建筑電氣專業(yè)畢業(yè)設(shè)計(jì)英文翻譯

變壓器摘要：變壓器是變電所的主要設(shè)備，功能是實(shí)現(xiàn)電網(wǎng)電壓的等級變換，基本工作原理是電磁感應(yīng)。變配電所是實(shí)現(xiàn)電壓等級變換和電能分配的場所。對供電電源進(jìn)行電壓等級變換，應(yīng)對電能進(jìn)行重新分配的場所稱為變電所。建筑變電所是供配電系統(tǒng)的樞紐，供電電源由電網(wǎng)引到變電所，在變電所完成降壓，電能分配等功能。關(guān)鍵詞:變電所；變壓器；繼電保護(hù)；1.介紹要從遠(yuǎn)端發(fā)電廠送出電能，必須應(yīng)用高壓輸電。因?yàn)樽罱K的負(fù)荷，在一些點(diǎn)高電壓必須降低。變壓器能使電力系統(tǒng)各個部分運(yùn)行在電壓不同的等級。本文我們討論的原則和電力變壓器的應(yīng)用。2.雙繞組變壓器變壓器的最簡單形式包括兩個磁通相互耦合的固定線圈。兩個線圈之所以相互耦合，是因?yàn)樗鼈冞B接著共同的磁通。在電力應(yīng)用中，使用層式鐵芯變壓器(本文中提到的)。變壓器是高效率的，因?yàn)樗鼪]有旋轉(zhuǎn)損失，因此在電壓等級轉(zhuǎn)換的過程中，能量損失比較少。典型的效率范圍在92到99%，上限值適用于大功率變壓器。從交流電源流入電流的一側(cè)被稱為變壓器的一次側(cè)繞組或者是原邊。它在鐵圈中建立了磁通φ，它的幅值和方向都會發(fā)生周期性的變化。磁通連接的第二個繞組被稱為變壓器的二次側(cè)繞組或者是副邊。磁通是變化的；因此依據(jù)楞次定律，電磁感應(yīng)在二次側(cè)產(chǎn)生了電壓。變壓器在原邊接收電能的同時也在向副邊所帶的負(fù)荷輸送電能。這就是變壓器的作用。3.變壓器的工作原理當(dāng)二次側(cè)電路開路是，即使原邊被施以正弦電壓Vp，也是沒有能量轉(zhuǎn)移的。外加電壓在一次側(cè)繞組中產(chǎn)生一個小電流Iθ。這個空載電流有兩項(xiàng)功能：（1）在鐵芯中產(chǎn)生電磁通，該磁通在零和φm之間做正弦變化，φm是鐵芯磁通的最大值；（2）它的一個分量說明了鐵芯中的渦流和磁滯損耗。這兩種相關(guān)的損耗被稱為鐵芯損耗。變壓器空載電流Iθ一般大約只有滿載電流的2%—5%。因?yàn)樵诳蛰d時，原邊繞組中的鐵芯相當(dāng)于一個很大的電抗，空載電流的相位大約將滯后于原邊電壓相位90o。顯然可見電流分量Im=I0sinθ0，被稱做勵磁電流，它在相位上滯后于原邊電壓VP90o。就是這個分量在鐵芯中建立了磁通；因此磁通φ與Im同相。第二個分量Ie=I0sinθ0，與原邊電壓同相。這個電流分量向鐵芯提供用于損耗的電流。兩個相量的分量和代表空載電流，即I0=Im+Ie應(yīng)注意的是空載電流是畸變和非正弦形的。這種情況是非線性鐵芯材料造成的。如果假定變壓器中沒有其他的電能損耗一次側(cè)的感應(yīng)電動勢Ep和二次側(cè)的感應(yīng)電壓Es可以表示出來。因?yàn)橐淮蝹?cè)繞組中的磁通會通過二次繞組，依據(jù)法拉第電磁感應(yīng)定律，二次側(cè)繞組中將產(chǎn)生一個電動勢E，即E=NΔφ/Δt。相同的磁通會通過原邊自身，產(chǎn)生一個電動勢Ep。正如前文中討論到的，所產(chǎn)生的電壓必定滯后于磁通90o，因此，它于施加的電壓有180o的相位差。因?yàn)闆]有電流流過二次側(cè)繞組，Es=Vs。一次側(cè)空載電流很小，僅為滿載電流的百分之幾。因此原邊電壓很小，并且Vp的值近乎等于Ep。原邊的電壓和它產(chǎn)生的磁通波形是正弦形的；因此產(chǎn)生電動勢Ep和Es的值是做正弦變化的。產(chǎn)生電壓的平均值如下Eavg=turns×即是法拉第定律在瞬時時間里的應(yīng)用。它遵循Eavg=N=4fNφm其中N是指線圈的匝數(shù)。從交流電原理可知，有效值是一個正弦波，其值為平均電壓的1.11倍；因此E=4.44fNφm因?yàn)橐淮蝹?cè)繞組和二次側(cè)繞組的磁通相等，所以繞組中每匝的電壓也相同。因此Ep=4.44fNpφm并且Es=4.44fNsφm其中Np和Es是一次側(cè)繞組和二次側(cè)繞組的匝數(shù)。一次側(cè)和二次側(cè)電壓增長的比率稱做變比。用字母a來表示這個比率，如下式a==假設(shè)變壓器輸出電能等于其輸入電能——這個假設(shè)適用于高效率的變壓器。實(shí)際上我們是考慮一臺理想狀態(tài)下的變壓器；這意味著它沒有任何損耗。因此Pm=Pout或者VpIp×primaryPF=VsIs×secondaryPF這里PF代表功率因素。在上面公式中一次側(cè)和二次側(cè)的功率因素是相等的；因此VpIp=VsIs從上式我們可以得知=≌≌a它表明端電壓比等于匝數(shù)比，換句話說，一次側(cè)和二次側(cè)電流比與匝數(shù)比成反比。匝數(shù)比可以衡量二次側(cè)電壓相對于一次惻電壓是升高或者是降低。為了計(jì)算電壓，我們需要更多數(shù)據(jù)。終端電壓的比率變化有些根據(jù)負(fù)載和它的功率因素。實(shí)際上,變比從標(biāo)識牌數(shù)據(jù)獲得,列出在滿載情況下原邊和副邊電壓。當(dāng)副邊電壓Vs相對于原邊電壓減小時，這個變壓器就叫做降壓變壓器。如果這個電壓是升高的，它就是一個升壓變壓器。在一個降壓變壓器中傳輸變比a遠(yuǎn)大于1(a>1.0)，同樣的，一個升壓變壓器的變比小于1(a<1.0)。當(dāng)a=1時，變壓器的二次側(cè)電壓就等于起一次側(cè)電壓。這是一種特殊類型的變壓器，可被應(yīng)用于當(dāng)一次側(cè)和二次側(cè)需要相互絕緣以維持相同的電壓等級的狀況下。因此，我們把這種類型的變壓器稱為絕緣型變壓器。顯然，鐵芯中的電磁通形成了連接原邊和副邊的回路。在第四部分我們會了解到當(dāng)變壓器帶負(fù)荷運(yùn)行時一次側(cè)繞組電流是如何隨著二次側(cè)負(fù)荷電流變化而變化的。從電源側(cè)來看變壓器，其阻抗可認(rèn)為等于Vp/Ip。從等式=≌≌a中我們可知Vp=aVs并且Ip=Is/a。根據(jù)Vs和Is，可得Vp和Ip的比例是==但是Vs/Is負(fù)荷阻抗ZL，因此我們可以這樣表示Zm(primary)=a2ZL這個等式表明二次側(cè)連接的阻抗折算到電源側(cè)，其值為原來的a2倍。我們把這種折算方式稱為負(fù)載阻抗向一次側(cè)的折算。這個公式應(yīng)用于變壓器的阻抗匹配。4.有載情況下的變壓器一次側(cè)電壓和二次側(cè)電壓有著相同的極性，一般習(xí)慣上用點(diǎn)記號表示。如果點(diǎn)號同在線圈的上端，就意味著它們的極性相同。因此當(dāng)二次側(cè)連接著一個負(fù)載時，在瞬間就有一個負(fù)荷電流沿著這個方向產(chǎn)生。換句話說，極性的標(biāo)注可以表明當(dāng)電流流過兩側(cè)的線圈時，線圈中的磁動勢會增加?？偟膩碚f，變壓器為了保持磁通是常數(shù)，對磁通變化的響應(yīng)是瞬時的。更重要的是，在空載和滿載時，主磁通φ0的降落是很少的（一般在）1至3%。其需要的條件是E降落很多來使電流Ip增加。在一次側(cè)，電流Ip’在一次側(cè)流過以平衡Is產(chǎn)生的影響。它的磁動勢NpIp’只停留在一次側(cè)。因?yàn)殍F芯的磁通φ0保持不變，變壓器空載時空載電流I0必定會為其提供能量。故一次側(cè)電流Ip是電流Ip’與I0’的和。因?yàn)榭蛰d電流相對較小，那么一次側(cè)的安匝數(shù)與二次側(cè)的安匝數(shù)相等的假設(shè)是成立的。因?yàn)樵谶@種狀況下鐵芯的磁通是恒定的。因此我們?nèi)耘f可以認(rèn)定空載電流I0相對于滿載電流是極其小的。當(dāng)一個電流流過二次側(cè)繞組，它的磁動勢（NsIs）將產(chǎn)生一個磁通，于空載電流I0產(chǎn)生的磁通φ0不同，它只停留在二次側(cè)繞組中。因?yàn)檫@個磁通不流過一次側(cè)繞組，所以它不是一個公共磁通。另外，流過一次側(cè)繞組的負(fù)載電流只在一次側(cè)繞組中產(chǎn)生磁通，這個磁通被稱為一次側(cè)的漏磁。二次側(cè)漏磁將使電壓增大以保持兩側(cè)電壓的平衡。一次側(cè)漏磁也一樣。因此，這兩個增大的電壓具有電壓降的性質(zhì)，總稱為漏電抗電壓降。另外，兩側(cè)繞組同樣具有阻抗，這也將產(chǎn)生一個電阻壓降。把這些附加的電壓降也考慮在內(nèi)，這樣一個實(shí)際的變壓器的等值電路圖就完成了。由于分支勵磁體現(xiàn)在電流里，為了分析我們可以將它忽略。這就符我們前面計(jì)算中可以忽略空載電流的假設(shè)。這證明了它對我們分析變壓器時所產(chǎn)生的影響微乎其微。因?yàn)殡妷航蹬c負(fù)載電流成比例關(guān)系，這就意味著空載情況下一次側(cè)和二次側(cè)繞組的電壓降都為零。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,whichlinksthesecondarywindi