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1、外文資料翻譯TRANSFMER1.INTRODUCTIONThehighvoltagetransmissionwasneedfthecaseelectricalpoweristobeprovidedatconsiderabledistancefromageneratingstation.Atsomepointthishighvoltagemustbereducedbecauseultimatelyismustsupplyaload.Th

2、etransfmermakesitpossiblefvariouspartsofapowersystemtooperateatdifferentvoltagelevels.Inthispaperwediscusspowertransfmerprinciplesapplications.2.TOWWINDINGTRANSFMERSAtransfmerinitssimplestfmconsistsoftwostationarycoilsco

3、upledbyamutualmagicflux.Thecoilsaresaidtobemutuallycoupledbecausetheylinkacommonflux.Inpowerapplicationslaminatedsteelcetransfmers(towhichthispaperisrestricted)areused.Transfmersareefficientbecausetherotationallossesnmal

4、lyassociatedwithrotatingmachineareabsentsorelativelylittlepowerislostwhentransfmingpowerfromonevoltageleveltoanother.Typicalefficienciesareintherange92to99%thehighervaluesapplyingtothelargerpowertransfmers.Thecurrentflow

5、inginthecoilconnectedtotheacsourceiscalledtheprimarywindingsimplytheprimary.Itsetsupthefluxφinthecewhichvariesperiodicallybothinmagnitudedirection.Thefluxlinksthesecondcoilcalledthesecondarywindingsimplysecondary.Theflux

6、ischangingtherefeitinducesavoltageinthesecondarybyelectromagicinductioninaccdancewithLenz’slaw.Thustheprimaryreceivesitspowerfromthesourcewhilethesecondarysuppliesthispowertotheload.Thisactionisknownastransfmeraction.3.T

7、RANSFMERPRINCIPLESWhenasinusoidalvoltageVpisappliedtotheprimarywiththesecondaryopencircuitedtherewillbenoenergytransfer.TheimpressedvoltagecausesasmallcurrentIθtoflowintheprimarywinding.Thisnoloadcurrenthastwofunctions:(

8、1)itproducesthemagicfluxinthecewhichvariessinusoidallybetweenzeroφmwhereφmisthemaximumvalueoftheceflux(2)itprovidesa?componenttoaccountfthehysteresiseddycurrentlossesinthece.Therecombinedlossesarenmallyreferredtoasthecel

9、osses.ThenoloadcurrentIθisusuallyfewpercentoftheratedfullloadcurrentofthetransfmer(about2to5%).Sinceatnoloadtheprimarywindingactsasalargereactanceduetotheironcethenoloadcurrentwilllagtheprimaryvoltagebynearly90.Itisreadi

10、lyseenthatthecurrentcomponentIm=I0sinθ0calledthemagizingcurrentis90inphasebehindtheprimaryvoltageVP.ItisthiscomponentthatsetsupthefluxintheceφistherefeinphasewithIm.ThesecondcomponentIe=I0sinθ0isinphasewiththeprimaryvolt

11、age.Itisthecurrentcomponentthatsuppliesthecelosses.ThephassumofthesetwoVpIpprimaryPF=VsIssecondaryPFwherePFisthepowerfact.FtheabovestatedassumptionitmeansthatthepowerfactonprimarysecondarysidesareequaltherefeVpIp=VsIsfro

12、mwhichisobtained=≌≌apsVVpsIIpsEEItshowsthatasanapproximationtheterminalvoltageratioequalstheturnsratio.Theprimarysecondarycurrentontheotherhareinverselyrelatedtotheturnsratio.Theturnsratiogivesameasureofhowmuchtheseconda

13、ryvoltageisraisedloweredinrelationtotheprimaryvoltage.Tocalculatethevoltageregulationweneedmeinfmation.Theratiooftheterminalvoltagevariessomewhatdependingontheloaditspowerfact.Inpracticethetransfmationratioisobtainedfrom

14、thenameplatedatawhichlisttheprimarysecondaryvoltageunderfullloadcondition.WhenthesecondaryvoltageVsisreducedcomparedtotheprimaryvoltagethetransfmationissaidtobeastepdowntransfmer:converselyifthisvoltageisraiseditiscalled

15、astepuptransfmer.Inastepdowntransfmerthetransfmationratioaisgreaterthanunity(a1.0)whilefastepuptransfmeritissmallerthanunity(a1.0).Intheeventthata=1thetransfmersecondaryvoltageequalstheprimaryvoltage.Thisisaspecialtypeof

16、transfmerusedininstanceswhereelectricalisolationisrequiredbetweentheprimarysecondarycircuitwhilemaintainingthesamevoltagelevel.Therefethistransfmerisgenerallyknowsasanisolationtransfmer.Asisapparentitisthemagicfluxinthec

17、ethatfmstheconnectinglinkbetweenprimarysecondarycircuit.Insection4itisshownhowtheprimarywindingcurrentadjustsitselftothesecondaryloadcurrentwhenthetransfmersuppliesaload.Lookingintothetransfmerterminalsfromthesourceanimp

18、edanceisseenwhichbydefinitionequalsVpIp.From=≌≌awehaveVp=aVspsVVpsIIpsEEIp=Isa.IntermsofVsIstheratioofVptoIpis==ppVIssaVIa2ssaVIButVsIsistheloadimpedanceZLthuswecansaythatZm(primary)=a2ZLThisequationtellsusthatwhenanimpe

19、danceisconnectedtothesecondarysideitappearsfromthesourceasanimpedancehavingamagnitudethatisa2timesitsactualvalue.Wesaythattheloadimpedanceisreflectedreferredtotheprimary.Itisthispropertyoftransfmersthatisusedinimpedancem

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