Protection relay继电保护外文翻译资料.docx
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Protection relay继电保护外文翻译资料.docx
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Protectionrelay继电保护外文翻译资料
Protectionrelay
●Protectiverelaying
Protectiverelayingisthatareaofpowersystemdesignconcernedwithminimizingserviceinterruptionandlimitingdamagetoequipmentwhenfailuresoccur.Thefunctionofprotectiverelayingistocausethepromptremovalofadefectiveelementfromapowersystem.Thedefectiveelementmayhaveashortcircuitoritmaybeoperatinginanabnormalmanner.Protectiverelayingsystemsaredesignedtodetectsuchfailuresorabnormalconditionsquicklyandtoopenaminimumofcircuitbreakerstoisolatethedefectiveelement.Theeffectofquickisolationisthreefold:
(1)itminimizesorpreventsdamagetothedefectiveelement,thusreducingthetimeandexpenseofrepairsandpermittingquickerrestorationoftheelementtoservice;
(2)itminimizestheseriousnessanddurationofthedefectiveelementsaffectingonthenormaloperationofthepowersystem;and(3)itmaximizesthepowerthatcanbetransferredonpowersystems.Thesecondandthirdpointsareofparticularsignificancebecausetheyindicatetheimportantroleprotectiverelayingplaysinassuringmaximumservicereliabilityandinsystemdesign.Thepowerthatcanbetransmittedacrosssystemwithoutthelossofsynchronismisthefunctionoffaultclearingtimes.Itisapparentthatfastfaultclearingtimespermitahigherpowertransferthanlongerclearingtimes.High-speedclearingoffaultscanoftenprovideameansforachievinghigherpowertransfersandtherebydeferinvestmentinadditionaltransmissionfacilities.
Aprotectiverelayingsystemisbasedondetectingfaultconditionsbycontinuouslymonitoringthepowersystemvariablessuchascurrent,voltage,power,frequency,andimpedance.Measuringofcurrentsandvoltageisperformedbyinstrumenttransformersofthepotentialtype(PT)orcurrenttype(CT).Instrumenttransformersfeedthemeasuredvariablestotherelaysystem,whichinturn,upondetectingafault,commandscircuitbreaker(CB)todisconnectthefaultedsectionofthesystem.
Anelectricpowersystemisdividedintoseveralprotectivezonesforgenerators,transformers,buses,transmissionanddistributioncircuit,andmotors.Thedivisionissuchthatzonesaregivenadequateprotectionwhilekeepingserviceinterruptiontoaminimum.Itistobenotedthateachzoneisoverlappedtoavoidunprotect(blind)areas.Theconnectionsofcurrenttransformersachievetheoverlapping.Thegeneralphilosophyofrelayapplicationistodividethepowersystemintozonesthatcanbeadequatelyprotectedbysuitableprotectiveequipmentandcanbedisconnectedfromthepowersysteminaminimumamountoftimeandwiththeleasteffectontheremainderofthepowersystem.Theprotectiverelayingprovidedforeachzoneisdividedintotwocategories:
(1)primaryrelayingand
(2)backuprelaying.Primaryrelayingisthefirstlineofdefensewhenfailuresoccur,andisconnectedtotriponlythefaultedelementfromthesystem.Ifafailureoccursinanyprimaryzonetheprotectiverelayswilloperatetotripallofthebreakerswithinthatzone.Ifabreakerisomittedbetweentwoadjacentelements,bothelementswillbedisconnectedforafailureineitherone.Thislatterarrangementisillustratedbytheunitgenerator-transformerconnectioninthepowerplant.Onbulkpowergeneratingandtransmissionsystems,primaryprotectionisdesignedtooperateathighspeedforallfaults.Slowerprotectionmaybeusedinlessimportantsystemareasbut,ingeneral,anysystemareawillbenefitbythefastestpossibleprimaryrelaying.
Ifthefaultisnotclearedbytheprimaryprotection,backuprelayingoperatestoclearthefaultfromthesystem.Ingeneral,backuprelayingdisconnectsagreaterportionofthesystemtoisolatethefault.Backupprotectionisprovidedforpossiblefailureintheprimaryrelayingsystemandforpossiblecircuitbreakerfailures.Anybackupschememustprovidebothrelaybackupaswellasbreakerbackup.Ideally,thebackupprotectionshouldbearrangedsothatanythingthatmaycausetheprimaryprotectiontofailwillnotalsocausefailureofthebackupprotection.Moreover,thebackupprotectionmustnotoperateuntiltheprimaryprotectionhasbeengivenanopportunitytofunction.Asaresult,thereistimedelayassociatedwithanybackupoperation.Whenashortcircuitoccurs,boththeprimaryandthebackupprotectionstarttooperate.Iftheprimaryprotectionclearsthefault,thebackupprotectionwillresetwithoutcompletingitsfunction.Ifthefaultisnotclearedbytheprimaryprotection,thebackuprelayingwilltimeoutandtripthenecessarybreakerstoclearthefaultfromthesystem.
Therearetwoformsofbackupprotectionincommonuseonpowersystems.Theyareremotebackupandlocalbackup.
(1)Remotebackup.Inremotebackuprelaying,faultsareclearedfromthesystemonestationawayfromwherethefailurehasoccurred.
(2)Localbackup.Inlocalbackuprelaying,faultsareclearedlocallyinthesamestationwherethefailurehasoccurred.Forfaultsontheprotectedline,boththeprimaryandthebackuprelayswilloperatetopreparetrippingthelinebreaker.Relaybackupmaybejustasfastasthefrontlinerelays.Wheneitheroftheserelaysoperatestoinitiatetrippingofthelinebreaker,italsoenergizesatimertostartthebreakerbackupfunction.Ifthebreakerfailstoclearthefault,thelinerelayswillremainpickedup,permittingthetimertotimeoutandtripthenecessaryotherbreakersontheassociatedbussection.
●Computerrelaying
Theelectricpowerindustryhasbeenoneoftheearliestusersofthedigitalcomputerasafundamentalaidinthevariousdesignandanalysisaspectsofitsactivity.Computer-basedsystemshaveevolvedtoperformsuchcomplextasksasgenerationcontrol,economicdispatch(treatedinchapter11)andload-flowanalysisforplanningandoperation,tonamejustafewapplicationareas.researcheffortsdirectedattheprospectusingdigitalcomputerstoperformthetasksinvolvedinpowersystemprotectiondatebacktothemien-sixtiesandweremotivatedbytheemergenceofprocess-controlcomputersagreatdealofresearchisgoingoninthisfield,whichisnowreferredtoascomputerrelaying.Uptotheearly1980stherehadbeennocommerciallyavailabilityprotectionsystemsofferingdigitalcomputer-basedrelays.However,theavailabilityofmicroprocessortechnologyhasprovidedanimpetustocomputerrelaying.*Microprocessorsusedasareplace*andsolidstaterelaysnonprovideanumberofadvantageswhilemeetingthebasicprotectionphilosophyrequirementofdecentralization.
Therearemanyperceivedbenefitsofadigitalrelayingsystem:
1.Economics:
withthesteadydecreaseincostofdigitalhardware,coupledwiththeincreaseincostofconventionalrelaying.Itseemsreasonabletoassumethatcomputerrelayingisanattractivealternative.Softwaredevelopmentcostcanbeexpectedtobeevenedoutbyutilizingeconomiesofscaleinproducingmicroprocessorsdedicatedtobasicrelayingtasks.
2.Reliability:
adigitalsystemiscontinuouslyactiveprovidingahighlevelofaself-diagnosistodetectaccidentalfailureswithinthedigitalrelayingsystem.
3.Flexibility:
revisionsormodificationsmadenecessarybychangingoperationalconditionscanbeaccommodatedbyutilizingtheprogrammabilityfeaturesofadigitalsystem.Thiswouldleadtoreducedinventoriesofpartsforrepairandmaintenancepurposes
4.Systeminteraction:
theavailabilityofdigitalhardwarethatmonitorscontinuouslythesystemperformanceatremotesubstationscanenhancethelevelofinformationavailabletothecontrolcenter.Postfaultanalysisoftransientdatacanbeperformedonthebasisofsystemvariablesmonitoredbythedigitalrelayandrecordedbytheperipherals.
Themainelementsofadigitalcomputer-basedrelayareindicatedinFigure9-59.Theinputsignalstotherelayareanalog(continuous)anddigitalpowersystemvariables.Thedigitalinputsareoftheorderoffivetotenandincludestatuschanges(on-off)ofcontactsandchangesinvoltagelevelsinacircuit.Theanalogsignalsarethe60-Hzcurrentsandvoltages.Thenumberofanalogsignalsneededdependsontherelayfunctionbutisintherangeof3to30inallcases.Theanalogsignalsarescaleddown(attenuated)toacceptablecomputerinputlevels(
10voltsmaximum)andthenconvertedtodigital(discrete)formthroughanalog/digitalconverters(ADC).Thesefunctionsareperformedintheblocklabeled“AnalogInputSubsystem.”
Thedigitaloutputoftherelayisavailablethroughthecomputer’sparalleloutputport,five-to-tendigitaloutputsaresufficientformostapplications.
Theanalogsignalsaresampledataratebetween210Hztoabout2000Hz.Thesampledsignalsareenteredintothescratchpad(RAM)andarestoredinasecondarydatafileforhistoricalrecording.Adigitalfilterremovesnoiseeffectsfromthesampledsignals.Therelaylogicprogramdeterminesthefunctionaloperationoftherelayandusesthefilteredsampledsignalstoarriveatatripornotripdecisionwhichisthencommunicatedtothesystem.
Theheartoftherelaylogicprogramisarelayingalgorithmthatisdesignedtoperformtheintendedrelayfunctionsuchasovercurrentsdetection,differentialprotection,ordistanceprotection,etc.Itisnotourintentioninthisintroductorytexttopursethisinvolvedinarelayingalgorithm,wediscussnextoneideaforpeakcurrentdetectionthatisthefunctionofadigitalovercurrentrelay.
●Microcomputer-basedRelaying
Anewerdevelopmentinthefieldofpowersystemprotectionistheuseofcomputers(usuallymicrocomputers)forrelaying.Althoughcomputersprovidethesameprotectiona
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