IEC_60909-1995_Short_Circuit.pdf

09155129131-133159133135/NORME INTERNATIONALECEIINTERNATIONAL STANDARDIEC909Premiere editionFirst editionCommission Electrotechnique Internationale1988International Electrotechnical CommissionMemAyHapoAHaR 3neKTpoTeXHnecHaR HOMCCHRCalcul des courants de court-circuitdans les rseaux triphass a courant alternatifVar IEc 702685Short-circuit current calculationin three-phase a.c.systemsEJEMPLAR DISTRIBUIDO POR ELCOMITE ELECTROTECNICO ARGENTINOPOSADAS 1669-(11121 CAPITAL FEDERALTEL.804-3454 Y604-1532CE 1988 Droits de reproduction reserves-Copyright-all rights reservedAucune partie de cette publication ne peut etre reproduite hiutilise sous quel-No part of this publication may be teproduced or utilized in any form or by anyque forme que ce soit en par aucun proced.electronique ou mecanique,y com-means,electronic or mechanical,including photocopying and microfilm,with-pris la photocopie et les micrcfilms,sans Iaccord ecrit de editeur.out permission in writing from the publisher.Bureau Central de la Commission Electrotechnique Internationale 3,rue de Varembe Geneve,SuisseCode prix86Price codePour prix,oir caalogue en vigueuFor price.see current caalogue909(1)IEC-3-CONTENTSFOREWORDPagePREFACE5Clause1.Scope2.Object.3.Definitions4.Symbols,subscripts and superscripts.94.1 Symbols.4.2 Subscripts.143 Superscripts.5.Calculation assumptions.,.,.6.Equivalent voltage source at the short-circuit location.,.,.1SECTION ONE-SYSTEMS WITH SHORT-CIRCUIT CURRENTS HAVING NO A.C.COMPONENT DECAY(FAR-FROM-GENERATOR SHORT CIRCUITS)8.Short-circuit parameters.28.1 Balanced short circuit.28.2 Unbalanced short circuit8.3 Short-circuit impedances28.4 Conversion ofimpedances,currents and voltages.459.Calculation of short-circuit currents.,9.1 Calculation method for balanced short circuits.49.2 Calculation method for line-to-line and line-to-earth short circuits.9.3 The minimum short-circuit currents.535SECTION TWO SYSTEMS WITH SHORT-CIRCUIT CURRENTS HAVING DECAYING A.C.COMPONENTS(NEAR-TO-GENERATOR SHORT CIRCUITS)10.General.l1.Short-circuit parameters.11.1 General611.2 Balanced short circuit.1l1.3 Unbalanced short circuit.11.4 Equivalent voltage source at the short-circuit location6l1.5 Short-circuit impedances.11.6 Conversion ofimpedances,currents and voltagesl2.Calculation of short-circuit currents.712.1 General12.2 Calculation method for balanced short circuits.12.3 Calculation method for line-to-line and line-to-earth short circuits7512.4 The minimum short-circuit currents,99l3.Influence of motors,l3.1 Synchronous motors and synchronous compensators.913.2 Asynchronous motorsl3.3 Static converter fed drives.,.,.9914.Consideration of non-rotating loads and capacitors110714.1 Parallel capacitors.107l4.2 Series capacitors.107APPENDIX A-Calculation of short-circuit currents,examples.109909(1)IEC-5-INTERNATIONAL ELECTROTECHNICAL COMMISSIONSHORT-CIRCUIT CURRENT CALCULATIONIN THREE-PHASE A.C.SYSTEMSFOREWORD1)The formal decisions or agreements of the IECon technical matters,prepared by Technical Committees on which all theNational Committees having a special interest therein are represented,express,as nearly as possible,an interationalconsensus of opinion on the subjects dealt with.2)They have the form of recommendations for international use and they are 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 IECrecommendation and the corresponding national rules should,as far as possible,be clearly indicated inthe latter.PREFACEThis standard has been prepared by IEC Technical Committee No.73:Short-circuit currents。The text of this standard is based on the following documents:Six MonthsRuleReport on Voting73(C0)573(C0)7Full information on the voting for the approval of this standard can be found in the Voting Reportindicated in the above table.The following IEC publications are quoted in this standard:Publication Nos.38(1983):IEC standard voltages.50:International Electrotechnical Vocabulary(IEV).50(131)(1978):Chapter 131:Electric and magnetic circuits50(151)(1978):Chapter 151:Electrical and magnetic devices.50(441)(1984):Chapter 441:Switchgear,controlgear and fuses.865(1986):Calculation of the effects of short-circuit currents909(1)IEC7SHORT-CIRCUIT CURRENT CALCULATIONIN THREE-PHASE A.C.SYSTEMS1.ScopeThis standard is applicable to the calculation of short-circuit currents:-in low-voltage three-phase a.c.systems,-in high-voltage three-phase a.c.systems with nominal voltages up to 230kV operating atnominal frequency(50 Hz or 60 Hz).This standardized procedure is given in such a form as to facilitate as far as possible its use bynon-specialist engineers.2.ObjectThe object of this standard is to establish a general,practicable and concise procedureleading to conservative results with sufficient accuracy.For this purpose,an equivalent voltagesource at the short-circuit location is considered,as described under Clause 6.This does notexclude the use of special methods,for example the superposition method,adjusted toparticular circumstances,if they give at least the same precision.Short-circuit currents and short-circuit impedances may also be determined by system tests,by measurement on a network analyzer,or with a digital computer.In existing low-voltagesystems it is possible to determine the short-circuit impedance on the basis of measurements atthe location of the prospective short circuit considered.The calculation of the short-circuit impedance based on the rated data of the electricalequipment and the topological arrangement of the system has the advantage of being possibleboth for existing systems and for systems at the planning stage.There are two different short-circuit currents to be calculated which differ in theirmagnitude:-the maximum short-circuit current which determines the capacity or rating of electricalequipment;-the minimum short-circuit current which can be a basis,for example,for the selection offuses and for the setting of protective devices and for checking the run-up of motors.One has to distinguish between:-systems with short-circuit currents having no ponent decay(far-from-generatorshort circuit),treated in Section One,-systems with short-circuit currents having decaying ponents(near-to-generatorshort circuit),treated in Section Two.This section also includes the influence of motors.This standard does not cover short-circuit currents deliberately created under controlledconditions(short-circuit testing stations).This standard does not deal with installations on board ships and areoplanes.For the calculation of the thermal equivalent short-circuit currents see Section Two of IECPublication 865.An application guide,dealing with non-meshed low-voltage three-phase a.c.systems and atechnical report on the derivation of the parameters and various calculation factors of thisstandard are under consideration.909(1)IEC9-3.DefinitionsFor the purpose of this standard,the following definitions apply.Reference is made to theInternational Electrotechnical Vocabulary(IEV)IEC Publication 50when applicable.3.1 Short circuitThe accidental or intentional connection,by a relatively low resistance or impedance,of twoor more points in a circuit which are normally at different voltages(IEV 151-03-41).3.2 Short-circuit currentAn over-current resulting from a short circuit due to a fault or an incorrect connection in anelectric circuit(IEV 441-11-07).Note.-It is necessary to distinguish between the short-circuit current at the short-circuit location and in the networkbranches.3.3.Prospective(available)short-circuit currentThe current that would flow if the short circuit were replaced by an ideal connection ofnegligible impedance without any change of the supply.Note.-The current in a three-phase short circuit is assumed to be made simultaneously in all poles.Investigationsof non-simultaneous short circuits,which can lead to higher aperiodic components of short-circuit current,are beyond the scope of this standard.3.4 Symmetrical short-circuit currentThe r.m.s.value of the a.c.symmetrical component of a prospective(available)short-circuitcurrent(see Sub-clause 3.3),the aperiodic component of current,if any,being neglected.3.5 Initial symmetrical short-circuit currentThe r.m.s.value of the a.c.symmetrical component of a prospective(available)short-circuitcurrent(see Sub-clause 3.3)applicable at the instant of short circuit if the impedance remains atzero-time value(see Figures 1 and 12,pages 19 and 63).3.6 Initial symmetrical short-circuit(apparent)power SThe fictive value determined as a product of the initial symmetrical short-circuit current(see Sub-clause 3.5),the nominal system voltage U(see Sub-clause 3.14),and the factor3S=3U.R3.7D.C.(aperiodic)component ipcof short-circuit currentThe mean value between the top and bottom envelope of a short-circuit current decayingfrom an initial value to.zero according to Figures 1 and 12.3.8 Peak short-circuit current ip.The maximum possible instantaneous value of the prospective(available)short-circuit.current(see Figures 1 and 12).Note.-The magnitude of the peak short-circuit current varies in accordance with the moment at which the shortcircuit occurs.The calculation of the peak three-phase short-circuit currentip applies for the phaseconductor and moment at which the greatest possible short-circuit current exists.Sequential faults are notconsidered.For three-phase short circuits it is assumed that the short circuit occurs simultaneously in allphase conductors.