建筑电气专业毕业设计英文翻译

变压器摘要：变压器是变电所的主要设备，功能是实现电网电压的等级变换，基本工作原理是电磁感应。变配电所是实现电压等级变换和电能分配的场所。对供电电源进行电压等级变换，应对电能进行重新分配的场所称为变电所。建筑变电所是供配电系统的枢纽，供电电源由电网引到变电所，在变电所完成降压，电能分配等功能。关键词:变电所；变压器；继电保护；1.介绍要从远端发电厂送出电能，必须应用高压输电。因为最终的负荷，在一些点高电压必须降低。变压器能使电力系统各个部分运行在电压不同的等级。本文我们讨论的原则和电力变压器的应用。2.双绕组变压器变压器的最简单形式包括两个磁通相互耦合的固定线圈。两个线圈之所以相互耦合，是因为它们连接着共同的磁通。在电力应用中，使用层式铁芯变压器(本文中提到的)。变压器是高效率的，因为它没有旋转损失，因此在电压等级转换的过程中，能量损失比较少。典型的效率范围在92到99%，上限值适用于大功率变压器。从交流电源流入电流的一侧被称为变压器的一次侧绕组或者是原边。它在铁圈中建立了磁通φ，它的幅值和方向都会发生周期性的变化。磁通连接的第二个绕组被称为变压器的二次侧绕组或者是副边。磁通是变化的；因此依据楞次定律，电磁感应在二次侧产生了电压。变压器在原边接收电能的同时也在向副边所带的负荷输送电能。这就是变压器的作用。3.变压器的工作原理当二次侧电路开路是，即使原边被施以正弦电压Vp，也是没有能量转移的。外加电压在一次侧绕组中产生一个小电流Iθ。这个空载电流有两项功能：（1）在铁芯中产生电磁通，该磁通在零和φm之间做正弦变化，φm是铁芯磁通的最大值；（2）它的一个分量说明了铁芯中的涡流和磁滞损耗。这两种相关的损耗被称为铁芯损耗。变压器空载电流Iθ一般大约只有满载电流的2%—5%。因为在空载时，原边绕组中的铁芯相当于一个很大的电抗，空载电流的相位大约将滞后于原边电压相位90º。显然可见电流分量Im=I0sinθ0，被称做励磁电流，它在相位上滞后于原边电压VP90º。就是这个分量在铁芯中建立了磁通；因此磁通φ与Im同相。第二个分量Ie=I0sinθ0，与原边电压同相。这个电流分量向铁芯提供用于损耗的电流。两个相量的分量和代表空载电流，即I0=Im+Ie应注意的是空载电流是畸变和非正弦形的。这种情况是非线性铁芯材料造成的。如果假定变压器中没有其他的电能损耗一次侧的感应电动势Ep和二次侧的感应电压Es可以表示出来。因为一次侧绕组中的磁通会通过二次绕组，依据法拉第电磁感应定律，二次侧绕组中将产生一个电动势E，即E=NΔφ/Δt。相同的磁通会通过原边自身，产生一个电动势Ep。正如前文中讨论到的，所产生的电压必定滞后于磁通90º，因此，它于施加的电压有180º的相位差。因为没有电流流过二次侧绕组，Es=Vs。一次侧空载电流很小，仅为满载电流的百分之几。因此原边电压很小，并且Vp的值近乎等于Ep。原边的电压和它产生的磁通波形是正弦形的；因此产生电动势Ep和Es的值是做正弦变化的。产生电压的平均值如下Eavg=turns×即是法拉第定律在瞬时时间里的应用。它遵循Eavg=N=4fNφm其中N是指线圈的匝数。从交流电原理可知，有效值是一个正弦波，其值为平均电压的1.11倍；因此E=4.44fNφm因为一次侧绕组和二次侧绕组的磁通相等，所以绕组中每匝的电压也相同。因此Ep=4.44fNpφm并且因此，这两个增大的电压具有电压降的性质，总称为漏电抗电压降。另外，两侧绕组同样具有阻抗，这也将产生一个电阻压降。把这些附加的电压降也考虑在内，这样一个实际的变压器的等值电路图就完成了。由于分支励磁体现在电流里，为了分析我们可以将它忽略。这就符我们前面计算中可以忽略空载电流的假设。这证明了它对我们分析变压器时所产生的影响微乎其微。因为电压降与负载电流成比例关系，这就意味着空载情况下一次侧和二次侧绕组的电压降都为零。TRANSFORMERAbstract：Thetransformeristhetransformersubstationmajorinstallation,thefunctionrealizesthenetworkvoltageranktransformation,thekeyjobprincipleistheelectromagneticinduction.Changesthesubstationisrealizesthevoltageclasstransformationandtheelectricalenergyassignmentplace.Carriesonthevoltageclasstransformationtotheelectricpowersupply,dealswiththeplacewhichtheelectricalenergycarriesonredistributestobecalledthetransformersubstation.Constructsthetransformersubstationisforelectricalpowerdistributionsystem'skeyposition,theelectricpowersupplydirectsthetransformersubstationfromtheelectricalnetwork,completesthevoltagedroppinginthetransformersubstation,functionsandsoonelectricalenergyassignment.Key-words:substation；transformer；Relayprotection；1.INTRODUCTIONThehigh-voltagetransmissionwasneedforthecaseelectricalpoweristobeprovidedatconsiderabledistancefromageneratingstation.Atsomepointthishighvoltagemustbereduced,becauseultimatelyismustsupplyaload.Thetransformermakesitpossibleforvariouspartsofapowersystemtooperateatdifferentvoltagelevels.Inthispaperwediscusspowertransformerprinciplesandapplications.2.TOW-WINDINGTRANSFORMERSAtransformerinitssimplestformconsistsoftwostationarycoilscoupledbyamutualmagneticflux.Thecoilsaresaidtobemutuallycoupledbecausetheylinkacommonflux.Inpowerapplications,laminatedsteelcoretransformers(towhichthispaperisrestricted)areused.Transformersareefficientbecausetherotationallossesnormallyassociatedwithrotatingmachineareabsent,sorelativelylittlepowerislostwhentransformingpowerfromonevoltageleveltoanother.Typicalefficienciesareintherange92to99%,thehighervaluesapplyingtothelargerpowertransformers.Thecurrentflowinginthecoilconnectedtotheacsourceiscalledtheprimarywindingorsimplytheprimary.Itsetsupthefluxφinthecore,whichvariesperiodicallybothinmagnitudeanddirection.Thefluxlinksthesecondcoil,calledthesecondarywindingorsimplysecondary.Thefluxischanging;therefore,itinducesavoltageinthesecondarybyelectromagneticinductioninaccordancewithLenz’slaw.Thustheprimaryreceivesitspowerfromthesourcewhilethesecondarysuppliesthispowertotheload.Thisactionisknownastransformeraction.3.TRANSFORMERPRINCIPLESWhenasinusoidalvoltageVpisappliedtotheprimarywiththesecondaryopen-circuited,therewillbenoenergytransfer.TheimpressedvoltagecausesasmallcurrentIθtoflowintheprimarywinding.Thisno-loadcurrenthastwofunctions:(1)itproducesthemagneticfluxinthecore,whichvariessinusoidallybetweenzeroandφm,whereφmisthemaximumvalueofthecoreflux;and(2)itprovidesacomponenttoaccountforthehysteresisandeddycurrentlossesinthecore.Therecombinedlossesarenormallyreferredtoasthecorelosses.Theno-loadcurrentIθisusuallyfewpercentoftheratedfull-loadcurrentofthetransformer(about2to5%).Sinceatno-loadtheprimarywindingactsasalargereactanceduetotheironcore,theno-loadcurrentwilllagtheprimaryvoltagebynearly90º.ItisreadilyseenthatthecurrentcomponentIm=I0sinθ0,calledthemagnetizingcurrent,is90ºinphasebehindtheprimaryvoltageVP.Itisthiscomponentthatsetsupthefluxinthecore;φisthereforeinphasewithIm.Thesecondcomponent,Ie=I0sinθ0,isinphasewiththeprimaryvoltage.Itisthecurrentcomponentthatsuppliesthecorelosses.Thephasorsumofthesetwocomponentsrepresentstheno-loadcurrent,orI0=Im+IeItshouldbenotedthattheno-loadcurrentisdistortesandnonsinusoidal.Thisistheresultofthenonlinearbehaviorofthecorematerial.Ifitisassumedthattherearenootherlossesinthetransformer,theinducedvoltageIntheprimary,Epandthatinthesecondary,Escanbeshown.Sincethemagneticfluxsetupbytheprimarywinding，therewillbeaninducedEMFEinthesecondarywindinginaccordancewithFaraday’slaw,namely,E=NΔφ/Δt.Thissamefluxalsolinkstheprimaryitself,inducinginitanEMF,Ep.Asdiscussedearlier,theinducedvoltagemustlagthefluxby90º,therefore,theyare180ºoutofphasewiththeappliedvoltage.Sincenocurrentflowsinthesecondarywinding,Es=Vs.Theno-loadprimarycurrentI0issmall,afewpercentoffull-loadcurrent.ThusthevoltageintheprimaryissmallandVpisnearlyequaltoEp.Theprimaryvoltageandtheresultingfluxaresinusoidal;thustheinducedquantitiesEpandEsvaryasasinefunction.TheaveragevalueoftheinducedvoltagegivenbyEavg=turns×whichisFaraday’slawappliedtoafinitetimeinterval.ItfollowsthatEavg=N=4fNφmwhichNisthenumberofturnsonthewinding.Formaccircuittheory,theeffectiveorroot-mean-square(rms)voltageforasinewaveis1.11timestheaveragevoltage;thusE=4.44fNφmSincethesamefluxlinkswiththeprimaryandsecondarywindings,thevoltageperturnineachwindingisthesame.HenceEp=4.44fNpφmandEs=4.44fNsφmwhereEpandEsarethenumberofturnontheprimaryandsecondarywindings,respectively.Theratioofprimarytosecondaryinducedvoltageiscalledthetransformationratio.Denotingthisratiobya,itisseenthata==Assumethattheoutputpowerofatransformerequalsitsinputpower,notabadsumptioninpracticeconsideringthehighefficiencies.Whatwereallyaresayingisthatwearedealingwithanidealtransformer;thatis,ithasnolosses.ThusPm=PoutorVpIp×primaryPF=VsIs×secondaryPFwherePFisthepowerfactor.Fortheabove-statedassumptionitmeansthatthepowerfactoronprimaryandsecondarysidesareequal;thereforeVpIp=VsIsfromwhichisobtained=≌≌aItshowsthatasanapproximationtheterminalvoltageratioequalstheturnsratio.Theprimaryandsecondarycurrent,ontheotherhand,areinverselyrelatedtotheturnsratio.Theturnsratiogivesameasureofhowmuchthesecondaryvoltageisraisedorloweredinrelationtotheprimaryvoltage.Tocalculatethevoltageregulation,weneedmoreinformation.Theratiooftheterminalvoltagevariessomewhatdependingontheloadanditspowerfactor.Inpractice,thetransformationratioisobtainedfromthenameplatedata,whichlisttheprimaryandsecondaryvoltageunderfull-loadcondition.WhenthesecondaryvoltageVsisreducedcomparedtotheprimaryvoltage,thetransformationissaidtobeastep-downtransformer:conversely,ifthisvoltageisraised,itiscalledastep-uptransformer.Inastep-downtransformerthetransformationratioaisgreaterthanunity(a>1.0),whileforastep-uptransformeritissmallerthanunity(a<1.0).Intheeventthata=1,thetransformersecondaryvoltageequalstheprimaryvoltage.Thisisaspecialtypeoftransformerusedininstanceswhereelectricalisolationisrequiredbetweentheprimaryandsecondarycircuitwhilemaintainingthesamevoltagelevel.Therefore,thistransformerisgenerallyknowsasanisolationtransformer.Asisapparent,itisthemagneticfluxinthecorethatformstheconnectinglinkbetweenprimaryandsecondarycircuit.Insection4itisshownhowtheprimarywindingcurrentadjustsitselftothesecondaryloadcurrentwhenthetransformersuppliesaload.Lookingintothetransformerterminalsfromthesource,animpedanceisseenwhichbydefinitionequalsVp/Ip.From=≌≌a,wehaveVp=aVsandIp=Is/a.IntermsofVsandIstheratioofVptoIpis==ButVs/IsistheloadimpedanceZLthuswecansaythatZm(primary)=a2ZLThisequationtellsusthatwhenanimpedanceisconnectedtothesecondaryside,itappearsfromthesourceasanimpedancehavingamagnitudethatisa2timesitsactualvalue.Wesaythattheloadimpedanceisreflectedorreferredtotheprimary.Itisthispropertyoftransformersthatisusedinimpedance-matchingapplications.4.TRANSFORMERSUNDERLOADTheprimaryandsecondaryvoltagesshownhavesimilarpolarities,asindicatedbythe“dot-making”convention.Thedotsneartheupperendsofthewindingshavethesamemeaningasincircuittheory;themarkedterminalshavethesamepolarity.Thuswhenaloadisconnectedtothesecondary,theinstantaneousloadcurrentisinthedirectionshown.Inotherwords,thepolaritymarkingssignifythatwhenpositivecurrententersbothwindingsatthemarkedterminals,theMMFsofthetwowindingsadd.Ingeneral,itwillbefoundthatthetransformerreactsalmostinstantaneouslytokeeptheresultantcorefluxessentiallyconstant.Moreover,thecorefluxφ0dropsveryslightlybetweennoloadandfullload(about1to3%),anecessaryconditionifEpistofallsufficientlytoallowanincreaseinIp.Ontheprimaryside,Ip’isthecurrentthatflowsintheprimarytobalancethedemagnetizingeffectofIs.ItsMMFNpIp’setsupafluxlinkingtheprimaryonly.Sincethecorefluxφ0remainsconstant.I0mustbethesamecurrentthatenergizesthetransformeratnoload.TheprimarycurrentIpisthereforethesumofthecurrentIp’andI0.Becausetheno-loadcurrentisrelativelysmall,itiscorrecttoassumethattheprimaryampere-turnsequalthesecondaryampere-turns,sinceitisunderthisconditionthatthecorefluxisessentiallyconstant.ThuswewillassumethatI0isnegligible,asitisonlyasmallcomponentofthefull-loadcurrent.Whenacurrentflowsinthesecondarywinding,theresultingMMF(NsIs)createsaseparateflux,apartfromthefluxφ0producedbyI0,whichlinksthesecondarywindingonly.Thisfluxdoesnolinkwi