電力專業(yè)英語4-繼電保護2

電力專業(yè)英語4

--繼電保護2電氣工程學院12/27/20231繼電保護2DistanceRelay距離保護UndervoltageRelay低電壓保護OvervoltageRelay過電壓保護BlockingRelay閉鎖繼電器PhaseAngleorOutofStepRelay失步保護FrequencyRelay頻率繼電器DirectionalPowerRelay方向功率繼電器InstantaneousOvercurrentRelay瞬時過流保護DifferentialRelay差動保護12/27/20232GroundingSystemFormerly,manypowersystemswereungroundedsystemsusingdelta-deltatransformers.Ungroundedsystemssufferformseveralproblems,includingtransientovervoltagesthatnecessitatetheuseoftwosurgearrestersforasingle-phasetransformer(oneoneachsideofthewinding),andtroublewithrapid,automaticclearingoftheverycommonphasetogroundshortcircuit.以前，許多電力系統(tǒng)采用角型接線變壓器，為不接地系統(tǒng)。不接地系統(tǒng)會帶來很多嚴重的問題，包括暫態(tài)過電壓，因此，即使是單相變壓器，也需要分別在原邊和副邊繞組各安裝一個避雷器。而且對于非常常見的相接地故障的快速自動切除非常困難。12/27/20233Anungroundedsystemisconnectedtogroundonlybystraycapacitances,soasinglephasetogroundshortcircuitdrawsverylittlefaultcurrent.不接地系統(tǒng)通過隔離電容接地，因此單相接地故障會產生非常小的故障電流Toallowrapiddetectionandautomaticclearingofgroundfaults,andtoreduceinsulationandarrestercosts,groundedsystemshavebecomemorecommonthanungroundedones.為了快速檢測和去除接地故障，并且降低投資在隔離設備和避雷器上的費用，接地系統(tǒng)的應用越來越廣泛。12/27/20234Inmanycases,thepowertransformersinagroundedsystemareconnecteddeltawye,withthewyeneutralgroundedtothesubstationgroundmat.很多情況下，接地系統(tǒng)中的電力變壓器的連接方式為三角星型接線，星型接線的中性點和變電站的接地網(wǎng)相連。Generatorsandstep-downtransformersservingonlythree-phaseloadsareoftengroundedthrougharesistancetolimitthegroundfaultcurrenttolowvalues.發(fā)電機和只帶三相負荷的降壓變壓器一般通過電阻接地，以降低接地故障電流的大小。12/27/20235Generatorstep-uptransformersandstep-downtransformersservingfour-wiredistributionsystemareusuallyconnecteddeltaontheprimaryandwyeonthesecondary.Rememberprimarymeansinputandsecondmeansoutput,soastep-uptransformerprimaryisthelow-voltagesidebutastep-downtransformerprimaryisthehigh-voltageside.發(fā)電機升壓變壓器和向四線配電系統(tǒng)供電的降壓變壓器通常在原邊側為三角型連接，在副邊側位星型鏈接。需要注意的是原邊指輸入，副邊指輸出，因此升壓變壓器的原邊為低壓側，但降壓變壓器的原邊為高壓側。12/27/20236Distributiontransformersonfour-wiresystemsareconnectedphasetoneutral(singlephase)orwye(threephase)ontheprimaryside.Thesecondarysideofthree-phasedistributiontransformersmaybeconnectedineitherwyeordelta.四線系統(tǒng)的配電變壓器的原邊連接在相和中線上〔單相變壓器〕或連接成星型〔三相變壓器〕。三相配電變壓器的副邊可以星型或三角型連接。12/27/20237Thewye-wyedistributiontransformerisusedforfour-wire(threephaseconductorsandaneutralconductor)systems,andthewye-deltadistributiontransformerisusuallyconnectedwiththebankneutralnotconnectedtoground.星星連接配電變壓器用于四線系統(tǒng)〔三相導線和中線〕，星角接線配電變壓器的中性點通常不接地。12/27/20238Iftheneutralisgrounded,thebanktriestogroundthefeeder,andwhengroundfaultsoccurontheprimaryside,thedistributionbankswillsupplygroundcurrent.Thisusuallycausesalargenumberofblownfusesonwye-deltadistributiontransformerswithgroundedneutrals.如果中性點接地，….，當在原邊側發(fā)生接地故障時，配電變壓器組中有接地電流流過。這會導致星型中性點接地接線的配電變壓器的保險熔斷。12/27/20239Floatingthebankneutralalleviatestheproblem,butmaycauseovervoltageproblemssuchasferroresonance.Wye-wyebanksavoidtheferroresonanceproblemsincetheyinvariablyhavegroundedneutralsonbothsides.變壓器中性點浮地能減輕這一問題，但可能造成過電壓問題，例如鐵磁共振。星星連接變壓器組不會產生鐵磁共振問題，因為在原邊和副邊中性點均接地。12/27/202310Instrumenttransformers儀用〔或測量用〕互感器Instrumenttransformersaretheinputtransducerforprotectiverelays,butalsometering(bothfrorevenuemeteringandfordataacquisition).Thetwomaintypesofinstrumenttransformersarecurrenttransformers(CTs)andpotentialtransformers(PT’s).Thelatterarealsocalledvoltagetransformers(VT’s),withnodifferenceintended.測量用互感器指的是保護繼電器的輸入傳感器，也指計量儀表〔例如電費計量和數(shù)據(jù)采集〕的輸入傳感器。兩種主要的測量用互感器為電流互感器〔CT〕和電壓互感器〔PT〕,后者也簡稱VT。12/27/202311TheCTactstostepthecurrentdown,sayfrom1000Aontheprimaryto5Aonthesecondary.ThiswouldgiveaCTratioof1000:5Aor200:1A,andwouldrequire200turnsonthesecondary(assumingoneprimary“turn〞).CT的作用是降低電流，例如將原邊1000A的電流降至副邊的5A。那么CT的變比為1000:5A或200:1A，副邊繞組的匝數(shù)為200〔假設原邊繞組匝數(shù)為1〕12/27/202312Currenttransformersecondariesaretypicallyratedat5A,althoughsomeareratedat1A.Thisisthecontinuousrating,anditmaybeexceededbyafactorof10or20forashorttime,especiallyduringashortcircuitinsupplyingrelaysthatprovideovercurrentprotection.電流互感器二次側典型額定電流為5A，有時為1A.這只是額定標稱值，其二次側允許短時過電流10-20倍，尤其是作為過流保護的輸入傳感器，有短路電流流過時。12/27/202313Currenttransformersforrelayingpurposesaregivenaccuracyclassratings,suchasC400orT400(sometimeswrittenas10C400or10T400).TheletterCindicatesthatitsperformancemaybecalculatedfromitsmagnetizationcurve.TheletterTindicatesthatitsperformancemustbedeterminedbytest.保護用電流互感器均給出其〔測量〕精度等級，例如C400或T400〔有些標為10C400或10T400〕。字母C表示其特性通過其磁化曲線計算出來。字母T表示其特性由實驗決定。12/27/202314ThenumberfollowingtheletterCorTisthevoltagerating:thesecondaryvoltageproducedby20timesratedsecondarycurrent