1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA BU 1.2-2013Application Information for Busway Rated 600 V or LessNEMA Standards Publication BU 1.2-2002 (R2008, R2013) Application Information for Busway Rated 600 Volts or Less Published by National Electrical Manufacturers
2、 Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2014 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and A
3、rtistic Works, and the International and Pan American copyright conventions. NOTICE AND DISCLAIMER The information in this publication was considered technically sound by a consensus among persons engaged in its development at the time it was approved. Consensus does not necessarily mean there was u
4、nanimous agreement among every person participating in the development process. The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which the document herein is one, are developed through a voluntary standards development process. This process brings tog
5、ether volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. Although NEMA administers the process and establishes rules to promote fairness in the development of consensus, it does not write the documents, nor does it independently test, eval
6、uate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property, or other damages of any nature, whether special, indirect, consequential, or compensato
7、ry, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any information published herein, and disclaims and makes no warranty that the inf
8、ormation in this document will fulfill any particular purpose(s) or need(s). NEMA does not undertake to guarantee the performance of any individual manufacturers or sellers products or services by virtue of this standard or guide. In publishing and making this document available, NEMA is not underta
9、king to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a com
10、petent professional in determining the exercise of reasonable care in any given circumstance. Information and other standards on the topic covered by this publication may be available from other sources, which the user may wish to consult for additional views or information not covered by this publi
11、cation. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health purposes. Any certification or other statement of compliance with any health- or safet
12、y-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. BU 1.2-2002 (R2008, R2013) Page i 2014 National Electrical Manufacturers Association CONTENTS Page Foreword . ii Section 1 SCOPE 1 Section 2 REFERENCE
13、D STANDARDS . 2 Section 3 RESISTANCE, REACTANCE, AND IMPEDANCE . 3 3.1 Method to Determine Resistance, Reactance, and Impedance 3 3.1.1 Readings Taken During the Temperature-Rise Test 3 3.1.2 Calculate the Average Phase-to-Neutral Impedance Z . 3 3.1.3 Calculate for Each Individual Phase 4 Section 4
14、 VOLTAGE DROP 6 4.1 Voltage Drop Ratings . 6 4.2 Voltage Drop Test for Three-Phase BuswaysGeneral . 6 4.3 Calculation of Three-Phase Voltage Drop and Voltage Drop Deviation 6 4.3.1 Average Phase-to-Phase Voltage Drop 6 4.3.2 Phase-to-Phase Voltage Drop (VD) for Each Phase. 7 4.3.3 The VDavg Calculat
15、ed in Paragraph 4.3.2 7 4.3.4 The Percent Voltage Drop Deviation Per 100 Feet . 7 4.4 All Voltage Drops and Deviations Indicated in Section 4.3 7 4.5 The Voltage Drop of the Busway . 7 4.6 All Preceding Voltage Drop Formulas 8 Section 5 RESISTANCE WELDING APPLICATION 9 5.1 General 9 5.2 Current Carr
16、ying Requirements . 9 5.2.1 Group of Welders 10 5.2.2 Single-Phase Distribution Systems . 10 5.2.3 Three-Phase Distribution Systems 10 5.3 Voltage Drop Requirements 10 5.3.1 General 10 5.3.2 Determine Total During-weld kVA for Voltage Drop Calculations . 11 5.3.3 Determine Total During-weld Current
17、for Voltage Drop Calculations 11 5.3.4 Determine the Welder Multiplier for Voltage Drop Calculations 12 5.3.5 Determine the Voltage Drop 12 5.4 Example Of Determining Proper Busway For Resistance Welder Application 12 5.4.1 Example of Current Carrying Requirement Calculations. 12 5.4.2 Example of Vo
18、ltage Drop Requirement Calculations 12 5.5 Summary . 13 Table 5-1 DUTY CYCLE MULTIPLIERS . 9 Figure 3-1 METER CONNECTIONS 4 BU 1.2-2002 (R2008, R2013) Page ii 2014 National Electrical Manufacturers Association Foreword This Standards Publication is intended to provide a basis of common understanding
19、 within the electrical community. The purpose of this Standards Publication is to provide a guide of practical application information for busway rated 600 volts or less. User needs have been considered throughout the development of this publication. Proposed or recommended revisions should be submi
20、tted to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 This Standards Publication was developed by the LVDE 04 Busway Product Group of the LVDE Section. Approval of the publication does not necessarily im
21、ply that all members voted for its approval or participated in its development. At the time it was approved, the Group/Section was composed of the following members: GE Industrial SystemsPlainville, CT Siemens Energy thus reasonable assumptions should be made for these varying quantities and then us
22、ed for the following determinations. To determine the busway current carrying capacity required, it is necessary to convert the intermittent welder loads to an equivalent continuous load or effective kVA. If the during-weld kVA demand and the duty cycle for a welder are known, the effective kVA can
23、be obtained by multiplying the during-weld kVA demand by the square root of the duty cycle divided by 10. The duty cycle is the percentage of the time during which the welder is loaded. For simplicity sake, multipliers for various duty cycles are listed in Table 5.1. Based upon the welders duty cycl
24、e, the proper multiplier is chosen. This multiplier times the during-weld kVA demand determines the effective kVA. Table 5-1 DUTY CYCLE MULTIPLIERS Percent Duty Cycle Multiplier 50 0.71 40 0.63 30 0.55 25 0.50 20 0.45 15 0.39 10 0.32 7.5 0.27 5 or less 0.22 If the during-weld kVA demand is unknown,
25、it can be assumed to be 70 percent of the welder secondary short-circuit kVA. BU 1.2-2002 (R2008, R2013) Page 10 2014 National Electrical Manufacturers Association If both the during-weld kVA and the duty cycle are unknown, the effective kVA can be assumed to be 70 % of the nameplate kVA rating for
26、seam and automatic welders and 50 percent of the nameplate kVA for manually operated welders other than seam. Nameplate kVA rating is defined as the maximum load that can be imposed on the welding machine transformer at a 50 % duty cycle. 5.2.1 Group of Welders It has been found by actual measuremen
27、t that the total effective kVA of a group of welders is equal to the effective kVA of the largest welder plus 60 % of the sum of the effective kVA of the remaining welders. Once the total effective kVA has been determined, the busway current carrying requirement can be easily calculated as follows:
28、5.2.2 Single-Phase Distribution Systems (Total Effective kVA) x 1000 (Busway Current carrying requirement) = (Line to Line Voltage) 5.2.3 Three-Phase Distribution Systems (Total Effective kVA) x 1000 (Busway Current carrying requirement) = (Line to Line Voltage) x 3 5.3 VOLTAGE DROP REQUIREMENTS To
29、assure consistently good welds, the overall voltage drop in a distribution system should be limited to 10 percent. In some instances this may be excessive; therefore, specific permissible voltage drop information should be obtained whenever possible. The overall 10% value includes voltage drop in th
30、e primary distribution system, the distribution transformers, and the secondary distribution system. The voltage drop in the primary distribution system can be obtained from the power company provided the maximum kVA demand and the power factor of the largest welder is furnished. The voltage drop in
31、 the distribution transformer can be calculated from the formula: (Voltage drop Percent) = (During-weld kVA) x (Transformer Impedance Percent) (Transformer kVA Rating) Voltage drop curves for busway can be used as a basis for determining the voltage drop in the secondary distribution system. It is g
32、eneral practice to permit 2 % voltage drop in the primary distribution system, 5 % in the distribution transformer, and the remaining 3 % in the secondary distribution system. 5.3.1 General Voltage drop for welder circuits can be determined in the same way as for conventional circuits except that it
33、 must be based on a welder multiplier factor which equates to the total during-weld current divided by the busway current rating. BU 1.2-2002 (R2008, R2013) Page 11 2014 National Electrical Manufacturers Association 5.3.2 Determine Total During-weld kVA for Voltage Drop Calculations Large welders ar
34、e sometimes interlocked to prevent excessive voltage drop caused by the possibility of simultaneous firing. In such cases, it is necessary to consider only the largest of the interlocked welders in calculating voltage drop. a) Total the nameplate kVA ratings of all large production or butt welders,
35、excluding interlocked welders. b) Total the nameplate kVA ratings of all other non-interlocked welders. c) Record the nameplate kVA rating of the largest of any interlocked welders. The during-weld kVA can be assumed to be approximately 4 times the nameplate kVA rating for large projection or butt w
36、elders and 2 1/2 times the nameplate kVA rating for other types. 1) Multiply the total from “a” above by 4. 2) Multiply the total from “b” above by 2-1/2. 3) Multiply the number from “c” above (if any) by either 4 or 2-1/2 as applicable. 4) Sum the total of 1, 2 and 3. Total kVA of all non-interlock
37、ed large production or butt x 4 Total kVA of all other non-interlocked x 2.5 Largest Interlocked kVA x (4 or 2.5 as applicable) _ Total During-weld kVA This is the total during-weld kVA for Voltage Drop Calculations 5.3.3 Determine Total During-weld Current for Voltage Drop Calculations Multiply the
38、 total during-weld kVA (see 5.3.2) by 1000. Divide by the line to line system voltage times the square root of 3. (Total during-weld kVA) x 1000 (Total During-weld Current) = (Line to Line Voltage) x This is the total during-weld current for Voltage Drop Calculations. 3BU 1.2-2002 (R2008, R2013) Pag
39、e 12 2014 National Electrical Manufacturers Association 5.3.4 Determine the Welder Multiplier for Voltage Drop Calculations Divide the total during-weld current (see 5.3.3) by the proposed busway current rating. (Total during-weld current) (Welder Multiplier Factor) = (Busway Current Rating) This is
40、 the welder multiplier factor for Voltage Drop Calculations. 5.3.5 Determine the Voltage Drop Determine the voltage drop of the proposed busway from the manufacturers data for the appropriate power factor and distance the same as for conventional circuits. Multiply this voltage drop by the welder mu
41、ltiplier factor (see 5.3.4). 5.4 EXAMPLE OF DETERMINING PROPER BUSWAY FOR RESISTANCE WELDER APPLICATION It is desired to determine the minimum size busway that will meet current carrying and voltage drop requirements for an industrial plant with 440-volt, 3-phase, 3-wire service. The busway is to su
42、pply the following group of welders which are balanced on the phases and evenly distributed along a 200 foot feeder run: (1) 300 kVA butt, (1) 175 kVA butt, (1) 150 kVA seam, (4) 100 kVA spot, (5) 50 kVA spot, (10) 5 kVA spot. The welders are manually operated and the 300 and 175 kVA welders are int
43、erlocked to prevent their firing simultaneously. Power factor of the welders is given as 40 % and permissible voltage drop in the feeder duct is 3 percent. Specific information regarding during-weld kVA and duty cycles is not available. 5.4.1 Example of Current Carrying Requirement Calculations a) E
44、ffective kVA of largest welder 300 x 50% = 150 kVA. b) Effective kVA of seam welder 150 x 70% = 105 kVA. c) Effective kVA of remaining welders 700 x 50% = 350 kVA excluding the interlocked 175 kVA welder. d) Total effective kVA 150 + (105 + 350) x 60% = 423 kVA. e) Equivalent continuous current: a m
45、 p55531000440k V A423 Thus, 600-amp low-impedance busway will meet the current carrying requirement. 5.4.2 Example of Voltage Drop Requirement Calculations a) Total nameplate kVA of butt welders-300 kVA excluding the interlocked 175 kVA welder. b) Total nameplate kVA of remaining welders-850 kVA. c)
46、 During-weld kVA of butt welders 4 x 300 = 1200 kVA. d) During-weld kVA of remaining welders: 2 1/2 x 850 = 2125 kVA. e) During-weld kVA is 1200 + 2125 = 3325 kVA. f) Three-phase during-weld current: BU 1.2-2002 (R2008, R2013) Page 13 2014 National Electrical Manufacturers Association a m p43703440
47、1000k V A3325 For example, using the voltage drop calculations shown in section 4. At 40 % power factor the voltage drop per 100 feet of 600 ampere low impedance busway carrying rated load would be about 2.7 volts. Since the load is distributed, use half this value. Voltage drop for feeder system is
48、: v o l t s6.19f e e t200f e e t100v o l t s7.221A600A4370 %.5.4or440 6.19is d r o p v o l t a g e P e r c e n t This exceeds the permissible voltage drop of 3 %, and it will be necessary to go to a larger size busway. An 800 ampere low impedance busway would have a voltage drop of 3.3 %. Because of
49、 the conservative nature of the assumptions made, this would be the logical choice. 5.5 SUMMARY Since it is difficult to obtain specific information concerning the operation of welders (particularly in new installations) and to determine accurately the possibilities for simultaneous firing of the welders, exact solutions to problems of distribution systems for resistance welders are not feasible. In the example, it was stated that the load was balanced and d
