外文翻譯---變壓器.doc

河南理工大學(xué)畢業(yè)設(shè)計(論文)說明書-1-中英文對照翻譯原文：TRANSFORMERTransformerscomeinmanysizes.Somepowertransformersareasbigasahouse.Electronictransformers,ontheotherhand,canbeassmallasacubeofsugar.Alltransformershaveatleastonecoil.Mosthavetwoalthoughtheymayhavemanymore.Theusualpurposeoftransformersistochangethelevelofvoltage.Butsometimestheyareusedtoisolatealoadfromthepowersource.TYPESOFTRANSFORMERSStandardpowertransformershavetwocoils.ThesecoilsarelabeledPRIMARYandSECONDARY.Theprimarycoilistheoneconnectedtothesource.Thesecondaryistheoneconnectedtotheload.Thereistonoelectricalconnectionbetweentheprimaryandsecondary.Thesecondarygetsitsvoltagebyinduction.TheonlyplacewhereyouwillseeaSTEP-UPtransformerisatthegeneratingstation.Typically,electricityisgeneratedat13,800volts.Itissteppeddowntodistributionlevels,around15,000volts.Largesubstationtransformershavecoolingfinstokeepthemfromoverheating.Othertransformersarelocatednearpointswheretheelectricpowerisused.TRANSFORMERCONSTRUCTIONThecoilsofatransformerareelectricallyinsulatedfromeachother.Thereisamagneticlink,however.Thetwocoilsarewoundonthesamecore.Currentintheprimarymagnetizesthecore.Thisproducesamagneticfieldinthecore.Thecorefieldthen河南理工大學(xué)畢業(yè)設(shè)計(論文)說明書-2-affectscurrentinbothprimaryandsecondary.Therearetwomaindesignsforcores:1.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河南理工大學(xué)畢業(yè)設(shè)計(論文)說明書-3-field.Hysteresislossiscausedbytheenergyusedinliningupmagneticdomainsinthecore.Thealignmentgoesoncontinuously,firstinonedirection,thenintheother.Theotherpartoftheexcitationcurrentmagnetizesthecore.Itisthismagnetizingcurrentthatsuppliesthe“shuttlepower”.Shuttlepowerstoredinthemagneticfieldandreturnedtothesourcetwiceeachcycle.Magnetizingcurrentisquadrature(90degreesoutofphase)withtheappliedvoltage.1.INTRODUCTIONThehigh-voltagetransmissionwasneedforthecaseelectricalpoweristobeprovidedatconsiderabledistancefromageneratingstation.Atsomepointthishighvoltagemustbereduced,becauseultimatelyismustsupplyaload.Thetransformermakesitpossibleforvariouspartsofapowersystemtooperateatdifferentvoltagelevels.Inthispaperwediscusspowertransformerprinciplesandapplications.2.TOW-WINDINGTRANSFORMERSAtransformerinitssimplestformconsistsoftwostationarycoilscoupledbyamutualmagneticflux.Thecoilsaresaidtobemutuallycoupledbecausetheylinkacommonflux.Inpowerapplications,laminatedsteelcoretransformers(towhichthispaperisrestricted)areused.Transformersareefficientbecausetherotationallossesnormallyassociatedwithrotatingmachineareabsent,sorelativelylittlepowerislostwhentransformingpowerfromonevoltageleveltoanother.Typical河南理工大學(xué)畢業(yè)設(shè)計(論文)說明書-4-efficienciesareintherange92to99%,thehighervaluesapplyingtothelargerpowertransformers.Thecurrentflowinginthecoilconnectedtotheacsourceiscalledtheprimarywindingorsimplytheprimary.Itsetsupthefluxinthecore,whichvariesperiodicallybothinmagnitudeanddirection.Thefluxlinksthesecondcoil,calledthesecondarywindingorsimplysecondary.Thefluxischanging；therefore,itinducesavoltageinthesecondarybyelectromagneticinductioninaccordancewithLenzslaw.Thustheprimaryreceivesitspowerfromthesourcewhilethesecondarysuppliesthispowertotheload.Thisactionisknownastransformeraction.3.TRANSFORMERPRINCIPLESWhenasinusoidalvoltageVpisappliedtotheprimarywiththesecondaryopen-circuited,therewillbenoenergytransfer.TheimpressedvoltagecausesasmallcurrentItoflowintheprimarywinding.Thisno-loadcurrenthastwofunctions:(1)itproducesthemagneticfluxinthecore,whichvariessinusoidallybetweenzeroandm,wheremisthemaximumvalueofthecoreflux；and(2)itprovidesacomponenttoaccountforthehysteresisandeddycurrentlossesinthecore.Therecombinedlossesarenormallyreferredtoasthecorelosses.Theno-loadcurrentIisusuallyfewpercentoftheratedfull-loadcurrentofthe