变压器外文翻译.docx

变压器外文翻译.docx

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变压器外文翻译

摘要

XF110KV变电所是地区重要变电所，是电力系统110KV电压等级的重要部分。

其设计分为电气一次部分和电气二次部分设计。

一次部分由说明书，计算书与电气工程图组成，说明书和计算书包括变电所总体分析;负荷分析与主变选择;电气主接线设计;短路电流计算;电气设备选择;配电装置选择;变电所总平设计及防雷保护设计。

二次部分由说明书，计算书与电气工程图组成。

说明书和计算书包括整体概述;线路保护的整定计算;主变压器的保护整定计算;电容器的保护整定计算;母线保护和所用变保护设计。

计算书和电气工程图为附录部分。

其中一次部分电气AutoCAD制图六张；二次部分为四张手工制图。

本变电所设计为毕业设计课题，以巩固大学所学知识。

通过本次设计，使我对电气工程及其自动化专业的主干课程有一个较为全面，系统的掌握，增强了理论联系实际的能力，提高了工程意识，锻炼了我独立分析和解决电力工程设计问题的能力，为未来的实际工作奠定了必要的基础。

关键词:

变电所；变压器；继电保护

Abstract

XFcounty110KVsubstationisanimportantstationinthisdistract,whichisoneoftheextremelynecessarypartsofthe110KVnetworkinelectricpowersystem.

Thedesignofthesubstationcanbeseparatedintwoparts:

primarypartandsecondarypartoftheelectricdesign.

Thefirstpartconsistsofspecifications,computationbookandElectricalengineeringdrawingsaboutthedesign.ThespecificationshasseveralpartswhichareGeneralanalysisofthestation,Loadanalysis,Theselectionofthemaintransformer,Layoutofconfiguration,Computationofshortcircuit;Selectofelectricdevices,Powerdistributiondevices,Generaldesignofsubstationplaneandthedesignofthunderboltprotection.

Thesecondpartalsoconsistsofspecifications,computationbookandelectricaldrawingsaboutthedesign。

Specificationsandcomputationbookincludefollowingsection:

General,Theevaluationandcalculateoflineprotection,Transformerprotection,capacitorprotection,BusprotectionandSelf-usingtransformerprotection.

Computationbook,Electricalengineeringdrawingsandcatalogueofdrawingsareattachedintheend。

Thereareninedrawingstotal,inwhichfourarepreparedbyhand,othersarepreparedbycomputerinwhichinstalledthesoftwareelectricalAutoCAD.Fromotherview,italsocanbeclassifiedasfirstpartandsecondpart.

Thisisadesignofsubstationforgraduationdesigntest.Itcanstrengthenourspecifiedknowledge.

Key-words:

substation；transformer；Relayprotection

TRANSFORMER

1.INTRODUCTION

Thehigh-voltagetransmissionwasneedforthecaseelectricalpoweristobeprovidedatconsiderabledistancefromageneratingstation.Atsomepointthishighvoltagemustbereduced,becauseultimatelyismustsupplyaload.Thetransformermakesitpossibleforvariouspartsofapowersystemtooperateatdifferentvoltagelevels.Inthispaperwediscusspowertransformerprinciplesandapplications.

2.TOW-WINDINGTRANSFORMERS

Atransformerinitssimplestformconsistsoftwostationarycoilscoupledbyamutualmagneticflux.Thecoilsaresaidtobemutuallycoupledbecausetheylinkacommonflux.

Inpowerapplications,laminatedsteelcoretransformers（towhichthispaperisrestricted）areused.Transformersareefficientbecausetherotationallossesnormallyassociatedwithrotatingmachineareabsent,sorelativelylittlepowerislostwhentransformingpowerfromonevoltageleveltoanother.Typicalefficienciesareintherange92to99%,thehighervaluesapplyingtothelargerpowertransformers.

Thecurrentflowinginthecoilconnectedtotheacsourceiscalledtheprimarywindingorsimplytheprimary.Itsetsupthefluxφinthecore,whichvariesperiodicallybothinmagnitudeanddirection.Thefluxlinksthesecondcoil,calledthesecondarywindingorsimplysecondary.Thefluxischanging;therefore,itinducesavoltageinthesecondarybyelectromagneticinductioninaccordancewithLenz’slaw.Thustheprimaryreceivesitspowerfromthesourcewhilethesecondarysuppliesthispowertotheload.Thisactionisknownastransformeraction.

3.TRANSFORMERPRINCIPLES

WhenasinusoidalvoltageVpisappliedtotheprimarywiththesecondaryopen-circuited,therewillbenoenergytransfer.TheimpressedvoltagecausesasmallcurrentIθtoflowintheprimarywinding.Thisno-loadcurrenthastwofunctions:

（1）itproducesthemagneticfluxinthecore,whichvariessinusoidallybetweenzeroand

φm,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,or

I0=Im+Ie（3-1）

Itshouldbenotedthattheno-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.Theaveragevalueoftheinducedvoltagegivenby

Eavg=turns×

（3-2）

whichisFaraday’slawappliedtoafinitetimeinterval.Itfollowsthat

Eavg=N

=4fNφm（3-3）

whichNisthenumberofturnsonthewinding.Formaccircuittheory,theeffectiveorroot-mean-square（rms）voltageforasinewaveis1.11timestheaveragevoltage;thus

E=4.44fNφm（3-4）

Sincethesamefluxlinkswiththeprimaryandsecondarywindings,thevoltageperturnineachwindingisthesame.Hence

Ep=4.44fNpφm（3-5）

and

Es=4.44fNsφm（3-6）

whereEpandEsarethenumberofturnontheprimaryandsecondarywindings,respectively.Theratioofprimarytosecondaryinducedvoltageiscalledthetransformationratio.Denotingthisratiobya,itisseenthat

a=

=

（3-7）

Assumethattheoutputpowerofatransformerequalsitsinputpower,notabadsumptioninpracticeconsideringthehighefficiencies.Whatwereallyaresayingisthatwearedealingwithanidealtransformer;thatis,ithasnolosses.Thus

Pm=Pout（3-8）

or

VpIp×primaryPF=VsIs×secondaryPF（3-9）

wherePFisthepowerfactor.Fortheabove-statedassumptionitmeansthatthepowerfactoronprimaryandsecondarysidesareequal;therefore

VpIp=VsIs（3-10）

fromwhichisobtained

=

≌

≌a（3-11）

Itshowsthatasanapproximationtheterminalvoltageratioequalstheturnsratio.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.From3-11,wehaveVp=aVs

andIp=Is/a.IntermsofVsandIstheratioofVptoIpis

=

=

（3-12）

ButVs/IsistheloadimpedanceZLthuswecansaythat

Zm（primary）=a2ZL（3-13）

Thisequationtellsusthatwhenanimpedanceisconnectedtothesecondaryside,itappearsfromthesourceasanimpedancehavingamagnitudethatisa2timesitsactualvalue.Wesaythattheloadimpedanceisreflectedorreferredtotheprimary.Itisthispropertyoftransformersthatisusedinimpedance-matchingapplications.

4.TRANSFORMERSUNDERLOAD

Theprimaryandsecondaryvoltagesshownhavesimilarpolarities,asindicatedbythe“dot-making”convention.Thedotsneartheupperendsofthewindingshavethesamemeaningasincircuittheory;themarkedterminalshavethesamepolarity.Thuswhenaloadisconnectedtothesecondary,theinstantaneousloadcurrentisinthedirectionshown.Inotherwords,thepolaritymarkingssignifythatwhenpositivecurrententersbothwindingsatthemar