel bolts, makes the use of a pressure compensating device deSirable where steel bolts are used in an aluminum joint. Equally important to good joint design is the ability of the Belleville washer to distribute the bolt force to the bus bars in a region relatively remote from the bolt hole, as shown in Fig. 15. This not only gives a lower unit stress but serves to better distribute the
0
I
I I
I
I
I
I I
I I
I--LAPPE~ BARS-+HOLE+LAPPE~ BARS--l I I I I I I
I I
I I
I
I
I
I I
!
I I
I
I I
I
I I
I
I
Fig. 15 - Pressure Distribution with Belleville Washer
Belleville Washer Design Several manufacturers produce standard designs of Belleville spring washers. From these, a spring washer can be selected to match the load characteristics of the bolt to be used in the installation. The Belleville designs shown in Table 4 are the recommended sizes for bus bar joints. The important design characteristic of a Belleville washer is its load versus deHection characteristics. The load rating of a Belleville washer for bus bar applications is the load that will completely Hatten the washer. This load rating determines the selection of a size for a joint assembly. A Belleville washer designed for bolting bus bars is stressed to its maximum design fibre stress when Hattened or subjected to its rated load. This stress is usually 200,000-325,000 psi depending upon the grade of 85
section N - joining
TABLE 4-BELLEVILLE SPRING CHARACTERISTICS *
or heavier than commercial thickness platings are recommended. Where zinc' and cadmium coatings are used, the thickness of these coatings should conform to ASTM specifications.
!--'D'-l
~J
~O'D,h
jr Selection of a Belleville Washer
Dimensions and Load Rating
Bolt Diameter
lh %6
ID
(inches)
%2 %2 1%2 1%2
OD (inches)
% % 1 1
%
1%2 1%2
lh
1%2 1%2
1*6 1%6 1% 1%
%
11A6 1*6
2% 3'12
%
Thickness (inches)
h Free Height (inches)
~e¥i~~~~
0.075 0.0875
0.011 0.010
1,100 1,800
0.0875 0.1046 0.1046 0.1495
0.012 0.011
1,600 2,500
0.020 0.013
3,000 4,600
0.140 0.187
0.028 0.017
6,000 6,700
0.187 0.312
0.040 0.034
9,000 16,000
t
Load
(lbs.)
* Courtesy Union Spring and Mfg. Co., New Kensington, Pennsylvania. steel used and the type of loading it will be subjected to, whether static or repeated loading. For bus bar applications, static loading values are used, and Belleville spring washers are usually designed for maximum static stress values. The thickness of a Belleville washer and its free height for a given load rating are usually calculated using a standard Belleville formula. The. maximum stress is then determined from a Belleville stress formula. If the calculated stress exceeds the maximum desired, another thickness and free height are selected and the calculation repeated. This dish or free height represents the maximum deflection that the washer can withstand for bus bar applications without exceeding the maximum fibre stress of the washer and represents the total available deflection for maximum design loading of the spring washer.
Belleville Spring Materials and Finish Several spring steel materials may be selected for Belleville washers. The most widely used of these materials is 1095 high carbon steel. Other materials that are often used are stainless steel type 316 and AISI 6150 steel which is a chromium-vanadium steel. A protective finish should be provided on Belleville washers fabricated from 1095 spring steel and chromium-vanadium steel to prevent rusting in service but may be unnecessary when fabricated from stainless steel. Common protective finishes are galvanizing; cadmium, tin, or zinc electroplating; and organic materials such as heavy grease type compounds or bitumastic materials. For corrosive conditions, galvanizing
86
The selection of a Belleville washer for a bus bar joint should be correlated with the selection of the bolt size and grade. Having selected the size and grade of the bolt, its clamping force can be determined approximately if the tightening torque is known. Many factors inB.uence the tightening torque that can be applied to a bolt; some of these may be listed as: The accessibility of the bolt-where located in tight or cramped spaces, it will often be difficult to exert maximum tightening forces. The leverage that a man can normally exert from the position in which he is making the joint. The length of the lever arm of the wrench coupled with the sh'ength of the workman. A more precise determination of tightening torque can be made if all fastenings are tightened with a torque wrench to a predetermined value. Where this is not feasible, a number of joints can be made up using tightening torques that normally will be applied. The nominal tightening torque can then be determined by checking the torque values on these fastenings. In lieu of this, the nominal values given in Table 1 can be used. From a predetermined tightening torque, the bolt clamping force can be determined approximately from the graph, Fig. 14, giving bolt clamping force as a function of tightening torque. Due consideration should be given to the type of lubricant used on the bolt as the clamping force developed for a given torque will vary depending upon the coefficient of friction. A Belleville washer should be selected that has a load rating when flattened that is close to the value of the clamping force developed by the bolt. Where the load required to flatten the Belleville washer is greater than the bolt clamping force, it is not necessary to back off the nut as maximum tightening torque will always leave a small amount of dish in the Belleville washer. If a Belleville washer is selected that will be completely flattened by a load that is less than the force the bolt will normally develop, care should be exercised to prevent over-tightening. In many installations the procedure is to back off one quarter of a tum. This practice will leave a certain amount of dish in the washer depending upon the thread pitch. Since the pitch of the thread is extremely variable in nature, depending upon whether a small or large bolt is used or whether the threads are of the nne series or coarse series, this "rule of thumb" practice may give ex-
joining - section IV
tremely variable results. In the past, plated or galvanized Belleville washers were found to be subject to failures resulting from hydrogen embrittlement incurred by an acid cleaning operation or in a plating process. Bolts were tightened and backed off Y4 to lh a turn to reduce washer stresses, and thereby prevent these failures. Belleville washers are now processed according to ASTM B-242 which renders them free from the detrimental effects of hydrogen embrittlement. This is a low temperature baking operation. Any procedure requiring reduction of the applied pressure by backing off the nut may, in time, increase joint resistance. It also means that the maximum potential clamping force of each bolt is not utilized to its fullest extent. Indushy practices indicate that the following installation methods will make satisfactory bus bar joints: 1. Tighten the bolt until the Belleville washer is just
flat, making sme that the bolt is not tightened beyond this point. The Belleville washer is thus assmed of operating at its maximum design load and not at the maximum force that the bolt is capable of exerting. To produce a uniform effect, a torque wrench can be used to tighten each bolt to a predetermined value. 2. Select a Belleville washer that has a load rating when flattened that is greater than the clamping force of the bolt at the torque which is to be applied. The tightened bolt will then develop a force which will always be just short of completely flattening the Belleville washer, and here again, unifOlmity can be achieved by the use of a torque
wrench in tightening the bolts to a predetermined value. The following will illush'ate a method of determining the proper size Belleville for a % inch-13, cadmium plated steel bolt tightened to a prescribed torque. Assuming a torque of 600 inch-pounds will be applied to the % inch-13 bolt, a clamping force of approximately 6100 pounds will be obtained, Fig. 14. Where a grade 2 steel bolt is selected, having a proof load of 7,800 pounds, a safety factor of 1.3 is provided. A grade 5 bolt in. this size has a proof load of 12,050 pounds which gives a safety factor of approximately 2.0, see Table 3. A Belleville washer is required that has a load rating near the clamping force developed by the bolt6,100 pounds. From Table 4, two standard Belleville washer designs are available that can be used with this clamping force. These are as follows: ID
(inches) 1%2 1%2
OD
Thickness (inches)
1% 1%
0.140 0.187
(inches)
Free Height (inches)
Load Rating to Flatten (pounds)
0.028 0.017
6,000 6,700
Either Belleville design would be satisfactory, but the latter may be preferred as little or no precaution is necessary to prevent over-tightening. The nominal torque selected will develop a clamping force slightly below the load rating of the washer thereby utilizing the full potential of the bolt and leaving a slight remaining dish for free expansion and contraction.
WELDING ALUMINUM BUS BAR The characteristics of aluminum that influence its weldability are described under the following: Melting point and thermal capacity; Thermal conductivity; Oxidation; Gas porosity; Thermal expansion and contraction; Effects of welding on mechanical and elech'ical properties. An understanding of the foregoing characteristics as they apply to fundamental welding principles is essential to establishing sound practices for welding aluminum bus bar.
Melting Point and Thermal Capacity Pure aluminum melts at 1220 F whereas the alu• minum alloys melt at varying temperatures that range
from 1020 F to 1220 F, depending upon the amount of alloying constituents present. It is important to note that there is no color change in aluminum when it is heated. This makes it difficult to judge when the metal is near the melting point and the welding temperature. In gas welding, therefore, the inexperienced weldor finds it difficult to avoid melting and "sagging" caused by overheating. Troubles encountered from overheating are lessened by the arc welding process.
.Thermal Conductivity Aluminuri:J. conducts heat from the point of welding velY rapidly, and it is, therefore, necessary to supply more heat when welding aluminum than is required for welding steel. This means that for welding like thicknesses of the two metals, a larger torch will be required to gas weld aluminum and a higher current will be needed to arc weld aluminum. On the other hand, copper has a higher thermal conductivity than 87
section IV - ioining
aluminum, and more heat will be required to weld copper than aluminum. To insure satisfactory results when welding heavy sections of ahuninum, preheating is generally neceSSaIy, note Table 5.
Oxide Films Aluminum and its alloys rapidly develop a continuous oxide surface film when exposed to air. This oxide film is very tenacious and has a melting point in excess of 3600 F which is about 2400 F above the melting point of pure altuninum. This difference in melting points makes it possible to melt aluminum without fusing the oxide film. When this occurs, coalescence cannot take place because the metal will not flow freely. The oxide IDm must therefore be removed or broken down by a suitable chemical flux or by mechanical abrasion. In gas welding and metallic arc welding, fluoride and chloride fluxes. of lithium, sodium, and potassium are used to combine chemically with the oxide to form compounds which have a melting point lower than aluminum. These fluxes also provide a fused flux coating over the weld metal preventing further oxidation while the metal is hot. The chloride and fluoride salt residues left by the flux will, however, in the presence of moisture, attack aluminum. Thorough cleaning is therefore necessary to remove all traces of flux after welding is completed. The fluxes for gas welding are usually mixed with water to form a paste which can be brushed on the welding surfaces before heating or it can be applied to the filler rod during welding. Electrodes used for metallic arc welding are manufactured with a suitable fused flux coating. The flux is melted by the heat of the arc and is thus introduced into the weld area. A major advantage of the inert-gas-shielded metalarc processes is that they do not require the use of fluxes. The action of the welding arc breaks up the oxide and permits coalescence of the filler metal and the parent material.
Porosity Molten aluminum readily absorbs large amounts of nascent hydrogen but releases much of it when the aluminum freezes because the solubility of hydrogen in solid alumimun is very low. This released hydrogen produces porosity in the weld and may result in weld unsoundness and impairment of the weld properties. Hydrogen may be introduced into the molten weld by moisture from various sources such as the aluminum bus surfaces, the welding rod, fluxes; from the gas flame; or from the atmosphere. To reduce the incidence of porosity, each of the above should be carefully checked to eliminate moisture.
88
Thermal Expansion and Contraction Aluminum decreases in vohune about 6 per cent when it changes from the molten to the solid state. Excessive distortion may result from stresses induced by this contraction unless correct allowances are made and proper procedures are followed for the specific welding method. Also, component sections which are restrained from moving during cooling may cause the weld to crack. This cracking tendency is most pronounced in gas welds where the welding speed is low. An increase in the welding rate will decrease the tendency to cracking, and, therefore, inert-gas-shielded arc welds are not as prone toward cracking as gas welds. Thermal expansion of altuninum is approximately twice that of steel and one-third greater than copper. This increase in thermal expansion necessitates greater allowances for expansion when welding aluminum to prevent buckling. Thermal expansion of the bus may also reduce the root opening when making butt joints and may, therefore, reduce the amount of filler metal required for the weld. This reduction in filler metal coupled with the contraction of the IDler metal on cooling may increase the susceptibility of the weld to cracking.
Effects of Welding Heat on Bus Bar Properties Aluminum alloys for bus conductor are of two types-the work hardened alloys such as EC and 1100 and the heat-treatable alloys such as 6101, 6061, and 6063. Strain or work hardened alloys are hardened and strengthened by cold working processes such as cold rolling or drawing and lose a part or all of their increased hardness and strength when they are heated to a high temperature. The degree of this loss is a function of time and temperature; however, at temperatures above 900 F, the time interval is almost negligible. Therefore, as a result of welding, the mechanical properties in the region of a bus joint are reduced to the typical properties of the annealed parent bus. Heat-treatable alloys attain improved properties over those of the typical annealed condition by solution heat treatment at elevated temperatures-about 900 F followed usually by a cold quench. A low temperature aging treatment at about 300 F is then given the material to precipitate certain alloying constituents. When these alloys are reheated to a high temperature as in welding, their strength is sacrificed depending upon the time and the maximum welding temperatme. The resulting strength, however, is generally somewhat higher than that of the annealed bus. The electrical conductivity of heat treated or work hardened alloys is improved very slightly during welding if enough heat is introduced to partially anneal the
joining - section IV
bus material. This increase in conductivity is greater for heat treated and aged alloys than it is for the work hardened alloys.
Preparing Aluminum Bus Bar for Weldillg Joint Design and Edge Preparation-Joint design and edge preparation for welding are modified to suit the gage of the material and the process being used for joining. On thin gage materials 'l16 to 14 inch in thickness, the square butt joint is usually satisfactory for aU processes. In heavier gages, either a single V or double V may be necessary. Gas welding usually requires a greater amount of edge preparation than the metal arc processes. Back-up plates are recommended wherever possible to control weld penetration. Joint design and edge preparation are shown graphically for each welding process described. Cleaning of Welding Surfaces-Cleanliness is of major importance in welding aluminum regardless of
the welding process. Heavy grease or oil films picked up during fabrication may cause unsound welds if they are not removed before welding is started. Unsoundness will reduce both the mechanical and electrical efficiency of the weld. Mildly alkaline solutions or commercial degreasing solutions that do not evolve toxic fumes during welding are used successfully to remove surface contaminants. All welding swfaces should be dried after cleaning to avoid porosity in the weld metal. A heavy oxide film may be removed from the surface of the bus by wire brushing with clean brushes or other suitable abrading processes prior to joining. During welding, the weld metal and the welding surfaces should be protected from oxidation. In gas torch and metallic arc welding, this is done by the use of commercial welding fluxes which react with the surface oxide and provide a protective atmosphere in the welding area to prevent the molten metal from reoxidizing. With the inert-gas-shielded metal-arc processes, the arc breaks up the aluminum oxide on the surface, and protection is afforded by inert argon or
TABLE 5-PREHEAT TEMPERATURES Welding Tubular Aluminum Bus-Butt Joints
Tube Dimensions Wall Thickness O.D. Size Length 1 inch 2 inch 3 inch 4 inch 5 inch 6 inch 1 inch 2 inch 3 inch 4 inch 5 inch 6 inch
Va" Va" Va" Va" Va" Va"
12 ft. 12 ft. 12 ft. 12 ft. 12 ft. 12 ft.
1/11
12 ft. 12 ft. 12 ft. 12 ft. 12 ft. 12 ft.
'/4
1/ "
/4
~4"
14" 1/ "
/4 1/ /4 "
Approximate Preheat Degrees F Metal Arc
Oxy-Acetylene
*
TIG None None None Optional-400 0 Optional-400 0 Optional-400 0
None None None Optional-400 0 Optional-400 0 Optional-400 0
None None None Optional-400 0 Optional-400 0 Optional-400 0
None None None None None None
None None Optional-400 0 400 0 400 0 400 0
None None Optional-400 6 400 0 400 0 400 0
None None Optional-400 0 400 0 400 0 400 0
MIG
* *
*
*
*
Where a back-up ring is being used, higher current ranges can eliminate some of the preheating. Welding Rectangular Aluminum Bus Bar-Butt Joints
Thickness
Va" Y4" ¥2"
%" "
1 2 3
"
"
Bar Dimensions Width
Length
MIG
12 inch 12 inch 12 inch 12 inch 12 inch 12 inch 12 inch
10 ft. 10 ft. 10 ft. 10 ft. 10 ft. 10 ft. 10 ft.
None None None None None Optional-500 0 Optional-500 0
Approximate Preheat Degrees F Metal Arc TIG None None None None 500 0 600 0 500 0 * *700 0 * * *700 0 * *700 0
Oxy-Acetylene None None 600 0 600 0 *700 0 *700 0 *700 0
* Not recommended.
89
section N - joining
helium gas which surrounds the weld area and prevents reoxidation. Preheat-Preheat is necessary when the thickness or mass of the bus is such that heat is conducted away from the joint faster than the welding Hame or arc can supply the heat. Insufficient preheat is recognizable by poor fusion of the weld bead and insufficient melting of the parent plate. Preheating of parts being joined sometimes helps in producing a satisfactory weld, reducing distortion in the :finished product, and increasing the welding speed. Preheat temperatures are given for various thicknesses of aluminum tube and rectangular bar in Table 5. The preheat temperatures in these tables are only to be used as a guide. Weldors sometimes prefer to increase the welding current and thereby avoid preheating. Other weldors prefer to preheat and then use lower current settings. In winter time, it is often necessary to preheat the cold bus bar to prevent moishue condensation which will affect the weld quality.
Choice of Welding Method The choice of a process for welding aluminum bus bar will be influenced by the following factors: Physical dimensions of the parts being joined; Number of joints to be made; Equipment available; Welding site, whether field or shop welding, and power sources available; Cost of making the weld. The above factors will usually inHuence the selection of a welding method. Welding equipment designed for ferrous welding, although not the most suitable for joining aluminum, may often be utilized where only a few welds are to be made and the cost per weld is not a factor. The most suitable equipment for welding aluminum has a high initial cost and only extensive welding can justify the purchase of such equipment. The availability of portable electric welders makes :field fabrication feasible when employing one of the arc welding processes. Gas welding is the alternate method where arc welding equipment is not available.
Welding Methods for Aluminum Bus Bar A number of common welding methods are adaptable for joining aluminum and its alloys. These are listed below. Gas Welding Oxyacetylene; Oxyhydrogen; Arc Welding Metallic arc with consumable flux coated elech'odes;
90
Tungsten electrode inert-gas-shielded arc (TIG); Consumable electrode inert-gas-shielded arc (MIG); Carbon arc; Atomic hydrogen arc; Resistance Welding Flash welding; Pressure Welding. The four processes underlined are considered the most adaptable for welding aluminum bus bar. A description of these welding processes follows.
Gas Welding Gas welding is the most widely used process where only a few welds are to be made and the capital outlay for equipment must be kept to a minimum. This process :finds wide application for :field welding where a source of elech'ic 'power is not available for arc welding. EO aluminum and the aluminum alloys are often gas welded using mixtures of oxygen and fuel gases such as hydrogen, acetylene, or propane. The oxyacetylene Hame is extensively used because of its high heat output and its availability, as it is commonly used for welding other metals. Oxyhydrogen is the second most widely used. Weld quality, i.e., its soundness, strength, and appearance along with speed of welding, is equally good with either oxyhydrogen or oxyacetylene gas mixtures. Oxypropane and mixtures of oxygen and natural gas have been tried for welding aluminum, but they do not appear to be satisfactory because welding is comparatively slower. Equipment for Gas Welding-The equipment used for gas welding aluminum is similar to that used for gas welding other metals. Standard welding torches, hoses, gas regulators, and a series of torch tips are required. The size of the tip used for joining bus bar will depend on the metal thickness and to some extent, on the weldor's experience. Likewise, the gas pressures required will increase with an increase in bus cross section. The conditions for gas welding with oxyacetylene and oxyhydrogen are listed for various material thicknesses in Table 6. This table shows the approximate size of the torch tip and the gas pressure required for welding. The actual choice will depend upon the shape and the size of the parts being welded as well as their thickness. An experienced gas weldor will select a torch tip and a gas pressure to suit his welding technique. . Gas Flame Adjustment-The pressure used for either the oxyhydrogen or oxyacetylene gases should be adjusted to produce a neutral or slightly reducing flame. Both of these flames produce a clean weld with the
joining - section IV
best combination of welding speed and gas economy. The neutral oxyhydrogen flame has a well-defined blue cone in the center of the main flame. An excess of oxygen causes a small flame with a very short cone at the torch tip. Excessive hydrogen produces a long ragged flame without a well-defined cone at the center. The m'-'Yacetylene flame can be varied in a manner similar to that of the oxyhydrogen flame. A neutral flame is secured by reducing the acetylene pressure until only one white cone is visible at the center of the flame. A slight excess of acetylene will produce a carburizing or reducing flame and the molten aluminum will not be oxidized as much with this mixture.
Filler Rods-Filler materials for gas welding are available commercially as either bare or flux coated rod. Strips of metal cut from the parent metal may also be used as filler material. Whenever bare rod is used, a welding flux must be applied to the rod before it is introduced into the gas flame. The proper choice of filler metal will depend upon the alloy being joined. Metals of high purity, such as EC and commercially pure aluminum-lIOO alloy, are usually welded with EC or commercially pure aluminum. Bus alloys 6061, 6063, and 6101 are usually welded with a 95 per cent AI, 5 per cent Si alloy4043. The 4043 alloy has a substantially lower melting point than alloy 1100 and permits good weld fusion. It also minimizes the tendency for weld cracking as it cools. Other commercial filler rods containing magnesium, such as 5356 and 5154, may also be used for welding alloy 6061. Recommended filler rod alloys are shown in Table 7 for welding the commonly used aluminum bus bar materials. The metal composition of the common aluminum bus alloys and filler rod alloys are presented in Table 8.
TABLE 6-TYPICAL TIP SIZE AND GAS PRES· SURES FOR GAS WELDING OF ALUMINUM OF VARIOUS THICKNESSES Oxyacetylene
Oxyhydrogen
Metal Thickness (Inches)
0.020 0.032 . 0.050 0.080
%-~~6
%
~G
%
V2
%
Orifice Diameter in Tip of Torch (Inch)
0.035 0.045 0.065 0.075 0.095 0.105 0.115 0.125 0.140 0.150
(psi)
Hydrogen Pressure (psi)
Orifice Diameter in Tip of Torch (Inch)
Oxygen Pressure (psi)
1 1 2 2 3 4 4 5 8 8
1 1 1 1 2 2 2 3 6 6
0.025 0.035 0.055 0.065 0.075 0.085 0.085 0.095 0.100 0.105
1 1 2 3 4 5 5 6 7 7
Oxygen Pressure
Acetylene Pressure (psi)
-1 1 2 3 4 5 5 6 7 7
The size of the filler rod is related to the thickness of the bus being welded. A rod that is too large will prevent the operator from seeing the weld pool and
will chill the molten pool too rapidly. A small rod melts too fast for good operator control. Filler rod diameters for welding various bus thicknesses are as follows: APPROXIMATE FILLER ROD DIAMETER FOR GAS WELDING BUS OF VARIOUS THICKNESSES Bus Thickness (Inches)
Diameter of Round Rod (Inches)
TABLE 7-RECOMMENDED FILLER ROD ALLOYS FOR WELDING VARIOUS BUS ALLOYS Bus Alloy Designation
BC 1100 55 BC 56 BC 57 BC 59 BC 6061 6063
(6101) (6101) (6101) (6101)
Recommended Filler Rod
BC or 1100 1100 4043 4043 4043 4043 4043 4043
Welding Flux-A large number of commercial fluxes are available for gas welding aluminum and aluminum alloys. These fluxes are usually obtained in a powdered form and are mixed with alcohol or tap water to make a paste of the proper consistency. Fluxes for gas welding should preferably be mixed in a glass or ceramic container. If it is necessary to use a metal container for the flux, an aluminum container is preferred. Containers made of either steel or brass may contaminate the flux. The flux paste is applied to both the filler rod and the hase metal. It should then be heated slowly before welding to drive off moisture; otherwise, excessive spatter results. As soon as the flux fuses, the filler metal should be dipped into the appropriate flux and then added to the weld joint. Edge Preparation and Cleaning before WeldingIn order to produce sound welds that have good mechanical properties, it is essential to have the welding edges properly prepared. The generally recommended edge preparation for flat bus and tubular bus of various metal thicknesses is shown in Figs. 16 and 17. Overlap joints are not recommended for gas welding because there is danger of flux entrapment in the overlap. Wherever possible, the joint should be designed as a butt weld. If an overlap joint is made, it should be
91
section IV - ioining
TABLE 8-PERCENTAGE COMPOSITION OF BUS BAR AND FILLER ROD ALLOYS * Element
EC
5356
Silicon ............. {0.50 Iron .. '" ., ........ Copper ............ 0.10 Magnesium ......... 4.5 -5.5 Manganese ......... 0.05-0.20 Zinc ............... 0.10 Chromium ......... 0.05-0.20 Titanium .......... 0.06-0.20 Other Elements ..... 0.05 Other Elements ..... 0.15 Boron .............. Aluminum .........
1100
{ 1.00 0.20 0.05 0.10
0.05 each 0.15 total 99.45
99.00
6063
6101 (55 EC, 56 EC, 57 EC, and 59 EC)
4043
4.5-6.0 0.80 0.30 0.05 0.05 0.10
0.20-0.60 0.35 0.10 0.45-0.90 0.10 0.10 0.10 0.10 0.05 each 0.15 total
0.20 0.05 each 0.15 total
remainder
remainder
6061
0.30-0.70 0.50 0.10 0.35-0.80 0.03 0.10 0.03
0.40-0.80 0.70 0.15-0.10 0.80-1.20 0.15 0.20 0.15-0.35 0.15 0.05 each 0.15 total
0.03 each 0.10 total 0.06 remainder
remainder
* All elements shown as a single percentage in the above chart are maximum allowable. The percentage of aluminum shown is minimum allowable.
---j
I L
r----!I,.,N -
(
I I
A
6O '-120
·,,·,,0 ~
~
11."
%"-11./1
I A
~
~
45'-70'
\
v."-."\ T N
}'to
~
I
)ioN - %"
)
-
~
A
J;l
(
T
"11-7-
' ' UP-[V
~
~45'-70~
1" OR GREATER
(----I~
(i----------,\~ T
T
Va" & UP
Va"-%"
Fig. 16 - Butt Welds and Tee Joints
A \ 60'-90'/"'" / /" .--------',.
---------
I
lI, " & _UP
\ -----------)~
--------- -----------~~
~~
92
-'%"
Vi." Fig. 17 - Tubular Joints
Va"
&
UP
v."
;oining - section IV
completely welded around the edges to seal the overlapped area. Tubular sections require edge preparation similar to flat bus; however, the bevel angle should be slightly larger as indicated in Fig. 17. Proper alignment of abutting edges may be aided by tack welding at intervals along the seam. On bus bar ~ inch and up, tack welds may be spaced 3 to 7 inches apart, depending upon the length of the seam. Grease and oil may cause weld unsoundness and should be removed from the edges prior to welding. Commercial degreasing agents are readily available for this purpose. Cleaning should be immediately followed by fluxing. Preheating-Preheating bus bar for gas welding improves welding by increasing welding speed, reducing distortion in the finished joint, and reducing the amount of gas required to make the weld. Bus sections thicker than ~ inch should be preheated to 600-700 F. Preheating above 800 F is not desirable because there is danger of melting some of the alloying constituents. Heat should be applied uniformly to both parts being joined. The preheat temperature of the bus can be checked by the use of temperature sensitive crayons or a pyrometer adjusted for measuring the temperature of aluminum. Welding Procedure-Only flat or horizontal welding is recommended for gas welding. Overhead gas welding is not considered practical. On flat work, the flame points away from the completed weld and is directed to heat the welding rod and the two edges evenly. The flame is usually kept on the centerline of the weld area in order to insure uniform heating of the two edges and directed to make an angle of 30 to 45 degrees with . the vertical in the direction of travel. With the torch held in one hand and the welding rod in the other, the rod is introduced into the flame and the weld puddle as it is needed. The amount of flux used should be just sufficient to remove the oxide and maintain a clean surface. An excess of flux will increase the possibility of flux inclusion in the weld metal and weaken the joint. In starting the weld, the flame is given a circular motion with an ever-increasing radius at the starting point to heat and melt the adjacent metal. The center of the flame should not touch the molten metal that is formed but should be kept Y16 to ~ inch from it. The rod should not be introduced into the flame until both surfaces are liquid and a weld puddle has been established. The tip of the rod is then held in the flame just at or below the sUlface of the molten metal and added continually to build up a weld of the desired dimensions. The torch should be moved along the weld line so as to heat both edges ahead of the puddle. At the same time, the puddle should not be allowed to completely solidify. Filler metal is added continuously
until the weld is completed. At the end of the weld, a slight excess of weld material is added to compensate for shrinkage and to prevent crater cracks. Cleaning After Gas Welding-Flux residues on gas welded sections are corrosive to aluminum if moisture is present. Thorough cleaning is, therefore, important after welding. Small sections may be cleaned by a 20 to 30 minute immersion in a cold 10 per cent sulfuric acid bath or a 5 to 10 minute immersion in a 5 per cent sulfuric acid bath held at 150 F. A 10 to 20 minute immersion in a cold 10 to 50 per cent nitric acid bath is also effective for flux removal. In either case, the acid cleaning should be followed by a hot or cold water rinse. Large bus sections which cannot be immersed for flux removal are usually cleaned with hot water or steam. Vigorous brushing is recommended with hot water to remove the closely adhering flux residues. Physical Properties of Gas Welded Work Hard· ened Alloys (EC and 1l00)-The tensile and yield strength of the weld metal in EC and 1100 aluminum bus will closely. approximate the typical tensile and yield strengths of the annealed metal. Lower properties may result from weld unsoundness caused by porosity and/or flux entrapment. Typical physical properties of the weld metal and the parent bus in several tempers are shown in Table 9. Strain hardenable alloys such as EC and 1100 in all tempers will revert back to the typical properties of the annealed material when heated above the reClystallization temperature. The heat introduced during gas welding is usually sufficient to cause recrystallization adjacent to the weld, and it may, therefore, be assumed that the properties of the bus immediately adjacent to the weld will be those of the fully annealed metal. If the filler metal has a strength at least equal to that of the annealed bus material, the weld will support the same mechanical load as the parent metal adjacent to the weld. Maximum design stresses for welded EC and 1100 bus should, therefore, be based upon the properties of the annealed bus material.
The electrical resistance of a gas welded joint approximates that of the annealed filler metal. A slightly lower conductance results where weld unsoundness is encountered. Properties of Gas Welded, Heat-Treatable Alloys (6101, 6061, and 6063)-The heat-treatable alloys derive improved mechanical properties through a solution heat treatment and aging at a lower temperature for a specified length of time. When these alloys are reheated to a high temperature such as encountered in gas welding, their properties are also affected. Alumi-
93
section IV - ioining
num alloys 6101, 6061, and 6063 will decrease in strength appreciably. The properties of the parent metal adjacent to the weld are generally lower than the properties of the weld metal, Table 9. These lower properties in small bus parts may be improved by post-weld heat treatment. The larger sections encountered in bus bar do not lend themselves to a post-weld heat treatment.
Metallic Arc Welding The metallic arc welding process uses a flux-coated consumable electrode. This process has the advantage of producing a highly concentrated heat zone, and thus metallic arc welds have less distortion than gas welds. Joint edge preparation is simple, but welding is con:6.ned to flat and horizontal positions. The strength of a metallic arc welded joint is at least equal to that of a gas welded joint. In general, metallic arc welding aluminum alloys is faster than gas welding and considerably faster than the equivalent arc welding of steel. Metallic arc welding aluminum, however, requires more experience than the arc welding of steel.
imposed, high frequency arc produced by a spark oscillator will add arc stability and ease of striking. Straight polarity is also generally satisfactory. The proper polarity is usually determined by trial. Approximate current settings and electrode sizes for welding various aluminum thicknesses are shown in Table 10. Electrodes-Flux coated arc welding electrodes are commercially available. The two most widely used for metal arc welding are 99+ aluminum and 4043 aluminum alloy. For welding EC and 1100 bus bar, 99+ aluminum electrode is recommended; 4043 alloy rod is used for welding 6101, 6063, and 6061 bus alloys. The recommended electrode sizes for various thicknesses of butt joints are listed in Table 10.
TABLE IO-RECOMMENDED PRACTICES FOR METALLIC ARC WELDING WITH FLUX COATED CONSUMABLE ELECTRODES Metal Thickn;ess (Inches)
TABLE 9-TYPICAL PROPERTIES OF GAS AND METALLIC ARC WELDS IN ALUMINUM
BUS CONDUCTOR TJf~:Je;~OtI';,';~1' Bus Alloy and Temper
Filler Rod
EC-HIII EC or 1100 -H12 -H13 -H17
Conduc-
tivity * Per Cent
*
Square Butt Fillet
~ ~
55-65 60-70
~
Square Butt Fillet
~ ~
80 90
0/1.6
Square Butt Fillet
%2 %2
125
~
Square Butt Fillet
0/1.6
160 200
Single V Groove Fillets
~
0/1.6
220 260
of Parent
Metal
Approximate Welding Current (amps)
%2
Typical Properties Across Welas *
Ultimate Ultimate Yield Tensile Tensile Tensile Strength Strength** Stress (psi) (psi) (psi)
Edge Preparation
Electrode Diameter (Inches)
9,000 12,000 14,000 17,000
4,000 8,000 12,000 15,000
11,000 11,000 11,000
100 100 100
%
1100
13,000 24,000
5,000 22,000
13,000 13,000
100 100
Y2
Single V Groove
0/1.6to~
300
55 EC-T6 (6101)
4043
29,000
25,000
20,000
100
%
Double V Groove
~
375
6063-0 -T6
4043
13,000 32,000
7,000 25,000
1
Double V Groove
%6
450
20,000
100
6061-0 -T6
4043
22,000 42,000
12,000 35,000
2
Double V Groove
%6 to%
550
1100-0 -H14
27,000
100
~
to %6
", See Fig. 18 for edge preparation.
* Conductivity
and tensile properties were measured on a sample with a convexed weld bead. The cross sectional area of the weld is therefore larger than the cross section of the parent bus because of the weld bead build-up. A slightly lower conductivIty and strength would result if the bead were flush or machined to the same cross section as the parent bus. ** Stress to produce 0.2 per cent permanent set.
Equipment-Metallic arc welds can be made with standard doc motor generator power sources used for the joining of other metals. The capacity of the power source and the size of the electrode required are determined by the thickness of the material to be welded. Normally reverse polarity is used because it provides a stable arc with most flux coated electrodes. A super94
Edge Preparation and Cleaning Before WeldingBecause of the ease in obtaining good penetration with metallic arc welding, edge preparation is slightly different than for gas welding. No edge preparation, other than cleaning, is required on material 74 inch or less in thickness. Heavier materials should be beveled to produce a 60 to 90 degree included angle with the butting ends separated Ys inch or less. Details of edge preparation are illustrated in Figs. 18 and 19. Before welding, the surfaces should be cleaned of all oil and grease. When welding flat bus from one
ioining - section IV
/\OO-9~ ,-----.:..,
A
I
~.--------'-\---',
----- -------1
'-----------'IT YJ6" - Va"
60°_90°
OVER V."
r----"'"\.------'L
-------------~
BACKUP BAR OF EITHER ALUMINUM WATERCOOLED COPPER OR STEEL
L
v."
~
L~"">""------')l
c=--s
BACKUP BAR OF EITHER ALUMINUM WATERCOOLED COPPER OR STEEL
".~ Fig. 19 - Tubular Joints
erally not necessary for metal-arc welding bus under
% inch. On sections thicker than % inch, a slight pre-
PLATE THICKNESS GREATER THAN ,/.'
------J(
<----I
Fig. 18:- Butt Welds and Tee Joints
side, it is desirable to provide a back-up strip of aluminum or a grooved metal back-up bar to confine the root of the weld. This back-up strip may be either aluminum or water-cooled copper or steel. Where aluminum is used for a back-up, it is welded to the bus and then removed by chipping after the joint is com-. pleted. Highly skilled operators can usually make welds without using a back-up. Edge preparation for tubular bus is similar to that for flat bus of corresponding thickness, but an aluminum back-up is not recommended because flux may be trapped in the crevice between the tubing and the back-up.
Preheating and Welding Procedure-Preheat is gen-
heat to about 400-600 F makes welding easier, improves penetration, cuts down distortion, and reduces weld unsoundness. The amount of preheat necessary is dependent upon the thickness of the members being joined and also their length. The arc may be "shuck" by brushing the end of the electrode across the work in a manner similar to lighting a match. Touching the end of the electrode to the workpiece is not satisfactory because the rod will stick or fuse to the workpiece. Once the arc is established, an arc length of :yg inch to %6 inch should be maintained and the electrode fed into the weld area at a rate to compensate for burn off. The arc length should never exceed ~~ inch as poor peneh"ation will result, the flux will spatter, inclusions will be formed, and the weld bead will have excessive porosity. Too Iowa welding current gives irregular welds with overhanging weld metal and a very rough appearance of the finished weld. Where the welding travel is too fast, poor penetration will be experienced and undercutting will occur at the edges of the weld. The electrode should be held approximately vertical to the molten puddle and moved with a slight circular motion to permit the weld puddle to remain molten longer and, thereby, allow entrapped flux to rise to the top. If it is necessalY to make more than one pass, the flux coating should be removed from the metal deposited in the previous pass in order to avoid excessive porosity. This may be difficult when the weld is hot since the flux is usually sticky and gummy. When making successive passes, it is usually advisable to deposit metal at a slower rate in order to allow flux residues to rise to the top of the weld puddle.
section N - ioining
Cleaning After Metallic Arc Welding-Flux removal from metallic arc welds is necessalY to prevent corrosive action. Cleaning procedures are identical to those used for the cleaning of gas welds, see page 93. Properties of Metal·Arc Welds - The mechanical properties of the weld and base metal are affected by the heat developed in metal-arc welding, but the loss is less pronounced than that encountered in gas welding. Welds made in either the hardened or annealed tempers of 1100 or EC alloys with 1100 or EC £ller rod will have tensile strengths and electrical conductivities typical of the annealed alloy. Welds in the heat-treatable alloys 6101, 6061 and 6063, using 4043 £ller rod, will have electrical conductivity and tensile properties typical of the filler metal in the as-deposited condition. Typical properties of metal-arc welds are presented in Table 9. Metal adjacent to the weld in heat-treatable alloys is not completely annealed during metal-arc welding, and, therefore, will have properties somewhere between the hardened and the fully annealed alloys.
Tungsten-Inert-Gas Welding (TIG) The tungsten-inert-gas process (TIG) is widely used for welding aluminum bus. In this process, an arc is established between a non-consumable tungsten electrode and the aluminum section to be welded with a shield of inert gas enveloping the arc. The arc melts the aluminum base metal, and a bare filler rod of suitable composition is added to the molten pool by hand. Welding can be done at high speed from all positions. No flux is required in TIG welding because the action of the arc breaks up the oxide £lm and allows good weld metal flow. A shield of inert gas, either argon or helium or a mixture of argon and helium, surrounds the electrode and the weld pool to prevent oxidation during welding. Since the heat of the tungsten arc is concentrated in a small area, it is much faster than gas welding. Distortion in TIG welds is also appreciably less than for gas welds. Equipment-Tungsten-arc welding requires an a-c power supply with a capacity dependent upon the dimensions of the bus to be welded. A superimposed high frequency will greatly improve arc striking and welding characteristics. This can be done with a spark oscillator. Grounding condensers of 5 mfd. capacity (440 v) should be placed across the welding machine terminals to protect windings when a spark oscillator is used. The thickness of the material to be welded and the welding position will control the magnitude of the welding current. Recommended amperages for flat,
96
vertical, and overhead welding are shown in Table II. lt will be noted that currents for welding in the flat position are slightly higher than those for vertical and overhead welding. As with other processes, the size of the electrode increases with metal thickness. Recommended sizes of standard tungsten electrodes for welding bus of different thicknesses are also shown in Table 11. Filler Rods-Bare filler rods of EC, 1100, 4043, 5154, and 5356 are commercially available in various diameters. Special attention should be given to see that only clean rods are used as this can be a source of contamination in the weld. The rods should be stored in a warm, dry area and kept covered. Gas Coverage-Both argon and helium are used for shielding the arc in the TIG process. Helium requires a higher gas flow than argon, but the helium shield gives greater penetration and faster welding. This deeper penetration is obtained because the arc voltage in a helium atmosphere is higher than in an argon atmosphere. This higher voltage generates more heat and hence increases welding speed. Argon is preferred by most operators, however, as the cleaning action of the arc is more effective and arc stability is better. Mixtures of argon and helium are used for some applications to combine the desirable features of each gas. Mixtures of 75 per cent helium and 25 per cent argon are commercially available. Other gas mixtures, for example, 40 per cent argon and 60 per cent helium, are mixed by combined flow from separate tanks of helium and argon. Any helium over 10 per cent changes the arc characteristics markedly. Edge Preparation and Cleaning Before WeldingCleaning of the welding surfaces to remove oil and grease is also required for TIG welding. As with the other processes, edge preparation and the root opening required for welding are a function of bus thickness. Bevels vary from 0 degrees for Vs inch material to 30 . degrees for % inch material. Edge preparation for the common thicknesses of bus bar and recommended joint design is indicated in Figs. 20 and 21. On bars less than ~ inch in thickness, the edges need not be beveled. For bars VB inch to % inch thick, some root opening is recommended to insure complete penetration. In general, this gap should be approximately 25 per cent of the metal thickness. Welds should be suppOlted by a backing bar except where welding is done from both sides. The backing bar may be either aluminum, copper, or steel. An aluminum backing bar is widely used in TIG welding because there is no danger of flux entrapment with this process. All metal thicknesses can be TIG welded, but the most effective range is 7b to % inch.
joining - section IV
TABLE ll-RECOMMENDED PRACTICES FOR TUNGSTEN-INERT-GAS-SHIELDED (TIG) WELDING OF ALUMINUM Material Thickness (Inches)
Ys
Welding Position
Flat
Edge Preparation *
Current (Amps A-C)
Diameter of Tungsten Electrode (Inches)
I
I
i
Gas Flow CFH
Filler Rod Diameter (Inches)
Square Butt
oto % inch Root Opening
Preheat (Degrees F)
125
Ys
20
Ys
None
oto % inch Root Opening
115
%2
20
Ys
None
Square Butt o to % inch Root Opening
115
%2
25
Ys
None
Flat Vertical Overhead
60 degree Single Bevel 60 degree Single Bevel 60 degree Single Bevel
225 200 210
%6
30 30 35
%6 %6 %6
None None None
%
Flat Vertical Overhead
60 degree Single Bevel 60 degree Single Bevel 60 degree Single Bevel
325 250 275
1f4
35 35 40
1f4 1f4 1f4
Up to 400 Up to 400 Up to 400
Y2
Flat Vertical Overhead
60 degree Single Bevel 60 degree Single Bevel 60 degree Single Bevel
375 250 275
1f4 114
35 35 40
Up to 600 Up to 600 Up to 600
Flat
60 degree Single Bevel
500 to 600
%6 tO %
35 to 45
1f4 1f4 1f4 1f4 to %
Vertical Overhead 1! /4
1
* See Figs. 20 and
Square Butt
%2
%6 %6 %6 %6
Up to 600
21 for edge preparation.
,------------,
-
-- ---------
~
~
UP TO'Y4"
-----j
~o - Va"
75 '\
...-------..:,.
°7
r---
L
--
t
OVER
-----------~
\4"
~
---------------~.
~~ .
Fig. 20 - Butt Weld Joints
0- ~~"
Va '~\4"
Fig. 21- Tubular Joints
97
section IV - ioining
TABLE 12-TYPICAL PROPERTIES OF TIG AND MIG WELDS IN ALUMINUM BUS CONDUCTOR
For tubular sections with wall thicknesses greater than ~ inch, the edges should be beveled with a 60 to 90 degree included angle with a square butt lip of Ys to ~ inch, depending upon the bus thickness, Fig. 20. A tubular backing, such as shown on page 106, can be inserted into the tube before welding. This backing also reinforces the tube at the welded section.
T:r~:,Ie;~oM';,\~fS
Bus AIloy and Temper
Preheating and Welding Procedures-Preheating is desirable on sections 112 inch and up in thickness in order to make welding easier and to increase welding speed. Preheating can be done by any suitable method, but usually a gas torch will be used. Preheat temperahues will range between 400 to 800 F with the higher half ,of the temperature range favored for vertical and overhead welding. The electrode size, current setting, and gas coverage should be chosen to suit the metal thickness to be joined. The arc is initiated by bringing the ttmgsten electrode close to the bus material. The tungsten is then withdrawn from the bus to establish an arc of desired length. A %6 inch arc is satisfactory for most welding. The arc is held at the starting point and the electrode is given a circular motion until the base metal liquefies and a weld puddle is established. Filler rod is added manually from the side as needed to form the weld bead. The torch is usually inclined approximately 20 degrees to the vertical pointing toward the direction of travel. If more than one pass is required, the weld should be wire bmshed before the second pass to remove any surface dirt which has accumulated from the previous pass. Since no flux is used with this process, the finished welds do not require cleaning. The completed weld has a smooth appearance, hence the welding bead is not usually removed. Properties of TIC Welded Bus-The heat generated by welding affects the mechanical properties of the finished weld very much the same as in gas welding. A small zone extending Ys to liz inch on either side of the weld bead is at least partially annealed by the welding heat. In strain hardened alloys such as EC and 1100, the tensile strength of the heat affected zone is reduced to approximately that of the annealed parent metal. In heat-treatable alloys, the heat affected zone is reduced in mechanical strength to some intermediate point between the typical properties of the annealed and heat treated parent metal.· The typical tensile properties of both TIG and MIG' welded bus are shown in Table 12.
Metal-Inert-Gas Welding (MIG) The metal-inert-gas welding process (MIG) is widely used for bus fabrication. This method com-
98
Filler Alloy
*
(psi)
Conductivity Per Cent of Parent Metal
Ultimate
Yield
Ultimate
Tensile
Tensile
Tensile Stress
Strenfh Strength** (psi (psi)
- - -- - -
*
9,000
4,000
12,000 14,000
8,000 12,000
12,000 12,000
100 100
1100
13,000 24,000
5,000 22,000
13,500 13,500
100 100
4043
29,000
25,000
20,000
100
6063-0 -T6
4043
13,000 32,000
7,000 25,000
20,000
100
6061-0 -T6
4043
22,000 42,000
12,000 35,000
27,000
100
BC-H111
BC or 1100
-H12 -H13 1100-0 -H14 55 BC (6101-T6)
* Tensile properties
*
Typical Properties Across Weld
*
and conductivity reJ?orted were taken on a weld with a
convexed bead. This bead type results m a weld with a cross sectional area slightly greater than the cross sectional area of the parent plate. If the weld bead were flush or machined to the same cross section as the parent plate, the conductivity and strength would be slightly lower. Stress to produce 0.2 per cent permanent set.
bines the advantages of tungsten arc welding with increased welding speed. Welding speeds range from 20 inches per minute for ~ inch bus bar to 6 inches per minute for 1 inch bar. Any welding position can be utilized, and the process can be either manual or automatic. Heat is concentrated in a small area, and high current densities can be used for overhead and vertical welding. The techniques used for manual welding are somewhat different than those used with other methods; however, a weldor can be trained to use this process with only a few days of concentrated training. Equipment-Equipment for manual welding with the MIG process has these basic features: An electrode feeding mechanism; A gas cup and guide tube assembly for directing the welding rod and supplying gas coverage to the weld zone; A doc power source supplying reverse polarity current; An inert gas supply. In the MIG process, filler rod is supplied as a coil of bare wire. This wire is added to the weld at a preset rate by a motor driven feed that can be adjusted to the magnitude of the welding current. Equipment designed specifically for this process is commercially available. The power source for MIG welding may be any suitable doc generator, but a constant potential generator is preferred to produce high quality welds. A constant potential power source compensates for changes in arc length due to the human element, thus it provides more uniform welding. Reverse polarity
joining - section N
TABLE I3-APPROXIMATE PRACTICES FOR METAL·INERT·GAS·SHIELDED (MIG) WELDING OF ALUMINUM Material Thickness (Inches)
%
% % % 1
2 3
I
Welding Position
Edge Preparation
*
Current (amps)
Arc Voltage
Filler Rod Diameter ~n4, ~4,
Gas Flow (CFH)
Number of Passes
30A 30A 40A
1 1 1
40A 45A 50A
1 3 3
50Aor 90Re 50Aor 90Re 50Aor 90Re
2 3 5
50Aor 90Re 50A or 90Re 80Aor lOORe
2 or 3. 3 or 4 8 to 10
~6
~6
60Aor 95He 60Aor 95He 80Aor lOORe
4 to 5 4to 6 15 or more
%2 %2·
60Aor 95Re 60Aor 95He
12 or more
Flat Vertical Overhead
None None None
110 100 100
20 20 20
Flat Vertical Overhead
Single or bevel Single or bevel Single or bevel
200 170 180
26-28 26-28 26-28
Flat Vertical Overhead
Single or double bevel Single or double bevel Single or double bevel
280 180 200
26-28 26-28 26-28
116 116
Flat Vertical Overhead
Single or double bevel Single or double bevel Single or double bevel
300 210 225
26-30 26-30 26-30
%2
Flat Vertical Overhead
Single or double bevel Single or double bevel Single or double bevel
400 250 275
26-30 26-30 26-30
%2
Flat Flat
Double bevel Double bevel
425 450
26-30 26-30
0/64 Y16
~6
~6
~6 ~6
~6
* See Figs. 22 and 23 for edge preparation. direct current is always used in this process. The approximate conditions recommended for MIG welding are presented in Table 13. The MIG process is usually used for welding thicknesses greater than % inch, but special equipment will adapt it for welding thicknesses less than Vs inch.
Filler Wire-Filler wire of EC, noo, 4043, 5154, and 5356 is commercially available in %4, Jh6, %2, and Vs inch diameters. It is usually supplied as spooled bare wire.- Special attention should be given to maintaining the cleanliness of the filler wire. Frequently, unsound welds are caused by the use of filler wire which has been contaminated by oil, grease, dust, and fumes in the shop. Best results are obtained by using wire which has just been taken out of its carton. Filler wire should be stored in a warm, dry area and kept covered. Gas Coverage-Either helium, argon, or a mixture of helium and argon are suitable for MIG welding. Pure argon is the most widely used gas on materials less than % inch thick. Thicknesses over % inch are usually welded with a mixture of helium and argon. This mixture may range from 10 per cent helium and 90 per cent argon to 80 per cent helium and- 20 per cent argon. Flow requirements are presented in Table 13 for all welding positions. At any given arc voltage, the helium shielded arc is hotter than the argon arc, but
a smoother and more stable arc is obtained with argon. On heavy bus bar, the gases are usually mixed to combine the hotter arc characteristics of helium with the stabilizing effects of argon.
Edge Preparation and Cleaning Before WeldingEdge preparation and joint design for MIG welding is similar to that for TIG welding. Bus bar %6 to % inch thick inclusive can be welded satisfactorily with complete penetration using a square butt design. Bus bar greater than % inch thick should have a single V groove or a double V groove, Fig. 22. The edges of tubular sections are prepared the same as the edges of flat bus of corresponding thickness, Fig. 23. Aluminum back-up bars of the same composition as the parent material are often used with the MIG process. The back-up is usually left intact after welding is completed. On flat bus or tubular bus which is exposed to the aqnosphere, provision should be made to prevent moisture from collecting in the crevice between the back-up plate and the parent bus. Moisture entrained in this small crevice presents a COlTosion hazard which can be eliminated by welding around the back-up bar to seal the crevice. As with other welding methods, the surfaces should be clean and dry prior to MIG welding. Oil and grease can be removed with any standard commercial degreasing compound that is used for other welding 99
section N - joining
-------,~
j
I [
~O-1fs"
'---------I
i~·~~·
I
Fig. 22 - Butt Weld Joints
.------_~
~ UP TO 3fs"
--L~O-V8"
'\""; ~---------~
,--------;
--------------i3fs" OVER
--------------
~
~
-----~ o -7'16"
Fig. 23 - Tubular Joints
100
Y16"
methods. It is essential that the welding surface be free of moisture if unsoundness is to be avoided. A clean air blast is usually an effective drying agent after cleaning. Smface oxides should be removed by wire brushing prior to welding. This is a generally recommended practice to insure sound welds, but is not always employed. Preheating and Welding Procedures-As mentioned earliet, preheating of the bus bar before welding is neceSSalY when the thickness or mass of the bars is such that heat is conducted away from the joint faster than the arc can supply it. Insufficient preheat can be recognized by poor fusion of the weld bead and insufficient melting of the parent metal. Preheating of the parts being joined sometimes helps in producing a satisfactory weld, in reducing distortion in the finished product, and in increasing the welding speed. Commercially available equipment for MIG welding is designed to initiate gas coverage and automatically feed the aluminum electrode into the weld area when the arc is struck. A welding pool is formed immediately when the arc is established and welding progresses by moving the welding gun along the line of the joint at a rate to build up a bead of the desired dimensions. The electrode and weld pool are protected from oxidation by the shield of inert gas during welding. No flux is required with this process. In flat position welding, the gun is pointed in the direction of travel with a 10 to 20 degree angle to the vertical position. Bus bar up to % inch thick can be welded with one pass; bus bar over % inch thick may require two or more passes. Where more than one pass is required, the weld should be wire brushed between passes. Post weld cleaning is not necessary for MIG welds, and weld beads are not usually finished off. Properties of MIG Welds-The properties of MIG welds are similar to those made by the TIG process but are superior to those made by any other process. Like the TIG process, the concentrated arc heat does not raise the temperature of adjacent metal as much as the other processes. The heat affected zone is therefore narrow, and the properties of the adjacent metal are high. Welds produced by the MIG process are usually sound so that the properties of the weld metal itself are superior to weld metal properties produced by gas welding or the metallic arc process. Typical properties of TIG and MIG welds in ~C, 1100, 6101, 6061, and 6063 are shown in Table 12.
Carbon Arc Welding Carbon arc welding is used in only limited applications where suitable equipment is on hand. A flux coated rod is used to supply filler metal to the weld. Metal in thicknesses of Y16 inch to approximately %
ioining - section IV
inch can be welded commercially with a manual process. Carbon arc welding can also be adapted to automatic equipment if the quantity of welding justifies . the initial capital outlay. Post weld cleaning is ad~ visable to remove flux residues.
tion. For such applications, flash butt welding· is the most common process, but the initial cost of flash butt welding equipment is high and can only be justified for quantity production.
Pressure Welding Atomic Hydrogen Welding Atomic hydrogen welding is adaptable to both manual and automatic processes on metal Y16 inch thick and greater. A flux coated filler rod similar to that used for gas welding is fed into tlle arc during welding. Joint preparation and flux removal are similar to that employed for gas welding. This method of welding is limited in bus bar applications.
Resistance Welding Resistance welding is seldom used for joining bus bar and can only be economically adapted for fabricating small sections that are suitable for high produc-
(' ~{g-AIC1 y60 ( \(/AI
Pressure welding of aluminum and aluminum alloys is relatively new. In tllis process, tlle joint is made by the application of high pressure to the surfaces to be joined either with or without heat in tlle complete absence of melting. Applications of pressure welding are very limited.
Joining Aluminum to Copper hy Welding Special applications may require that copper be joined to aluminum by welding. This may be necessary where it is desirable to introduce aluminum bus in an existing copper installation or to take copper tap-offs from an aluminum bus. Special processes are required to weld aluminum to copper. When aluminum is welded directly to copper, a brittle inter-metallic compound of CuAl2 is formed. This brittle material makes the weld unsuitable for most bus applications. In order to avoid the formation of CuA12 , the copper must be coated with a material which is metallurgically compatible with
f-/-------,// Cu
Cu
~
....Y/
0
AI
Cu
Cu
AI Fig. 24 - Butt and Lap Weld Joints
Fig. 25 - Tee Joint Designs
101
section N - joining
both copper and aluminum. Many silver solders have proven satisfactory for this purpose. Mter properly coating the copper with silver solder, either the TIG or MIG process can be used to make the aluminum to copper weld.
Joint Design-Butt joint designs and tee joints have been welded satisfactorily by this method. Recommended edge preparation for aluminum to copper welded joints is shown in Figs. 24 and 25. Silver Solder Coating the Copper Bar-The copper is first cleaned then coated with an all purpose brazing flux: paste. Heat is applied with a gas torch or other suitable heat source until the flux: liquefies and a layer of silver solder-consisting of 50 per cent Ag, 15.5 per cent Cu, 16.5 per cent Zn, and 18. per cent Cd-at least Y32 inch thick, is overlaid on all surfaces which are to be in contact with molten aluminum. Mter the copper is silver coated, it is cooled to room temperature and cleaned to remove all traces of flux before welding to the aluminum bus bar. Procedures-The silver coated copper and the aluminum bus are positioned as indicated and welded with 4043 filler rod. The arc is directed on the aluminum and molten pool is established. The weld pool is then brought into contact with the silver so as to avoid qomplete removal of the silver solder. It is ad-
a·
visable to keep the temperature of the copper below 500 F to prevent loss of the silver solder. This may be done by interpass cooling or other siniilar methods.
Physical Properties of Aluminum to Copper MIG Welds-Operating data have been accumulated on copper-aluminum welds which have been in service for approximately two and one-half years. These data show that joint efficiencies are excellent and these welds can meet all nonnal service conditions required for aluminum bus. A properly designed joint in EC or 1100 alloy will have a tensile strength equivalent to the annealed parent aluminum. .
Exothermic Welding Aluminum may be welded to itself or to copper by means of an exothennic reaction. This produces a molten aluminum alloy with sufficient superheat to fuse the ends of either flat rectangular or tubular bus conductor. It can also be used to terminate stranded aluminum cable into a copper or aluminum tenninal pad. This is a self-propagating process in which finely divided aluminum powder through direct oxidation reduces less stable metal oxides to superheated free metal. In practice, a weld of this type is made in a semipennanent graphite mold consisting of two chambers (see Fig. 25). * The upper chamber or crucible holds *Cadweld Process, ERICO PRODUCTS, INC.
Fig. 25 - Graphite Mold and Cadwelded Aluminum Tube
102
joining - section N
Aluminum to Aluminum Joints
aluminum powder on an aluminum disc until the exothermic reduction is complete. The superheated aluminmualloy melts the disc and flows into the lower chamber or mold cavity, causing melting of the ends of the conductors and fusion with the parent metal. The copper conductors are tinned with pure tin to maintain a chemically clean surface and the aluminum smfaces are fluxed to facilitate removal of the surface oxide during welding. By mming the copper conductor, the strength of the copper-aluminum weld section is improved. The tensile strength of a typical joint is equal to the annealed strength of the parent aluminum conductor. An aluminum thermic weld maintains its elec-
trical properties under severe overloads and will operate at the same or lower temperatures than tIle parent conductor' under any load condition. This process is applicable to the following sizes of rectangular bar and tubular conductors; other sizes are being developed. Aluminum Rectangular Conductor Size (Inches)
Alwninum IPS Conductor Size (Inches)
~x 1 114 x 2 ~x 4 Y2 x 4 Y2 x 6 . Y2 x 8 7~ x
10
103
section IV - ioining EXOTHERMIC WELDS
104
Aluminum to Aluminum Joint
.Aluminum to Copper Joint
Aluminum to Aluminum Joint
Copper Cable Welded to Aluminum Bar
ACCESSORIES
Most outdoor bus bar installations, in the past, have been assembled with bolted fittings. Although this practice is still popular, many outdoor substations are now being constructed by welding all conductor joints and taps. Various designs of welding fittings have be~n developed to facilitate this latter process. Both types of fittings are illustrated in the following pages.
SEE DETAil A
Welding Fittings Welded aluminum bus joints eliminate contact resistance between adjoining parts of the circuit. The resistance of the fused joint of two welded members is generally less than an equivalent length of parent bus. Cycles of heating due to current loading have no effect on the joint. The welding fittings shown are deb INSERT 3" LONG
ALUMINUM BUS RUN
KV.
DETAIL A
I
an""
b
115
11
"
2' 6"
230
15:1)."
3'6"
NOTES: *Approximate dimension. Inert gas weld as shown. All pipe is standard I. P. S. aluminum pipe: 37%0 X %G" chamfer on all ends to be welded. Cut, to template, abutting ends only.
105
WELDING· FITTINGS
--,
\
, \
I --,/
SLIDE OR GRIP BUS SUPPORT I
....
_-
-- __
------ --- ..... . . 1~~~~~~~~~1S::3~~1 ~""';~ II J:
I
--
, \
1/
I~
1\
,'/
-~~.,
SLIDE BUS SUPPORT
, I
I
'... ......
.......
.......
...........
I
If
II
........ ..... ..::;;/ \' / /
VERTICAL TEE CONNECTOR
FREE FIT
A-" '1
ANGLE TEE CONNECTOR
WELD
_ ~ ~~U.!:L.:.R
I•
... _- .....- .... ..,. ....
ANGLE TEE CONNECTOR
WELD
EXPANSION JOINT WITH GUIDE
BUS SUPPORT 3" BOLT CIRCLE
BUS SUPPORT 5" BOLT CIRCLE Cotl-rtesy Penn-Union. Elect-ric Gorp.
106
VERTICAL BUS SUPPORT
.
accessories - section V
signed to simplify the assembly of a joint, support, or tap connection and reduce to a minimum the edge preparation of the conductors. The aluminum alloys generally used for welding fittings are those that provide strength in the "as welded" condition. These aluminum alloys do not require heat treatment to establish high strength propelties. The process of natural aging after welding increases the strength considerably over the "as welded" condition. Consideration should be given to the annealing effect of the bus conductors as they will have a narrow heat affected zone on either side of the weld. The properties of this heat affected zone are described in the section on welding.
Welded Bus Joint -
yI- I~ Sf x.~
b-."'>-..""0<.""~)
11'1
~• .!.Yn"
: : : \
I'o"--H'H' '' '1
II II 1~ I I 11'11
INr RT
1 11 I I 1I I 1
: 111
~,(y
~
1 I.P.S. AlUMINUM
LAlloy
PIPE BUS.
%IIAPPROX,
~,N
_ I
I.P.S. ALUMINUM ALLOY PIPE----.""
~~3--e I \
60TH ENDS
j- - - - - - - ---------1
SUIT1~~T S;fDTH
Welding Insert
, BUS RUN
INSERT
Std. I.P.S.
a.D.
I.D.
a.D.
LP.S.
1%"
1.660
1.380
1.315
1
1%,'
1.900
1.610
1.660
1%"
12"
"
2.375
2.067
1.900
llh"
15"
21\J"
2.875
2.469
2.375
2
"
18"
2
"
la (Min.)
12"
"
3.500
3.068
2.875
21\J"
21"
31\J"
4.000
3.548
3.500
3 "
24"
4.500
4.026
4.000
3%"
27"
3
4
"
I
NOTES: Material is standard 1. P. S.Alu1l1inum alloy pipe. Collapse or spread as required for light drive fit in pipe bus and applicable fittings. Circumferential weld shall be made in two passes. Alignment insert shall be tack welded in position with approximately half its length exposed, before driving on the other length of bus.
Bolted Accessories Bolted accessories that are used to join, tap, and terminate the various shapes of bus conductor must be properly installed to insure continued low resistance electrical continuity. Recommended surface treatments as outlined in the section on joining, should be followed for all aluminum contact surfaces. The mating surfaces on tlle conductors must also be prepared in a similar manner. This surface treatment is generally accomplished by applying a connector sealing paste or compound to the contact surfaces and abraiding through this paste with emery cloth, wire brush, fiber-glass brush, or other acceptable device. The bus and fitting are then assembled without removing this compound. The excess paste will exude from the joint where it can be wiped off. This installation practice . will assure a low resistance bus joint. Some manufacturers of fittings are rough grinding the contact surfaces of their fittings and immediately applying a sealing paste to prevent re-oxidation. These fittings need no surface preparation prior to installation. The rough grind finish produces a multitude of peaks and valleys. When pressure is applied the coincident mating peaks produce a multitude of parallel conducting paths through the joint. The area of contact of each of these minute conductors broadens with increasing clamping force, thereby growing in current capacity as well as in size. It is therefore necessary in conservatively designed aluminum fittings to increase not only the area of contact between the fitting and the bus but to progressively increase tlle clamping force as conductors become larger and gain greater current capacity. This increase in clamping force is obtained by either a greater number of bolts or bolts of large diameter. Standard copper bodied accessories are used to a limited extent on aluminum bus. They are usually plated with tin or cadmium or may be tinned to reduce tlle possibility of corrosion. The reliability of these fittings on aluminum bus is not generally considered adequate for the importance attached to substations tllat demand trouble-free operation. Such fittings generally do not have adequate clamping force for aluminum conductors and consequently may run hot. Any significant temperature rise will create an increase in clamping force due to difference in expansion of tlle joint materials. This results in deformation of tlle fitting and bus on tlle load peak of tlle cycle. After cooling to the lightly loaded portion of tlle cycle, these fittings exert less clamping force on the conductor due to the greater contraction of the aluminum bus. Unless copper bodied fittings are used for light duty operation where the temperature rise of the bus and fitting are negligible, this joining method can lead to a gradual increase in joint resistance and may in time cause failure. No surface preparation is necessary for plated copper fittings, but sealing pastes should be used liberally when tlley are installed.
107
section V - accessories
TEE CONNECTORS
Photographs courtesy of: Burndy Corp.; Velta-StOl' Electric Viv., H. K. Porter Co.; Royal Electric Mfg. Co.
accessories - section V
TEE CONNECTORS
Photographs courtesy of:'Bumcly C011'.; Royal Electric Mfg. Co.; Delta-8tm' Electric Div., H. K. Porter Co.; Memco Eng. & Mfg. Co., Inc.
109
section V - accessories
EXPANSION CONNECTORS
Photographs cou,tesy of: Delta-Stm' Electric Div., H. K. Porter Co.; Dosert Mfg, Corp.; Memco Eng, & Mfg, Co., Inc.; Royal Electric Mfg, Co,
110
accessories - section V
EXPANSION CONNECTORS
Photographs courtesy of: Burndy Corp.; Delta-Star Electric Div., H. K. Porter Co.; Penn-Union Elect,'ic Co,-p.
III
section V - accessories
STUD CONNECTORS
Photograph courtesy Delta-Star Electric DiD., II. K. Porter Co.
112
accessories - section V
STUD CONNECTORS
Photographs cow'tesy of; Delta-Stcll' Electric DiG" H, K. po,.te,' Co,; Royal Elect,'ic Mfg, Co,
113
section V - accessol'ies
BUS SUPPORTS
Photographs courtesy of: Burndy Corp.; Memco Eng. & Mfg. Co.; R. & I. E. Equip. Vivo of I-T-E Circuit Bl'eaker Co.; Royal Electric Mfg. Co.
114
accessories - section V
BUS SUPPORTS
Photographs co';',tesy of: General Electric Company; Memco Eng. & Mfg. Co.; Penn-Union Electric Corp.; Royal Electric Mfg· Co.
115
section V - accessories
COUPLERS AND TERMINALS
Photogmphs courtesy of: Burndy Corp.; Delta-Star ElcGtric DiD., H. K. PorteI' Co.; Memco Eng. & Mfg. Co.; Royal Elect"ic Mig.Ca.
116
:1
TABLES AND SPECIFICATIONS CONTENTS Tables
Page
Rectangular Bus Bar EC-Grade Aluminum Current Rating . 57EC (6101-T61) Aluminum Alloy Current Rating. Physical Properties . Electrical Properties
118 119 120 122
Solid Round Bus Conductor Physical Properties . Electrical Properties
124 125
Extruded Aluminum Tubing Physical Properties . Electrical Properties
126 127
Round Tubular Bus Bar Deflections and Stresses Standard Iron Pipe Sizes Extra-Heavy Pipe Sizes .
128 130
Aluminum Channel Bus Conductors Physical Characteristics of Single Channel Sections . Electrical Characteristics
132 133
Aluminum Angle Bus Conductors Physical Characteristics of Single Angle Sections Electrical Characteristics
134 135
Square Aluminum Tubular Conductors Physical Properties . Electrical Properties .
136 136
Inductive Reactance Spacing "Factors"
137
Bare, All Aluminum Stranded Conductor, Hard Drawn Physical Dimensions and Breaking Strength . Electrical Characteristics and Weight
138 139
Specifications and Tolerances Designations for Aluminum Alloys Aluminum Association Designations ASTM Designations . Extruded Shapes and Extruded Rod and Bar Cross Sectional Dimensions Standard Tolerances
140 141 141 141-2 141-2-3
Physical Requirements for Bolts, Capscrews, Studs and Nuts
144
Tentative Specifications for Aluminum Bars for Electrical Purposes
149
Electroplating on Aluminum Alloys
155
Electrodeposited Coatings of Zinc on Steel
163
Electrodeposited Coatings of Cadmium on Steel
166 117
section VI - tables and specifications
RECTANGULAR BUS BAR EC·Grade Aluminum - 61 Per Cent Conductivity (Current Rating in Amperes*) I
~
]~
1 Bar
Size (Inches)
D-c
60 cps A-c
D-c
Y4, xl 1* 2 3 4 5 6 8 %x2 3 4 5 6 8 *x3 4 5 6 8
310 435 560 790 1020 1250 1470 1900 705 990 1270 1550 1820 2350 1160 1490 1800 2120 2740
310 430 550 775 990 1200 1400 1780 690 955 1200 1440 1680 2130 1100 1380 1650 1900 2410
615 860 1080 1480 1850 2200 2530 3140 1330 1810 2260 2670 3080 3800 2040 2540 3000 3450 4280
~~~
2 Bars
I
~~~~
3 Bars
60 cps A-c
D-c
60 cps A-c
D-c
60 cps A-c
610 845 1050 1410 1720 2010 2270 2750 1260 1660 2000 2310 2620 3150 1800 2150 2490 2800 3370
835 1140 1430 1980 2490 2970 3420 4280 1790 2450 3090 3660 4320 5260 2870 3555 4200 4830 5970
815 1100 1360 1820 2210 2570 2900 3530 1630 2120 2550 2960 3350 4040 2320 2760 3180 3580 4310
965 1330 1690 2350 2990 3560 4100 5160 2120 3020 3770 4480 5180 6430 3510 4440 5200 5970 7400
940 1260 1570 2070 2530 2930 3320 4050 1860 2430 2930 3390 3830 4610 2650 3160 3640 4100 4930
, i
I
i !
1 Bar
4 Bars
::2Bars
!
i
!
i i
!
!
3 Bars
i
!
: 4 Bars
i
i
Size (Inches)
D-c
60 cps A-c
D-c
60 cps A-c
D-c
60 cps A-c
D-c
60 cps A-c
Y4, xl 1* 2 3 4 5 6 8 %x2 3 4 5 6 8 *x3 4 5 6 8
305 430 550 775 990 1200 1360 1670 685 960 1210 1440 1670 2040 1120 1410 1680 1930 2350
305 425 545 760 960 1150 1300 1560 675 930 1160 1370 1560 1860 1070 1330 1550 1750 2090
595 820 1030 1430 1780 2060 2280 2720 1270 1740 2160 2500 2800 3340 1920 2360 2760 3140 3750
590 805 1010 1360 1650 1880 2060 2380 1200 1590 1910 2160 2390 2760 1690 2000 2290 2550 2960
790 1080 1380 1920 2380 2780 3080 3520 1675 2320 2900 3360 3800 4340 2640 3270 3760 4220 4950
775 1050 1310 1760 2120 2400 2610 2910 1530 2010 2400 2710 3010 3340 2130 2530 2850 3130 3560
920 1270 1620 2270 2840 3270 3550 4030 1990 2820 3480 3980 4430 4980 3170 3960 4520 4980 5700
895 1210. 1500 2000 2400 2680 2870 3160 1740 2280 2700 3010 3280 3570 2390 2820 3160 3410 3800
* Current ratings
are for 30 C rise over 40 C ambient temperature in still but unconfined air. This is equivalent to an indoor rating with an average emissivity of 0.35. The space between bars in multiple bar arrangements is equal
118
;
to the bar thickness. For phase spacing less than 18 inches, these ratings should be reduced, due to the effect of proximity. See page 19 for comparative effect of 4 inch spacing on current ratings.
tables and specifications - section VI
RECTANGULAR BUS BAR 57EC (6101.T61) Aluminum Alloy - 57 Per Cent Minimum Conductivity (Current Rating in Amperes *)
Size (Inches)
%x1 1Y2 2 3 4 5 6
8 %x2 3 4 5 6 8 Y2 x 3 4 5 6 8
~ D-c
60 cps A-c
305 425 545 765 990 1210 1430 1850 680 960 1230 1500 1770 2280 1120 1450 1750 2060 2660
305 420 535 750 960 1170 1360 1730 670 930 1170 1410 1640 2080 1080 1350 1610 1860 2360
I
Size (Inches)
%x1 1Y2 2 3 4 5 6 8
%x2 3 4 5 6 8 Y2 x 3 4 5 6 8
~~
1 Bar
i
D-c
605 835 1050 1430 1790 2140 2450 3050 1280 1750 2180 2580 2980 3690 1990 2460 2915* 3340 4150
I
1 Bar
I
~~~~
3 Bars
4B=
60 cps A-c
D-c
60 cps A-c
D-c
60 cps A-c
600 820 1020 1370 1670 1960 2220 2680 1230 1620 1940 2250 2560 3080 1760 2100 2430 2730 3300
815 1100 1380 1920 2420 2890 3300 4140 1720 2360 2980 3540 4090 5100 2780 3440 4060 4660 5800
800 1070 1320 1760 2150 2510 2830 3440 1590 2060 2480 2890 3260 3950 2270 2700 ·3110 3500 4220
940 1290 1640 2260 2890 3460 3980 4990 2040 2910 3640 4340 5000 6230 3400 4280 5030 5760 7160
910 1230 1530 2010 2460 2860 3240 3940 1810 2370 2850 3310 3740 4510 2590 3090 3560 4000 4840
I I I
: 2 Bars
D-c
60 cps A-c
D-c
60 cps A-c
300 420 535 750 955 1160 1320 1620 670 935 1190 1420 1630 2000 1100 1390 1650 1890 2310
300 415 530 735 930 1120 1270 1520 660 905 1130 1340 1520 1820 1050 1300 1520 1710 2050
585 800 1010 1380 1720 2000 2220 2640 1230 1680 2080 2420 2710 3240 1870 2290 2680 3050 3640
580 785 980 1310 1600 1830 2010 2320 1170 1550 1860 2110 2330 2700 1650 1960 2240 2490 2900
* Current Ratings are for
~~~
2 Bars
30 C rise over 40 C ambient temperature in still but unconfined air. This is equivalent to an indoor rating with an average emissivity of 0.35. The space between bars in multiple bar arrangements is equal
-
I I I
I
I
!
J
3 Bars
I I
I
4 Bars
I
D-c
60 cps A-c
D-c
60 cps A-c
775 1060 1340 1850 2300 2670 2970 3410 1620 2250 2800 3250 3680 4210 2560 3150 3630 4060 4790
765 1020 1280 1700 2050 2330 2540 2840 1490 1960 2340 2650 2940 3270 2080 2470 2780 3050 3490
905 1240 1560 2180 2740 3160 3440 3900 1920 2730 3360 3850 4280 4820 3070 3800 4370 4800 5510
880 1180 1460 1940 2330 2610 2800 3080 1700 2220 2630 2940 3200 3490 2340 2750 3090 3330 3720
to the bar thickness. For phase spacing less than 18 inches, these ratings should be reduced due to the effect of proximity. See page 19 for effect of 4 inch spacing on the current rating of .'}S BC bus bars.
119
section VI - tables and specifications
RECTANGULAR ALUMINUM BUS CONDUCTOR PHYSICAL PROPERTIES
(1)
Axis x-x Cross Sectional Area Cir Mils
Axis y-y
I
Weight(2) per foot (lbs. )
of Inertia Ix-x (Inches) •
Section Modulus S (Inches)S
of Gyration r (Inches)
Moment of Inertia Iy-y (Inches)·
Radius
Moment
Section Modulus S (Inches)"
Radius of Gyration r (Inches)
Size (Inches)
Square
72X1B %X1B
0.0625 0.0938 0.1250 0.1563 0.1875 0.2500
79,600 119,400 159,200 199,000 238,700 318,300
0.073 0.110 0.146 0.183 0.220 0.293
0.001302 0.004395 0.01042 0.02035 0.03516 0.08333
0·005208 0.01172 0.02083 0.03255 0.04688 0.08333
0.1443 0.2165 0.2887 0.3608 0.4330 0.5774
0.00008138 0.0001221 0.0001628 0.0002035 0.0002441 0.0003255
0.001302 0.001953 0.002604 0.003255 0.003906 0.005208
0.03608 0.03608 0.03608 0.03608 0.03608 0.03608
% X 0/16 % x 0/16 1 X 0/16 1% X 0/16 1% X0/16 2 X0/16
0.0938 0.1406 0.1875 0.2344 0.2813 0.3750
119,400 179,000 238,700 298,400 358,200 477,500
0.110 0.165 0.220 0.275 0.330 0.439
0.001953 0.006592 0.01563 0.03052 0.05273 0.1250
0.007813 0.01758 0.03125 0.04883 0.D7031 0.1250
0.1443 0.2165 0.2887 0.3608 0.4330 0.5774
0.0002747 0.0004120 0.0005493 0.0006866 0.0008240 0.001099
0.002930 0.004395 0.005859 0.007324 0.008789 0.01172
0.05413 0.05413 0.05413 0.05413 0.05413 0.05413
lhx14 %x14 1 x 14 l%x14 Ph x 14 2 x14
0.1250 0.1875 0.2500 0.3125 0.3750 0.5000
159,200 238,700 318,300 397,900 477,500 636,600
0.146 0.220 0.293 0.366 0.439 0.586
0.002604 0.008789 0.02083 0.04069 0.07031 0.1667
0.01042 0.02344 0.04167 0.06510 0.09375 0.1667
0.1443 0.2165 0.2887 0.3608 0.4330 0.5774
0.0006510 0.0009766 0.001302 0.001628 0.001953 0.002604
0.005208 0.007813 0.01042 0.01302 0.01563 0.02083
0.07217 0.07217 0.07217 0.07217 0.07217
21hx 14 3 x14 3%x14 4 x14 5 x14 6 x 14 8 x14
0.6250 0.7500 0.8750 1.0000 1.2500 1.5000 2.000
795,800 954,900 1,114,000 1,273,000 1,592,000 1,910,000 2,546,000
0.732 0.879 1.025 1.172 1.465 1.758 2.344
0.2604 0.3750 0.5104 0.6667 1.042 1.500 2.667
0.7217 0.8660 1.010 1.155 1.443 1.732 2.309
0.003255 0.003906 0.004557 0.005208 0.006510 0.007812 0.01042
0.02604 0.03125 0.03646 0.04167 0.05208 0.0625 0.08333
. 0.07217 0.07217 0.07217 0.07217 0.07217 0.07217 0.07217 0.07217
%X%6 %x%o 1 X%6 l%x %0 2 X 0/10 2%x %0
0.1563 0.2344 0.3125 0.4688 0.6250 0.7813
199,000 298,400 397,900 596,900 795,800 994,800
0.183 0.275 0.366 0.549 0.732 0.916
0.01302 0.02930 0.05208 0.1172 0.1302 0.3255
0.1443 0.2165 0.2887 0.4330 0.5774 0.7217
0.001272 0.001907 0.002543 0.003815 0.005086 0.006358
0.008138 0.01221 0.01628 0.02441 0.03255 0.04069
0.09021 0.09021 0.09021 0.09021 0.09021 0.09021
3 x%o 3% X%6 4 X%6 5 X%6 6 x%o 8 X%6
0.9375 1.0938 1.2500 1.5625 1.8750 2.5000
1,194,000 1,393,000 1,592,000 1,989,000 2,387,000 3,183,000
1.099 1.282 1.465 1.831 2.197 2.930
0.4688 0.6380 0.8333 1.302 1.875 3.333
0.8660 1.010 1.155 1.443 1.732 2.309
0.007629 0.008901 0.01017 0.01272 0.01526 0.02035
0.04883 0.05697 0.06510 0.08138 0.09766 0.1302
0.09021 0.09021 0.09021 0.09021 0.09021 0.09021
%x% %x% 1 x% l%x% l%x% l%x% 2 x%
0.1875 0.2813 0.3750 0.4688 0.5625 0.6563 0.7500
238,700 358,200 477,500 596,900 716,200 835,600 954,900
0.220 0.330 0.439 0.549 0.659 0.769 0.879
0.01563 0.03516 0.06250 0.09766 0.1406 0.1914 0.2500
0.1443 0.2165 0.2887 0.3608 0.4330 0.5052 0.5774
0.002197 0.003296 0.004395 0.005493 0.006592 0.007690 0.008789
0.01172 0.01758 0.02344 0.02930 0.03516 0.04102 0.04688
0.1083 0.1083 0.1083 0.1083 0.1083 0.1083 0.1083
2%x% 2¥:ax % 3 x% 4 x% 5 x% 6 x% 8 x%
0.8438 0.9375 1.1250 1.5000 1.8750 2.2500 3.0000
1,074,000 1,194,000 1,432,000 1,910,000 2,387,000 2,865,000 3,820,000
0.989 1.099 1.318 1.758 2.197 2.637 3.515
0.3164 0.3906 0.5625 1.000 1.563 2.250 4.000
0.6495 0.7217 0.8660 1.155 1.443 1.732 2.309
0.009888 0.01099 0.01318 0.01758 0.02197 0.02637 0.03516
0.05273 0.05859 0.07031 0.09375 0.1172 0.1406 0.1875
0.1083 0.1083 0.1083 0.1083 0.J083 0.1083 0.1083
1 x1B P4x1B
172x1B 2
X1B
Inches
I
Note: (1), (2) see page 121.
120
0.3255 0.5625 0.8932 1.333 2.604 4.500 10.67 0.003255 0.01099 0.02604 0.08789 0.2083 0.4069 0.7031 1.117 1.667 3.255 5.625 13.33 0.003906 0.01318 0.03125 0.06104 0.1055 0.1675 0.2500 0.3560 0.4883 0.8438 2.000 3.906 6.750 16.00
tables and specifications - section VI
~
1
RECTANGULAR ALUMINUM BUS CONDUCTOR PHYSICAL PROPERTIES (1)
---1-I
~ Axis y-y
Axis x-x Size (Inches)
Cross Sectional Area Square Inches
Cir Mils
Weight(2) per foot (lbs.)
%:x3/z 1 X 3/z 1:J,i X 3/z 13/z X 3/z 1%: X 3/z 2 x 3/z
0.3750 0.5000 0.6250 0.7500 0.8750 1.0000
477,500 636,600 795,800 954,900 1,114,000 1,273,000
0.439 0.586 0.732 0.879 1.025 1.172
23/z 3 33/z 4 5 6 8
1.2500 1.500 1.750 2.000 2.500 3.000 4.000
1,592,000 1,910,000 2,228,000 2,546,000 3,183,000 3,820,000 5,093,000
1.465 1.758 2.051 2.344 2.930 3.515 4.687
%:x% 1X % 1:J,i X % 13/z X % 2 x%
0.4688 0.6250 0.7813 0.9375 1.2500
596,900 795,800 994,800 1,194,000 1,592,000
0.549 0.732 0.916 1.099 1.465
23/z X % 3 x% 4x% 5 x% )$ x% 8x%
1.5625 1.875C 2.5000 3.1250 3.7500 5.0000
1,989,000 2,387,000 3,183,000 3,979,000 4,775,000 6,366,000
1.831 2.197 2.930 3.662 4.394 5.859
1 x%: 1:J,i X %: 13/z X % 1%: X %: 2 X %: 23/z x%:
0.7500 0.9375 1.1250 1.3125 1.5000 1.8750
954,900 1,194,000 1,432,000 1,671,000 1,910,000 2,387,000
0.879 1.099 1.318 1.538 1.758 2.197
3 x% 4x% 5 X %: 6 X %: 8 X %:
2.2500 3.0000 3.7500 4.5000 6.0000
2,865,000 3,820,000 4,775,000 5,730,000 7,639,000
2.637 3.515 4.394 5.273 7.031
X X X X X X X
3/z 3/z 3/z 3/z 3/z 3/z 3/z
Moment of Inertia I (Inches)4
0.01758 0.04167 0.08138 0.1406 0.2233 0.3333 0.6510 1.125 1.786 2.667 5.208 9.000 21.33 0.02197 0.05208 0.1017 0.1758 0.4167 0.8138 1.406 3.333 6.510 11.25 26.67 0.06250 0.1221 0.2109 0.3350 0.5000 0.9766 1.688 4.000 7.813 13.50 32.00
Modulus S (Inches)8
Radius of Gyration r (Inches)
Moment of Inertia I (Inches)4
Section Modulus S (Inches)3
Radius of Gyration r (Inches)
0.04688 0.08333 0.1302 0.1875 0.2552 0.3333
0.2165 0.2887 0.3608 0.4330 0.5052 0.5774
0.007813 0.01042 0.01302 0.01563 0.01823 0.02083
0.03125 0.04167 0.05208 0.06250 0.07292 0.08333
0.1443 0.1443 0.1443 0.1443 0.1443 0.1443
0.5208 0.7500 1.021 1.333 2.083 3.000 5.333
0.7217 0.8660· 1.010 1.155 1.443 1.732 2.309
0.02604 0.03125 0.03646 0.04167 0.05208 0.06250 0.08333
0.1042 0.1250 0.1458 0.1667 0.2083 0.2500 0.3333
0.1443 0.1443 0.1443 0.1443 0.1443 0.1443 0.1443
0.05859 0.1042 0.1628 0.2344 0.4167
0.2165 0.2887 0.3608 0.4330 0.5774
0.01526 0.02035 0.02543 0.03052 0.04069
0.04883 0.06510 0.08138 0.09766 0.1302
0.1804 0.1804 0.1804 0.1804 0.1804
0.6510 0.9375 1.667 2.604 3.750 6.667
0.7217 0.8660 1.155 1.443 1.732 2.309
0.05086 0.06104 0.08138 0.1017 0.1221 0.1628
0.1628 0.1953 0.2604 0.3255 0.3906 0.5208
0.1804 0.1804 0.1804 0.1804 0.1804 0.1804
0.1250 0.2315 0.2813 0.4537 0.5000 0.7813
0.2887 0.3608 0.4330 0.5052 0.5774 0.7217
0.03516 0.04395 0.05273 0.06152 0.07031 0.08789
0.09375 0.1172 0.1406 0.1641 0.1875 0.2344
0.2165 0.2165 0.2165 0.2165 0.2165 0.2165
1.125 2.000 3.125 4.500 8.000
0.8660 1.155 1.443 1.732 2.309
0.1055 0.1406 0.1758 0.2109 0.2813
0.2813 0.3750 0.4688 0.5625 0.7500
0.2165 0.2165 0.2165 0.2165 0.2165
Section
.
(l) See page 2 for tensile, yield and elongation properties of aluminum bus bar conductor alloys. (2) Weight per foot based on a unit weight of O.097651bs. per cubic inch.
121
section VI - tables and specifications
RECTANGULAR ALUMINUM BUS CONDUCTOR. ELECTRICAL PROPERTIES D-C Resistance (Microhms per foot) at 70 C(2) at 20 C(1) Size (Inches)
60 cps Resistance (Microhms per foot at 70 C) (S)
D-C Current Rating (Amperes) (4) EC
57 EC
60 cps Current Rating (Amperes) (4) EC
57 EC
EC
57 EC
EC
57 EC
EC
57 EC
213.6 142.3 106.8 85.41 71.20 53.40
228.6 152.3 114.3 91.43 76.21 57.16
256.6 171.0 128.3 102.6 85.55 64.16
271.6 180.9 135.8 108.6 90.54 67.91
256.6 171.3 128.7 103.0 85.98 64.67
271.8 181.2 136.1 109.0 90.97 68.40
120 170 215 250 300 390
115 165 210 245 290 380
120 170 215 250 300 390
115 165 210 245 290 380
:lhx %6 %, x 0/16 1 X%6 1% x %6 1:lh x %0 2 X%6
142.3 94.95 71.20 56.95 47.46 35.60
152.3 101.6 76.21 60.96 50.80 38.11
171.0 114.1 85.55 68.43 57.02 42.77
180.9 120.7 90.54 72.42 60.35 45.27
171.3 114.4 85.98 68.98 57.53 43.37
181.2 121.1 90.97 72.91 60.87 45.88
155 210 270 310 375 480
150 205 260 300 365 465
155 210 270 310 375 475
150 205 260 300 365 460
:lhx% %,x% 1 x% 1% x % 1:lh x 1,4 2 x%
106.8 71.20 53.40 42.72 35.60 26.70
114.3 76.21 57.16 45.73 38.11 28.58
128.3 85.55 64.16 51.33 42.77 32.08
135.8 90.54 67.91 54.33 45.27 33.95
140.2 85.98 64.80 51.95 43.20 32.40
136.1 90.97 68.54 54.88 45.72 34.63
180 245 310 370 435 560
175 240 305 360 425 545
180 245 310 370 430 550
175 240 305 360 420 535
640 790 900 1020 1250 1470 1900
620 765 875 990 1210 1430 1850
630 775 880 990 1200 1400 1780
610 750 855 960 1170 1360 1730
210 280 350 490 630 720
205 270 340 475 610 700
210 280 350 485 620 705
205 270 340 470 600 685
:lhx1h %'x1h 1 x1h P4x1h
l:lhx1h 2
xl/s
25.66 21.39 18.33 16.04 12.83 10.69 8.Q20
27.16 22.63 19.40 16.98 13.58 11.32 8.488
26.48 22.25 19.25 17.00 13.93 11.86 9.246
27.93 23.54 20.30 18.00 14.67 12.45 9.676
2:lh x % 3 x% 3:lh x % 4 x% 5 x% 6 x% 8 x%
21.36 17.80 15.26 13.35 10.68 8.900 6.675
22.86 19.05 16.33 14.29 11.43 9.527 7.145
:lh x %6 %,X%6 1 X%6 1:lh x %6 2 X%6 2:lh x 0/16
85.41 56.95 42.72 28.48 21.36 17.09
91.43 60.96 45.73 30.48 22.86 18.29
3 X%6 3:lh x %6 4 X%6 5 X%6 6 X%6 8 X%6
14.24 12.21 10.68 8.544 7.120 5.340
15.24 13.06 11.43 9.146 7.621 5.716
17.11 14.67 12.83 10.27 8.555 6.416
18.11 15.52 13.58 10.87 9.054 6.791
18.14 15.70 13.91 11.42 9.795 7.635
19.04 16.53 14.66 12.04 10.29 8.000
890 1000 1150 1400 1650 2150
865 970 1120 1360 1600 2090
865 965 1100 1320 1540 1970
845 940 1080 1290 1500 1920
:lhx% %x% 1 x% 1:l4x % l:lhx% l%,x% 2 x%
71.20 47.46 35.60 28.48 23.73 20.34 17.80
76.21 50.80 38.11 30.48 25.40 21.77 19.05
85.55 57.02 42.77 34.22 28.51 24.44 21.39
90.54 60.35 45.27 36.21 30.18 25.86 22.63
85.98 57.53 43.37 34.94 29.28 25.30 22.35
90.97 60.87 45.88 36.89 30.92 26.71 23.54
230 310 390 460 540 600 705
225 300 380 445 525 585 680
230 310 385 455 535 590 690
225 300 380 440 520 575 670
2%x % 2:lhx% 3 x% 4 x% 5 x% 6 x% 8 x%
15.82 14.24 11.87 8.900 7.120 5.933 4.450
16.94 15.24 12.70 9.527 7.621 6.351 4.763
19.01 17.11 14.26 10.69 8.555 7.128 5.347
20.12 18.11 15.09 11.32 9.054 7.545 5.658
19.92 18.14 15.32 11.88 9.795 8.362 6.545
21.01 19.04 16.15 12.45 10.23 8.752 6.846
740 800 990 1270 1550 1820 2350
720 780 960 1230 1500 1770 2280
725 780 955 1200 1440 1680 2130
705 760 930 1170 1410 1640 2080
Notes: (1), (2), (3), (4) see page 123.
102.6 68.43 51.33 34.22 25.66 20.53
108.6 72.42 54.33 36.21 27.16 21.73
103.0 68.98 51.95 34.94 26.48 21.45
109.0 72.91 54.88 36.89 27.93 22.59
c'
tables and specifications - section VI
RECTANGULAR ALUMINUM BUS CONDUCTOR ELECTRICAL PROPERTIES i
D-O Resistance (Microhms per foot) at 70 0(2) at 200(1) Size (Inches)
EO
57 EO
EO
57 EO
60 cps Resistance (Microhms per foot at 70 0)(3) EO
57 EO
i
D-O Ourrent Rating (Amperes) (4) EO
I
I
60 cps Ourrent Rating (Amperes) (') 57 EO
57 EO
EO 360 445 530 615 685 795
350 435 520 600 665 775
%x1h 1 xlh l1.4xlh Ilhxlh l%xlh 2 xlh
35.60 26.70 21.36 17.80 15.26 13.35
38.11 28.58 22.86 19.05 16.33 14.29
42.77 32.08 25.66 21.39 18.33 16.04
45.27 33.95 27.16 22.63 19.40 16.98
43.37 32.82 26.48 22.35 19.25 17.00
45.88 34.65 27.93 23.48 20.30 17.96
360 450 540 630 700 820
350 440 525 610 680 800
2lhxlh 3 xlh 3lhxlh 4 xlh 5 xlh 6 xlh 8 xlh
10.68 8.900 7.629 6.675 5.340 4.450 3.338
11.43 9.527 8.166 7.145 5.716 4.763 3.573
12.83 10.69 9.166 8.020 6.416 5.347 4.011
13.58 11.32 9.701 8.488 6.791 5.658 4.245
13.91 11.88 10.39 9.319 7.718 6.609 5.173
14.66 12.45 10.92 9.761 8.081 6.903 5.391
930 1160 1300 1490 1800 2120 2740
900 1120 1260 1450 1750 2060 2660
890 1100 1220 1380 1650 1900 2410
865 1080 1190 1350 1610 1860 2360
%x% 1 x% l1.4x%· llhx% 2 x%
28.48 21.36 17.09 14.24 10.68
30.48 22.86 18.29 15.24 11.43
34.22 25.66 20.53 17.11 12.83
36.21 27.16 21.73 18.11 13.58
34.94 26.48 21.45 18.14 13.91
36.89 27.93 22.59 19.04 14.66
400 510 610 715 920
390 495 595 695 895
395 500 600 695 875
385 490 585 680 860
2lhx% 3 x% 4 x% 5 x% 6 x% 8 x%
8.544 7.120 5.340 4.272 3.. 560 2.670
9.146 7.621 5.716 4.573 3.811 2.858
10.27 8.555 6.416 5.133 4.277 3.208
10.87 9.054 6.791 5.433 4.527 3.395
11.42 9.864 7.763 6.437 5.539 4.356
12.04 16.29 8.000 6.759 5.795 4.549
1050 1300 1650 2030 2400 3100
1020 1260 1600 1970 2330 3010
990 1210 1500 1810 2110 2670
975 1180 1460 1760 2060 2600
1 x% l1.4x% 1lhx% l%x% 2 x% 2lhx%
17.80 14.24 11.87 10.17 8.900 7.120
19.05 . 15.24 12.70 10.89 9.527 7.621
21.39 17.11 14.26 12.22 10.69 8.555
22.63 18.11 15.09 12.94 11.32 9.054
22.25 18.05 15.26 13.34 11.90 9.838
23.48 19.04 16.12 14.05 12.47 10.29
560 670 790 870 1020 1160
545 650 770 845 990 1130
550 655 765 830 975 1080
535 635 745 810 945 1060
5.933 4.450 3.560 2.967 2.225
6.351 4.763 3.811 3.176 2.382
7.128 5.347 4.277 3.565 2.673
7.545 5.658 4.527 3.773 2.830
8.482 6.737 5.647 4.834 3.782
1450 1820 2230 2620 3400
1410 1770 2170 2550 3300
1330 1630 1950 2250 2860
1300 1580 1910 2220 2790
3 4 5 6 8
x% x% x% x% x%
(1) D-c resistance at 20 0 based on a minimum conductivity of 61 per cent lAOS at 20 0 for EO and 57 per cent at 20 0 for 57 EO. (2) D-c resistance at 70 0 is calculated from the 20 0 doc resistance values using the following thermal coefficients of resist~nce:
EO - 0.00403 at 20 0 57 EO - 0.00376 at 20 O. (3) A-c resistance values at 70 0 are calculated values using the
8.775 6.846 5.795 5.048 3.979
skin effect resistance ratios obtained from the curves on page 24. (4) A-c and doc current ratings are based on a 30 0 temperature rise over a 40 0 ambient temperature in still but unconfined air with a phase spacing of 18 inches. These ratings should be reduced for phase spacings less than 18 inches to compensate for proximity effect, see page 19. These data are approximate and subject to normal manufacturing tolerances. Data subject to change without notice.
123
section VI - tables and specifications
SOLID ROUND BUS CONDUCTOR EC.HI3 - 61 Per Cent Conductivity (lACS) PHYSICAL PROPERTIES :fominal Size (Inches)
(Sq. In.)
Weight (1) (Lbs/Ft)
Area (CirMil)
Section Modulus S (Inches) 3
-
Radius of Gyration (Inches)
% 1%2 %6 1%2
0.375 0.406 0.4375 0.469
140,625 165,039 191,406 219,726
0.1104 0.1296 0.1503 0.1726
0.1294 0.1519 0.1761 0.2023
0.0009707 0.001337 0.001798 0.002370
0.005177 0.006582 0.008219 0.01011
0.09375 0.1016 0.1094 0.1172
JI
0.500 0.531 0.5625 0.594
250,000 282,227 316,406 352,539
0.1964 0.2217 0.2485 0.2769
0.2300 0.2598 0.2912 0.3245
0.003068 0.003910 0.004914 0.006101
0.01227 0.01472 0.01747 0.02055
0.1250 0.1328 0.1406 0.1484
0.625 0.656 0:6875 0.719
390,625 430,664 472,656 516,602
0.3068 0.3382 0.3712 0.4057
0.3595 0.3963 0.4350 0.4754
0.007490 0.009104 0.01097 0.01310
0.02397 0.02775 0.03191 0.03645
0.1563 0.1641 0.1719 0.1797
0.750 0.781 0.8125 0.844 0.875
562,500 610,352 660,156 711,914 765,625
0.4418 0.4794 0.5185 0.5591 0.6013
0.5177 0.5618 0.6076 0.6552 0.7046
0.01553 0.01829 0.02139 0.02491 0.02877
0.04141 0.04682 0.05265 0.06193 0.06576
0.1875 0.1953 0.2031 0.2109 0.2188
0.9375 1.000 1.0469 1.0625 1.125
878,906 1,000,000 1,095,947 1,128,906 1,265,625
0.6903 0.7854 0.8608 0.8866 0.9940
0.8089 0.9203 1.009 1.039 1.165
0.03792 0.04909 0.05899 0.06256 0.07863
0.08090 0.09818 0.1127 0.1178 0.1398
0.2344 0.2500 0.2617 0.2656 0.2813
1.1875 1.250 1.3125 1.375
1,410,156 1,562,500 1,890,625
1.1075 1.2272 1.3530 1.4849
1.298 1.438 1.585 1.740
0.09761 0.1198 0.1457 0.1755
0.1644 0.1917 0.2220 0.2552
0.2969 0.3125 0.3281 0.3438
1.4375 1.5000 2.000
2,066,406 2,250,000 4,000,000
1.6230 1.7671 3.1416
1.902 2.071 3.681
0.2096 0.2485 0.7854
0.2916 0.3313 0.7854
0,3594 0.3750 0.5000
,2
1%2 %6 1%2
% 2%2 1116 2%2
% 2%2 1%6 2%2*
% 1%6 1 1%4 1116
*
1l1s 1%6
11,4 1%6 1% 17116 1~
2
Decimal Diameter (Inches)
Moment of Inertia I (Inches) 4
*
1,7~2,656
(1) Weights per foot are based on a unit weight of 0.09765 lbs. per cu. in.
* These sizes have the same diameter as IPS tubular conductor and can be substituted where greater current ratings are desired.
STANDARD TOLERANCES
Diameter (Inches)
Tolerances Plus or Minus (Inches)
0.375 to 0.500, Inc!. Over 0.500 to 1.000, Inc!. Over 1.000 to 1.500, Inc!.
0.0015 0.0020 0.0025
Length: - 0,
+ %inch, in lengths up to 12 feet, inc!.
Straightness: ~ inch maximum curvature (depth of arc) in any . 60 inch portion of total length.
tables and specifications - section VI
SOLID ROUND BUS CONDUCTOR EC-H13 - 61 Per Cent Conductivity ELECTRICAL PROPERTIES
Nominal Size (Inches)
D-C D-C Resistance Resistance at 20 C at 70 C (Microhms/ft) (Microhms/ft)
Approx. 60 cps A-CID-C Ratio at 70 C
60 cps A-C Resistance at 70 C (Microhms/ ft)
D-C Indoor Rating (Amperes)
120.90 103.14 88.82 77.29
145.26 123.92 106.72 92.86
1.0005 1.0007 1.0010 1.0013
145.33 124.01 106.82 92.98
0.1460 0.1581 0.1704 0.1826
101.3 99.50 97.79 96.19
225 250 275 300
165 180 200 220
165 180 200 220
67.99 60.30 53.73 48.18
81. 70 72.45 64.56 57.89
1.0017 1.0021 1.0026 1.0033
81.83 72.60 64.73 58.08
0.1947 0.2068 0.2190 0.2313
94.72 93.33 92.01 90.76
325 350 375 405
240 260 285 305
240 260 285 305
43.51 39.51 35.97 32.89
52.29 47.47 43.22 39.52
1.0040 1.0049 1.0058 1.0069
52.49 47.70 43.47 39.79
0.2434 0.2554 0.2677 0.2800
89.59 88.48 87.40 86.37
430 460 490 515
325 350 370 395
325 350 370 395
30.22 27.87 25.75 23.88
36.31 33.49 30.94 28.69
1.0082 1.0097 1.011 1.013
36.61 33.81 31.29 29.06
0.2921 0.3041 0.3164 0.3287
85.40 84.47 83.56 82.68
545 575 605 630
420 445 465 490
420 445 470 495
1%6 1 1%4 -x.
22.21 19.34 17.00 15.51
26.69 23.24 20.43 18.64
1.015 1.020 1.026 1.031
27.10 23.70 20.96 19.22
0.3407 0.3651 0.3894 0.4077
81.86 80.27 78.79 77.73
665 725 785 835
515 565 620 660
520 570 625 670
11'16 1JA, 1%6 * 1%
15.06 13.43 12.06 10.88
18.09 16.14 14.49 13.07
1.033 1.042 1.050 1.061
18.68 16.82 15.22 13.87
0.4137 0.4381 0.4624 0.4868
77.39 76.08 74.84 73.66
850 910 975 1030
670 725 780 830
685 740 800 855
11.86 10.80 9.885 9.079 5.106
1.073 1.086 1.105 1.122 1.325
12.73 11.73 10.92 10.17 6.765
0.5111 0.5354 0.5598 0.5841 0.7788
72.54 71.47 70.45 69.47 62.86
1100 1160 1220 1280 1725
885 940 990 1040 1440
915 980 1040 1110 1660
% 1%2 %6 1%2
liz 1%2 %6 1%2
%
2~b
11/16 2%2 % 2%2 1%6 2%2*
%
1%6 1% 1%6
llh 2
9.869 8.992 8.227 7.555 4.250
Resistance values are based on 61 per cent conductivity lACS for isolated conductors. A-c resistance includes skin effect only. The inductive reactance values in the above table are for a one foot spacing. To arrive at the total inductive reactance, the spacing factors as given on page 137 should be added to the above values. To convert these values to any other frequency, they should be multiplied by a ratio of the two frequencies, i.e., XL1
=X fo 60
Where: is the inductive reactance value desired at the frequency
X[,1
GMR (Inches)
Inductive 60 cps Reactance Current Rating at 60 cps (Amperes) 1Ft. Spacing Indoor (Microhms/ Outdoor ft) Rating I Rating
f·
Values of current carrying capacity are based on methods of calculation by Schurig & Frick, "Heating and Current Carrying Capacities of Bare Conductors for Outdoor Service," G.E. Review, Vol. 33, No.3, March, 1930, page 142. Outdoor ratings are given for a wind velocity of two feet per second, ambient air temperature of 40 C, conductor temperature of 70 C, (30 C rise) with a surface emissivity, e = 0.50. Indoor ratings are also calculated for a 30 C rise over an ambient temperature of 40 C in still but unconfined air and with a surface emissivity of e = 0.35. * These sizes have the same diameter as IPS tubular conductor and can be used where a greater current rating is desired.
125
section VI - tables and specifications
EXTRUDED ALUMINUM TUBING 6063·T6 Aluminum Alloy , PHYSICAL PROPERTIES Size of Tube (IPS)
Diameter of Tube (Inches) Outside
I
Inside
Wall Thickness (Inches)
Area Square (Inches)
Weight (Lbs./Ft.)
Moment of Inertia I (Inches) 4
Section Modulus S (Inches) 3
Radius of Gyration r
(Inches)
STANDARD PIPE SIZES
1h
0.675 0.840 1.050
0.493 0.622 0.824
0.091 0.109 0.113
0.167 0.250 0.333
0.196 0.294 0.390
0.0073 0.0171 0.0370
0.0216 0.0407 0.0705
0.2090 0.2613 0.3337
1 1*
1.315 1.660 1.900
1.049 1.380 1.610
0.133 0.140 0.145
0.494 0.668 0.800
0.580 0.785 0.939
0.0873 0.1947 0.3099
0.1328 ' 0.2346 0.3262
0.4205 0.5397 0.6226
2
2.375 2.875 3.500 4.000
2.067 2.469 3.068 3.548
0.154 0.203 0.216 0.226
1.075 1.704 2.228 2.680
1.262 2.002 2.617 3.147
0.6657 1.5300 3.0177 4.7877
0.5606 1.0649 1.7244 2.3938
0.7871 0.9474 1.1640 1.3370
4.500 5.000 5.563 6.625
4.026 4.506 5.047 6.065
0.237 0.247 0.258 0.280
3.174 3.688 4.300 5.581
3.729 4.333 5.051 6.556
7.2325 10.4433 15.1600 28.1400
3.2144 4.1773 5.4510 8.4960
1.5100 1.6830 1.8780 2.2450
1h
0.675 0.840 1.050
0.423 0.546 0.742
0.126 0.147 0.154
0.217 0.320 0.434
0.255 0.376 0.509
0.0086 0.0201 0.0448
0.0255 0.0478 0.0853
0.1991 0.2505 0.3214
1 1*
1.315 1.660 1.900
0.957 1.278 1.500
0.179 0.191 0.200
0.639 0.881 1.068
0.750 1.035 1.254
0.1056 0.2418 0.3912
0.1606 0.2913 0.4118
0.4066 0.5237 0.6052
2
2.375 2.875 3.500 4.000
1.939 2.323 2.900 3.364
0.218 0.276 0.300 0.318
1.477 2.254 3.016 3.678
1.735 2.647 3.543 4.321
0.8679 1.9264 3.8943 6.2800
0.7309 1.3397 2.2253 3.1400
0.7665 0.9241 1.1360 1.3070
4.500 5.000 5.563 6.625
3.826 4.290 4.813 5.761
0.337 0.355 0.375 0.432
4.407 5.180 6.112 8.405
5.178 6.086 7.180 9.874
9.6100 14.0532 20.6700 40.4900
4.2710 5.6212 7.4310 12.2200
1.4770 1.6470 1.8390 2.1950
%
%
11h
21h 3
31h 4
41h 5 6
EXTRA HEAVY PIPE SIZES
% %
I1h
21h 3
31h 4
41h 5 6
STANDARD TOLERANCES Nominal Pipe Size (Inches)
Allowable Deviation of Diameter at Any Point From Mean Diameter (Inches)
% to 1% inc!. 2 and over
0.031 ± 1 Per cent
+ 0.015, -
Wall Thickness: Allowable deviation of wall thickness at any point from nominal wall thickness: minus 12~ per cent. (This controls the minimum weight.)
126
Length: Allowable deviation from specified length: - O. (Lengths 20 feet and under.) Weight: Allowable deviation from nominal weight: (This controls maximum wall thickness.) NOTE:
+ ;4 inch,
+ 8 per cent.
See page 2 for tensile, yield, and elongation properties of 6063-T6.
tables and specifications - section VI
ELECTRICAL PROPERTIES EXTRUDED ALUMINUM TUBE 6063·T6 Aluminum Alloy - 53 Per Cent Typical Conductivity (lACS) STANDARD PIPE SIZES Size of Tube
(IPS)
D-C D-C Resistance Resistance at 70 C at 20 C (Microhms/ft) (Microhms/ft)
Approx. 60 cps A-C/D-C Ratio at 70 C
60 cps A-C Resistance at 70 C (Microhms/ft)
60 cps Current Rating (Amperes)
GMR (Inches)
Inductive Reactance at 60 cps l' Spacing (Microhms/ft)
Outdoor Rating
I
Indoor Rating
~
92.03 61.47 46.15
108.14 72.23 54.23
1.000 1.000 1.000
108.14 72.23 54.23
0.309 0.386 0.489
84.10 78.99 73.55
310 400 495
240 315 400
1 1*
31.11 23.01 19.21
36.55 27.04 22.57
1.000 1.000 1.000
36.55 27.04 22.57
0.617 0.783 0.901
68.21 62.73 59.51
650 810 930
535 680 790
2
14.30 9.019 6.898 5.735
16.80 10.60 8.105 6.739
1.000 1.000 1.0010 1.0020
16.80 10.60 8.113 6.752
1.137 1.376 1.679 1.919
54.16 49.77 45.20 42.13
1155 1550 1895 2170
1000 1365 1670 1945
4.842 4.167 3.574 2.754
5.689 4.896 4.199 3.236
1.0027 1.0035 1.0045 1.0065
5.704 4.913 4.218 3.257
2.168 2.442 2.699 3.230
39.33 36.59 34.29 30.16
2460 2750 3080 3735
2230 2515 2845 3500
%
%
1~
2~
3 3~
4 4~
5 6
EXTRA HEAVY PIPE SIZES
~
70.82 48.03 35.41
83.21 56.44 41.61
1.000 1.000 1.000
83.21 56.44 41.61
0.298 0.374 0.476
84.93 79.72 74.17
350 455 565
270 360 455
1 1*
24.05 17.44 14.39
28.26 20.49 16.91
1.000 1.0012 1.0014
28.26 20.51 16.93
0.600 0.768 0.885
68.85 63.18 59.92
740 930 1070
605 780 910
2
10.41 6.818 5.096 4.179
12.23 8.011 5.988 4.910
1.0017 1.0062 1.0098 1.0120
12.25 8.061 6.047 4.969
1.116 1.348 1.652 1.896
54.59 50.25 45.57 42.41
1355 1780 2195 2530
1175 1570 1935 2265
3.487 2.967 2.515 1.829
4.097 3.486 2.955 2.149
1.0165 1.0205 1.0255 1.0460
4.165 3.557 3.030 2.248
2.139 2.378 2.660 3.170
39.64 37.20 34.63 30.59
2880 3230 3635 4490
2605 2955 3355 4205
%
%
11!z
21!z 3
31!z 4
4Vz 5 6
Resistance values are based on 53 per cent conductivity (lACS) which is the typical conductivity for extruded 6063-T6 tubular bus bar. The inductive reactance values in the above table are for a one foot spacing. To convert these values to any other frequency, they should be multiplied by a ratio of the two frequencies, i.e., .
X L1
=X :0 so
Where: XL1 is the inductive reactance value desired at the frequency f.
Values of current carrying capacity are based on methods of calculation by Schurig & Frick, "Heating and Current Carrying Capacities of Bare Conductors for Outdoor Service," G.B. Review, Vol. 33, No.3, March, 1930, page 142. Outdoor ratings are given for a wind velocity of two feet per second, ambient air temperature of 40 C, conductor temperature of 70 C, (30 C rise) with a surface emissivity, e = 0.50. Indoor ratings are also calculated for a 30 C rise over an ambient temperature of 40 C in still but unconfined air and with a surface emissivity of, e 0.35.
=
127
section VI - tables and specifications
ROUND TUBULAR BUS BAR DEFLECTIONS AND STRl!:SSES Standard Iron Pipe Sizes SPAN IN FEET
%
*
*/1 ice 8# wind ..... 1/1 ice ...............
1360 6430 10070 15810
bare ................. l/~/1 ice ............... W' ice 8# wind ..... 1/1 ice ...............
0.02 0.09 0.13 0.21
270 1040 1535 2380
0.39 1.48 2.19 3,40
1085 4150 6135 9515
0.24 0.82 1.17 1.79
830 2880 4095 6255
1.20 4.17 5.92 9.05
1870 6485 9215 14080
-
-
-
-
0.15 0.44 0.59 0.89
655 1930 2600 3910
0.76 2.23 3.00 4.51
14·75 4345 5855 8795
2.39 7.05 9.50 14.27
2620 7725 10405 15635
-
0.09 0.25 0.32 0.47
500 1360 1770 2615
0.46 1.25 1.62 2.40
1130 3065 3985 5890
1.45 3.94 5.12 7.57
2010 5445 7090 10470
-
0.07 0.18 0.23 0.33
430 1120 1430 2090
0.35 0.89 1.14 1.67
970 2515 3215 4705
1.09 2.83 3.61 5.28
1725 4475 5715 8365
0.04 0.10 0.13 0.18
335 815 1015 1460
0.22 0.52 0.65 0.93
760 1835 2280 3290
0.68 1.65 2.05 2.95
1350 3265 4055 5845
0.03 0.06 0.07 0.10
280 575 685 960
0.15 0.31 0.36 0.51
635 1300 1535 2165
0.47 0.96 1.14 1.61
1130 2310 2730 3845
0.02 0.04 0.04 0.06
225 445 515 715
0.10 0.19 0.22 0.31
510 1000 1160 1610
0.31 0.61 0.71 0.98
910 1775 2060 2860
+
-
;2" ice ...............
bare .................
-
ice 8# wind ..... 1/1 ice ...............
-
-
-
-
+
bare ................. 12/1 ice ............... W' ice 8# wind ..... 1/1 ice ............... bare ............... ,. 112/1 ice ............... 112/1 ice 8# wind ..... I" ice ............... bare ................. 12/1 ice ............... W' ice 8# wind ..... 1/1 ice ............ " . bare ................. 112/1 ice ............... W' ice 8# wind ..... 1/1 ice ............... bare ................. ice ............... l/:!" ice 8# wind ..... 1" ice .....•.........
+
bare .................
Ih ice ............... W' ice + 8# wind ..... ll
1/1 ice ...............
4
bare ................. 12/1 ice ............... W' ice 8# wind ..... 1/1 ice ...............
+
4%
6
--
-
---
.-
-
-
-
--
-
-
--
-
-
-
-
-
-
-
-
195 370 425 585
0.07 0.14 0.16 0.22
445 840 960 1320
0.24 0.45 0.51 0.70
790 1490 1710 2350
-
0.01 0.02 0.02 0.03
175 320 360 495
0.06 0.11 0.12 0.17
390 720 815 1110
0.19 0.34 0.39 0.53
695 1275 1450 1975
0.01 0.02 0.02 0.03
155 280 315 425
0.05 0.08 0.10 0.13
350 625 705 955
0.15 0.27 0.30 0,41
620 1115 1255 1695
0.01 0.01 0.01 0.02
140 240 270 365
0.04 0.07 0.07 0.10
315 545 610 820
0.12 0.21 0.23 0.31
555 970 1085 1455
0.01 0.01 0.01 0.01
115 195 215 285
0.03 0.04 0.05 0.06
260 435 480 635
0.08 0.14 ·0.15 0.21
465 775 855 1135
---
-
-
-
-
bare ................. • lce ............... W' ice 8# wind ..... 1/1 ice ...............
-
-
-
-
-
... -
-
..-
-
-
-
-
--
The tabulated deflections are for single span, simply supported buses. Deflcctions for fixed end buses are one-fifth of the values given above, and the deflections for continuous buses for the center spans are also one-fifth of the values above. The deflections for
128
-
-
0.01 0.03 0.03 0.04
-
+
-
-
-
-
-
-
bare ................. 112/1 ice ............... W' ice 8# wind ..... 1/1 ice ...............
-
_. -
-
-
bare ................. 1/2" ice ............... W' ice 8# wind ..... 1/1 ice ...............
+
-
-
-
-
lL 72 /I
-
(psi)
-
-
--
+
5
-
bare ................. ¥2/1 ice ............... l/:!" ice 8# wind ..... 1/1 ice ...............
~~/1
312
-
0.60 2.86 4,48 7.03
ice ...............
+
3
--
340 1605 2515 3950
bare ................. ~2"
+
212
-
0.04 0.18 0.28 0.44
J6bading
+
2
Stress
Stress (psi)
+
1*
Deflection (Inches)
Deflection (Inches)
W'
1%
Stress (psi)
Stress (psi)
+
1
Deflection (Inches)
Deflection (Inches)
+
%
20
15
10
5 IPS Size (Inches)
the end spans are two-fifths of the values given, see page 65. The stresses given in the above table are the stresses in the outer fibres as calculated for the simply supported beams. with a uniformly distributed load.
tables and specifications - section VI
ROUND TUBULAR BUS BAR DEFLECTIONS AND STRESSES Standard Iron Pipe Sizes (Continued) SPAN IN FEET
Deflection (Inches)
-
-
-
--
-
-
-
-
Stress (psi)
-
-
-
-
Deflection (Inches)
Stress (psi)
Deflection (Inches)
Stress (psi)
Deflection (Inches)
Stress (psi)
Deflection (Inches)
Stress (psi)
-
-
-
-
-
-
--
-
-
-
-
-
-
-
-
-
3.54 9.61 12.51 18.48
3135 8510 11075 16360
2.66 6.90 8.81 12.90
2700 6990 8930 13070
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
--
-
-
2790 5440 6310 8755
5.00 9.74 11.30 15.68
3640 7105 8240 11435
2415 4565 5230 7190
3.79 7.15 8.20 11.27 2.97 5.45 6.18 8.42
3155 5960 6835 9390
2.39 4.28 4.81 6.51
1.15 2.36 2.78 3.92
3455 7080 8370 11780
0.76 1.49 1.72 2.39
1425 2775 3220 4465 1230 2330 2670 3670
1.58 3.08 3.58 4.96 1.20 2.26 2.59 3.57
2050 3995 4635 6430 1775 3355 3845 5280
2.93 5.71 6.62 9.19 2.22 4.19 4.81 6.61
1090 1995 2265 3085 970 1740 1960 2650 870 1520 1695 2275 725 1210 1335 1770
0.94 1.72 1.96 2.66 0.76 1.35 1.52 2.06
1565 2870 3260 4440
1.74 3.19 3.62 4.93
2130 3910 4435 6045
1400 2505 2820 3810
1.40 2.51 2.82 3.81
0.61 1.06 1.18 1.59 0.42 0.71 0.78 1.04
1250 2185 2440 3275 1040 1745 1925 2550
1.12 1.96 2.19 2.94 0.79 1.32 1.45 1.92
1905 3410 3840 5190 1705 2975 3320 4455 1420 2375 2615 3470
-
-
--
-
4.42 9.05 10.70 15.06
0.20 0.34 0.38 0.50
-
-
1765 3610 4270 6010
0.29 0.51 0.57 0.77
-
-'
-
0.36 0.65 0.73 0.99
-
-
-
0.58 1.09 1.25 1.72 0.45 0.83 0.94 1.28
-
-
-
3040 7345 9125 13150 2540 5200 6150 8655
2110 5100 6340 9135
--
-
-
-
-
-
3.45 8.35 10.38 14.95 2.38 4.89 5.77 8.13
1.67 4.03 5.00 . 7.21
50
45
40
35
30
25
-
The tabulated deflections are for single span, simply supported buses. Deflections for fixed end buses are one-fifth of the values given above, and the deflections for continuous buses for the center spans are also one-fifth of the values above. The deflections for
-
-
-
-
-
-
-
-
-
-
--
-
-
3995 7545 8650 11885
1.92 3.35 3.74 5.02
2490 4455 5015 6780 2225 3885 4335 5820
6.06 11.46 13.14 18.05 4.76 8.72 9.90 13.49 3.83 6.85 7.71 10.42 3.07 5.37 5.99 8.04
1.34 2.25 2.48 3.28
1850 3105 3420 4530
2.15 3.60 3.97 5.26
2345 3930 4325 5735
2785 5105 5795 7895
3525 6465 7335 9990 3150 5640 6345 8580 2815 4920 5490 7365
Deflection (Inches)
Stress (psi)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
7.25 13.30 15.09 20.55 5.83 10.44 11.75 15.89 4.69 8.L8 9.13 12.26 3.28 5.49 6.05 8.02
-
-
-4350 7980 9055 12330 3890 6960 7835 10590 3475 6070 6775 9095 2895 4850 5340 7080
the end spans are two-fifths of the values given, see page 65. The stresses given in the above table are the stresses in the outer fibres as calculated for the simply supported beams with a uniformly distributed load.
129
section VI - tables and specifications
ROUND TUBULAR BUS BAR DEFLECTIONS AND STItESSES Extra-Heavy Pipe Sizes SPAN IN FEET 10
5 IPS Size (Inches)
%
Loading
Stress (psi)
Deflection (Inches)
Stress (psi)
bare ................. ;2" ice ............... ;2:: ~ce 8# wind ..... 1 lce ...............
0.04 0.16 0.24 0.38
375 1450 2180 3440
0.67 2.58 3.88 6.12
1500 5805 8730 13770
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
0.03 0.08 0.12 0.18
295 945 1350 2090
0.12 1.35 1.93 2.98
1180 3790 5400 8355
+
*
+
%
bare ............. ;2" ice ............... 12" ice 8# wind ..... 1" ice . ..............
+
1
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
+
114
-
-
0.26 0.74 1.01 1.54
895 2590 3530 5375
1.29 3.75 5.11 7.78
2015 5825 7945 12100
-
-
-
-
0.16
700 1755 2270 3390
0.81 2.03 2.62 3.92
1575 3950 5110 7630
2.56 6.41 8.29 12.38
2800 7020 9085 13560
0.19 2.05
1200 2755 3435 5035
1.54 3.54 4.42 6.47
2130 4900 6110 8945
-
-
0.10
-
-
0.52 0.77
-
-
0.10 0.22 0.28
-
-
1825 4005 4895 7085
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice . ..............
-
-
-
-
-
0.04 0.09 0.11 0.15
355 725 860 1220
0.23 0.46 0.55 0.78
800 1625 1930 2740
1425 2890 3430 4870
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
-
-
-
0.03 0.06 0.06 0.09
295 530 600 835
0.16 0.28 0.32 0.44
665 1195 1360 1880
0.72 1.46 1.73 2.46 0.49 0.89 1.01
lAO
1185 2125 2420 3345
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
-
-
0.02 0.03 0.04 0.05
240 405 455 615
0.10 0.18 0.20 0.27
535 915 1020 1385
0.33 0.56 0.62 0.85
955 1625 1815 "\ 2465
0.02 0.03 0.03 0.04
205 340 375 505
0.08 0.13 0.14 0.19
465 765 845 1133
0.25 0.41 0.45 0.60
825 1360 1500 2015
0.01 0.02 0.02 0.03
180 290 320 420
0.06 0.10 0.11 0.14
410 655 715 950
0.19 0.31 0.34 0.45
725 1165 1270 1690
0.01 0.02 0.02 0.02
160 255 275 360
0.05 0.08 0.08 0.11
365 570 620 815
0.16 0.24 0.26 0.35
650 1015 1100 1445
0.01 0.01 0.01 0.02 0,01 0,01 0.01 0,01
145 220 240 310
0.04 0.06 0.06 0.08
325 495 535 695
0.13 0.19 0.21 0.27
580 885 950 1240
120 175 185 240
0.03 0.04 0.04 0.05
275 395 420 535
0.09 0.13 0.13 0.17
485 700 745 950
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ........ , ......
-
-
-
-
.-
-
-
-
-
-
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ............ , .,
-
-
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
--
-
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ............... bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...............
+
-
-
-
-
-
---
-
The tabulated deflections are for single span, simply supported buses. Deflections for fixed end buses are one-fifth of the values given above, and the deflections for continuous buses for the center spans are also one-fifth of the values above. The deflections for
130
-
1.15 2.53 3.09 4.47
+
6
-
-
-
1030 2250 2755 3985
+
5
-
0.37 0.80 0.98 1.42
+
4;2
-
-
--
455 1000 1225 1770
+
4
---
-
-
0.07 0.16 0.19 0.28
+
3;2
-
-
-
-
-
Stress (psi)
-
bare ................. ~2" ice ............... 12" ice 8# wind ..... 1" ice ...............
+
3
-
-
-
Deflection (Inches)
0.10
+
2*
-
20 Stress (psi)
-
+
2
Deflection (Inches)
535 1225 1530 2235
bare ................. ;2" ice ............... 12" ice 8# wind ..... 1" ice ...... " .......
+
1;2
15
Deflection (Inches)
1.12
lAO
the end spans are two-fifths of the values given, see page 65. The stresses given in the above table are the stresses in the outer fibres as calculated for the simply supported beams with a uniformly distributed load.
tables and specifications - section VI
ROUND TUBULAR BUS BAR DEFLECTIONS AND STRESSES Extra.Heavy Pipe Sizes (Continued) SPAN IN FEET 25 Stress (psi)
-
-
-
--
-
-
-
.-
-
Deflection (Inches)
-
-
-
-
-
-
-
-
2855 6255 7645 11070 2225 4520 5360 7610
-
2.82 6.17 7.55 10.92 \ 1.76 3.57 4.23 6.01 1.21 2.17 2.46 3.41 0.80 1.36 1.52 2.06 0.60 1.00 1.10 1.48 0.47 0.76 0.83 1.10 0.38 0.59 0.65 0.85 0.31 0.47 0.50 0.65 0.21 0.31 0.33 0.42
-
1850 3320 3780 5225 1495 2540 2840 3850 1290 2125 2345 3145 1135 1820 1990 2640 1015 1585 1720 2260 905 1380 1490 1935 755 1095 1165 1485
-
-
-
-
2.50 4.49 5.11 7.07 1.66 2.82 3.15 4.28 1.25 2.07 2.28 3.06 0.98 1.57 1.72 2.28 0.79 1.23 1.34 1.76 0.63 0.97 1.04 1.35 0.44 0.64 0.68 0.87
Stress (psi)
Deflection (Inches)
Stress (psi)
-
-
-
-
-
-
-
-
-
-
--
-
-
-
-
-
-
-
-
-
-
-
-
-
2665 4780 5440 7525 2150 3660 4085 5545 1860 3060 3380 4530 1635 2620 2865 3800 1460 2285 2475 3255 1305 1990 2140 2785 1090 1580 1675 2140
-
-
-
-
-
-
-
3.07 5.23 5.84 7.93 2.32 3.83 4.23 5.67 1.82 2.91 3.18 4.22 1.46 2.28 2.48 3.26 1.17 1.79 1.93 2.51 0.82 1.19 1.27 1.61
Deflection (Inches)
--
-
50
45
40
35
30
Deflection (Inches)
Stress
(psi)
-
-
-
-
-
-
Deflection (Inches)
Stre.. (psi)
-
-
-
-
-
-
-
-
-
-
-
-
Deflection (Inches)
-
Stress (psi)
-
-
-
-
-
-
-
-
-
--
-
-
-
-
-
-
-
-
-
-
-
-
-
-
2925 4980 5560 7550 2530 4165 4600 6170 2230 3565 3900 5170 1990 3110 3370 4430 1775 2710 2915 3795 1485 2150 2280 2910
The tabulated deflections are for single span, simply supported buses. Deflections for fixed end buses are one-fifth of the values given above, and the deflections for continuous buses for the center spans are also one-fifth of the values above. The deflections for
-
3.96 6.53 7.21 9.67 3.10 4.97 5.43 7.20 2.49 3.90 4.23 5.55 2.00 3.05 3.29 4.28 1.40 2.04 2.16 2.75
-
-
-
-
-
-
-
3305 5440 6010 8055 2910 4655 5095 6755 2600 4060 4405 5785 2320 3535 3810 4955 1940 2810 2980 3800
-
-
.-
-
-
-
-
-
-
-
---
-
--
-
4.97 7.96 8.70 11.54 4.00 6.24 6.77 8.90 3.20 4.89 5.26 6.85 2.25 3.26 3.46 4.41
-
-
-
-
-
-
-
3680 5895 6445 8550 3290 5135 5575 7320 2935 4475 4820 6270 2455 3555 3775 4810
-
-
-
-
-
-
-
-
-
7.58 12.13 13.26 17.59 6.09 9.51 10.32 13.56 4.88 7.45 8.02 10.44 3.43 4.97 5.27 6.72
-
-
-
-
-
-
-
-
-
-
-
-
-
-_. --
-
4545 7275 7955 10555 4060 6340 6880 9040 3625 5525 5950 7745 3030 4390 4660 5940
the end spans are two-fifths of the values given, see page 65. The stresses given in the above table are the stresses in the outer fibres as calculated for the simply supported beams with a uniformly distributed load.
131
'iii
r-f;l
ALUMINUM CHANNEL BUS CONDUCTORS (Physical Characteristics of Single Chann.el Sections) Axisx-x Channel Size
Web Thickness t (Inche~)
Flange Width b (Inches)
Inner Flat Surface c (Inches)
.... ~
ErE t ---JxL--I Iy
(Inches)
(Inches)
3 3 3
1.42 1.73 2.07
1.21 1.47 1.76
0.170 0.258 0.356
1.410 1.498 1.596
1% 1% 1%
1.66 1.85 2.07
1.10 1.24 1.38
1.17 1.12 1.08
0.20 0.25 0.31
0.20 0.23 0.27
0.40 0.41 0.42
0.44 0.44 0.46
4 4 4
1.85 2.16 2.50
1.57 1.84 2.13
0.180 0.247 0.320
1.580 1.647 1.720
2% 2% 2%
3.83 4.19 4.58
1.92 2.10 2.29
1.56 1.51 1.47
0.32 0.37 0.43
0.28 0.31 0.34
0.45 0.45 0.45
0.46 0.45 0.46
5 5 5
2.32 3.11 3.97
1.97 2.64 3.38
0.190 0.325 0.472
1.750 1.885 2.032
3% 3% 3%,
7.49 8.90 10.43
3.00 3.56 4.17
1.95 1.83 1.76
0.48 0.63 0.81
0.38 0.45 0.53
0.49 0.49 0.49
0.48 0.48 0.51
6 6 6
3.00 3.63 4.48
2.55 3.09 3.82
0.225 0.314 0.437
1.945 . 2.034 2.157
4% 4% 41h
13.57 15.18 17.39
4.52 5.06 5.80
2.31 2.22 2.13
0.73 0.87 1.05
0.51 0.56 0.64
0.54 0.53 0.52
0.51 0.50 0.50
7 7 7
4.23 5.10 5.96
3.60 4.33 5.07
0.314 0.419 0.524
2.194 2.299 2.404
5% 51h 51h
24.24 27.24 30.25
6.93 7.78 8.64
2.60 2.51 2.44
1.17 1.38 1.59
0.70 0.78 0.86
0.57 0.56 0.56
0.52 0.53 0.55
8 8 8
4.75 5.62 6.80
4.04 4.78 5.78
0.303 0.395 0.520
2.343 2.435 2.560
6~ 6~
614
36.11 40.04 45.37
9.03 10.01 11.34
2.99 2.90 2.80
1.53 1.75 2.07
0.85 0.93 1.04
0.61 0.61 0.60
0.55 0.55 0.57
10 10 10
8.58 9.32 10.05
7.30 7.93 8.55
0.375 0.438 0.500
3.500 3.563 3.625
7% 7% 7%
109.62 114.87 120.03
21.92 22.97 24.01
2.88 3.81 3.75
7.19 7.73 8.25
2.80 2.93 3.04
0.99 0.99 0.98
0.93 0.92 0.91
12 12 12
8.64 10.37 12.10
7.35 8.82 10.29
0.387 0.510 0.632
3.047 3.170 3.292
144.37 162.08 179.65
24.06 27.01 29.94
4.43 4.29 4.18
4.47 5.14 5.82
1.89 2.06 2.24
0.78 0.76 0.75
0.67 0.67 0.69
Section Area (lnches) 2
10 10 10
Moment of Inertia Ix-x (Inches)4
Section Modulus s (Inches)3
r
See page 2 for the physical characteristics of aluminum alloys for channel bus conductors.
Section Modulus s (Inches)"
c;-
~ l::. ~
~ <:':>
Distance toy-y Axis x (Inches)
Weight per foot (Lbs.)
I ~
C'>
Moment of Inertia Iy-) (Inches 4
Depth d (Inches)
:::;
~
Axis y-y Radius of Gyration
g'
Radius of Gyration r
'3;
g,
g'
'"
f--w-l ir---J
~
~
DOUBLE ALUMINUM CHANNEL BUS CONDUCTORS ELECTRICAL CHARACTERISTICS Aluminum Alloys - EC, 57EC, 6063.T6, and 606!.T6 DOlible Channel D-C Resistance"" (Microhms per foot)
Double Channel Channel Size 1nches-lbs/ foot
Depth d (lnches)
Width"""
at 20 C
w
(lnches)
EC
D-C Current Carrying Capacity* (amperes)
at 70 C EC
57 EC
6063-T6
6061-T6
EC
57EC
6063-T6
60 Cycle A-C Current Carrying Capacity" (amperes) EC
57 EC
6063-T6
6061-T6
2360 2610 2830
2290 2530 2770
2220 2450 2710
1980 2200 2430
2450 2640 2890
2890 3080 3330
2810 3010 3250
2690 2910 3170
2400 2590 2830
3350 3890 4390
2960 3440 3890
3470 3940 4290
3370 3850 4190
3260 3730 4100
2900 3340 3700
4210 4640 5160
4080 4500 5010
3610 3980 4430
4190 4550 4950
4090 4440 4840
3950 4280 4630
3520 3830 4180
5480 6020 6510
5330 5850 6330
5170 5680 6140
4570 5020 5430
5180 5560 5820
5060 5430 5710
4910 5250 5540
4390 4710 5000
2.854 2.412 1.995
6130 6670 7330
5950 6480 7130
5780 6290 6910
5110 5560 6110
5790 6160 6510
5650 6010 6370
5420 5720 6210
4840 5150 5610
1.056
1.579 1.454 1.343
9140 9520 9890
8870 9250 9610
8620 8980 9330
7620 7940 8250
8240 8350 8540
8040 8180 8360
7740 7950 8120
6990 7200 7370
1.229 1.024 0.8775
1.569 1.307 1.121
9100 10,000 11,000
8840 9710 10,680
8580 9430 10,370
7590 8340 9170
8200 8610 9100
8010 8410 8840
7760 8250 8620
6930 7380 7870
6061-T6
3 3 3 -
1.42 1.73 2.07
3 3 3
39h.6 315h.6 31%6
5.517 4.541 3.793
6.629 5.456 4.557
7.015 5.774 4.823
7.463 6.143 5.131
9.528 7.843 5.131
2400 2680 2970
2330 2600 2870
2260 2530 2800
2000 2240 2480
4 4 4 -
1.85 2.16 2.50
4 4 4
4~16
40/16 4%
4.252 3.628 3.134
5.109 4.359 3.766
5.407 4.613 3.985
5.752 4.908 3.985
7.343 6.266 5.413
2940 3170 3460
2860 3090 3360
2770 2990 3260
5 5 5 -
2.32 3.11 3.97
5 5 5
5 5 5
3.388 2.528 1.975
4.071 3.037 2.373
4.309 3.215 2.511
4.584 3.420 2.672
5.852 4.367 3.411
3550 4120 4660
3450 4000 4530
6 6 6 -
3.00 3.63 4.48
6 6 6
6 6 6
2.618 2.160 1.747
3.146 2.595 2.099
3.329 2.743 2.222
3.541 2.922 2.364
4.521 3.731 3.018
4330 4770 5310
7 7 7 -
4.23 5.10 5.96
7 7 7
7 7 7
1.854 1.542 1.317
2.228 1.853 1.582
2.358 1.960 1.674
2.508 2.085 1.781
3.202 2.663 2.274
8 8 8 -
4.75 5.62 6.80
8 8 8
8 8 8
1.652 1.396 1.155
1.985 1.677 1.388
2.101 1.776 1.469
2.235 1.889 1.562
10 - 8.58 10 - 9.32 10 -10.05
10 10 10
10 10 10
0.9144 0.8417 0.7807
1.099 1.011 0.9380
1.163 1.070 0.9928
1.237
12 - 8.64 12 -10.37 12 -12.10
12 12 12
9 9 9
0.9082 0.7568 0.6487
1.091 0.9093 0.7794
1.155 0.9624 0.8249
1.1 ~19
- - -- - -- - -- - -
~
tr'
~
£::
5.. ~ ('> C>
~
V:> V:>
*Current ratings are for a 30 C temperature rise over 40 C ambient temperature in still, but unconfined air. These ratings correspond to indoor current ratings with emissivity of conductor surfaces 0.35. **The following per cent (lACS) conductivities were used to determine re-
sistance and current ratings: EC-61 per cent; 57 EC-57 per cent; 6063-T6-53 per cent; 6061-T6--40 per cent. ***Width detennined by standard spacer support.
-;:l;
§.
o' ~ I
'"'""'" C>
o'
;:l
~ ......
f-'
~~ g ;:5
W
>I>-
I
Er (3""
f
~
ALUMINUM ANGLE BUS CONDUCTORS (Physical Characteristics of Single Angle Sections) Weight j,er oot (Lbs.)
Section Area (Inches) 2
2%x2 2%x 2
1.26 1.83
1.07 1.55
2%x2% 2lhx2%
1.40 2.05
1.19 1.74
3 3 3
x3 x3 x3
1.68 2.47 3.23
1.43 2.10 2.74
4 4 4 4
x3 x3 x3 x3
1.99 2.93 3.83 4.69
1.69 2.49 3.25 3.99
4 4 4 4
x4 x4 x4 x4
2.28 3.38 4.41 5.42
1.94 2.86 3.75 4.61
5 5 5
x3% x3% X 3%
3.58 4.70 5.79
3.05 4.00 4.92
4.24 5.58 6.88
3.60 4.74 5.85
6 x4 6 x4 6 x4
Thickness t (Inches)
1A % 1A % 1A % %
1A % %
% 1A % %
% % lh
% % lh
%
Section Modulus s (Inches)"
Radius of Gyration r (Inches)
Distance tox-x axis
:Jh :Jh :Jh % 1A 1A 1A 1A 1A 1A 1A 1A 1A 1A 1A
0.65 0.91
0.38 0.54
0.78 0.76
0.69 0.98
0.39 0.56
1.18 1.70 2.16
Radius of Gyration r (Inches)
Distance toy-;-y
(In!hes)
Section Modulus s (Inches)'
0.78 0.83
0.37 0.51
0.25 0.36
0.58 0.57
0.53 0.58
0.76 0.75
0.71 0.76
0.69 0.98
0.39 0.56
0.76 0.75
0.71 0.76
0.54 0.80 1.04
0.91 0.90 0.89
0.82 0.87 0.92
1.18 1.70 2.16
0.54 0.80 1.04
0.91 0.90 0.89
0.82 0.87 0.92
2.613 3.88 4.96 5.95
0.96 1.42 1.85 2.25
1.26 1.25 1.24 1.22
1.21 1.26 1.31 1.36
1.29 1.86 2.36 2.82
0.56 0.83 1.08 1.32
0.87 0.86 0.85 0.84
0.72 0.77 0.82 0.86
2.94 4.26 5.46 6.56
1.00 1.48 1.93 2.36
1.23 1.22 1.21 1.19
1.07 1.12 1.17 1.22
2.94 4.26 5.46 6.56
1.00 1.48 1.93 2.36
1.23 1.22 1.21 1.19
1.07 1.12 1.17 1.22
l}16 l}16 l}16
7.56 9.77 11.82
2.21 2.90 3.56
1.58 1.56 1.55
1.58 1.63 1.68
3.04 3.91 4.70
1.15 1.50 1.84
1.00 0.99 0.98
0.84 0.89 0.94
% % %
13.02 16.95 20.63
3.17 4.19 5.17
1.90 1.89 1.88
1.90 1.96 2.01
4.63 6.01 7.27
1.50 1.98 2.44
1.13 1.13 1.11
0.91 0.97 1.02
1A
1A 1A 5;16 l}16 l}16 % % % % % % % % 'K6 'K6 'K6 1,6 % 1,6
§.
Moment of Inertia Iy-y (Inches)'
Corner Radius f2 (Inches)
1,4
C'>
Axis y-y
Moment of Inertia Ix-x (Inches)'
Inside Radius h (Inches)
---
'"
-;i;
Axisx-x
Angle Size Length of Legs (Inches)
Co
""tl
See page 2 for the physical characteristics of aluminum alloys for angle bus conductors.
axIS
x (Inches)
c' 1:;
COWl DOUBLE ALUMINUM ANGLE BUS CONDUCTORS (Electrical Characteristics) (Aluminum Alloys - EC, 57 EC, 6063·T6, 6061.T6) Angle Size
Donble Angle
Weight per foot (lbs.)
(Inches)
21hx 2 21hx 2
1.26 1.83
21h 2:lh
2lh X 2:lh 2lh X 2:lh
1.40 2.05
(Inches)
Deth
Width w (Inches)
Double Angle D-C Resistance (Microhms per foot) at 20 C
**
D-C Current Carrying Capacity (Amperes)
at70C
*
ID
60 Cycle A-C Current Carrying Capacity* (Amperes)
~.
EC
EC
57 EC
6063-T6
6061-T6
EC
57EC
3 3
6.238 4.306
7.495 5.174
7.933 5.476
8.439 5.826
10.77 7.438
2010 2420
1950 2350
2:lh 2:lh
3:lh 3:lh
5.609 3.836
6.739 4.609
7.132 4.878
7.588 5.189
9.687 6.625
2230 2700
6063-T6
6061-T6
EC
57EC
6063-T6
6061-T6
1890 2280
1680 2020
1980 2310
1920 2260
1870 2200
1670 1980
2170 2620
2100 2540
1860 2250
2190 2580
2140 2520
2070 2450
1850 2200
- - -- - - - - -
3 3 3
x3 x3 x3
1.68 2.47 3.23
3 3 3
4 4 4
4.668 3.179 2.436
5.609 3.820 2.927
5.936 4.043 3.098
6.315 4.301 3.296
8.063 5.491 4.208
2610 3160 3570
2540 3080 3490
2460 2980 3360
2180 2640 2980
2550 3000 3260
2490 2930 3200
2420 2850 3110
2160 2570 2810
4 4 4 4
x3 x3 x3 x3
1.99 2.93 3.83 4.69
4 4 4 4
4 4 4 4
3.950 2.681 2.054 1.673
04.746 3.221 2.468 2.010
5.023 3.409 2.612 2.127
5.344 3.627 2.779 2.263
6.822 4.630 3.548 2.889
2980 3620 4110 4550
2900 3520 4000 4420
2810 3410 3870 4290
2490 3020 3430 3790
2910 3420 3730 3840
2840 3340 3650 3780
2750 3250 3560 3720
2450 2950 3230 3400
4 4 4 4
x4 x4 x4 x4
2.28 3.38 4.41 5.42
4 4 4 4
5 5 5:tA, 5:tA,
3.441 2.334 1.780 1.448
4.134 2.804 2.139 1.740
4.375 2.968 2.264 1.842
4.655 3.157 2.408 1.959
5.943 4.031 3.075 2.501
3390 4110 4710 5220
3290 4000 4580 5070
3190 3870 4440 4920
2830 3430 3930 4350
3290 3850 4230 4380
3210 3760 4160 4320
3120 3660 4070 4260
2790 3310 3690 3900
5 5 5
x31h X 3:lh X 3:lh
3.58 4.70 5.79
5 5 5
5 5 5
1.880 1.669 1.357
2.259 2.005 1.630
2.391 2.122 1.725
2.543 2.257 1.835
3.247 2.882 2.343
4340 4960 5490
4220 4830 5340
4090 4670 5170
3620 4140 4580
4090 4460 4640
3990 4380 4560
3890 4270 4480
3500 3870 4110
6 6 6
x4 x4 x4
4.24 5.58 6.88
6 6 6
6 6 6
1.854 1.408 1.141
2.228 1.692 1.371
2.358 1.791 1.451
2.509 1.905 1.544
3.203 2.432 1.971
5060 5790 6420
4910 5620 6240
4770 5460 6050
4220 4830 5350
4740 5160 5390
4620 5070 5310
4510 4970 5220
4060 4490 4770
* Current
ratings are for a 30 C temperature rise over 40 C ambient temperature in still, but unconfined air with a phase spacing sufficient to produce negligible proximity effect.
** The
following per cent (lACS) conductivities were used to determine resistance and current ratings: EC - 61 per cent, 57 EO - 57 per cent, 6063-T6 - 53 per cent, 6061-T6 - 40 per cent.
.,.. I::l
C?'
~
g
t:l.. Co
"13
"" C"l
'~
~
o' ~ I
Co
""~ t; Cil.
o';::I
:s
section VI - tables and specifications
SQUARE ALUMINUM TUBULAR CONDUCTORS (Physical Properties) Square a (Inches)
Corner Radius r (Inches)
Wall Thickness t (Inches)
3 3 3
% 112
%
Perimeter (Inches)
Cross Sectional Area (Square Inches)
Weight per foot (Lbs.)
Moment of Inertia I (Inches)
Section Modulus S (Inches)
Radius of Gyration (Inches)
14 %
11.36 11.14 10.71
2.643 3.736 4.571
3.108 4.394 5.375
3.272 4.215 4.600
2.181 2.810 3.067
1.113 1.062 1.003
8.215 11.30 13.06
4.108 5.652 6.532
1.513 1.469 1.410
lf2
4 4 4
lf2 lf2
%
14 % lf2
15.14 15.14 14.71
3.589 5.236 6.571
4.221 6.158 7.728
5 5 5
% % %
14 % lf2
18.71 18.71 18.71
4.482 6.575 8.571
5.271 7.732 10.08
16.26 22.73 28.32
6.503 9.093 11.33
1.905 1.859 1.818
6 6 6
% % %
14 %
22.71 22.71 22.71
5.482 8.075 10.57
6.447 9.496 12.43
29.36 41.59 52.35
9.786 13.86 17.45
2.314 2.269 2.225
lf2
SQUARE ALUMINUM TUBULAR CONDUCTORS (Electrical Properties) Wall Tube ThickSquare ness t a (Inches) (Inches)
57 EC
EC
60 cps Current Rating (amperes)
*
at 20 C
at 70 C
at 20 C
at 70 C
EC
57 EC
EC
57 EC
3 3 3
% % lf2
5.051 3.573 2.921
6.069 4.293 3.510
5.407 3.825 3.126
6.424 4.544 3.714
6.312 4.722 4.176
6.683 4.955 4.384
1930 2210 .2310
1880 2170 2250
4 4 4
Y4 % lf2
3.720 2.550 2.032
4.470 3.064 2.441
3.982 2.729 2.175
4.731 3.242 2.584
4.692 3.431 3.002
4.969 3.600 3.127
2520 2950 3110
2450 2880 3040
5 5 5
% lf2
1~
2.979 2.030 1.558
3.579 2.439 1.872
3.188 2.173 1.667
3.787 2.582 1.980
3.794 2.782 2.357
4.017 2.919 2.457
3060 3580 3880
2980 3490 3810
6 6 6
Y4 % lf2
2.435 1.653 1.263
2.926 1.986 1.517
2.607 1.770 1.352
3.097 2.103 1.606
3.160 2.304 1.972
3.346 2.419 2.056
3640 4260 4600
3540 4170 4520
* 30 C rise over 40 C ambient temperature in still but unconfined air.
136
60 cps A-C Resistance at 70 C (Microhms per foot)
D-C Resistance (Microhms per foot)
tables and specifications - section VI
INDUCTIVE REACTANCE SPACING "FACTORS" Microhms per Foot (For 1 to 251 Inches Total Spacing) FREQUENCY - 60 cps INCHES
SPACING (Feet)
7
0
1
2
3
4
5
0 15.9 25.2
-57.1 1.8 16.9 25.9
-41.2 3.5 17.8 26.5
-31.9 5.1 18.6 27.1
-25.3 6.6 19.5 27.7
-20.1 8.0 20.3 28.2
4 5 6 7
31.9 37.0 41.2 44.7
32.3 37.4 41.5 45.0
32.8 37.7 41.8 45.3
33.3 38.1 42.1 45.5
33.7 38.5 42.4 45.8
34.1 38.8 42.7 46.0
34.6 39.2 43.0 46.3
35.0 39.5 43.3 46.6
35.4 39.9 43.6 46.8
35.8 40.2 43.9 47.1
36.2 40.5 44.2 47.3
36.6 40.9 44.4 47.5
8 9 10 11
47.8 50.5 52.9 55.1
48.0 50.7 53.1 55.3
48.3 50.9 53.3 55.5
48.5 51.1 53.5 55.6
48.7 51.3 53.7 55.8
49.0 51.5 53.9 56.0
49.2 51.7 54.0 56.1
49.4 51.9 54.2 56.3
49.6 52.1 54.4 56.5
49.9 52.3 54.6 56.6
50.1 52.5 54.8 56.8
50.3 52.7 54.9 57.0
12 13 14 15
57.1 59.0 60.7 62.2
57.3 59.1 60.8 62.4
57.4 59.2 60.9 62.5
57.6 59.4 61.1 62.6
57.7 59.5 61.2 62.7
57.9 59.7 61.3 62.9
58.1 59.8 61.5 63.0
58.2 60.0 61.6 63.1
58.4 60.1 61.7 63.2
58.5 60.2 61.9 63.4
58.7 60.4 62.0 63.5
58.8 60.5 62.1 63.6
16 17 18 19 20
63.7 65.1 66.4 67.7 68.9
63.8 65.2 66.5 67.8 69.0
64.0 65.3 66.6 67.9 69.0
64.1 65.5 66.8 68.0 69.1
64.2 65.7 66.9 68.1 69.2
64.3 65.7 67.0 68.2 69.3
64.4 65.8 67.1 68.3 69.4
64.6 65.9 67.2 68.4 69.5
64.7 66.0 67.3 68.5 69.6
64.8 66.1 67.4 68.6 69.7
64.9 66.2 67.5 68.7 69.8
65.0 66.3 67.6 68.8 69.9
0 1 2 3
-
The inductive reactance spacing factors in the above table are given in microhms per foot. Spacings are total distance between conductors. To convert these values of inductive reactance to any other frequency, multiply by the ratio of the two frequencies, for example: XL2
Where: X L2
=
f
X oo X 60
is the value desired at the frequency f.
6
-15.9 ' -12.4 9.3 10.6 21.1 21.8 28.8 29.3
8
-
9.3 11.7 22.5 29.9
9
-
6.6 12.9 23.2 30.4
11
10
-
4.2 13.9 23.9 30.9
-
2.0 15.0 24.6 31.4
The 60 cps inductive reactance spacing factors in this table are calculated by the following formula: XL2 = 52.91 Log10 GMD (Microhms per foot). The GMD is the equivalent spacing of the circuit and for a 3 phase configuration is given by the formula,
GMD = iY A X B X C Where: A, B, and C are the total spacings between conductors.
137
section VI - tables and specifications
BARE, ALL ALUMINUM STRANDED CONDUCTOR, HARD DRAWN (Physical Dimensions and Breaking Strength) AREA
Cable
E'buivalent H . . Copper AWGor CM(2)
Breaking Strength (Pounds) (3)
Code Word (for harddrawn only)
Size AWGor CM(I)
Square Inches
Square mm
Stranding Class
Total Number of Strands
Wire Diameter (Inches)
Diameter
Peachbell Rose Lily Iris Pansy
*6 *4 3 *2 1
0.02061 0.03278 0.04133 0.05212 0.06573
13.30 21.15 26.66 33.63 42.41
A-B A-B A-B AA-A-B AA-A
7 7 7 7 7
0.0612 0.0772 0.0867 0.0974 0.1093
0.1836 0.2316 0.2601 0.2922 0.3279
No.8 No.6 No.5 No.4 No.3
529 826 1,023 1,267 1,538
1/0 *1/0 2/0 *2/0
0.08291 0.08291 0.1045 0.1045
53.49 53.49 67.42 67.42
AA-A B AA-A B
7 19 7 19
0.1228 0.0745 0.1379 0.0837
0.3684 0.3725 0.4137 0.4185
No.2 No.2 No.1 No.1
1,864 2,088 2,351 2,586
jj~~d~lion
3/0 *3/0 4/0 *4/0 250,000 *250,000
0.1318 0.1318 0.1662 0.1662 0.1963 0.1963
85.03 85.03 107.2 107.2 126.6 126.6
AA-A B AA-A B A B
7 19 7 19 19 37
0.1548 0.0940 0.1739 0.1055 0.1147 0.0822
0.4644 0.4700 0.5217 0.5275 0.5735 0.5754
No.lIO No. 1/0 No. 2/0 No. 2/0 157,200 157,200
2,847 3,203 3,590 3,889 4,506 4,858
Daisy Laurel Foxglove Peony Agave
266,800 266,800 *266,800 300,000 *300,000
0.2095 0.2095 0.2095 0.2356 0.2356
135.2 135.2 135.2 152.0 152.0
-A
B A B
7 19 37 19 37
0.1953 0.1185 0.0849 0.1257 0.0900
0.5859 0.5925 0.5943 0.6285 0.6300
No. 3/0 No. 3/0 No. 3/0 188,700 188,700
4,525 4,808 5,185 5,301 5,831
Tulip Hollyhock Daffodil Gardenia Canna
336,400 *336,400 350,000 *350,000 397,500
0.2642 0.2642 0.2749 0.2749 0.3122
170.5 170.5 177.4 177.4 201.4
A B A B AA-A
19 37 19 37 19
0.1331 0.0954 0.1357 0.0973 0.1447
0.6655 0.6678 0.6785 0.6811 0.7235
No. 4/0 No. 4/0 220,000 220,000 250,000
5,945 6,420 6,185 6,680 6,884
...... ...... ......
400,000 *400,000 450,000 *450,000 477,000 477,000
0.3142 0.3142 0.3534 0.3534 0.3746 0.3746
202.7 202.7 228.0 228.0 241.7 241.7
AA-A B All. A-B AA A-B
19 37 19 37 19 37
0.1451 0.1040 0.1539 0.1103 0.1585 0.1135
0.7255 0.7280 0.7695 0.7721 0.7925 0.7945
252,000 252,000 283,000 283,000 300,000 300,000
6,928 7,352 7,633 8,111 8,091 8,591
500,000 *500,000 556,500 556,500 *600,000
0.3927 0.3927 0.4371 0.4371 0.4712
253.4 253.4 282.0 282.0 304.0
AA A-B AA-A B
19 37 19 37 61
0.1622 0.1162 0.1711 0.1226 0.0992
0.8110 0.8134 0.8555 0.8582 0.8928
314,000 314,000 350,000 350,000 377,000
8,482 9,012 9,436 9,828 11,450
Fi~(
636,000 636,000 *700,000 715,500 715,500
0.4995 0.4995 0.5498 0.5620 0.5620
322.3 322.3 354.7 362.6 362.6
AA-A B A-B All. A-B
37 61 61 37 61
0.1311 0.1021 0.1071 0.1391 0.1083
0.9177 0.9189 0.9639 0.9737 0.9747
400,000 400,000 440,000 450,000 450,000
11,240 11,690 12,860 12,640 13,150
Petunia Cattail Arbutus Lilac
*750,000 750,000 *795,000 795,000 *800,00U
0.5890 0.5890 0.6244 0.6244 0.6283
380.0 380.0 402.8 402.8 405.4
All. A-B All. A-B A-B
37 61 37 61 61
0.1424 0.1109 0.1466 0.1142 0.1145
0.9968 0.9981 1.0262 1.0278 1.0305
472,000 472,000 500,000 500,000 503,000
12,990 13,520 13,770 14,340 14,420
Anemone Crocus Magnolia Goldenrod
874,500 874,500 954,000 954,000
0.6868 0.6868 0.7493 0.7493
443.1 443.1 483.4 483.4
All. A-B All. A-B
37 61 37 61
0.1538 0.1198 0.1606 0.1251
1.0766 1.0782 1.1242 1.1259
550,000 550,000 600,000 600,000
14,830 15,780 16,180 16,870
Camellia Bluebell Larkspur Marigold Hawthorn
*1,000,000 1,033,500 1,033,500 1,113,000 1,192,500
0.7854 0.8117 0.8117 0.8741 0.9366
506.7 523.7 523.7 563.9 604.3
A-B All. AA-A AA-A AA-A
61 37 61 61 61
0.1280 0.1672 0.1302 0.1351 0.1398
1.1520 1.1704 1.1718 1.2159 1.2582
629,000 650,000 650,000 700,000 750,000
17,670 17,530 18.270 19;670 21,070
Narcissus
1.272,000 1,351,500 1.431,000 1.510,500 1.590.000
0.9990 1.061 1.124 1.186 1.249
644.5 684.5 725.2 765.2 805.8
AA-A AA-A AA-A AA-A AA-A
61 61 61 61 61
0.1444 0.1489 0.1532 0.1574 0.1615
1.2996 1.3401 1.3788 1.4166 1.4535
800,000 850,000 900,000 950,000 "1,000.000
22,030 23,400 24,280 25,620 26,980
Poppy Geranium
Aster Buttercup Phlox Primrose
Oxlip
Sunflower
C·~s~~s Syringa Zinnia
Hyacinth Dahlia Mistletoe Lotus Orchid Vio et Nasturtium
......
Columbine Carnation Gladiolus Coreopsis
(1) The sizes marked with an asterisk are usually used for insulated conductors. For conductors to be insulated, a left-hand lay should be specified for the outer layer of wires. Bare conductors for overhead usc are normally furnished with a right-hand lay on the outer layer of wires unless otherwise specified. (2) For hard drawn copper conductor 97 per cent conductivity, lACS, havino; approximately the same doc resistance as aluminum conductor of 61 per cent conductivity, lACS, at 20 C.
138
(Inches)
(3) The breaking stren~th is 90 per cent of the total of all the individual strand average tensile strengths as given in ASTM B230 for hard drawn wire.
NOTE: These data are approximate and subject to normal manufacturing tolerances. Data subject to change without notice.
tables and specifications - section VI
BARE, ALL ALUMINUM STRANDED CONDUCTOR, HARD DRAWN (Electrical Characteristics and Weight) 60 cps Inductive Current
Code Word (for harddrawn only)
Size AWG or MCM
Stranding
RESISTANCE(2) (Ohms per 1000 feet)
Reactance
Carrying Capacity (1 ) (Amperes)
Geometric Mean Radius , GMR (Feet)
for I-foot
WEIGHT
at 70 C
spacing
at 20 C
(Ohms per 1000 ft.)
(D-C)
(D-C)
60 cps
Pounds per 1000'
Pounds per Mile
6 4 3 2 1
7 7 7 7 7
80 105 120 140 165
0.005551 0.007003 0.007864 0.008835 0.009914
0.1194 0.1140 0.1114 0.1087 0.1060
0.6613 0.4157 0.3297 0.2615 0.2073
0.7945 0.4995 0.3962 0.3142 0.2491
0.7945 0.4995 0.3962 0.3142 0.2492
24.6 39.2 49.4 62.3 78.6
130 207 261 329 415
1/0 1/0 2/0 2/0
7 19 7 19
190 190 220 220
0.01114 0.01176 0.01251 0.01321
0.1033 0.1021 0.1007 0.09943
0.1643 0.1643 0.1304 0.1304
0.1974 0.1974 0.1566 0.1566
0.1975 0.1975 0.1567 0.1567
99.0 99.0 124.9 124.9
523 523 660 660
D~~d~lion
3/0 3/0 4/0 4/0 250 250
7 19 7 19 19 37
255 255 300 300 335 335
0.01404 0.01484 0.01577 0.01665 0.01810 0.01841
0.09803 0.09676 0.09536 0.09411 0.09220 0.09180
0.1034 0.1034 0.08200 0.08200 0.06940 0.06940
0.1242 0.1242 0.09852 0.09852 0.08339 0.08339
0.1243 0.1243 0.09863 0.09863 0.08352 0.08352
157.5 157.5 198.6 198.6 234.7 234.7
832 832 1049 1049 1239 1239
Daisy Laurel Foxglove Peony Agave
266.8 266.8 266.8 300 300
7 19 37 19 37
345 345 350 375 375
0.01772 0.01870 0.01901 0.01984 0.02016
0.09268 0.09145 0.09107 0.09009 0.08972
0.06503 0.06503 0.06503 0.05784 0.05784
0.07814 0.07814 0.07814 0.06949 0.06949
0.07828 0.07828 0.07828 0.06965 0.06965
250.5 250.5 250.5 281.6 281.6
1322 1322 1322 1487 1487
Tulip Hollyhock Daffodil Gardenia
336.4 336.4 350 350 397.5
19 37 19 37 19
405 405 415 415 450
0.02101 0.02136 0.02142 0.02179 0.02284
0.08877 0.08839 0.08832 0.08793 0.08685
0.05158 0.05158 0.04957 0.04957 0.04365
0.06197 0.06197 . 0.05956 0.05956 0.05245
0.06215 0.06215 0.05975 0.05975 0.05266
315.8 315.8 328.6 328.6 373.2
1667 1667 1735 1735 1970
Syringa
400 400 450 450 477 477
19 37 19 37 19 37
450 450 490 490 505 505
0.02290 0.02329 0.02429 0.02470 0.02502 0.02542
0.08679 0.08640 0.08544 0.08505 0.08475 0.08439
0.04338 0.04338 0.03856 0.03856 0.03638 0.03638
0.05212 0.05212 0.04633 0.04633 0.04371 0.04371
0.05234 0.05234 0.04656 0.04656 0.04396 0.04396
375.5 375.5 422.4 422.4 447.8 447.8
1983 1983 2230 2230 2364 2364
Zinnia Hyacinth Dahlia Mistletoe Lotus
500 500 556.5 556.5 600
19 37 19 37 61
520 520 560 560 590
0.02560 0.02602 0.02700 0.02746 0.02872
0.08423 0.08385 0.08300 0.08262 0.08159
0.03470 0.03470 0.03118 0.03118 0.02892
0.04169 0.04169 0.03746 0.03746 0.03475
0.04195 0.04195 0.03775 0.03775 0.03506
469.4 469.4 522.4 522.4 563.2
24-78 2478 2758 2758 2974
Orchid
636 636 700 715.5 715.5
37 61 61 37 61
610 610 650 660 660
0.02936 0.02956 0.03101 0.03115 0.03135
0.08108 0.08092 0.07982 0.07972 0.07957
0.02728 0.02728 0.02479 0.02425 0.02425
0.03278 0.03278 0.02978 0.02914 0.02914
0.03311 0.03311 0.03015 0.02951 0.02951
597.0 597.0 657.1 671.7 671.7
3152 3152 3469 3547 3547
750 750 795 795 800
37 61 37 61 61
680 680 705 705 705
0.03189 0.03?!1 0.03283 0.03306 0.03315
0.07918 0.07902 0.07851 0.07835 0.07829
. 0.02313 0.02313 0.02183 0.02183 0.02169
0.02782 0.02782 0.02622 0.02622 0.02606
0.02821 0.02821 0.02664 0.02664 0.02648
704.0 704.0 746.3 746.3 751.0
3717 3717 3940 3940 3965
Magnolia Goldenrod
874.5 874.5 954 954
37 61 37 61
750 750 790 790
0.03444 0.03468 0.03597 0.03622
0.07741 0.07725 0.07641 0.07626
0.01984 0.01984 0.01819 0.01819
0.02384 0.02384 0.02185 0.02185
0.02429 0.02429 0.02235 0.02235
820.9 820.9 895.6 895.6
4334 4334 4729 4729
Camellia Bluebell Larkspur Marigold Hawthorn
1000 1033.5 1033.5 1113 1192.5
61 37 61 61 61
815 830 830 870 910
0.03706 0.03744 0.03769 0.03911 0.04047
0.07573 0.07549 0.07534 0.07449 0.07370
0.01735 0.01679 0.01679 0.01559 0.01455
0.02085 0.02017 0.02017 0.01873 0.01748
0.02136 0.02071 0.02071 0.01930 0.01809
938.7 970.2 970.2 1045 1119
4956 5123 5123 5518 5908
Narcissus Columbine
1272 1351.5 1431 1510.5 1590
61 61 61 61 61
945 985 1020 1050 1085
0.04180 0.04311 0.04435 0.04557 0.04675
0.07296 0.07225 0.07160 0.07098 0.07039
0.01364 0.01284 0.01213 0.01149 0.01091
0.01639 0.01543 0.01457 0.01380 0.01311
0.01704 0.01611 0.01529 0.01457 0.01391
1194 1268 1343 1418 1493
6304 6695 7091 7487 7883
Peachbell Rose Lily Iris Pansy Poppy Geranium
Aster Buttercup Phlox Primrose
Oxlip Sunflower
Canna
...... ...... ...... c·o·s;";~s
Fi~g" Violet Nasturtium Petunia
Cattail Arbutus Lilac
......
Anemone Crocus
Carnation
Gladiolus Coreopsis
(1) Current Carrying Capacity based on methods of calculation by Sehurig & Frick, "Heating and Current Carrying Capacity of Bare Conductors for Outdoor Service," G. E. Review, Vol. 33, No.3, March 1930, page 141, for a wind velocity of 2 feet per sec., ambient air temperature of 40 C, conductor maximum temperature of 70 C, and a tarnished surface with an emissivity of e 0.5.
=
(2) D-C resistance based on 60.97 per cent conductivity aluminum lACS with a resistivity of 17.011 ohms (mil, foot) at 20 C with standard increments added for stranding per ASTM Specification B231. A-C resistance values include skin effect. NOTE: These data are approximate and subject to normal manufacturing tolerances. Data subject to change without notice.
139
section VI - tables and specifications
NEW DESIGNATIONS FOn ALUMINUM ALLOYS Wrought aluminum and wrought aluminum alloys are designated by a four digit index system. Temper designations are not changed and follow the alloy designations. The new system of four-digit numbers, effective October 1, 1954, is expected to meet all present and future needs for wrought alloy designations. To aid in the transition to the new system, many of the old numbers are retained as the last two digits of the new numbers. The first digit of the designation serves to indicate alloy groups as shown in Table I. The last two digits identify the aluminum alloy or indicate the aluminum purity. The second digit indicates modifications of the original alloy or impurity limits. Although most aluminum alloys contain several alloying elements, the major groups are determined by the major alloying element. Except that one group, 6x:xx for alloys with magnesium and silicon as major alloying elements, designates two elements as indicated in Table 1. In the lx:xx group for aluminum of 99.00 per cent minimum and greater, the last two digits indicate the minimum aluminum percentage to the nearest 0.01 per cent above the 99.000 base amount. The second digit in the designation of the lxxx group indicates modifications in impurity limits. If the second digit is zero, there is no special control on individual impurities; while integers 1 through 9 (assigned consecutively as needed) indicate special control of one or more individual impurities. Thus 1030 indicates 99.30 per cent minimum aluminum without special control on individual impurities; and 1130, 1230, 1330, indicate the same purity with special control of one or more impurities as designated by the second integer 1, 2, and 3. '
TABLE I-NEW DESIGNATIONS FOR ALUMINUM ALLOY GROUPS AA Number
Aluminum-99.00 per cent minimum and greater .... " .1= MAJOR ALLOYING ELEMENT
Copper
Aluminum alloys grouped by . 11' 1 major a oymg e ements. .
Unused series
. . . .. 2= ~anganese . . . . . . . . . .. 3= Silicon. . . . . . . . . . . . .. 4= ~agnesium 5= ~agnesium and Silicon. 6= Zinc 7= Other element 8= " 9=
(1) EC-The designation for electrical conductor metal is not being changed since it is so firmly established in the electrical industry. (2) No.1 Reflector Sheet.
140
TABLE II-ALUMINUM ALLOY DESIGNATION CONVERSIONS NEW AA Number
OLD Commercial Designation
EC(l) 1030 1050 1060 1070
EC AE1S AD1S BD1S AC1S
1075 1080 1085 1090 1095
JC1S BC1S AB1S FB1S AA1S
1099 1100 1130(2) 1145 1150
BA1S 2S R308 BE1S ED1S
1160 1175(3) 1180 1187 1197
CD1S, 99.6 99.75 CC1S,R998 EB1S, 99.87 CA1S
1230(4) 1235 2011 2014 2017
99.3 R995 l1S 14S, R301 Core 17S
2018 2024 2025 2117 X2214
18S 24S 25S A17S XB14S
2218 2225 X2316 2618 3003
B18S B25S XC16S F18S 3S
3004 X3005
4S XA5S
NEW
OLD
AA Number
Commercial Designation
4032 4043 4045
32S 43S, K145 45S
4343 C43S, 44S, K143 X4543 XE43S 5005 A50S, R305, K155 5050 50S 5052 52S 5056 5083 5086 5154 5254 X5356 5357 X5405 5652 6003(5)
56S LK183 K186 A54S B54S XC56S C57S, K157 XD50S F52S R306, K162
6053 6061 6062 6063 6066
53S 61S 62S 63S 66S
6151 X6251 6253 X6453 6553
A51S XB51S B53S XD5.3S E53S
6951 7070 7072 7075 X7178
J51S, K160 70S 72S 75S XA78S
7277 8099 8112 X8280
B77S R399 K112 XB80S
(3) Cladding on No.2 Reflector Sheet. (4) Cladding on Alclad 2024 (Alclad 24S). (5) Cladding on Alclad 2014 (R301 and Alclad 14S).
tables and specificatiol1s - sectiol1 VI
ALUMINUM ASSOCIATION DESIGNATIONS AND EQUIVALENT ASTM DESIGNATIONS
WROUGHT ALUMINUM ALLOYS ASTM
AA
ASTM
CAST ALUMINUM ALLOYS
AA
990A MIA MGllA
1100 3003 3004
CG42A GR20A GSllB
2024 5052 6053
CB60A CM41A
2011 2017
GSllA GSI0A
6061 6063
ASTM
AA
S12A * S12B S5B SC54A ** CS72A
13 13 43 85 113
* Outmoded Desig. S5 ** Outmoded Desig. SC2
AA
ASTM
CZ72A C4A SC64C SC51A SG70A SC84B***
112 195 Alcast 60 355 356 A380
*** Outmoded Desig.
SC7
ALUMINUM EXTRUDED SHAPES AND EXTRUDED ROD AND BAR Standard Tolerances (6) (7) CROSS·SECTIONAL DIMENSIONS COl.2
COL. 4
NOTE 131
COlS.4,5,6.7
COL. 3
CO~
2
COL. 2~..J,..:=::::::;==:"":::;::===:;;:==:::=JTOLERANCE (1) (2) (Inch)
SPECIFIED DIMENSIONS (Inches)
METAL DIMENSIONS
SPACE DIMENSIONS
Allowable deviation from specified dimension where 75 per cent Or more of the dimension is metal
Allowable deviation from specified dimension where more than 25 per cent of the dimension is space (3) (4)
All excePtin~ those covere by column 3 Column 1
Column 2
Under 0.125 0.125 to (not inc!.) 0.25 0.25 to (not incl.) 0.5 0.5 to (not inc!.) 0.75
±0.006 ±0.007 ±0.008 ±0.009
0.75 1 1.5 2
I
Wall thickness (5) completely enclosing space 0.11 sq. in. and over (Eccentricity )
At dimensioned points 1,4 inch to 4notinCl.) inch from ase of leg
Column 3
Column 4
At dimensioned points % inch to (not incl.) 11~ inch from ase of leg
At dimensioned points 114 inch to (not incl.) 21\ inches from ase of leg
At dimensioned points 21h inche. or more from base of leg
Column 5
Column 6
Column 7
±0.010 ±0.012 ±0.014 ±0.016
±0.012 ±0.014 ±0.016 ±0.018
±0.014 ±0.016 ±0.018 ±0.020
±0.016 ±0.020 ±0.022 ±0.026
I
to to to to
(notinc!.) (not inc!.) (not inc!.) (not inc!.)
1 1.5 2 4
±0.010 ±0.012 ±0.016 ±0.024
Plus or minus 10 per cent
±0.018 ±0.020 ±0.024 ±0.032
±0.020 ±0.022 ±0.028 ±0.036
±0.022 ±0.026 ±0.034 ±0.048
±0.030 ±0.034 ±0.050 ±0.064
4 6 8 10
to to to to
(not inc!.) (not inc!.) (not inc!.) (not inc!.)
6 8 10 12
±0.034 ±0.044 ±0.054 ±0.064
max. ±0.060 min. ±0.01O
±0.042 ±0.054 ±0.064 ±0.074
±0.050 ±0.062 ±0.074 ±0.088
±0.064 ±0.082 ±0.100 ±0.116
±0.088 ±0.112 ±0.136 ±0.160
12 14
to (notinc!.) 14 to (incl.) 15
±0.074 ±0.080
±0.084 ±0.090
±0.100 ±0.106
±0.134 ±0.142
±0.184 ±0.196
(1 ) The tolerance applicable to a dimension composed of two or more component dimensions is the sum of the tolerances of the component dimensions, if all of the component dimensions are indicated. (2) When a dimension tolerance is specified other than as an equal bilateral tolerance, the value of the standard tolerance is that which would apply to the mean of the maximum and minimum dimensions permissible under the tolerance. (3) At points less than ;i inch from base of leg, the tolerances in Co!. 2 are applicable.
(4) Where the space is completely enclosed (hollow shapes), the tolerances in Col. 4 are applicable. (5) In the case of Class 1 Hollow Shapes, allowable deviation is plus or minus 10 per cent of mean wall thickness, max. ±0.060, min. ±0.010. (6) These Standard Tolerances are applicable to the average shape. Tolerances wider than standard may be necessary for some shapes; tolerances closer than standard may be possible for others. (7) These Standard Tolerances conform to the standards of The Aluminum Association, Extrusion Division.
141
section VI - tables and specifications
ILLUSTRATIONS - STANDARD TOLERANCES - CROSS·SECTIONAL DIMENSIONS I - Closed Space Dimensions
X ICOL 4)
X (COL 4) Y (COL 2) X (COL 4)
All dimensions designated "Y" are classed as "metal dimensions" and tolerances are determined from column 2. Dimensions designated "X" are classed as "space dimensions through an enclosed void" and the tolerances applicable are determined from column 4 unless 75 per cent or more of the dimension is metal, in which case Column 2 applies.
II - Open Space Dimensions
~ ~X--i
If TB ~ _--1 L A Y
Tolerances applicable to dimensions "X" ar.. determined as follows: 1. locate dimension "X" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance "A." 3. locate proper tolerance in column 4, 5, 6 or 7 in the same line as dimension "X." Dimensions "Y" are "metal dimensions"; tolerances are determined from column 2. Distances "B" are shown merely to indicate incorrect values for determining which of columns 4, 5, 6 or 7 apply.
r-x--J
~rn f--B---J
Y Tolerances applicable to dimensions "X" are determined as follows: 1. locate dimension "X" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance "A." 3. locate proper tolerance in column 4, 5, 6 or 7 in the same line
as dimension "X." Dimension
llyll
is a
II
Tolerances applicable to dimensions "X" are determined as follows: 1. locate distance "B" in column 1. 2. Determine which of columns 4, 5, 6 or 7 is applicable, dependent upon distance itA. II
3. locate proper tolerance in column 4, 5, 6 or 7 in same line as value chose'n in column 1.
metol dimension"; tolerance is determined from column 2.
Tolerances applicable to dimension "X" are determined by standard tolerances applicable to angles "A".
142
tables and specifications - sectwn v 1
ALUMINUM EXTRUDED SHAPES AND EXTRUDED ROD AND BAR (Concluded) Standard Tolerances (4) (5) LENGTH *
STRAIGHTNESS
Tolerance (Inches) Circumscribing circle diam-
eter (shapes); specified diameter (rod); specified width
or depth, whichever greater
(bar (Inches)
Under 3.000 ......... 3.000-7.999 .......... 8.000 and over ........
Allowable deviation from specified length Specified length (Feet) Up Through 12
Over 12 Through 30
Over 30 Through 50
Over 50 --~
+Ys
+% +916 +%
+%6 +%
+% +%6 +~~
+1 +1 +1 TOLERANCE (2,3) (INCH)
*Applicable to straight length only. Circumscribing circle diameter (1)
TWIST
Allowable deviation from straight
Minimum
thickness (inches)
(inch'S)
In each foot of length
In total length of piece
Under 1% Under 1%
0.094 or under 0.050 (3) Over 0.094 0.0125
Length, ft., X 0.050 Length, ft., X 0.0125
1% and over
............
Length, ft., X 0.0125
0.0125
(1) The circumscribing circle diameter is the diameter of the smallest circle
that will completely enclose the shape.
(2) Not appli~able to extruded shapes in the !,~ne.aled ("9':) temper. (3) When welght of shape On flat 'surface m1111mIZeS deVIatIOn.
ANGULARITY TOLERANCE (DEGREES) TOLERANCE (2) (DEGREES)
(inches)
In each foot of length
Under 1% Ph to (notincl.) 3
1 degree % degree
3 andover
% degree
from s)'eeified angle
Length, ft., X 1 degree Length, ft., X % degree not over 5 degrees Length, ft., X % degree not over 3 degrees
Under 0.188 0.188to (notincl.) 0.750 0.750 to solid
CURVED SURFACES: Allowable deviation from specified inch per inch of chord length,
minimum not applicable to more than
90
0.005
inch
. . .
±2 ±1% ±1
CORNER AND FILLET RADII TOLERANCE (INCH)
SPECIFIED RADIUS (INCHES)
that will completely enclose the shape. (2) Not applicable to extruded shapes in the annealed ("0") tem)'er.
0.005
deviation
In total length of piece
(1) The circumscribing circle diameter is the diameter of the smallest circle
contour,
Allowable
MINIMUM SPECIFIED LEG THICKNESS (INCHES)
Allowable deviation from straight
Circumscribing circle diameter (1)
Sharp corners Under 0.188 0.188 and over
degrees of any
Allowable deviation from specified radius
+164, ±164,
. . .
± 10 per cent
EXTRUSION" TOLERANCE TERMINOLOGY
arc.
KAISER ALUMINUM STANDARD TOLERANCES are those (and only those) published FLAT SURFACES:
in
Kaiser Aluminum Stand-
ard Tolerances Engineering Data. To avoid misunder-
Allowable
0.004
standing they should be referred to as "Kaiser Aluminum
inch per inch of width;
Standard Tolerances," and not as "commercial" or "published" tolerances. .
deviation
0.004
from
flat,
inch minimum.
I
A
L
A SPECIAL tolerance is any tolerance that is closer or wider than Kaiser Aluminum Standard, whatever shape applied to.
CUT ENDS: Allowable deviation from square-l degree.
A CLOSE tolerance is any Special tolerance that is closer
(4) These Standard Tolerances are applicable to the average shape. Toler-
than Kaiser Aluminum Standard.
closer than standard may be possible for others. (5) These Standard Tolerances conform to the standards of The Aluminum
than Kaiser Aluminum Standard.
ances wider than standard may be necessary for some shapes; tolerances Association) E.xtrusiol1 Division.
A WIDE tolerance is any Special tolerance that is wider
143
tables and specifications - section VI
PHYSICAL REQUIREMENTS FOR BOLTS, CAPSCREWS, STUDS, AND NUTS
*
SAE STANDARD
Scope-These specifications cover the physical requirements for steel bolts, capscrews, studs, and nuts used in the automotive and other industries. Whenever the term ''bolt'' is used, it is understood to include capscrews, studs, and similar externally threaded fasteners. General Data-The following grades are included: Grade O-Bolts without physical requirements; Grade I-Commercial steel bolts; Grade 2-Low-carbon steel bolts; Gi-ade 3-Medium-carbon steel, cold-worked, hexagon-head bolts and studs; Grade 5-Medium-carbon steel, quenched-and-tempered bolts; Grade 6-Medium-carbon steel, quenched-and-tempered, high-strength bolts; Grade 7-Medium-carbon alloy steel, quenchedand-tempered, medium-strength bolts; Grade 8-Medium-carbon alloy steel, quenchedand-tempered, high-strength bolts. For Grade and Grade 1 bolts and all nuts, openhearth, electric-furnace, or Bessemer steel may be used. For all other grades, open-hearth or electric-furnace steel shall be used. Unless otherwise specified, there are no limitations on the composition of the steels used, thus giving the manufacturer freedom in the selection of steels which will provide the required physical properties. It is intended that nuts shall be designated by grades, the same as bolts. Each grade of nut shall be required to meet the strip-load requirements which are equal to the minimum tensile strength of the corresponding grade of bolt. These are shown in Table 4. It is recommended that nuts be supplied in Grades 2, 5, and 8. Grade 2 nuts will pull Grades 0, 1, and 2 bolts. Grade 5 nuts will pull all grades of bolts up to and including Grade 5. Grade 8 nuts will pull all grades of bolts up to and including Grade 8.
°
Grades and Requirements-The various grades and their requirements are shown in Table 1. The following additional requirements apply. Wedge Test-Bolts and capscrews shall be subjected to a wedge test, the details of which are given under Methods of Testing. The wedge test on special-formed or drilled-head bolts shall be conducted with the lO-degree wedge under the nut. This also applies to studs (wedge at fine-threaded end) .
* Report
of Iron and Steel Technical Committee approved January 1949 and last revised December 1953.
144
Physical Properties-Bolts shall meet the hardness requirements prescribed in Table 1. When tested in full size for tensile properties, bolts shall also meet the tensile-strength and proof-load requirements specified in Table 4. Tensile requirements will be waived for bolts with special or drilled heads which are weaker than the threads. When bolts are too large for a full-size tension test, (usually above % inch in diameter), machined specimens shall have the minimum tensHe strength, yield strength, elongation, and reduction of area specified in ,Table 2. When bolts or thread lengths are too short for a tension test, acceptance shall be determined by the hardness range specified in Table 1. TABLEI--TENS~E,PROOFLOAD,AND
HARDNESS REQUIREMENTS Grade, Description, and Size (Dia.)
Minimtnn Tensile Strength (psi)
-
Grade Q-No requirements ...... Grade I-Commercial Steel Bolts 55,000 Grade 21 -Low-Carbon Steel Bolts (6 in. in length and under) Up to Ih in................. 69,000 Ih to % in.................. 64,000 % to l:1h in................ 55,000 (over 6 In. in length) All diameters .............. 55,000 Grade 3'-Medium-Carbon Steel, Cold-Worked, Hexagon-Head Bolts and Studs Up to 1/2 in................. 110,000 Over 1/2 to % in............ 100,000 Grade 58 -Medium-Carbon Steel, Quenched-and-Tempered Bolts Up to % in................. 120,000 Over % to I in............. 115,000 Over I to I Ih in............ 105,000 Grade 6<-Meditnn-Carbon Steel, Quenched-and-Tempered, High-Strength Bolts Up to %in................. 140,000 Over % to % In............. 133,000 Grade 75-Meditnn-Carbon AIloy Steel, Quenched-and-Tempered, Medium-Strength Bolts Up to Ph in................ 130,000 Grade 80-Meditnn-Oarbon AIloy Steel, Quenched-and-Tempered, High-Strength Bolts Up to l:1h in................ 150,000
Hardness Proof Load (psi)
-
Brinell
-
Rockwell
-
207 max
B95 max
241 max 241 max 207 max
B100 max BlOOmax B95 max
207 max
B95 max
85,000 80,000
207-269 207-269
B95-B104 B95-B104
85,000 78,000 74,000
241-302 235-302 223-285
023-032 022-C32 019-030
110,000 105,000
285-331 269-331
030-036 028-036
105,000
269-321
028-034
120,000
302-352
032-038
55,000 52,000
-
(1) Grade 2-00Id-headed low-carbon steel bolts, stress-relieved or hot-forged bolts heat-treated where necessary to meet requirements. Proof-load values apply only to hexagon-head bolts and studs. (2) Grade 3-00Id-worked bolts, stress relieved. (3) Grade 5-Minimtnn tempering temperature 800 F. (4) Grade 6-Minimum tempering temperature 800 F. (5) Grade 7-Minimum tempering temperature 800 F. This grade is recOI~ mended only for bolts which are thread rolled after heat-treatment. It 15 recommended that the minlmtnn as-quenched hardness be Rockwell 0 47 for sizes to Ih in. in diameter and Rockwell C 45 for sizes above 1h in. In diameter. (6) Grade 8-MInimum tempering temperature 800 F. It is recommended that the minimum as-quenched hardness be Rockwell 0 47 for sizes to II.! in. in diameter and Rockwell C 45 for sizes above 1h in. in diameter.
tables and specifications - section
All standard nuts, except jam, slotted, and castellated nuts, shall meet a proof strip load as specified in Table 4.
TABLE 3-STRESS AREAS (MEAN EQUIVA· LENT AREAS) AND THREADS PER INCH Bolt
Grade 5 Over % to 1 in.... Over 1 to g~ in... Grade 7 Up to 1112 in...... Grade 8 Up to 1112 in......
Minimum
Minimum
Tensile Strength (psi)
Yield Strength (psi)
115,000 105,000
81,000 77,000
Stress area (sq. in.)
1,4
0.0317 0.0522 0.0773 0.1060 0.1416
20 18 16 14 13
0.0362 0.0579 0.0876 0.1185 0.1597
28 24 24 20 20
0.1816 0.2256 0.3340 0.4612 0.6051
12 11 10 9 8
0.2026 0.2555 0.3724 0.5088 0.6791
18 18 16 14 14
0.7627 0.9684 1.1538 1.4041
7 7 6 6
0.8549 1.0721 1.3137 1.5799
12 12 12 12
0/16
Minimum
%
(per cent)
112
14 14
35 35
%6
%6
%
%
%
130,000
105,000
10
35
1
150,000
120,000
10
35
1% 11,4 1%
Methods of Testing-Tension and Wedge TestTension tests of bolts shall be made preferably on the finished (full-size) bolt. The nut or fixture shall be assembled on the bolt, leaving six complete bolt threads exposed and unengaged between the grips. The grips of the testing machine shall be self-aligning to avoid side thrust on the specimen. The nut or fixture shall be assembled freely to the thread runout and then unscrewed six full turns. Fig. 1 illustrates the method for testing a full-size specimen. The bolt shall be subjected to the elastic proof load shown in Table 1. Then a 10-degree wedge shall be placed under the head of the bolt and the tensile test continued until failure. Bolts shall be so placed that the corner of the hexagon or square does not take the bearing load. To meet the requirements of this test, there must be a tensile failure in the body or threads with no fracture of the head. The bolts shall meet the requirements for minimum tensile strength shown in Table 1 without failure.
I
Threads per inch
Reduction of Area (per cent)
Hardness and Tensile Strength-Tensile strength, in pounds per square inch, in addition to being not less than the minimum value shown in Table 1, shall not be less than the product of the Brinell hardness number times 450.
Fine Thread
Stress area (sq. in.)
Minimum
EliC:~i~~n
Coarse Thread
Diameter
TABLE 2-TENSILE REQUIREMENTS OF MACillNED TEST SPECIMENS Grade and Size (Dia.)
Y1
1~
Threads pel' inch
The tensile-strength determination shall be based upon the cross-sectional area of the bolt where the break occurs. When the break occurs in the threaded portion, the cross-sectional area shall be taken from Table 3. For sizes not included in Table 3 the area shall be calculated from the following formula: A=: 3.1416
(P ~ R)
2
Where: A =: mean equivalent area (stress area) P =: mean pitch diameter R =: mean root diameter Where equipment of sufficient capacity is not available for testing bolts in full size, tests shall be made as follows: Bolts % to 1% in. in diameter, inclusive, shall have their shanks machined to a standard O.505-in. test specimen, concentric with the axis of the bolt, leaving the head and the threaded section of the bolt intact. (See Fig. 2.) The load shall then be applied between a nut or suitable fixture and the bolt head. For bolts I1h in. in diameter and over, a standard 0.505in. test specimen shall be turned from the bolt having an axis midway between the center and outside surface of the bolt shank. (See Figs. 3 and 4. ) MINIMUM RADIUS RECOMMENDED 'At" BUT NOT LESS THAN Y." PERMITTED
FIG. I-TENSION TESTING OF FULL-SIZE BOLT
The determination of tensile strength and proof load, both in pounds per square inch, shall be based upon the stress areas shown in Table 3.
2 '~O.005.!!.-.-j GAGE LENGTH FOR ElONGATION AFTER FRACTURE
FIG. 2-TENSION-TEST SPECIMEN FOR BOLT WITH TURNED-DoWN SHANK
145
section VI - tables and specifications
the bolt. The load applied shall be equal to the specified elastic proof load, the bolt then removed from the testing machine, and the over-all length of the bolt again determined. The length after loading shall not exceed that before loading by more than 0.0005 in. (It is intended that no permanent elongation take place, and the limit of 0.0005 in. is set to include errors of measurement. ) FIG. 3-LoCATION OF STANDARD ROUND 2-IN. GAGE LENGTH TENSION-TEST SPECIMEN WHEN TURNED FROM LARGE-SIZE BOLT
f----2!4" PARALlEL SECTION
MINIMUM RADIUS RECOMMENDED %" BUT NOT LESS THAN lAI" PERMITTED
Y2" '±'O.Ol"
-- - ---r-- - -
Yield Strength (Extenso meter Method)-Where determination of yield strength is required (where elastic proof load cannot be determined on the full-size bolt) a standard 0.505-in. test bar shall be turned and tested using an extensometer to measure deformation over the gage length. The yield strength shall be the load at which permanent set in the gage length of 0.2% occurs.
I-- 2"±O.005 ~
GAGE LENGTH FOR ELONGATION AFTER FRACTURE FIG. 4-STANDARD ROUND TENSION-TEST SPECIMEN WITH 2-IN. GAGE LENGTH
The 10-degree wedge for use in the tension test shall have a thickness of one half the bolt diameter measured at the short side of the hole. The edge of the hole, top and bottom of the wedge shall be rounded to a maximum radius as follows: Maximul11
*
Bolt Size, in.
Radius, in.
to Y2 Y:32 716 to 1.................................................... Y1.6 1Ys to 1Y2 Ys The clearance in the wedge hole shall be substantially as follows:
*%6
Bolt Size, in.
to Y2 to % : % to 1% to 1112 Fig. 5 illustrates the wedge test.
1*
Oversize Clearance of Wedge Hole, in.
0.030
0.050 0.063 0.094
Proof Load-In case the purchaser and supplier differ in opinion as to the procedure of test, the following will be used as the referee method: The over-all length of a straight sample bolt shall. be measured at the tme centerline. The preferred method for measuring the length shall be between conical centers on the centerline of the bolt at the head and point end using mating centers on the measuring anvils. The sample bolt shall be marked on the shank or head so that it can be placed in the measuring fixture in the same position for all measurements. The measming instmment shall be capable of measurement to 0.0001 in. The bolt shall then be loaded as in the tensile-strength test except a Hush bearing plate shall be used against the head of
146
T
J'---_-+--__-----==~
1
dl+c FIG. 5-VVEDGE-TEST DETAILS
= clearance of wedge hole = diameter of bolt R = maximum radius
c d
T = thickness of wedge at short side of hole equals one half diameter of bolt
tables and specifications - section VI
TABLE 4-PROOF LOADS AND MINIMUM TENSILE STRENGTHS
Grade
Bolt and Stud Diame~er,
m.
Grade 1Commercial Steel Bolts
%
'riG
%
7116 l/2
-
Pis
%
%6 %
%6 :1:2
%6
% % %
%6 %
%6 :1:2 9h.6
% Grade 5Medium-Carbon Steel, Quenchedand-Tempered Bolts
-
-
1% 1% 1:1:2
Grade 3Medium-Carbon Steel, Cold-Worked, Hexagon-Head Bolts and Studs
'1
9h.G
1
Grade 2Low-Carbon Stee! Bolts 2
Elastic fOO oad,£ bolts,lb
% %
%
%
0/16 %
%6 :Ih 9h.6
% %
% 1
Fine Thread
Coarse Thread
-
-
-
-
I Minimum tensile strength,' bolts,lb
1,750 2,850 4,250 5,850 7,800 10,000 12,400 18,350 25,350 33,300 41,950 53,250 63,450 77,250
Elastic roof oad,
bolts, lb
-
-
-
-
IMinimum tensile
Grade
strength l 1.
bolts,lb
2,000 3,200 4,800 6,500 8,800 11,150 14,050 20,500 28,000 37,350 47,000 58,950 72,250 86,900
1,750 2,850 4,250 5,850
2,200 3,600 5,350 7,300
2,000 3,200 4,800 6,500
2,500 4,000 6,050 8,150
7,800 9,450 11,750 17,350
9,750 11,600 14,450 21,300
8,800 10,550 13,300 19,350
11,000 12,950 16,350 23,850
2,700 4,450 6,550 9,000 12,050 14,550 18,050
3,500 5,750 8,500 11,650 15,550 18,150 22,550
3,050 4,900 7,450 10,050 13,550 16,200 20,450
4,000 6,350 9,650 13,050 17,550 20,250 25,550
2,700 4,450 6,550 9,000 12,050
3,800 6,250 9,250 12,700 17,000
3,050 4,900 7,450 10,050 13,550
4,350 6,950 10,500 14,200 19,150
15,450 19,150 28,400 35,950 47,200
21,800 27,050 40,100 53,000 69,600
17,200 21,700 31,650 39,700 52,950
24,300 30,650 44,700 58,600 78,100
Grade 5(Continued)
Grade 6Medium-Carbon Steel, Quenchedand-Tempered, High-Strength Bolts
Bolt and Stud Dialll-
Fine Thread
m.
bolts, lb
bolts, lb
Pis
56,450 71,650 85,400 103,900
80,100 101,700 121,150 147,450
63,250 79,350 97,200 116,900
89,750 112,550 137,950 165,900
3,500 5,750 8,500 11,650
4,450 7,300 10,800 14,850
4,000 6,350 9,650 13,050
5,050 8,100 12,250 16,600
15,550 19,950 24,800 35,050
19,800 25,400 31,600 44,400
17,550 22,300 28,100 39,100
22,350 28,350 35,750 49,500
3,350 5,500 8,100 11,150 14,850
4,100 6,800 10,050 13,800 18,400
3,800 6,100 9,200 12,450 16,750
4,700 7,500 11,400 15,400 20,750
19,050 23,700 35,050 48,400 63,550
23,600 29,350 43,400 59,950 78,650
21,250 26,800 39,100 53,400 71,300
26,350 33,200 48,400 66,150 88,300
80,100 101,700 121,150 147,450
99,150 125,900 150,000 182,550
89,750 112,550 137,950 165,900
111,150 139,350 170,800 205,400
3,800 6,250 9,250 12,700 17,000
4,750 7,850 11,600 15,900 21,250
4,350 6,950 10,500 14,200 19,150
5,450 8,700 13,150 17,800 23,950
21,800 27,050 40,100 55,350 72,600
27,250 33,850 .50,100 '69,200 90,}50
24,300 30,650 44,700 61,050 81,500
30,400 38,300 55,850 76,300 101,850
91,500 114,400 116,200 145,250 138,450 173,050 168,500 210,600
102,600 128,650 157,650 189,600
128,25i91> 160,800 197,050, 237,000
e~er,
1% 1% 1:1:2
14 5h.G %
7116 :1:2
% % 14
0/16 %
%6 :1:2
%6
% %
% 1 Ills
114 1% 1:1:2 Grade 8Medium-Carbon Alloy Steel, Quenched-andTempered, HighStrength Bolts
IMinimum tensile
Elastic proof load, bolts,lb
%6
Grade 7Medium-Carbon Alloy Steel, Quenched-andTempered, Medium-Strength Bolts
Coarse Thread
14 0/16 %
7116 :1:2
%6
% % % 1
llfs 1% 1% 1:Ih
Elastic proof load,
strength,1.
Minimum tensile strength, 1 bolts,lb
(1) Also proof load for nuts. (2) Proof loads shown apply only to hexagon-head bolts and studs.
Yield Strength (Autographic Stress-Strain Method) -By agreement between supplier and purchaser, the yield strength instead of proof load may be determined on the full-size bolt by using an autographic method approved by the purchaser. When this is done, the minimum yield strength at 0.2% offset method, in pounds, shall be equal to the values shown for Elastic Proof Load in Table 4.
the threaded portion of the bolt at a point one quarter of the nominal diameter from the axis of the bolt. This section shall be taken at a distance of one diameter from the end of the bolt. The preparation of test specimens and the method of performing the hardness tests shall be in conformity with the requirements appearing in the SAE Handbook.
Hardness-For final arbitration, the hardness of bolts shall be determined on a transverse section through
Stripping Test for Nuts-The sample nut shall be assembled on a hardened, threaded mandrel and the
147
section VI - tables and specifications
load specified in Table 4 applied to the nut. Threads of the nut shall not strip at this load. If the threads of the mandrel are damaged during the test, the test shall be discarded. The mandrel shall be threaded to the American Standard Class 3 tolerance, except that the major diameter shall be the minimum major diameter with a plus tolerance of 0.002 in. If the unit tensile stress developed in the mandrel is required, the loads thus obtained shall be divided by the mean thread area as given in Table 3. Number of Tests-The requirements of these specifications are those met in continuous mass production for stock during which the manufacturer has made such sample inspections as to insure normally that the material is controlled within the specified limits. Three bolts may be selected for tension test from each lot of bolts, and three nuts may be selected for stripping test from each lot of nuts. A lot of bolts or nuts or both shall consist of 25,000 or fraction thereof for diameters ~ to % in. inclusive, 15,000 or fraction thereof for diameters over % to % in. inclusive, 5000 or fraction thereof for diameters over % to 1 in. inclusive, and 2500 or fraction thereof for diameters over 1 in.
Retest-Should any sample from the same lot fail to meet the requirements of a specified test, twice the number of samples shall be tested, in which case all of the additional samples shall meet the specifications. Identification-Bolt heads shall be marked to identify the manufacturer. In addition, the following bolt head markings are prescribed:
148
Grades 0, 1, and 2--No marking.
CD Grade 3-2 radial dashes 180 degrees apart.
Grade 5-3 radial dashes 120 degrees apart,
Grade 6-4 radial dashes 90 degrees apart.
Grade 7-5 radial dashes 72 degrees apart.
Grade 8-6 radial dashes 60 degrees apart.
TENTATIVE SPECIFICATIONS FOR ALUMINUM BARS FOR ELECTRICAL PURPOSES (BUS BARS)J. ASTM DESIGNATION: B 236 . 56 T Issued, 1948; Revised, 1952, 1955, 1956. 2 These Tentative Specifications have been approved by the sponsoring committee and accepted by the Society in accordance with established procedures, for use pending adoption as standard. Suggestions for revisions should be addressed to the Society at 1916 Race St., Philadelphia 3, Pa.
Scope 1. These specifications cover EC aluminum bus bar for electrical conductors as follows: Type A.-Cold finished rectangular bar in Hl3 and H17 tempers. . Type B.-Hot finished rectangular bar in H12, HU1, and Hll2 tempers.
Basis of Purchase 2. Orders for material under these specifications shall include the following information: (1) Pieces or pounds, (2) Temper (Section 4), ( 3) Dimensions-thickness, width, and length (specific or stock) (Section 10), ( 4) Edge contour (Section 15), (5) Finish (Section 16), ( 6) Whether marking for identification is required (Section 17), and ( 7) Place of inspection (Section 19).
sHe properties prescribed in Table I for the specified temper.
TABLE I.-TENSILE REQUIREMENTS. NOTE.-For purposes of determining conformance with these specifications, each value for tensile strength and yield strength shall be rounded off to the nearest 100 psi, in accordance with the rounding off method of the Recommended Practices for Designating Significant Places in Specified Limiting Values (ASTM Designation: E 29).
Temper
Thickness, in.
H17 ...... H13 ...... H12 ......
%to %, inc!.. .... %to %,inc!.. .... % to 1, incl....... % to %,inc!.. ....
H1l2 .....{
Over % to 1, inc!.. Over 1 to 1 Y.!, incl. All thicknesses. . ..
H11l .....
Tensile Strength, min, psi
Yield Strength, min, psi·
17000 14 000 12000 12000 11000 10 000 9 000
15000 12000 8 000 7000 5 000 4 000 4000
• Yield strength is defined as the stress which produces a permanent set of 0.2 per cent of the initial gage length.
Manufacture 3. The materials used shall be such as to produce bars that will comply with the requirements as to tensile properties, bend tests, and electrical conductivity prescribed in these specifications:
Tensile Properties 4. The bars shall be supplied in the temper specified and shall conform to the requirements as to ten1 Under the standardization procedure of the Society, these speciflcations are under the jurisdiction of the ASTM Committee B-7 on Light Metals and Alloys, Cast and Wrought. By publication of these specifications, the American Society for Testing Materials does not undertake to insure anyone utilizing the specifications against liability for infringement of Letters Patent nor assume any such liability, and such publication should not he construed as a recommendation of any patented or proprietary application that may be involved. 2 Latest revision accepted by the Society at the Annual Meeting, June,
1956.
Bend Properties 5. (a) Flatwise Bend Test.-Bars in the H12, H13, HIll, and H112 tempers shall be capable of being bent flatwise at room temperature through an angle of 90 deg around a pin having a radius equal to the thickness of the specimen, without cracking and with no apparent evidence of slivers or other imperfections. ( b) Edgewise Bend Test (See Note).-Bars in the H12, Hlll, and HI3 tempers, whose width-to-thickness values are not in excess of 12, 12, and 8 respectively, shall be capable of being bent cold edgewise 90 deg around a mandrel having the ramus shown in Table II, without cracking or excessive localized thinNOTE.-Edgewise bend tests are not required for bars over 4 in. in width.
149
section VI - tables and specifications
Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) nings as defined below. Edgewise bends shall be considered satisfactory if the thickness within the vicinity of any localized thinning is not less than 90 per cent of the maximum thickness within the central 60 deg -of the bend when measured only along the outer edge of the bend.
TABLE n.-EDGEWISE BENDING RADIUS. Width of Bus Bar, in.
*
V2 and under. . . . . . . . . . . . . . . . . . . . . . . . . Over to 1, incl.. . . . . . . . . . . . . . . . . . . . . Over 1 to 1V2, incl.. . . . . . . . . . . . . . . . . . . . Over 1* to 2, incl.. . . . . . . . . . . . . . . . . . . . Over 2 to 2V2, incl. . . . . . . . . . . . . . . . . . . . . Over 2* to 3, incl.. . . . . . . . . . . . . . . . . . . . Over 3 to 3V2, incl. . . . . . . . . . . . . . . . . . . . . Over 3V2 to 4, incl.. . . . . . . . . . . . . . . . . . . .
Mandrel Radius, in.
V2 1 1V2
2
2V2 3
3V2 4
Electrical Properties 6. The resistivity of specimens selected as prescribed in Section 7 shall not exceed 0.07640 ohms (meter, gram) at 20 C (68 F) corresponding to a conductivity not less than 61 per cent of the International Annealed Copper Standard.
Test Specimens 7. (a) Tension.- Tension test specimens shall be the full section of the bar, or specimens machined from the bar with the axis parallel to the length of the bar and having the form and dimensions specified in the Methods of Tension Testing of Metallic Materials (ASTM Designation: E 8), for sheet type specimens or for round specimens. (b) Bend.-Bend test specimens shall be a full section of the material. (c) Resistivity or Conductivity.-Specimens for determining resistivity or conductivity should preferably be a full section of the material, but may be of any suitable size or shape appropriate to the instrument to be used in making the determination.
Number of Tests 8. (a) Specimens shall be selected from each size and temper of bars in the shipment according to the following schedule: Minil111U11 Number of Specimens to be Number of Pieces in Lot Selected It050...................... 1 51 to 200. .. . . . . . . . .. . . . . . . . . 2 201 to 1500. . . . . . . . . . . . . . . . . . 3 Over 1500 0.2 per cent of number of pieces in lot 150
( b) When more than one specimen is required to be taken from the lot, no two specimens for the same type of test shall be taken from the same bar.
Methods of Testing 9. (a) Tension.- Tension tests shall be made in accordance with the Methods of Tension Testing of Metallic Materials (ASTM Designation: E 8). NOTE.-The values obtained for the tensile properties covered by these specifications are not seriously affected by variations in speed of testing. A considerable range of testing speed is permissible, however, the rate of stressing to the yield sh'ength should not exceed 100,000 psi per min, and above the yield sh'ength the movement per minute of the head under load should not exceed 0.5 in. per in. of gage length (or distance between grips for specimens not having reduced sections). Care must be exercised, especially when making yield strength determinations, that the speed of testing does not exceed the ability of the strain and load-indicating equipment to function satisfactorily. (b) Bend.-Bend test specimens may be bent by either pressure or blows provided that, in the case of dispute, bends made under pressure shall be the basis of acceptance or rejection. (c) Electrical Resistivity. - Electrical resistivity shall be determined in accordance with the Method of Test for Resistivity of Electrical Conductor Materials (ASTM Designation: B 193).
TABLE III.-PERMISSIBLE VARIATIONS IN THICKNESS FOR TYPE A BARS. Specified Thickness, in.
Permissible Variations in Thickness, plus and minus, in.,. for Widths Given in Inches Over Over Over Over 2.00 to 4.00 to Yz to 1% 8.00, Yz and 1%, to 2.00, 4.00, inc!. inc!. Under incl. inc!.
0.125 to 0.188 0.0025 0.189 to 0.500 0.003 0.501 to 0.750 ....
0.0035 0.004 0.003 0.0035 0.004 0.0045 0.004 0.0045 0.005
0.0025 0.003 0.004
a If all plus or all minus variations are desired, double the values given.
TABLE IV.-PERMISSIBLE VARIATIONS IN WIDTH FOR TYPE A BARS. Permissible Variations in Width, plus and minus, in. a
Specified Width, in. 0.500 to 1.25 1.26 to 2.00 2.01 to 4.00 4.01 to 8.00
. . . .
0.005 0.008 0.012 0.30 per cent b
a When variations are specified as ali plus or all minus, doub the values given. b Expressed to the nearest 0.001 in.
tables and specifications - section VI
Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) Permissible Variations in Dimensions 10. (a) Thickness and Width. _ Thickness and width variations from the specified dimensions for the type of bar ordered shall not exceed the amount prescribed in Tables III, IV, V, and VI.
terial is ordered in stock lengths, it may include short lengths as prescribed in Table VIII.
TABLE VII.-PERMISSIBLE VARIATIONS IN LENGTH FOR SPECIFIC AND MULTIPLE LENGTHS.
TABLE V.-PERMISSIBLE VARIATIONS IN THICKNESS FOR TYPE B BAR.
I
Thickness, in.
0.125 0.501 0.751 1.001
to to to to
0.500 0.750 1.000 2.000
. . . .
Specified Width, in.
Permissible Variations in Thickness, plus and minus, in.
18 and Under
3.499 and under. 3.500 and over
FINISHED EDGE
Permissible Variation in Inches over the Specified Length Given in Feet
0.006 0.008 0.012 0.020
. .
TABLE VID.-SCHEDULE OF LENGTHS (STOCK WITH SHORT LENGTHS).
SAWED EDGE
0.250 0.321 0.439 0.626 0.876 1.126 1.376 1.626 1.876 2.251 2.751
to to to to to to to to to to to
0.320. . . . . . . . . . . . . . . . . . . 0.438. . . . . . . . . . . . . . . . . . . 0.625. . . . . . . . . . . . . . . . . . . 0.875. . . . . . . . . . . . . . . . . . . 1.125. . . . . . . . . . . . . . . . . . . 1.375. . . . . . . . . . . . . . . . . . . 1.625. . . . . . . . . . . . . . . . . . . 1.875. . . . . . . . . . . . . . . . . . . 2.250. . . . . . . . . . . . . . . . . . . 2.750......... 3.000...................
0.013 0.019 0.025 0.030 0.035 0.040 0.045 0.052 0.060 0.075 0.090
TABLE VI.-PERMISSIBLE VARIATIONS IN WIDTH FOR TYPE B BAR. Width, in.
Permissible Variations in Width, plus and minus, in.
FINISHED EDGE
0.500 1.501 4.001 6.001
to to to to
1.500 " 4.000. . . . . . . . . . . . . . . . . . . 6.000. . . . . . . . . . . . . . . . . . . 10.000. . . . . . . . . . . . . . . . . .
0.016 0.032 0.047 0.063
Area, sq in. a
Stock Length, ft
0.250 and under Over 0.250 to 1, incl. Over 1 to 2.25, incl. Over 2.25 to 4, incl. Over 4 to 9, incl.
6 to 6 to 6 to 6 to 6 to
0.094 0.125
( b) Specified Lengths.-When exact lengths are ordered, the lengths shall not be less than the ordered length and not exceeded by more than prescribed in Table VII. ( c) Stock Lengths. - Material ordered in stock lengths shall be not less than the designated length and shall not exceed it by more than 1 in. When ma-
20, indo 20, indo 20, incl. 20, incl. 10, incl.
Shortest Permissible Length, b per cent of Nominal Length
75 70 70 60 60
Maxim.um Permissible Weight of Short Lengths, per cent of lot Weight
20 30 30 30
gO
• Width times thickness, disregarding any rounded corners or edges. Expressed to the nearest Y. ft.
b
Straightness 11. Unless otherwise speci£ed, the material shall be furnished in straight lengths. The deviation from straightness of any longitudinal surface or edge shall not exceed the limitations prescribed in Table IX. TABLE IX.-PERMISSIBLE VARIATIONS IN STRAIGHTNESS APPLICABLE TO ANY LONGITUDINAL SURFACE OR EDGE:
Type
Temper
SAWED EDGE
2.000 to 6.000. . . . . . . . . . . . . . . . . . . 6.001 to 14.000 ... , .... ,. . . . .. . ..
Over 18
H17 ..... A ........ { H13 ..... B........ All ......
Maximum Curvature (Depth of Arc), in. Flatwise
Edgewise
1;4 1;4 1;4
% % 1;4
Portion of Total Length in Which Depth of Arc is Measured, in.
96 60 60
NOTE.-To determine compliance w'ith this section, bar shall, in case of disagreement, be checked by the following method: Place the bar on a level table so that the arc or departure from straightness is horizontal. Measure the maximum depth of arc to the nearest 1~2 in. using a steel scale and a straight edge. 151
section VI - tables and specifications
Aluminum Bus Bars for Electrical Purposes (B 236 -56 T) (c) Rounded Edge.-When specified, bar may be
Flatness
12. Flat surfaces of both type A and B material shall not deviate from flat by more than 0.004 in. per inch of width, with a deviation of 0.004 in. permitted for all widths under 1 in.
finished with edges rounded as shown in Fig. 2, the radius of curvature being approximately one and one quarter times the thickness of the bar for bar 1Js in. and over in thickness. The tolerance on the radius shall be one-fourth the thickness of the bar.
I·
Retests
i
13. If any test specimen fails to meet the applicable requirements of these specifications, two additional specimens shall be selected from other bars in the lot and both specimens shall meet the applicable requirements or the lot shall be subject to rejection.
Significance of Numerical Limits 14. For purposes of determining compliance with the specified limits for requirements of the properties listed in the following table, an observed value or a calculated value shall be rounded off as indicated in accordance with the rounding-off methods of the Recommended Practices for Designating Significant Places in Specified Limiting Values (ASTM Designation: E 29). Property
NOTE.-The arc shall be substantially symmetrical with the axis of the product. The corners will usually be sharp but shall not have rough or projecting edges. FIG. 2.-Rounded Edge.
(d) Full-Rounded Edge.-When specified, bar may be finished with substantially uniform round edges, the radius of curvature being approximately one-half the thickness of the product, as shown in Fig. 3, but in no case to exceed one-half the thickness of the product by more than 25 per cent.
Rounded-Off Unit for Observed or Calculated Value
Electrical resistivity ..... nearest unit in the last right hand place of figures Tensile strength . . . . . . . .nearest 500 psi Yield strength nearest 500 psi
Edge Contours 15. (a) Square Corners.- Unless otherwise specified, bar shall be finished with commercially square corners with a maximum permissible radius of Y:32 in. for bar lh in. to 1 in., inclusive, in thickness, and VJ.6 in. for bar over 1 in. in thickness. (b) Rounded Corners.-When specified, bar may be finished with corners rounded as shown in Fig. 1 to a quarter circle with a radius of Ys2 in. for bar VB to %6 in. inclusive, in thickness; VJ.6 in. for bar over %6 in. to 1 in. inclusive, in thickness; and lh in. for bar over 1 in. in thickness.
NOTE.-The arc shall not necessarily be tangent but the product shall be commercially free from sharp, rough or projecting edges. FIG. I.-Rounded Corners. 152
R
R
NOTE.-The arc shall not necessarily be tangent but shall be substantially symmetrical with the a..xis of the product, and the product shall be commercially free from sharp, rough, or projecting edges. FIG. 3.-Full Rounded Edge.
(e) Sawed Edge.-A rough surfaced edge showing saw marks and very slight or no deformation of the corners. The sawing operation leaves a slight burr on the corners, which is generally not completely removed and which may necessitate care in handling.
Finish 16. (a) Class I.-Material shall be free from blisters, slivers, and pick up, as well as from all other imperfections not consistent with the best commercial practice and shall be commercially bright and clean. It shall be suitable for use as electrical bus bar. . (b) Class n.-Material shall be uniform in quality and condition, free from laps, folds, slivers, seams, and cracks. Surface appearance as such is not a primary factor; and stains, abrasions, saw burrs, and minor handling marks within the limits of commercial practices shall be acceptable.
tables and specifications - section VI
Aluminum Bus Bars for Electrical Purposes (B 236 . 56 T) Marking for Identification 11. (a) When identification marking is specified on the purchase order, all bars shall be marked with the manufacturer's name or trade mark and the applicable alloy and temper designations, the latter to be in accordance with the ASTM codification systems (ASTM Designation: B 275 and B 296) or the commercial systems. Identification characters shall have a minimum height of % in. The marking material shall be such as to resist obliteration during normal handling and shall be removable by normal cleaning methods; however, ghost images of the characters may remain. Markings shall appear at each end of each piece. ( b) The, foregoing requirements are minimum, marking systems which involve added information, larger characters, and greater frequencies are accept·able under these specifications.
Packaging 18. The material shall be properly and adequately bundled, crated, or otherwise packaged to protect it against injury during shipment. The type of packaging shall be left to the discretion of the manufacturer, unless otherwise agreed upon. Each package shall
contain only one size of material, unless otherwise agreed upon by the manufacturer and the purchaser.
Inspection 19. (a) Inspection may be made at the manufacturer's works or at the point at which the material is received, at the option of the purchaser. ( b) If the purchaser elects to have the inspection made at the manufacturer's works, the manufacturer shall afford the inspector representing the purchaser all reasonable facilities, ~thout charge, to satisfy him that the material is being furnished in accordance with these specifications. All tests and inspection shall be so conducted as not to interfere unnecessarily with the operation of the works.
Rejection 20. Material failing to conform to the requirements of these specifications or in which defects are discovered-during subsequent manufacturing operations may be rejected and, if rejected, the manufacturer's responsibility shall be limited to replacing the rejected material without charge to the purchaser. The full weight of the rejected original material shall be returned to the manufacturer.
Appendix The most common form of aluminum bus conductor is bar which, for purposes of this specification, is defined as follows: Bar.-Includes material of solid rectangular or square cross-section, or a solid section with two plane parallel sUlfaces having round or other simple regularshaped edges. Unless otherwise specified, bars are generally finished with commercially square corners in accordance with the definition in Section 15(a ). EC aluminum rectangular bar may be manufactured commercially by the following methods: (1) Hot-Rolled.-Hot-rolled to the final dimensions. (2) Extruded.-Extruded to the final dimensions. (3) Cold-Finished.-Hot-rolled or extruded to a size larger than specified and reduced to final dimensions by drawing or cold rolling. (4) As Fabricated Bar Sawed from Plate.-Hot- or cold-rolled to final thickness and sawed to final ~dth. . EC aluminum bar is normally selected on the basis of the desired strength requirements and bending characteristics required for fabrication and installa-
tion. Dimensional tolerances and surface finish may be of equal importance in some applications. Surface finish may be related to the method of fabrication. Commercial mill hot-finished bar, class II finish, is used where surface quality as such is not a primary requirement. By employing controlled fabricating practices, hot-worked bar may be produced to class I finish. This bar would have a variation in luster typical of a hot-worked finish, but fewer handling marks or other surface irregularities than class II finish. Cold working of the bar to finish it will, by the nature of this operation, result in a class I finish. It produces a more uniform finish as a result of the controlled fabricating practices employed. The harder tempers produced by cold finishing are less subject to abrasion marking. Bar produced with a class I finish requires boxing for proper protection during shipment. Some applications require that flat bus bar be bent either flatwise or edgewise. The specifications define the flatwise and edgewise bending requirements applicable to the various temper designations of bar. In
153
section VI - tables and specifications
Aluminum Bus Bars for Electrical Purposes (B 236·56 T) general, the higher the tensile strength or the greater the thickness of the bar the greater the radius required to bend it flatwise without cracking. EC-H17 bar can be successfully bent 90 deg flatwise over a radius of one times the thickness, although slight surface cracking may sometimes develop. It is, therefore, suggested that a larger bending radius be employed for flatwise bending this temper. Edgewise bending is much more severe and is more difficult to do. Success in making satisfactory edgewise bends depends to a considerable extent upon the equipment and procedures used. The radius (in terms of width of bar) around which a bar can be bent edgewise depends upon the tensile properties and also upon the ratio of width to thickness, Wit, of the bar. When bars are bent edgewise the changes in dimensions appear to be a function of the geometry of the bend regardless of the tensile properties of the bar. With a bend radius of 1W, the thickness along the inner edge increases about 20 per cent, and along the outer edge it decreases about 16 per cent. For EC-H12 and EC-H13 a radius greater than 1W will normally be required for bars having a Wit exceeding 12 and 8, respectively. In special cases where these width thickness ratios are exceeded, a larger bend radius should be used. Table X reflects the in:8.uence of bar dimensions.
Samples for chemical analysis shall be taken in accordance with the Method of Sampling Wrought Non-Ferrous Metals and Alloys for Determination of Chemical Composition (ASTM Designation: E 55), except that the weight of the prepared sample may be a minimum of 75 g. A portion shall be taken to represent each 2,000 lb or fraction thereof of each temper and size of bars in the shipment, and a sample prepared from each portion. If agreed upon by the manufacturer and the purchaser, a composite sample representing all portions taken from a given temper and size may be used for the analysis in lieu of analyzing samples from each portion. If the manufacturer has made an analysis during the course of manufacture, he shall not be required to sample and analyze the finished product. The chemical analysis shall be made in accordance with the Method of Chemical Analysis of Aluminum and Aluminum-Base Alloys (ASTM Designation: E 34) 3 or by any other approved methods agreed upon by the manufacturer and the purchaser. The analysis may be made spectrochemically, provided that, in the case of dispute, the results secured by Methods E 34 shall be the basis for acceptance. 3
1956 Book of ASTM Methods for Chemical Analysis of Metals.
TABLE X.-·READILY AVAILABLE WIDTHS. Thickness, in.
Width, in.
1h
VB ....... .
% I 114 1112 1% --------
X X X X Y4 ....... . X X % .. . .... . . , . .. . liz ....... . . . .. . % .. . .... . . , . .. . % ....... . . . .. . 1 ........ . . . .. . %6 ...... .
,
, ,
X ® ® X X X X X X .. . .. . .. . .. . . .. .. . . .. .. . .. .
.. .
.. . .. .
.. .
.. .
.. .
2
214
21h
2%
3
31h
4
5
6
NOTE.-Symbols used in the table are explained as follows: X.-Hlll, Hl2 and Hl3 tempers required to meet edgewise bend test. 0.-HI3 temper not required to meet edgewise bend test. fRI.-Neither HIll, H12 nor Hl3 tempers required to meet edgewise bend test. * -Bending requirements for bar wider than 4 in. shall be as agreed upon by the manufacturer and the purchaser.
154
I 8
I 10
1-----
l8J l8J . , . .. . .. . .. . .. . .. . .. . .. . . .. ... ® ® ® l8J l8J l8J .. . .. . .. . ... . .. . .. .. X X ® ® ® ® l8J l8J * * * .. . X X X X X ® ® * * * ... .. . X X X X X .. . X * * * ... . . .. . .. . .. . .. . .. . ... X * * * * .. . .. . .. . .. . . .. .. . ... X * * * * .. . .. . .. . .. . . .. .. . ... X * * * *
RECOMMENDED PRACTICE FOR PREPARATION OF AND ELECTROPLATING ON ALITMINUM ALLOYS
1
ASTM DESIGNATION: B 253 . 53 Adopted, 1953. 2 !his Recommended Practice of the American Society for Testing Materials is Issued under the fixed designation B 253; the final number indicates the year of original adoption or, in the case of revision, the year of last revision.
Scope . 1. (a) Various metals are electrodeposited on alummum alloys to obtain a decorative finish or one which is more wear resistant or suitable for some other specific service. The electroplates applied for finish are usually chromium, nickel, copper, brass, silver, gold or modifications of these. Silver is applied to electrical equipment to decrease contact resistance or to improve smface conductivity; brass to facilitate vulcanization of rubber to aluminum; copper, nickel or tin for as. sembly by soft soldering; chromium to reduce fIiction and obtain increased resistance to wear; zinc to threaded parts where organic lubricants are not permissible; while tin is frequently employed to reduce friction on bearing surfaces. ( b) This recommended practice is presented as a guide for the plating of aluminum alloys. Electroplating of these alloys is commercially practical and economically sound. Aluminum alloys, however, do not respond satisfactorily to many of the usual preparatory procedures for plating; hence, different procedures are requir~d to obtain a satisfactory basis for plating. Of the dIfferent methods available, the zinc-immersion method is considered to be the most satisfactory and practical for plating substantially all of the different aluminum alloys with various other metals.
Nature of Aluminum 2. (a) Microstructure.-It has been difficult to find a preplating procedure that will be equally satisfactory for all types and tempers of aluminum alloys because the various alloys and products behave diffel'ently electrochemically since they have different metallurgical structures. When elements are added for alloying purposes, they may appear in an aluminum alloy in several different forms; tllat is, tlley may 1 Under the standardization procedure of the Society, this recommended practice is under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption, this recommended practice was published as tentative from 1951 to 1953.
be in solid solution in the aluminum lattice, be present as micro-particles of the elements themselves, or be present as particles of intermetallic compounds formed by combination with the aluminum. The several solid solution matrices and the twenty or more microconstituents that may occur in commercial alloys may have different chemical and electrochemical reactivities and their smfaces may not respond uniformly to various chemical and elech'ochemical treatments. In addition, the response may be influenced by variations in the microstructure of different lots or products of the same alloy. The plater should know, if possible, the type of aluminum alloy that is to be plated in order to select the best plating procedure. (b) Oxide Film.-In addition to differences in microstructure that may affect response to preplating conditioning h'eatments, all aluminum products have an ever-present natural oxide film. This oxide film can be removed by various acid and alkaline treatments, but after rinsing the surface will still have an oxide film that re-formed during tlle treatment. For best results with the zinc-immersion process, the new oxide film should be thinner and more unifonn and provide a suitable smface for deposition of the zinc-immersion layer.
Cleaning and Conditioning Treatments 3. (a) To obtain consistent results with the zincimmersion process for plating aluminum alloys, it is essential that the various cleaning and conditioning treatments provide a smface of uniform activity for the deposition of the zinc layer. First, the surface should be free of any oil, grease, or other foreign material. For removing oil or grease, vapor degreasing or solvent cleaning may be necessary. Ordinarily, a mild etching-type alkaline cleaner is recommended. One can be made conveniently by using 23 g per I (3 oz per gal) each of sodium carbonate and trisodium phosphate. This solution should be used at a temperature of 140 to 180 F (60 to 82 C) for 1 to 3 min. 155
section VI - tables and specifications
Preparation of and Plating on Aluminum Alloys (B 253 . 53) (b) After appropriate cleaning, further treatment Zinc Immersion of the surface is generally required. For this conditioning treatment to be effective, it must accomplish two things: (1) remove. the original oxide film; and (2) remove any microconstituents which may interfere with the formation of a continuous zinc-immersion layer or which may react with subsequent plating solutions.
(c) For wrought alloys of the 990 A and MIA types, 3 fairly good conditioning may be obtained by using the carbonate-phosphate cleaner followed by a dip in a nitric acid solution (50 per cent by volume). These alloys do not contain interfering constituents and for some applications this method of conditioning may be ample. (d) One of the more effective conditioning treatments for removing the surface oxide film and any undesirable microconstituents comprises the use of a hot acid etch containing sulfuric acid (15 per cent by volume) fot a period of 2 to 5 min at a temperature of 180 F (82 C). The time of the dip depends upon the alloy involved. Generally the shorter time is used on castings. This treatment is satisfactory for all wrought and most cast aluminum alloys. It not only leaves the surface in an excellent condition for the formation of the zinc-immersion layer, but it also eliminates the undesirable effects of the magnesium-containing constituents in alloys of the GR20A,3 GSllA/' and GSI0N types. (e) Another conditioning treatment which has considerable merit consists of a double zinc-immersion treatment with the first zinc layer being removed by a dip in a nitric acid solution (50 per cent by volume). This treatment has been found to be very effective for use with many cast alloys and with wrought alloys that do not contain appreciable percentages of magnesium and when the identity of the alloy is not known. With this procedure, the first immersion dip removes the original oxide film and replaces it with a zinc layer. Removal of the zinc layer by the nitric acid dip leaves the surface in suitable condition for deposition of the final zinc-immersion layer. (f) For casting alloys containing high percentages of silicon, S12B,5 SC64C,6 SG70A6 and SC84B,5 type alloys, a dip for 3 to 5 sec in a solution containing 3 parts (by volume) of concentrated commercial nitric acid plus 1 part (by volume) of commercial hydrofluoric acid (48 per cent) is recommended for conditioning the surface. • See Tentative Specifications for Aluminum and Aluminum-Alloy Sheet and Plate (ASTM Designation: B 209). 1954 Supplement to Book of ASTM Standards, Part 2. • See Tentative Specifications for Aluminum and Aluminum-Alloy Extruded Bars, Rods, and Shapes (ASTM Designation: B 221), 1954 Supplement to Book of 1\.STM Standards, Part 2. • See Tentative Specifications for Aluminum-Base Alloy Die Castings (ASTM Designation: B 85), 1954 Supplement to Book of ASTM Standards, Part 2. . • See Standard Specifications for Aluminum-Base Alloys in Ingot Form for Sand Castings, Die Castings, and Permanent Mold Castings (ASTM Designation: B 179), 1952 Book of ASTM Standards, Part 2.
156
4. (a) In the zinc-immersion step, the oxide film is removed from the surface to be plated and is replaced by a thin and adherent layer of metallic zinc. d f TIllS provides a surface that will respon to most 0 the plating procedures for depositing other metals. (b) For the immersion step, a highly alkaline solution 7 containing the following components is used at room temperature (60 to 80 F; 16 to 27 C): ZINC-IMMERSION SOLUTION
Sodium hydroxide, commercial (76 per cent Na 2 0) 70 oz per gal (525 g per 1) Zinc oxide (Technical Grade) .. 13 oz per gal (100 g perl) The thickness and quality of the immersion coating are influenced by the conditions of deposition. When deposition is too rapid, heavy coarsely crystalline and non-adherent deposits are formed. Since the thinner zinc deposits give the best results, it is recommended that the temperature of the zincate solution be kept below 80 F (27 C) and the immersion time be from 30 sec to 1 min. Recently, a modification of the zincate solution has been developed for wrought and cast alloys, which in most applications gives more uniform and satisfactory results than the standard zinc immersion treatment. The modified zinc immersion procedure 8 has the following advantages: (1) More uniform coverage by subsequent plating baths, (2) Greater operating range for the "Double Immersion" surface conditioning treatment, and (3) Improved resistance to corrosion on all plated aluminum alloys except for the 2024 and 7075 type alloys. The modified solution is prepared by dissolving the zinc oxide in a sodium hydroxide solution in the usual way and cooling to room temperature. Before the bath is diluted to volume, a water solution of ferric chloride crystals and Rochelle Salts is added. The bath should be stirred while the ferric chloride-Rochelle Salts solution is added. The modified zincate solution should be made up as follows: ZINC-IMMERSION SOLUTION
Sodium hydroxide (commercial) (76 per cent Na~O) Zinc oxide Ferric chloride crystals Rochelle salts 7
BATH I
70 oz per gal (525 g per I) 13 oz per gal (100 g per I) 0.13 oz per gal (1.0 g per I) 1.3 oz per gal (10 g per 1)
Proprietary sodium zincate solutions of this general type are available
cOffiluercially.
• The modified zinc immersion procedures described are the subjects of pending patent applications. When a U. S. patent or patents are issued, royalty free licenses will be granted thereunder.
tables and specifications - section VI
Preparation of and Plating on Aluminum Alloys (B 253 . 53) This bath should also be operated under 80 F (27 C) and for immersion times on the order of 30 sec to 1 min. It is recommended that the modified zincate solution be utilized whenever the "double immersion" conditioning treatment is employed. Likewise, it will be found advantageous on all wrought and cast alloys, excepting of course the 2024 and 7075 types for corrosion-resistant applications. Another variation of the modified zinc immersion procedure 9 has been developed for applications where the rinsing and drag-out are problems. This variation consists of reducing the bath viscosity by lowering the concentration of the principal components. At the same time, a low coating weight must be maintained by a closer control of operating conditions and by addition agents. Two typical dilute baths, which may be prepared in the usual manner, are as follows: ZINc-IMMERSION SOLUTION
Sodium hydroxide Zinc oxide Rochelle salts Ferric chloride crystals Sodium nitrate ZINC-IMMERSION SOLUTION
Sodium hydroxide Zinc oxide Rochelle salts Ferric chloride crystals Sodium nitrate
BATH II
6.7 oz per gal (50 0.67 oz per gal (5 6.7 oz per gal (50 0.27 oz per gal (2 0.13 oz per gal (1
g per g per g per g per g per
1) 1) 1) 1) I)
BATH III
16.0 oz per gal (120 g per I) 2.7 oz per gal (20 g per 1) 6.7 oz per gal (50 g per 1) 0.27 oz per gal (2 g per 1) 0.13 oz per gal (1 g per 1)
Bath III will provide a greater zinc reserve for high production work with only a small sacrifice in rinsing and drag-out properties. When using these dilute solutions, the temperature must be maintained at 70 to 75 F (21 to 24 C) and the immersion time must not exceed 30 sec. ( c) The zincate solution is very viscous and losses occur largely from drag-out. This is advantageous as it limits the accumulation of impurities resulting from attack on the aluminum. (d) The specific gravity of the solution should be checked occasionally and any loss made up by adding more of the components. Loss of volume by drag-out should be corrected by the addition of more solution of the specified composition. ( e) When a properly conditioned aluminum alloy article is immersed in the zincate solution, the thin natural oxide film that is present on the sUlface of the alticle dissolves and, as soon as any underlying aluminum is exposed, it also starts to dissolve and is imme• The modified zinc immersion procedures described are the subjects of pending patent applications. When a U. S. patent or patents are issued, royalty free licenses will be granted thereunder.
diately replaced by an equivalent weight of zinc. When the aluminum surface is completely covered with an extremely thin layer of zinc, action in this solution virtually ceases. (f) With correct procedure, the resulting zinc deposit will be fairly uniform and firmly adherent to the surface. The appearance of the surface, however, will vary with the alloy being coated as well as with the rate at which the coating forms. The weight of zinc deposit should be of the order of 0.1 to 0.3 mg per sq in. (0.016 to 0.048 mg per sq cm) (0.02 to 0.07 p.. in thickness). Generally, it is desirable to limit the weight of the deposit to not over 0.2 mg per sq in. (0.03 mg per sq em). ( g) The thinner and more uniform zinc deposits are the most suitable for plating preparation and for the performance of plated coatings in service. Heavy zinc deposits tend to be spongy and less adherent and do not provide as good a surface for obtaining adherence as the thimler deposits. The weight of zinc deposit will vary with the alloy and the conditioning treatment that is used.
Plating Aluminum Alloys 5. (a) After the surface of an aluminum alloy article has been conditioned and the zinc-immersion deposit has been formed, other metals can be plated on this surface by any of the methods suitable for plating on zinc. One factor, however, must be taken into consideration; that is, the zinc deposit is extremely thin and any plating treatment that penetrates the zinc layer and attacks the underlying aluminum will result in a poor deposit. ( b) Ordinarily, it is advisable to apply a suitable copper strike over the zinc-immersion layer before· other metals are deposited. Silver, brass, zinc, nickel, or chromium, however, may be deposited on the zincimmersion layer provided the plating procedures are suitable for plating over zinc.
Copper Strike 6. (a) For applying a copper strike prior to plating with other metals, a Rochelle-type copper cyanide solution of the following composition is recommended: ROCHELLE-TYPE COPPER STRIKE SOLUTION
Copper cyanide Total sodium cyanide Sodium carbonate Rochelle salts Free sodium cyanide, max
5.5 oz per gal (41.3 6.5 oz per gal (48.8 4.0 oz per gal (30.0 8.0 oz per gal (60.0 0.5 oz per gal ( 3.8
g perl) g per I) g per I) g per I) g per I) 157
section VI - tables and specifications
Preparation of and Plating on Aluminum Alloys (B 253 . 53) ( b) This sh-ike solution is generally employed at 100 to 130 F (38 to 54 C) and pH of 10.2 to 10.5. Electrical contact should be made before the article is immersed in the bath and a high initial current density (24 amp per sq ft (2.6 amp per sq dm)) should be used to get rapid coverage. After deposition for about 2 min at this current density, the current may be reduced to 12 amp per sq ft (1.3 amp per sq dm) anQ. deposition continued for an additional 3 to 5 min depending upon thickness desired. A solution of higher pH, such as is sometimes used for copper strikes of this type, will give blistered copper deposits on aluminum alloys, especially on alloys 5052,3 6061,4 and 6063 4 • Mter this strike, the work can be transferred to other standard plating solutions for further plating.
Copper Plating 9. Copper can be applied as a thin deposit on the zinc-immersion layer from the Rochelle-type copper cyanide solution described in Section 6. It is recommended that the thickness be limited to less than 0.3 mil (7.6 f.L), as rough deposits generally occur on high current density areas. By employing a lower current density, the time in this solution may be extended to give heavier deposits, but when a thickness of 0.3 mil (7.6 f.L) has been obtained, it is advisable to transfer the work to one of the proprietary copper plating baths which will plate at a faster rate.
Chromium Plating Brass Plating 7. Brass can be applied from a standard brass plating solution operated at room temperature after the zinc immersion step. A brass plating bath of the following composition is suitable: BRASS PLATING SOLUTION
Copper cyanide Zinc cyanide Sodium cyanide Sodium carbonate Temperature Current density Anodes
3.5 oz per gal (26.3 g per 1) 1.5 oz per gal (11.3 g per 1) 6.0 oz per gal (45.0 g perl) 1.0 oz per gal ( 7.5 g per 1) 80 to 90 F (27 to 32 C) 10 amp per sq ft (1.1 amp per sq elm) 75Cu, 25Zn alloy
10. (a) Chromium may be applied directly to aluminum alloys as a thin deposit (0.02 to 0.05 mil (0.5 to 1.3 f.L) ). It is necessary, however, to first etch the work in a 45 g per 1 (6 oz per gal) sodium hydroxide solution at 150 F (66 C) for sufficient time (1 to 2 min) to develop a slight amount of roughening. Mter water rinsing, the parts should be dipped in a commercial nitric acid solution (50 per cent by volume) for 10 sec, again rinsed, and finally chromium plated in a standard chromium plating bath. A chromium plate applied by this method does not have as good adhesion as one applied over a zinc-immersion coating. The following chromium-plating solution is recommended for use with aluminum alloys: CHROMIUM PLATING SOLUTION
Cadmium Plating' 8. Cadmium may be plated directly on the zincimmersion layer. The use of a strike solution prior to plating is recommended for maximum adhesion. In some cases it may be desirable to apply a nickel coating prior to cadmium plating. Cadmium strike and . cadmium plating baths of the following composition are suitable: CADMIUM STRIKE SOLUTION
Cadmium oxide Sodium cyanide Time Temperature Current density
1.0 oz per gal (7.5 g per 1) 8.0 oz per gal (60 gperl) l min room 25 amp per sq ft (2.7 amp per sq dm)
CADMIUM PLATING SOLUTION
Cadmium oxide .. , Sodium cyanide Brightener Temperature Current density, Anodes 158
3.5 oz per gal (26.3 g per 1) 13.4 02 per gal (100 g per 1) as required room 15 to 45 amp per sq ft (1.6 to 4.8 amp per sq dm) in still tanks cadmium balls
Chromic acid, Cr0 3 • 33 oz per gal (250 g per 1) Sulfate, S04' 0.3302 per gal (2.5 g per 1) Temperature 110 to 115 F (43 to 46 C) CUlTent density 150 amp per sq ft (16 amp per sq dm)
( b) When the chromium is applied over the zincimmersion layer, it should be deposited first at a temperature of 65 to 70 F (18 to 21 C). After the initial deposit at low temperahlre, plating can be continued at a high temperahu'e. The transition from low to high temperature can be accomplished by heating the .chromium plating bath after the low temperahlre plate has been formed. The work can also be transferred without rinsing from a cold to a high temperature bath. The work should be held in the hightemperature solution, without current however, until it reaches the temperature of the bath. Plating is then started at 150 amp per sq ft (16 amp per sq dm) and the current should be raised gradually to 300 or more amp per sq ft (32 amp per sq dm). (c) Bright decorative chromium deposits can be applied to aluminum alloys in the conventional manner, that is, the surface plated with copper and then with the required thickness of nickel. Mter nickel
tables and specifications - section VI
Preparation of and Plating on Aluminum Alloys (B 253.53) plating, the surface should be buffed before applying the chromium deposit. When a bright nickel is used, the chromium deposit can be applied directly. Standard recommendations regarding rinsing and activating the nickel surface should be followed. ( d) Another method for producing chromium deposits having a bright metallic luster consists in applying a 5 to 10-min deposit from a low-temperature solution (65 to 70 F; 18 to 21 C) directly over the zincimmersion layer. The deposit produced in this manner is slate gray, but may be buffed to an attractive metallic luster by using special chrome buffing compounds. This method can be used for applications requiring an inexpensive bright chromium finish. Surfaces finished in this manner will not smudge and are suitable for applications where corrosive conditions will not be encountered. The chromium layer is very thin, however, and will not be nearly as resistant to abrasion and mechanical damage as the copper-nickel-chromium system usually employed for decorative applications.
( e) Heavy, hard chromium deposits can be applied to aluminum alloys by plating the chromium from a high-temperature (130 F (54 C )) chromiumplating solution at a current density of 150 amp per sq ft (16 amp per sq dm) depending upon the racking, contour of work and thickness of plating. The work must first be given a 3 to 5-min strike in the Rochelletype copper cyanide solution, then rinsed and finally transferred to the hot chromium-plating solution for application of hard chromium to the desired thickness.
(f) Hard chromium plates may also be deposited directly over the zinc-immersion layer when the initial deposit is formed from a chromium-plating bath operated in the range of 65 to 70 F (18 to 21 C). After application of the initial chromium deposit at the low temperature, plating is continued in a bath operated at 130 F (54 C). The work should be held in the latter bath until it reaches the temperature of the bath before the current is applied. Plating should be started at 150 amp per sq ft (16 amp per sq dm) and the current should be raised gradually to 300 amp per sq ft (32 amp per sq dm) depending on the shape of the article, method of racking, etc.
Gold Plating 11. Gold may be plated on aluminum alloys by first applying a strike in the Rochelle-type copper cyanide solution or in a brass-plating solution. After this, a suitable deposit of nickel should be applied before application of the gold. The plating bath and conditions for gold plating are as follows:
GOLD PLATING SOLUTION Potassium gold cyanide .. lh ozpergal (3.8gperl) Potassium carbonate 1 oz per gal (7.5 g perl) Potassium cyanid~ lh ozper gal (3.8 gperl) Temperature 120 to 160 F (49 to 71 C) CUlTent density 5 to 15 amp per sq ft (0.5 to 1.6 amp per sq dm) Voltage 2 to 6 v Anodes Chromium-nickel steel or carbon, or combinations of these with gold.
Nickel Plating 12. (a) Nickel may be applied directly over the zinc-immersion layer by using baths formulated for plating over zinc. This method, however, is difficult to control and satisfactory adhesion is not always obtained. Where dull or bright nickel is to be applied, it is preferable to do it after a thin copper plate has been deposited from the Rochelle-type copper cyanide strike solution. For the nickel plating of aluminum alloys, subsequent to copper plating, the following types of nickel baths are suitable: WATTS' TYPE NICKEL SOLUTION (DULL NICKEL) Nickel sulfate crystals. 30 oz per gal (225 g per I) Nickel chloride 6 oz per gal (48 g per I) Boric acid 5 ozper gal (31.5 gperl) pH : 5.0 Temperature. " 130 to 140 F (54 to 60 C) Current density 40 amp per sq ft (4.3 amp per sq dm) BRIGHT NICKEL SOLUTIONS Bright nickel solutions are satisfactory for use with aluminum alloys. Use brightening agents and operating conditions recommended by vendor.
( b) When nickel plating aluminum alloys, all the precautions usually recommended should be followed for obtaining a sound nickel plate-frequent carbon treatment, continuous purification, and filh'ation-to keep the nickel bath in good operating condition. Because of the large elech'olytic potential between nickel and aluminum alloys, the nickel plate should be of good quality and of sufficient thickness to provide adequate protection for the application at hand. ( c) For applications where corrosion is not a critical factor, nickel plate of the order of 0.3 to 0.5 mil (8 to 13 p.) in thickness will be satisfactory. Where corrosive conditions. may be encountered in service, however, the nickel plate should be from 1 to 2 mil (25 to 50 p.) in thickness. In addition, the application of a final chromium plate 0.01 to 0.02 mil (0.25 to 0.50 p.) in thickness is essential, as it will increase the 159
section VI - tables and specifications
Preparation of and Plating on Aluminum Alloys (B 253- 53) service life of a plat~d aluminum article to a surprising degree and will greatly reduce the detrimental effects of pores and exposed areas of bare metal.
(d) Ordinarily, nickel plating by itself is not recommended for use on aluminum alloys when even moderately corrosive conditions are likely to be encountered in service. When relatively heavy nickel deposits are applied to obtain protection, a ductile type of nickel plate should be used and plating baths or operating conditions that produce highly stressed deposits should be avoided. With highly stressed deposits, stress cracks may develop on exposure and blistering and spalling of the plating will occur.
posits can be formed on aluminum from hot sodium stannate solutions.
Zinc Plating 15. Zinc can be plated over the zinc-immersion layer from either acid or cyanide solutions at room temperature. The current, however, should be applied as the work is immersed in the plating solution. Zinc can also be applied directly to aluminum alloys without employing the zinc-immersion dip, but operating conditions are too critical for production use. A zinc plating bath of the following composition is suitable: ZINC PLATING SOLUTION
Silver Plating 13. Silver can be deposited on the zinc-immersion
coating by following the silver plating procedure employed for steel. This involves the use of two preliminary strikes and making contact before the work enters the solution. It is better, however, to apply silver over a copper plate without using the first silver strike. The following solutions may be used:
Zinc cyanide Sodium cyanide Sodium hydroxide Temperature " Current density
8.0 oz per gal (60 g perl) 5.6 oz per gal (42 gperl) 10.5 ozper gal (78.8 g perl) 75 to 95 F (24 to 35 C) 5 to 50 amp per sq ft (0.54 to 5.4
amp per sq dm)
Racking FIRST SILVER STRIKE SOLUTION
Silver cyanide Sodium cyanide Temperature Current density Tank voltage Time
0.13 oz per gal (1 g per 1) 12 oz per gal (90 g per 1) 80 F (27 C) 15 to 25 amp per sq ft (1.6 to 2.7 amp per sq dm) 6v 10 sec
SECOND SILVER STRIKE SOLUTION
Silver cyanide Sodium cyanide Temperature Current density Tank voltage Time
0.7 oz per gal (5.3 g perl) 9 oz per gal (67.5 g per 1) 80 F (27 C) 15 to 25 amp per'sq ft (1. 6 to 2.7 amp per sq dm) 6v 10 sec
16. (a) Aluminum racks are preferred when plating aluminum alloys. It is recommended that 990 A alloy be used for the spines of the racks and CG42A alloy for the contacts. By increasing the cross-sectional area of the spines by about 40 per cent, a conductance equal to that of a copper rack is obtained. In cases where contact marks are not important, regular phosphor-bronze contacts may be used. When using phosphor-bronze contacts, however, the area adjacent to the contact may develop small blisters as a result of a non-uniform zinc deposit during the immersion step. Aluminum alloy contacts will eliminate this condition and their use is recommended when contact marks would be on an exposed surface of the article being plated. When the nitric-hydrofluoric acid etch is used for conditioning, aluminum contacts should be used.
SILVER PLATING SOLUTION
Silver cyanide .4 oz per gal (30 g perl) Potassium cyanide (total) .. 7.4 ozper gal (55.5 gperl) Potassium carbonate 6 oz per gal (45 g per 1) Free potassium cyanide 5.5 oz per gal (41.3 g per 1) Temperature 80 F (27 C) 5 amp per sq ft (0.54 amp per Current density sqdm)
Tin Plating 14. Tin can be plated on a surface that has a zincimmersion coating and a copper strike. Either a stannate or a fluoborate-type tin plating solution can be used. For some applications, useful tin immersion de160
(b) When aluminum alloys are used for the plating racks,. the various electrodeposits may be stripped from these racks by reversed current treatment in a sulfuric acid solution (60 per cent by volume) or a phosphoric acid solution (75 per cent by volume) at room temperature. In either case, only slight attack occurs on the aluminum because of the oxide film that forms on the aluminum during these anodic treatments. The oxide film resulting from this stripping operation should be removed from contact areas either chemically or mechanically. When phosphor-bronze contacts are used, it is recommended that they be stripped in the sulfuric acid solution (60 per cent by volume).
tables and specifications - section VI
Preparation of and Plating on Aluminum Alloys (B 253 . 53) Rinsing 17. (a) Effective rinses should follow eveq step in the plating procedure. The rinses must be reasonably clean and the rinsing thorough to prevent contamination of succeeding solutions. A combination of dip and spray rinsing has been found to use the least
water for good rinsing. Since th~ zinc-immersion solution is rather viscous, the subsequent rinsing operation is veq important. A double rinse is needed to remove all traces of the zincate solution. Two combination "dip and spray" rinses are desirable. Water from the second dip rinse can be made to overflow into the first dip rinse, thereby effecting an economy.
Appendix Cleaning and Conditioning Summary of Cleaning and Conditioning T1'eatments: AI. The following cleaning and conditioning treatments are suitable for the wrought and cast aluminum alloys covered by this recommended practice: Treatment A: (1) Clean: (a) By vapor degreasing or with mineral spirits. (b) With alkaline cleaner and water rinse. (2) Acid dip, in nitric acid solution (50 per cent by volume). (3) Water rinse. (4) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). (5) Double water rinse. ( 6) Electroplate. Treatment B: (1) Clean: (a) By vapor degreasing or with mineral spirits. . (b) With alkaline cleaner and water rinse. (2) Acid dip, in sulfuric acid solution (15 per cent volume), 2 to 5 min at 180 F. (3) Water rinse. (4) Acid dip, in nitric acid solution (50 per cent by volume) at room temperature. (5) Water rinse. (6) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). ( 7) Double water rinse. ( 8) Electroplate. T1'eatment C: (1) Clean: (a) By vapor degreasing or with mineral spirits. ( b) With mild alkaline cleaner and water rinse. (2) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C).
( 3) Water rinse. ( 4) Acid dip, in nitric acid solution (50 per cent by volume) at room temperature. (5) Water rinse. (6) Zinc-immersion dip, ~ to 1 min at 60 to 80 F (16 to 27 C). (7) Double water rinse. ( 8) Electroplate. Treatment D: (1) Clean: ( a) By vapor degreasing or with mineral spirits. ( b) With mild etching alkaline cleaner and water rinse. (2) Mixed acid dip (nitric-hydrofluoric at room temperature, 3 to 5 sec).
TABLE I.-CLEANING AND CONDITIONING TREATMENTS. Alloy
*
Treatments Suitable
Wrought Aluminum Alloys: 990A MIA , MGllA CP60A CM41A CG42A GR20A GSllB GSllA Cast Aluminum Alloys: S5 S5B SC2 CS43A C272B CS40A SC64C . . . . . . . . . . . . . . . . . . . . . . . . . . .. SC51A SG70A SC7 '"
A,B,C A,B,C B,C B, C B, C B,C B,C B, C B, C C,D C B, C B, C B B, C B, C, D B, C C, D D
* See page 141 for Alum. Assoc. designations. 161
section VI - tables and specifications
Preparation of and Plating on Aluminum Alloys (B 253 . 53) (3) Water rinse. (4) Zinc-immersion dip, ;f to 1 min at 60 to 80 F (16 to 27 C). (5) Double water rinse. (6) Electroplate. The treatments applicable to specific alloys are shown in Table 1.
Solutions fo1' Cleaning and Conditioning Aluminum Alloys: A2. The solutions described in Paragraphs (a) to (f) are suitable for cleaning and conditioning aluminum alloys. (a) CARBONATE-PHOSPHATE Sodium carbonate Trisodium phosphate Temperature Time Container ( b) SULFURIC ACID DIP: Sulfuric acid (H2S0.( 66 deg Baume) Water TemperahIre Time Container
CLEANER: 3 oz per gal (23 g per 1) 3 oz per gal (23 g per 1) 140 to 180 F (60 to 82 C) 1 to 3 min steel
1.5 vol 8.5 vol 175 to 180 F (79 to 82 C) 5nlin lead-lined steel
( c) NITRIC ACID DIP: Commercial nitric acid (sp gr 1.37) Water Temperature Container
1 vol 1 vol room steel lined with type 347 stainless steel NOTE: Catttion.-Exhaust fmnes are toxic.
(d) MIXED ACID DIP: Commercial nitric acid (sp gr 1.42) Commercial hydrofluoric acid (48 per cent) Time Temperature Container
162
3 vol 1 vol 3 to 5 sec room steel, lined with a suitable plastic lining, such as Koroseal or car-
bon brick; preferably a combination of both. NOTE: Catttion.-Exhaust fumes are toxic. (e) STANDARD ZINC-IMMERSION SOLUTION: Sodium hydroxide 70 oz per gal (525 g per 1) Zinc oxide 13 oz per gal ( 100 g per 1) Time V2 to 1 min Temperature 60 to 80 F (16 to 27 C) Container steel
MODIFIED ZINC IMMERSION SOLUTIONS: I Sodium hydroxide (commercial) (76 per cent Na20) 70 oz per gal (525 g perl) Zinc oxide 13 oz per gal ( 100 g perl) Ferric chloride crystals .. 0.13 oz per gal (1.0 g per 1) Rochelle salts 1.3 oz per gal (lOg perl) Time V2 to 1 min. Temperature 60 to 80 F (16 to 27 C) Container steel II Sodium hydroxide 6.7 oz per gal (50 g per 1) Zinc oxide 0.67 oz per gal (5 g perl) Rochelle salts 6.7 oz per gal (50 g per 1) Ferric chloride clystals .. 0.27 oz per gal (2 g per 1) Sodimn nitrate 0.13 oz per gal (1 g per 1) Time 30 sec. or less 70 to 75 F (21 to 24 C) Temperature Container steel III Sodium hydroxide 16.0 oz per gal (120 g per 1) Zinc oxide 2.7 oz per gal (20 g perl; Rochelle salts 6.7 oz per gal (50 g per 1) Ferric chloride crystals .. 0.27 oz per gal (2 g per 1) Sodium nitrate 0.13 oz per gal (1 g perl) Time , 30 sec. or less Temperahrre 70 to 75 F (21 to 24 C) Container steel
(f) CAUSTIC DIP: Sodium hydroxide Time Temperature Container NOTE: Caution.-Exhaust
6 oz per gal (45 g per 1) 10 sec 150 F ( 66 C) steel fumes are toxic.
STANDARD SPECIFICATIONS FOR ELECTRODEPOSITED COATINGS OF ZINC ON STEEL
1
ASTM DESIGNATION: A 164· 55 Adopted, 1953; Revised, 1955. 2 This Standard of the American Society for Testing Materials is issued under the fixed designation A 164; the final number indicates the year of original adoption as standard or, in the case of revision, the year of last revision.
These specifications were prepared faintly by the American Electmplated Society, the National BU1'eau of Standards, and the American Society for Testing Materials.
Scope 1. These specifications cover requirements for electroplated zinc coatings on steel articles that are required to withstand corrosion. Three types of coatings (Notes 1 and 2) are covered: namely,
Type GS, Type LS, and TypeRS. NOTE 1: Explanation of Symbols.-The initial letters, G, L, and R were adopted as arbib:ary designations of grades of plating. The second letter S refers to steel as the basis metal; other basis metals are indicated by the letters B for brass, C for copper, and Z for zinc. NOTE 2: Classification.-The conditions of exposure and use of plated steel are so varied that it is not possible to predict the average life of articles plated in accordance with type GS, type LS, or type RS, or to predetermine just which type of plating should be specified for a given article. Such a selection must be based upon the experience of the manufacturers and users. It is recognized that uses exist for which thicker coatings than those of type GS will be required. For articles that are intended for a short period of use, no standard specification for plating is recommended. It is suggested, however, that subject to the prevailing manufactming conditions, certain minimum requirements be mutually agreed upon by the manufacturer and the purchaser in order to insure that the plated coatings render a useful service.
Manufacture 2. The steel to be plated shall be substantially free from flaws or defects that will be detrimental to the appearance or the protective value of the coatings. It shall be subjected to such cleaning, pickling, and plating procedures as are necessary to yield deposits with 1 Under the standardization procedure of the ASTM, these specifications are under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption as standard, these specifications were published as tentative from 1935 to 1953, being revised in 1939, 1940, 1949 and 1951.
the desired quality. The zinc coating shall have a uniform appearance, shall be adherent and free from blisters, and substantially free from other defects that may affect the appearance or protective value of the coatings.
Minimum Thickness of Coating 3. (a) Type GS .-On significant surfaces of the finished articles the minimum thickness of type GS zinc coating shall be 0.0010 in. (25j.L).
(b) Type LS .-On significant smfaces of the finished articles, the minimum thickness of type LS zinc coating shall be 0.00050 in. (13j.L). (c) Type RS .-On significant smfaces of the finished articles, the minimum thickness of type RS zinc coating shall be 0.00015 in. (3.8j.L). NOTE.-l
p. (micron) = 0.0000394 in.
0.001 in.
= 1 mil = 25p. (microns).
2.-See Appendix II. NOTE 3.-The performance of a zinc coating depends largely on its thickness and the kind of environment to which it is exposed. Without proof of satisfactory cOlTelation, accelerated tests, such as the salt spray test, cannot be relied upon to predict performance in other environments, nor will these serve as comparative measures of the con-osion protection afforded by coatings of different metals. Thus the marked superiority shown by cadmium coatings over zinc coatings of equal thickness in the standard salt spray test cannot be conshlled as proof that this will hold h'ue in all ahnospheric environments. NOTE
Significant Surfaces 4. In general, significant smfaces (Note) are those surfaces that are visible and subject to wear or corrosion or both, or surfaces on which the coating is otherwise fl.U1ctionally necessary. The designation of significant surfaces shall be agreed upon by the manufacturer 163
section VI - tables and specifications
Specifications for Electrodeposited Zinc (A 164 . 55) and the purchaser and may be indicated on the drawings. Surfaces on which a controlled deposit ordinarily cannot be obtained, such as holes, recesses, bases of angles, and similar areas, are normally exempt from the requirements for significant surfaces, unless they are specifically designated as such. When such areas are designated as significant surfaces, and the thickness requirements must be met, the manufacturer and the purchaser shall recognize the necessity for either thicker deposits on the more accessible surfaces or for special racking. Special racks may involve the use of conforming, auxiliary,·· interior, or bi-polar electrodes. NOTE.-It is suggested that significant surfaces generally may be defined as those parts of the visible surface that can be touched with a %-in. diameter sphere or with a sphere of a diameter agreed upon by the manufacturer and the purchaser.
Hydrogen Emhrittlement 5. Mter plating and any necessary subsequent operations (Note) the steel shall be free from the detrimental effects of hydrogen embrittlement. The test methods and their evaluation for freedom from hydrogen embrittlement shall be agreed upon by the manufacturer and the purchaser. NOTE.-Hardened steels and cold-worked steels are susceptible to embrittlement by hydrogen in both cleaning and plating operations. This embrittlement should be minimized to the greatest possible extent by careful control of these operations. Embrittlement unavoidably present after plating should be removed by a subsequent treatment such as baking. A procedure for baking to minimize embrittlement is covered in Sections 2 ( b) and 7 of the Recommended Practice for the Preparation of High-Carbon Steel for Electroplating (ASTM Designation: B 242).
Test for Thickness of Coating 8. (a) All the samples selected may be tested by the purchaser to determine the minimum thickness of coating on significant surfaces. Unless otherwise agreed upon by the manufacturer and the purchaser, the thiclmess of coating shall be determined on crosssections taken perpendicular to the significant surfaces by the microscopic method described in the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219). NOTE.-It is advisable to determine thickness of coating on large or irregularly shaped parts at several points.
( b) Unless otherwise agreed upon by the manufacturer and the purchaser, measurements of the thickness of coating on threaded articles, such as nuts, bolts, screws and similar fasteners with complementary threads, shall be made on the shank or other smooth surfaces as nearly adjacent to the thread as practicable. ( c) When agreed upon by the manufacturer and the purchaser, the thickness of a zinc coating directly on steel may be determined by the magnetic method described in Appendix I or by the dropping test described in Appendix II of the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219).
Acceptance and Rejection 9. (a) The number of samples permitted to fail in the tests, the number of samples which shall be taken for retest when the first are indecisive, and the number of samples that may fail in the retest shall be agreed upon by the manufacturer and the purchaser.
( b) The purchaser shall notify the manufacturer of the rejection of any lot within two weeks of receipt of shipment.
Selection of Samples
Retest
6. Out of a lot of similar pads, a number of samples shall be selected at random. The size of the lot and the number of samples to be selected shall be agreed upon by the manufacturer and the purchaser. All of the samples selected shall be visually examined for any defects as described in Section 2.
10. Disagreements shall be settled by an umpire test made by an independent laboratory agreed upon in advance by the manufacturer and the purchaser.
Number of Tests 7. All of the samples shall be tested for thickness of coating in accordance with Section 8. NOTE.-Wherever possible, thicknesses should be measured by magnetic methods on the maximum number of samples practicable since such measurements are nondestructive and inexpensive.
164
Cost of Tests 11. (a) The purchaser shall pay for his own tests. He shall not be required to pay for specimens destroyed in testing lots that are rejected. The cost of umpire tests shall be paid by the loser.
( b) When the contract involves only the plating of pads, the plating firm shall be permitted to destroy, without cost to it, for testing purposes, twice the number of parts agreed upon in accordance with Sections 6,9, and 10.
tables and specifications - section VI
Specifications for Electrodeposited Zinc (A 164 . 55) Appendix I Control: In order to meet the specifications the manufacturer is advised to: ( a) Maintain regular control of all solutions and inspect the equipment at regular intervals, paying special attention to electrical contacts and accuracy of instruments. ( b) Maintain his own inspection department, using the test methods called for in these specifications, and to trace immediately the source of irregularities. On jobs running continuously over any length of time, the quality of the coatings on each part should be checked at least twice every shift, after initial difficulties have been- overcome. (c) Maintain his own requirements at least 10 per cent above those of the specifications. Time Required for Plating: Any specified thickness of plating can be produced consistently only if the current density and time of plating are controlled. Regulation of the voltage is of no value except so far as it produces the desired current density. The average thickness of deposit that is required to produce a specified minimum thickness of deposit will depend upon the shape of the article, the shape
and position of the anodes, and the throwing power of the solution. Purely for illustration, it will be assumed that the average thickness will be 50 per cent greater than the mininmm thickness. The resultant figures serve only as a rough guide and must be confinned by trial for the articles concerned. To deposit 0.0010 in. (25p.) of zinc with high efficiency in either acid or cyanide baths, it requires about 14 amp hr per sq ft. To produce an average thickness of 0.0015 in. (38p.) (that is, 50 per cent more than the minimum thickness of 0.0010 in. (25JL) specified for type GS), it will therefore require about 21 amp hr per sq ft. This is equivalent to plating for 1 hr at 21 amp per sq ft, or to a corresponding period for any other current density. Similarly, for type LS it will re~ quire about 11 amp hr per sq ft and for type RS about 3.5 amp hr per sq ft to deposit an average thickness about 50 per cent greater than the specified minimum thickness. For complicated shapes, longer periods will be required. When a large number of small articles are plated simultaneously (for example, on a rack or in a barrel), the time of plating must be increased to insure the specified thickness on those articles that receive less than the average current density.
Appendix II Coating Thickness on Threaded Articles with Complementary Threads
The dimensional tolerance of most threaded articles, such as nuts, bolts, screws and similar fasteners with complementary threads, nonnally does not permit the application of coating thickness much greater than Type RS. The limitation of coating thickness on threaded fasteners imposed by dimensional tolerances (including class or fit) should be a subject for con-
sideration wherever practicable, both by the manufacturer and by the purchaser, to prevent the application of greater coating thicknesses than are generally permissible. If heavier coatings are required for satisfactory corrosion resistance, allowances must be made in the manufacture of the threaded fasteners for the tolerance necessary for plate build-up.
165
STANDARD SPECIFICATIONS FOR ELECTRODEPOSITED COATINGS OF CADMIUM ON STEELl ASTM DESIGNATION: A 165 . 55 Adopted, 1953; Revised, 1955. 2 This Standard of the American Society for Testing Materials is issued under the fixed designation A 165; the final number indicates the year of original adoption as standard or, in the case of revision, the year of last revision.
These Specifications were prepared faintly by the American Electroplaters' Society, the Natwnal Bureau of Standards, and the American Society for Testing Materials.
Scope 1. These specifications cover requirements for elech'oplated cadmium coatings on steel articles that are required to withstand corrosion. Three types of coating (Notes 1 and 2) are covered: namely,
Type NS, Type O~, and Type TS. NOTE 1: Explanation of Symbols.-The initial letters N, 0, and T were adopted as arbitrary designations of grades of plating. The second letter S refers to steel as the basis metal; other basis metals are indicated by the letters B for brass, C for copper, and Z for zinc. NOTE 2: Classification.-The conditions of exposure and use of plated steel are so varied that it is not possible to predict the average life of articles plated in accordance with type NS, type OS, or type TS, or to predetermine just which type of plating should be specified for a given article. Such a selection must be based upon the experience of the manufacturers and users. It is recognized that uses exist for which thicker coatings than those of type NS will be required. _ For articles that are intended for a short period of use, no standard specification for plating is recommended. It is suggested, however, that subject to the prevailing manufacturing conditions, certain minimum requirements be mutually agreed upon by the manufacturer and the purchaser in order to insure that the plated coatings render a useful service.
be adherent and free from blisters, and substantially free from other defects that may affect the appearance or protective value of the coatings.
Minimum Thickness of Coating 3. (a) Type NS.-On significant surfaces of the finished articles, the minimum thickness of type NS cadmium coating shall be 0.00050 in. (13,u.).
(b) Type OS.-On significant surfaces of the finished articles, the minimum thickness of type as cadmium coating shall be 0.00030 in. (7.6,u.). (c) Type TS.-On significant surfaces of the finished articles, the minimum thickness of type TS cadmium coating shall be 0.00015 in. (3.8,u.). NOTE 1.-11£ (micron) 0.0000394 in. 0.001 in. 1 mil 251£ (microns). NOTE 2.-See Appendix II. NOTE 3.-The performance of a cadmium coating depends largely on its thickness and the kind of environment to which it is exposed. Without proof of satisfactory correlation, accelerated tests, such as the salt spray test, can not be relied upon to predict performance in other environments, nor will these serve as comparative measures of the corrosion protection afforded by coatings of different metals. Thus the marked superiority shown by cadmium coatings over zinc coatings of equal thickness in the standard salt spray test cannot be construed as proof that this will hold true in all atmospheric environments.
=
=
=
Manufacture 2. The steel to be plated shall be substantially free from flaws or defects that will be deh'imental to the appearance or the protective value of the coatings. It shall be subjected to such cleaning, pickling, and plating procedures as are necessary to yield deposits with the desired quality. The cadmium coating shall have a uniform appearance, bright or dull as specified, shall 1 Under the standardization procedure of the ASTM, these specifications are under the jurisdiction of the ASTM Committee B-8 on Electrodeposited Metallic Coatings. 2 Prior to adoption as standard, these specillcations were published as tentative from 1935 to 1953, being revised in 1939, 1940, 1949 and 1951.
166
Significant Surfaces 4. In general, significant surfaces (Note) are those surfaces that are visible and subject to wear or corrosion or both, or surfaces on which the coating is otherwise functionally necessary. The designation of significant surfaces shall be agreed upon by the manufacturer and purchaser and may be indicated on the drawings. Surfaces on which a controlled deposit ordinarily cannot be obtained, such as holes, recesses, bases of angles, and similar areas, are normally exempt
tables and specifications - section VI
Specifications for Electrodeposited Cadmium (A 165 . 55) from the requirements for significant surfaces, unless they are spec~fically desig~at.ed as such. When such areas are desIgnated as slgmficant surfaces, and the thickness requirements must be met, the manufacturer and the purchaser shall recognize the necessity for either thicker deposits on the more accessible smfaces or for special racking. Special racks may involve the use of conforming, auxiliary, interior, or bi-polar . electrodes. NOTE.-It is suggested that significant surfaces generally may be defined as those parts of the visible surface that can be touched with a %-in. diameter sphere or with a sphere of a diameter agreed upon by the manufacturer and the purchaser.
Hydrogen Embrittlement 5. Mter plating and any necessary subsequent operations (Note) the steel shall be free from the detrimental effects of hydrogen embrittlement. The test methods and their evaluation for freedom from hydrogenembrittlement shall be agreed upon by the manufacturer and the purchaser. NOTE.-Hardened steels and cold-worked steels are susceptible to embrittlement by hydrogen in both cleaning and plating operations. This embrittlement should be minimized to tlle greatest possible extent by careful control of these operations. Embrittlement unavoidably present after plating should be removed by a subsequent treatment such as baking. A procedure for baking to minimize embrittlement is covered in Sections 2 (b) and 7 of the Recommended Practice for the Preparation of High-Carbon Steel for Elecb.-opIating (ASTM Designation: B 242).
Test for Thickness of Coating 8. (a) All the samples selected may be tested by the purchaser to determine the minimum thickness of coating on significant surfaces. Unless otherwise agreed upon by the manufacturer and the purchaser, the thickness of coating shall be determined on crosssections taken perpendicular to the significant surfaces by the microscopic method described in the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219). NOTE.-It is advisable to determine thickness of coating on large or inegularly shaped parts at several points. (b) Unless otherwise agreed upon by the manufacturer and the purchaser, measurements of the thickness of coating on threaded articles, such as nuts, bolts, screws and similar fasteners with complementalY threads, shall be made on the shank or other smooth surfaces as nearly adjapent to the thread as practicable.
( c) When agreed upon by the manufacturer and the purchaser, the thickness of a cadmium coating directly on steel may be determined by tlle magnetic metllod described in Appendix I or by the dropping test described in AppendiX II of the Methods of Test for Local Thickness of Electrodeposited Coatings (ASTM Designation: A 219).
Acceptance and Rejection 9. (a) The number of samples permitted to fail in tlle tests, the number of samples which shall be taken for retest when the first are indecisive, and the number of samples tllat may fail in the retest shall be agreed upon by tlle manufacturer and the purchaser. ( b) The purchaser shall notify tlle manufacturer of tlle rejection of any lot within two weeks of receipt of shipment.
Selection of Samples 6. Out of a lot of similar parts, a number of samples shall be selected at random. The size of the lot and the number of samples to be selected shall be agreed upon by the manufacturer and the purchaser. All of the samples selected shall be visually examined for any defects as described in Section 2.
Retest 10. Disagreements shall be settled by an umpire test made by an independent laboratory agreed upon in advance by the manufacturer and the purchaser.
Cost of Tests Number of Tests 1. All of the samples shall be tested for thickness of coating in accordance with Section 8. NOTE.-Wherever possible, tllicknesses should be measured by magnetic methods on the maximum number of samples practicable since such measurements are nondestructive and inexpensive.
11. (a) The purchaser shall pay for his own tests. He shall not be required to pay for specimens destroyed in testing lots that are rejected. The cost of umpire tests shall be paid by tlle loser.
( b) When the contract involves only tlle plating of parts, the plating firm shall be permitted to destroy, without cost to it, for testing purposes, twice the number of parts agreed upon in accordance with Sections 6,9, and 10.
167
section VI - tables and specifications
Specifications for Electrodeposited Cadmium (A 165 . 55) Appendix I Control: In order to meet the speci£cations the manufacturer is advised to: (a) Maintain regular control of all solutions and to inspect the equipment at regular intervals, paying special attention to electrical contacts and accuracy of instruments. ( b) Maintain his own inspection department, using the test methods called for in these speci£cations, and to trace immediately the source of irregularities. On jobs mnning continuously over any length of time the quality of the coatings on each part should be checked at least twice every shift, after initial difficulties have been overcome. ( c) Maintain his own requirements at least 10 per cent above those of the speci£cations. Time Required for Plating: Any speci£ed thickness of plating can be produced consistently only if the current density and time of plating are controlled. Regulation of the voltage is of no value except so far as it produces the desired current density. The average thickness of deposit that is required to produce a specified minimum thickness of deposit will depend upon the shape of the article, the shape
and position of the anodes, and the throwing power of the solution. Purely for illustration, it will be assumed that the average thickness will be 50 per cent greater than the minimum thickness. The resultant £gures serve only as a rough guide and must be confirmed by trial for the articles concerned. To deposit 0.0010 in. (250 ) of cadmium with high efficiency, it requires about 10 amp lu' per sq ft. To produce an average thickness of 0.00075 in. (190) (that is, 50 per cent more than the minimum thickness of 0.00050 in. (130) specified for type NS), it will therefore require about 7.5 amp hr (450 amp min) per sq ft. This is equivalent to plating for 1 hr at 7.5 amp per sq ft, or to a corresponding period for any other current density. Similarly, for type OS it will require about 4.5 amp hr per sq ft and for type TS about 2.5 amp hr per sq ft to deposit an average thickness 50 per cent greater than the specified minimum thickness. For complicated shapes, longer periods will be required. When a large number of small articles are plated simultaneously (for example, on a rack or in a barrel), the time of plating must be increased t'O insure the specified thickness on those articles that receive less than the average current density.
Appendix II Coating Thickness on Threaded Articles with Complementary Threads
The dimensional tolerance of most threaded articles, such as nuts, bolts, screws'and similar fasteners with complementary threads, normally does not permit the application of coating thickness much greater than Type TS. The limitation of coating thickness on threaded fasteners imposed by dimensional tolerances (including class or fit) should be a subject for consid-
eration wherever practicable, both by the manufacturer and by the purchaser, to prevent the application of greater coating thicknesses than are generally permissible. If heavier coatings are required for satisfactory corrosion resistance, allowances must be made in the manufacture of the threaded fasteners for the tolerance necessary for plate build-up.
