IEC_60905-1987_scan.pdf

TNORME INTERNATIONALECEIINTERNATIONAL STANDARDIEC905Premiere editionCommission Electrotechnique InternationaleFirst edition1987International Electrotechnical CommissionMemAyHapoAHa neKTpOTeXHn4ecHaR HOMHCCHAGuide de charge pour transformateurs de puissancedu type secLoading guide for dry-type power transformers001143 Ac27.A.2534CEI 1987 Droits de reproduction reserves-Copyright-al rights reservedAucune partie de cette publication ne peut tre reproduite ni utilisee sous quel-No part of this publication may be reproduced or utilized in any form or by anyque forme que ce soit et par aucun procede.electronique ou mcanique,ycom-means,electronic or mechanical,including photocopying and microfilm,with-pris la photocopie et les microfilms.sans Iaccord ecrit de lediteur.out permission in writing from the publisherBureau Central de la Commission Electrotechnique Internationale 3,rue de Varembe Geneve.SuisseCode prix 26905IEC1987-3-CONTENTSPageFOREWORD.55PREFACE.5Clause1.Scope.72.Object.73.Symbols.9PART14.Basisofguide.115.Algorithm for basicuse of lifecalculations.266.Limitations.29PART27.Basis ofestablishing load curves.298.Selection of appropriate load curve with examples.2905IEC1987-5-INTERNATIONAL ELECTROTECHNICAL COMMISSIONLOADING GUIDEFOR DRY-TYPE POWER TRANSFORMERSFOREWORD1)The formal decisions or agreements of the IEC on technical matters,prepared by Technical Committees on which all theNational Committees having a special interest therein are represented,express,as nearly as possible,an internationalconsensus of opinion on the subjects dealt with.2)They have the form of recommendations for international use and they ara accepted by the National Committees in thatsense.3)In order to promote international unification,the IEC expresses the wish that all National Committees should adopt thetext of the IEC recommendation for their national rules in so far as national conditions will permit.Any divergencebetween the IECrecommendations and the corresponding national rules should,as far as possible,be clearly indicated inthe latter.PREFACEThis guide has been prepared by IEC Technical Committee No.14:Power transformers.The text of this guide is based on the following documents:Six MonthsRuleReport on Voting14(CO)6014(CO)63Full information on the voting for the approval of this guide can be found in the Voting Reportindicated in the above table.The following IEC Publications are quoted in this guide:Publications Nos.76-1(1976):Power transformers.Part 1:General.726(1982):Dry-type power transformers.905IEC1987-7-LOADING GUIDEFOR DRY-TYPE POWER TRANSFORMERS1.ScopeThis guide is applicable to naturally cooled dry-type power transformers complying withIEC Publication 726 and operated within the limitations referred to in Clause 6.Six differentinsulation systems are taken into account,identified by their system temperatures.Because there are numerous combinations of different insulation systems and constructionsit is possible to make loading recommendations only of a general nature.For this reason theguide is in two parts:the first part makes no loading recommendations,but gives the method of calculatingloading conditions when the variable parameters are known as the result of prototypetesting of a particular construction and/or insulation system.The calculations are given inthe form of an algorithm from which computer programs can be written;the second part assumes constant values for the variable parameters.with the exception ofthe insulation temperature limits(Table I)and the temperature of external cooling air.irrespective of insulation system or construction.thereby enabling load curves to beproduced.The guide indicates how dry-type transformers may be operated without exceeding theacceptable limit of deterioration of insulation through thermal effects.The acceptable limit ofdeterioration of insulation is defined as that which occurs when the dry-type transformer isoperating under rated conditions at the basic temperature of the external cooling air.2.ObjectThe object of this guide is to permit the calculation of,and to indicate the permissible loadingunder certain defined conditions in terms of rated current,for the guidance of users and to helpplanners to choose the rated power of transformers required for new installations.The basic temperature of the external cooling air is assumed to be 20C.Guidance is givenfor this temperature,and also for external cooling air temperatures of 10 C and 30 C.Deviations from these temperatures are provided for in such a way that the increased use oflifewhen operated with a higher external cooling air temperature is balanced by a reduced use oflife with a lower external cooling air temperature.2In practice,uninterrupted continuous operation at full rated current is unusual,and thisguide gives recommendations for cyclic daily loads,taking into account seasonal variations ofambient temperature.The daily use of life due to thermal effects is compared with normal dailyuse of life which results when the dry-type transformer is operating at rated voltage andcurrent,with an external cooling air temperature of 20C.