1、STD.NEMA C57.2.20-EN6L1997b47024705148145T2MERICAN NATIONAL STANDARDAmerican Natio StanoardANSI C57.12.20-1997AMERICAN NATIONAL STANDARDFOR TRANSFORMERS-STANDARD FOR OVERHEAD TYPEDISTRIBUTION TRANSFORMERS,500 KVA AND SMALLER:HIGH VOLTAGE,34500 VOLTS ANDBELOW:LOW VOLTACE,7970/13800YVOLTS AND BELOWNAT
2、IONAL ELECTRICAI MANUFACTURERS ASSOGIATION1300 NORTH 17TH STREET.SUITE 1847,ROSSLYN,VA 2320970￥R41320Copyright por National Electrical Manufacturers AssociationSun May0507:19442002STD.NEMA C57.12.20-EN6L19976470247051489L375ANS1C57.1220-1997ecaApproval of an American National Standard requires verif
3、ication by ANSI that therequirements for due process,consensus,and other criteria for approval have beenNationalmet by the standards developer.StandardConsensus is established when,in the judgment of the ANSI Board of StandardsReview,substantial agreement has been reached by directly and materially
4、affectedinterests.Substantial agreement means much more than a simple majority,but notnecessarily unanimity.Consensus requires that all views and objections beconsidered,and that a concerted effort be made toward their resolution.The use of American National Standards is completely voluntary;their e
5、xistence doesnot in any respect preclude anyone,whether he has approved the standards or not,from manufacturing,marketing,purchasing,or using products.processes,orprocedures not conforming to the standards.The American National Standards Institute does not develop standards and will in nocircumstanc
6、es give an interpretation of any American National Standard.Moreover,noperson shall have the right or authority to issue an interpretation of an AmericanNational Standard in the name of the American National Standards Institute.Requestsfor interpretations shall be addressed to the secretariat or spo
7、nsor whose nameappears on the title page of this standard.CAUTION NOTICE:This American National Standard may be revised or withdrawn atany time.The procedures of the American National Standards Institute require thataction be taken to reaffirm,revise,or withdraw this standard no later than five year
8、sfrom the date of approval.Purchasers of American National Standards may receivecurrent information on all standards by calling or writing the American NationalStandards Institute.Published byNational Electrical Manufacturers Assoclation1300 N.17th Street,Rosslyn,Virginia 22209Copyright 1998 Nationa
9、l Electrical Manufacturers AssociationAll rights reserved.No part of this pul中lication may be reproduced in ar可fomm.in an electronic retrieval system or otherwise,without prior written permission of the publisher.Printed in the United States of AmericaCopyright por National Electrical Manufacturers
10、AssociationSun May0507:19:442002STD.NEMA C57.12.20-ENGL1997b4702470514897201ANS1C57.12.20-1997CONTENTSSectionPage1Scope.Relerenced and related publications.2.1Referenced American National Standards.12.2Related publications.Ratings3.1Kilovolt-ampere ratings.423.2Voltage ratings and tap ratings.42424B
11、asic lighting impulse insulation levets and dielectric test leve!s.5.5Tests5.1General.5.2Dielectric tests.5Construction.66.1Bushings and terminais.6.1.1Bushings.6.12Terminals.8486.1.3Neutral termination.216.1.4Terminal boards.6.221Accessory equipment.6.2.1Tap changer.216,22Series-multiple connection
12、s.6.23Liquid-level marking.24246.2.4Lifting lugs.6.2.524Relief of excessive pressure.246.2.6Enclosure integrity.6.3Polarity,terminal markings,and angular displacement.6.3.1Polarity.266.3.2Angular displacement.4+6.3.3256.3.4Instruction nameplate.6.3.5Kilovolt-ampere rating on tank.6.3.6Connections fo
13、r shipment by the manufacturer.26.476.5Tanks.6.5.1Covers and handholes.376.5.2Support ugS.376.5.3Tank finish.376.5.4Tank grounding provisions.,387Storage and installation.387.1Storage.,387.2Installation.38iCopyright por National Electrical Manufacturers AssociationSun May0507:19:442002STD.NEMA C57.1
14、2.20-EN6L199764702470514898148ANSC57.12.20-19978Design tests for fault current capebility of overhead distribution transformer enclosures.388.1bjeCtiVe444t4aantiiaasaaia4i4t444s44stit88.2Definitions.38.2.18.2.2Internal fusible element.行下1中4+4行卡，+4144无号4+0404444有非4444卡4转年年8.2.3Back-up protection.38.2
15、.48.2.5398.3.98.4Test相m408.5Test number 1-an arcing fault in an enclosure.408.5.1Fir俗t fault.a,ate9t+t444t时5t408.5.2Second fault.408.6Test number 2-for enclosures with intemnal fusible elements.408.6.108.6.2B”au此，308.7Test results,41Annex A.ni.A-1Copyright por National Electrical Manufacturers AssociationSun May0507:19:442002