IEC电气装置蓝色安全保护防止过流保护(外文文献翻译)文档格式.doc
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IEC电气装置蓝色安全保护防止过流保护(外文文献翻译)文档格式.doc
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Providedthatbothofthefollowingconditionsaresimultaneouslyfulfilled:
•thewiringisinstalledinsuchawayastoreducetheriskofashort-circuittoaminimum(seeitemb)of434.2.1),and
•thewiringisnotplacedclosetocombustiblematerial,devicesforprotectionagainstshort-circuitneednotbeprovidedforapplicationssuchas:
a)conductorsconnectinggenerators,transformers,rectifiers,accumulatorbatteriestotheassociatedcontrolpanels,theprotectivedevicesbeingplacedinthesepanels;
b)circuitswheredisconnectioncouldcausedangerfortheoperationoftheinstallationsconcerned,suchasthosecitedin433.3.3;
c)certainmeasuringcircuits;
d)attheoriginofaninstallationwherethedistributorinstallsoneormoredevicesprovidingprotectionagainstshort-circuitandagreesthatsuchadeviceaffordsprotectiontothepartoftheinstallationbetweentheoriginandthemaindistributionpointoftheinstallationwherefurthershort-circuitprotectionisprovided.
434.4Short-circuitprotectionofconductorsinparallel
Asingleprotectivedevicemayprotectconductorsinparallelagainsttheeffectsofshortcircuitprovidedthattheoperatingcharacteristicsofthatdeviceensuresitseffectiveoperationshouldafaultoccuratthemostonerouspositioninoneoftheparallelconductors.Accountshallbetakenofthesharingoftheshort-circuitcurrentsbetweentheparallelconductors.Afaultcanbefedfrombothendsofaparallelconductor.
Ifoperationofasingleprotectivedeviceisnoteffective,thenoneormoreofthefollowingmeasuresshallbetaken:
a)Thewiringshallbecarriedoutinsuchawayastoreducetoaminimumtheriskofashort-circuitinanyparallelconductor,forexamplebyprotectionagainstmechanical
damage,andconductorsshallbeinstalledinsuchamannerastoreducetoaminimum
theriskoffireordangertopersons.
b)Fortwoconductorsinparallel,ashort-circuitprotectivedeviceshallbeprovidedatthesupplyendofeachparallelconductor.
c)Formorethantwoconductorsinparallel,short-circuitprotectivedevicesshallbeprovidedatthesupplyandloadendsofeachparallelconductor.GuidanceisgiveninClauseA.3.
434.5Characteristicsofshort-circuitprotectivedevices
Eachshort-circuitprotectivedeviceshallmeettherequirementsgivenin434.5.1.
434.5.1Theratedbreakingcapacityshallbenotlessthantheprospectivemaximumshortcircuitcurrentattheplaceofitsinstallation,exceptwherethefollowingparagraphapplies.
Alowerratedbreakingcapacityispermittedifanotherprotectivedevicehavingthenecessarybreakingcapacityisinstalledonthesupplyside.Inthatcase,thecharacteristicsofthedevicesshallbecoordinatedsothattheenergyletthroughbythesetwodevicesdoesnotexceedthatwhichcanbewithstoodwithoutdamagebythedeviceontheloadsideandtheconductorsprotectedbythesedevices.
NOTEIncertaincasesothercharacteristicsmayneedtobetakenintoaccountsuchasdynamicstressesandarcingenergyforthedeviceontheloadside.Detailsofthecharacteristicsneedingcoordinationshouldbeobtainedfromthemanufacturersofthedevicesconcerned.
434.5.2Forcablesandinsulatedconductors,allcurrentcausedbyashort-circuitoccurringatanypointofthecircuitshallbeinterruptedinatimenotexceedingthatwhichbringstheinsulationoftheconductorstothepermittedlimittemperature.
Foroperatingtimesofprotectivedevices<
0,1swhereasymmetryofthecurrentisof
importanceandforcurrent-limitingdevicesk2S2shallbegreaterthanthevalueoftheletthroughenergy(I2t)quotedbythemanufactureroftheprotectivedevice.
Forshort-circuitsofdurationupto5s,thetimet,inwhichagivenshort-circuitcurrentwillraisetheinsulationoftheconductorsfromthehighestpermissibletemperatureinnormaldutytothelimittemperaturecan,asanapproximation,becalculatedfromtheformula:
t=(k*S/I)2(3)
where
tistheduration,ins;
Sisthecross-sectionalarea,inmm2;
Iistheeffectiveshort-circuitcurrent,inA,expressedasanr.m.s.value;
kisafactortakingaccountoftheresistivity,temperaturecoefficientandheatcapacityoftheconductormaterial,andtheappropriateinitialandfinaltemperatures.Forcommonconductorinsulation,thevaluesofkforlineconductorsareshowninTable43A.
434.5.3ForbusbartrunkingsystemscomplyingwithIEC60439-2andpowertrackcomplyingwiththeIEC61534series,oneofthefollowingrequirementsshallapply:
•Theratedshort-timewithstandcurrent(ICW)andtheratedpeakwithstandcurrentofabusbartrunkingorpowertracksystemshallnotbelowerthantheprospectiveshort-circuitcurrentr.m.s.valueandtheprospectiveshort-circuitpeakcurrentvalue,respectively.ThemaximumtimeforwhichtheICWisdefinedforthebusbartrunkingorpowertracksystemshallnotbelessthanthemaximumoperatingtimeoftheprotectivedevice.
•Theratedconditionalshort-circuitcurrentofthebusbartrunkingorpowertracksystemassociatedwithaspecificprotectivedevice,shallnotbelowerthantheprospectiveshortcircuitcurrent.
435Coordinationofoverloadandshort-circuitprotection
435.1Protectionaffordedbyonedevice
Aprotectivedeviceprovidingprotectionagainstoverloadandshort-circuitcurrentsshallfulfiltheapplicablerequirementsofClausesof433and434.
435.2Protectionaffordedbyseparatedevices
TherequirementsofClauses433and434apply,respectively,totheoverloadprotectivedeviceandtheshort-circuitprotectivedevice.
Thecharacteristicsofthedevicesshallbecoordinatedsothattheenergyletthroughbytheshort-circuitprotectivedevicedoesnotexceedthatwhichcanbewithstoodwithoutdamagebytheoverloadprotectivedevice.
NOTEThisrequirementdoesnotexcludethetypeofcoordinationspecifiedinIEC60947-4-1.
436Limitationofovercurrentbycharacteristicsofsupply
Conductorsareconsideredtobeprotectedagainstoverloadandshort-circuitcurrentswheretheyaresuppliedfromasourceincapableofsupplyingacurrentexceedingthecurrentcarryingcapacityoftheconductors(e.g.certainbelltransformers,certainweldingtransformersandcertaintypesofthermoelectricgeneratingsets).
AnnexA
(informative)
Protectionofconductorsinparallelagainstovercurrent
A.1Introduction
Overcurrentprotectionforconductorsconnectedinparallelshouldprovideadequate
protectionforalloftheparallelconductors.Fortwoconductorsofthesamecross-sectionalarea,conductormateriallengthandmethodofinstallationarrangedtocarrysubstantiallyequalcurrents,therequirementsforovercurrentprotectionarestraightforward.Formorecomplexconductorarrangements,detailedconsiderationshouldbegiventounequalcurrentsharingbetweenconductorsandmultiplefaultcurrentpaths.Thisannexgivesguidanceonthenecessaryconsiderations.
NOTEAmoredetailedmethodforcalculatingthecurrentbetweenparallelconductorsisgiveninIEC60287-1-3.
A.2Overloadprotectionofconductorsinparallel
Whenanoverloadoccursinacircuitcontainingparallelconductorsofmulticorecables,thecurrentineachconductorwillincreasebythesameproportion.Providedthatthecurrentissharedequallybetweentheparallelconductors,asingleprotectivedevicecanbeusedtoprotectalltheconductors.Thecurrent-carryingcapacity(Iz)oftheparallelconductorsisthesumofthecurrent-carryingcapacityofeachconductor,withtheappropriategroupingandotherfactorsapplied.
Thecurrentsharingbetweenparallelcablesisafunctionoftheimpedanceofthecables.Forlarge,single-corecablesthereactivecomponentoftheimpedanceisgreaterthantheresistivecomponentandwillhaveasignificanteffectonthecurrentsharing.Thereactivecomponentisinfluencedbytherelativephysicalpositionofeachcable.If,forexample,acircuitconsistsoftwolargecablesperphase,havingthesamelength,constructionandcross-sectionalareaandarrangedinparallelbutwithadverserelativepositioning(i.e.cablesofthesamephasebunchedtogether)thecurrentsharingmaybe70%/30%ratherthan50%/50%.
Wherethedifferenceinimpedancebetweenparallelconductorscausesunequalcurrentsharing,forexamplegreaterthan10%difference,thedesigncurrentandrequirementsforoverloadprotectionforeachconductorshouldbeconsideredindividually.
Thedesigncurrentforeachconductorcanbecalculatedfromthetotalloadandtheimpedanceofeachconductor.
Foratotalofmconductorsinparallel,thedesigncurrentIBKforconductorkisgivenby:
(A.1)
IBisthecurrentforwhichthecircuitisdesigned;
IBKisthedesigncurrentforconductork;
Zkistheimpedanceofconductork;
Z1andZmaretheimpedancesofconductors1andm,respectively.
Incaseofparallelconductorsuptoandincluding120mm2thedesigncurrentIBKforconductorkisgivenby:
(A.2)
Skisthecross-sectionalareaofconductork;
S1…Smisthecross-sectionalareaoftheconductors.
Inthecaseofsingle-corecables,t
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