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外文翻译---变压器.doc

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外文翻译---变压器.doc

河南理工大学毕业设计论文说明书1中英文对照翻译原文TRANSFORMERTransformerscomeinmanysizes.Somepowertransformersareasbigasahouse.Electronictransformers,ontheotherhand,canbeassmallasacubeofsugar.Alltransformershaveatleastonecoil.Mosthavetwoalthoughtheymayhavemanymore.Theusualpurposeoftransformersistochangethelevelofvoltage.Butsometimestheyareusedtoisolatealoadfromthepowersource.TYPESOFTRANSFORMERSStandardpowertransformershavetwocoils.ThesecoilsarelabeledPRIMARYandSECONDARY.Theprimarycoilistheoneconnectedtothesource.Thesecondaryistheoneconnectedtotheload.Thereistonoelectricalconnectionbetweentheprimaryandsecondary.Thesecondarygetsitsvoltagebyinduction.TheonlyplacewhereyouwillseeaSTEPUPtransformerisatthegeneratingstation.Typically,electricityisgeneratedat13,800volts.Itissteppeddowntodistributionlevels,around15,000volts.Largesubstationtransformershavecoolingfinstokeepthemfromoverheating.Othertransformersarelocatednearpointswheretheelectricpowerisused.TRANSFORMERCONSTRUCTIONThecoilsofatransformerareelectricallyinsulatedfromeachother.Thereisamagneticlink,however.Thetwocoilsarewoundonthesamecore.Currentintheprimarymagnetizesthecore.Thisproducesamagneticfieldinthecore.Thecorefieldthen河南理工大学毕业设计论文说明书2affectscurrentinbothprimaryandsecondary.Therearetwomaindesignsforcores1.TheCOREtypehasthecoreinsidethewindings.2.TheSHELLtypehasthecoreoutside.Smallerpowertransformersareusuallyofthecoretype.Theverylargetransformersareoftheshelltype.Thereisnodifferenceintheiroperation,however.Coilsarewoundwithcopperwire.Theresistanceiskeptaslowaspossiblekeeplosseslow.IDEALIZEDTRANSFORMERSTransformersareveryefficient.Thelossesareoftenlessthan3percent.Thisallowsustoassumethattheyareperfectinmanycomputations.Perfectmeansthatthewirehasnoresistance.Italsomeansthattherearenopowerlossesinthecore.Further,weassumethatthereisnofluxleakage.Thatis,allofthemagneticfluxlinksalloftheturnsoneachcoil.EXCITATIONCURRENTTogetanideaofjusthowsmallthelossesare,wecantakealookattheEXCITATIONCURRENT.Assumethatnothingisconnectedtothesecondary.Ifyouapplyratedvoltagetotheprimary,asmallcurrentflows.Typically,thisexcitationcurrentislessthan3percentofratedcurrent.Excitationcurrentismadeupoftwopartisinphasewiththevoltage.Thisisthecurrentthatsuppliesthepowerlostinthecore.CorelossesareduetoEDDYCURRENTSandHYSTERESIS.Eddycurrentscirculatinginthecoreresultfrominduction.Thecoreis,afterall,aconductorwithinachangingmagnetic河南理工大学毕业设计论文说明书3field.Hysteresislossiscausedbytheenergyusedinliningupmagneticdomainsinthecore.Thealignmentgoesoncontinuously,firstinonedirection,thenintheother.Theotherpartoftheexcitationcurrentmagnetizesthecore.Itisthismagnetizingcurrentthatsuppliestheshuttlepower.Shuttlepowerstoredinthemagneticfieldandreturnedtothesourcetwiceeachcycle.Magnetizingcurrentisquadrature90degreesoutofphasewiththeappliedvoltage.1.INTRODUCTIONThehighvoltagetransmissionwasneedforthecaseelectricalpoweristobeprovidedatconsiderabledistancefromageneratingstation.Atsomepointthishighvoltagemustbereduced,becauseultimatelyismustsupplyaload.Thetransformermakesitpossibleforvariouspartsofapowersystemtooperateatdifferentvoltagelevels.Inthispaperwediscusspowertransformerprinciplesandapplications.2.TOWWINDINGTRANSFORMERSAtransformerinitssimplestformconsistsoftwostationarycoilscoupledbyamutualmagneticflux.Thecoilsaresaidtobemutuallycoupledbecausetheylinkacommonflux.Inpowerapplications,laminatedsteelcoretransformerstowhichthispaperisrestrictedareused.Transformersareefficientbecausetherotationallossesnormallyassociatedwithrotatingmachineareabsent,sorelativelylittlepowerislostwhentransformingpowerfromonevoltageleveltoanother.Typical河南理工大学毕业设计论文说明书4efficienciesareintherange92to99,thehighervaluesapplyingtothelargerpowertransformers.Thecurrentflowinginthecoilconnectedtotheacsourceiscalledtheprimarywindingorsimplytheprimary.Itsetsupthefluxφinthecore,whichvariesperiodicallybothinmagnitudeanddirection.Thefluxlinksthesecondcoil,calledthesecondarywindingorsimplysecondary.Thefluxischangingtherefore,itinducesavoltageinthesecondarybyelectromagneticinductioninaccordancewithLenzslaw.Thustheprimaryreceivesitspowerfromthesourcewhilethesecondarysuppliesthispowertotheload.Thisactionisknownastransformeraction.3.TRANSFORMERPRINCIPLESWhenasinusoidalvoltageVpisappliedtotheprimarywiththesecondaryopencircuited,therewillbenoenergytransfer.TheimpressedvoltagecausesasmallcurrentIθtoflowintheprimarywinding.Thisnoloadcurrenthastwofunctions1itproducesthemagneticfluxinthecore,whichvariessinusoidallybetweenzeroandφm,whereφmisthemaximumvalueofthecorefluxand2itprovidesacomponenttoaccountforthehysteresisandeddycurrentlossesinthecore.Therecombinedlossesarenormallyreferredtoasthecorelosses.ThenoloadcurrentIθisusuallyfewpercentoftheratedfullloadcurrentofthetransformerabout2to5.Sinceatnoloadtheprimarywindingactsasalargereactanceduetotheironcore,thenoloadcurrentwilllagtheprimaryvoltagebynearly90º.ItisreadilyseenthatthecurrentcomponentImI0sinθ0,calledthemagnetizingcurrent,is90ºinphasebehindtheprimary

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