电气工程及其自动化专业英语PPT课件

.,1,电气工程及其自动化专业英语SpecializedEnglishforElectricalEngineeringItsAutomation戴文进主编杨植新副主编,.,2,Contents,Part1ElectricsandElectronicsPart2ElectricMachineryPart3ElectricalEngineeringPart4ModernComputerControlTechniques,.,3,Unit1SpecializedEnglishWords,circuitcomponents电路元件circuitparameters电路参数thedielectric电介质storagebattery蓄电池electriccircuit电路wire导线electricaldevice电气设备electricenergy电能energysource电源primarycell原生电池secondarycell再生电池energyconverter电能转换器e.m.f.electromotiveforce电动势unidirectionalcurrent单方向电流circuitdiagram电路图loadcharacteristic负载特性terminalvoltage端电压externalcharacteristic外特性Conductor导体loadresistance负载电阻generator发电机heatingappliance电热器direct-current(D.C.)circuit直流电路magneticandelectricfield电磁场time-invariant时不变的self-(ormutual-)induction自（互）感displacementcurrent位移电流voltagedrop电压降conductance电导volt-amperecharacteristics伏安特性metal-filamentlamp金属丝灯泡carbon-filamentlamp碳丝灯泡non-linearcharacteristics非线性特性,.,4,Unit1CircuitElementsandParameters,Anelectriccircuit(ornetwork)isaninterconnectionofphysicalelectricaldevices.Thepurposeofelectriccircuitsistodistributeandconvertenergyintosomeotherforms.Accordingly,thebasiccircuitcomponentsareanenergysource(orsources),anenergyconverter(orconverters)andconductorsconnectingthem（连接它们的）.Anenergysource(aprimaryorsecondarycell,ageneratorandthelike)convertschemical,mechanical,thermalorsomeotherformsofenergyinto（将-转换成-）electricenergy.Anenergyconverter,alsocalledload(suchasalamp,heatingapplianceorelectricmotor),convertselectricenergyintolight,heat,mechanicalworkandsoon.,.,5,Eventsinacircuitcanbedefinedintermsof（用-，根据-）e.m.f.(orvoltage)andcurrent.Whenelectricenergyisgenerated,transmittedandconvertedunderconditionssuchthatthecurrentsandvoltagesinvolvedremainconstantwithtime,oneusuallyspeaksofdirect-current(D.C.)circuits.Withtime-invariantcurrentsandvoltages,themagneticandelectricfieldsoftheassociatedelectricplantarealsotime-invariant.Thisisthereasonwhynoe.m.f.sofself-(ormutual-)induction（自感或互感）appearinD.C.circuits,norarethere（倒装结构）anydisplacementcurrents（位移电流）inthedielectricsurroundingtheconductors(导体周围的电介质）.,.,6,Fig.1.1showsinsimplifiedformahypotheticalcircuitwithastoragebatteryasthesourceandalampastheload.Theterminalsofthesourceandloadareinterconnectedbyconductors(generallybutnotalwayswires).Asisseen,thesource,loadandconductorsformaclosedconductingpath.Thee.m.f.ofthesourcecausesacontinuousandunidirectionalcurrenttocirculateroundthisclosedpath.Thissimplecircuitmadeupofasource,aloadandtwowiresisseldom,ifever,metwithinpractice.PracticalcircuitsmaycontainalargenumberofsourcesandloadsinterconnectedinavarietyofwaysFig.1.1（按不同方式连接的）.,.,7,Tosimplifyanalysisofactualcircuits,itisusualtoshowthemsymbolicallyinadiagramcalledacircuitdiagram,whichisinfactafictitiousor,rather,idealizedmodelofanactualcircuitofnetwork.Suchadiagramconsistsofinterconnectedsymbolscalledcircuitelementsorcircuitparameters.TwoelementsarenecessarytorepresentprocessesinaD.C.circuit.Theseareasourceofe.m.f.Eandofinternal(orsource)resistanceRS,andtheloadresistance(whichincludestheresistanceoftheconductors)R(Fig.1.2)Fig.1.2,.,8,Whateveritsorigin(thermal,contact,etc.),thesourcee.m.f.E(Fig.1.2(a)isnumericallyequaltothepotentialdifferencebetweenterminals1and2withtheexternalcircuitopen,thatis,whenthereisnocurrentflowingthroughthesourceE=12=V12(1.1)Thesourcee.m.f.isdirectedfromtheterminalatalowerpotentialtothat（代替terminal）atahigherone（代替potential）.Ondiagram,thisisshownbyarrows（箭头）.Whenaloadisconnectedtothesourceterminals(thecircuitisthensaidtobeloaded)andthecircuitisclosed,acurrentbeginstoflowroundit.Nowthevoltagebetweensourceterminals1and2(calledtheterminalvoltage)isnotequaltoitse.m.f.becauseofthevoltagedropVSinsidethesource,thatis,acrossthesourceresistanceRSVS=RSI,.,9,Fig.1.3showsatypicalso-calledexternalcharacteristicV=12=V(I)ofaloadedsource(henceanothernameistheloadcharacteristicofasource).Asisseen,increaseofcurrentfromzerotoII1causestheterminalvoltageofthesourcetodecreaselinearlyV12=V=EVS=ERSI,Fig.1.3,Inotherwords,thevoltagedropVSacrossthesourceresistancerisesinproportiontothecurrent.Thisgoesonuntilacertainlimitisreached.Thenasthecurrentkeepsrising,theproportionalitybetweenitsvalueandthevoltagedropacrossthesourceisupset,andtheexternalcharacteristicceasestobe（不再是）linear.Thisdecreaseinvoltagemaybecausedbyareductioninthesourcevoltage,byanincreaseintheinternalresistance,orboth.,.,10,Thepowerdeliveredbyasourceisgivenbytheequality（等式）PS=EI(1.2)wherePSisthepowerofthesource.Itseemsrelevantatthispointtodispelacommonmisconceptionaboutpower.Thusonemayhearthatpowerisgenerated,delivered,consumed,transmitted,lost,etc.Inpointoffact,however,itisenergythatcanbegenerated,delivered,consumed,transmittedorlost.Powerisjusttherateofenergyinputorconversion,thatis,thequantityofenergygenerated,delivered,transmittedetcperunittime.So,itwouldbemorecorrecttousethetermenergyinsteadofpowerintheabovecontext.Yet,wewouldratherfallinwiththetradition.,.,11,TheloadresistanceRasageneralizedcircuitelement,givesanideaabouttheconsumptionofenergy,thatis,theconversionofelectricenergyintoheat,andisdefinedasP=RI2(1.3)Inthegeneralcase,theloadresistancedependssolelyonthecurrentthroughtheload,whichinfactissymbolizedby（用符号）thefunctionR(I).ByOhmslaw,thevoltageacrossaresistanceisV=RI(1.4)Incircuitanalysis,useisoftenmadeofthereciprocaloftheresistance,termedtheconductance,whichisdefinedasg=1/RInpracticalproblems,oneoftenspecifiesthevoltageacrossaresistanceasafunctionofcurrentV(I),ortheinverserelationI(V)havecometobeknownasvolt-amperecharacteristics.,.,12,Fig.1.4showsvolt-amperecurvesforametal-filamentlampV1(I),andforacarbon-filamentlampV2(I).Asisseen,therelationbetweenthevoltageandthecurrentineachlampisotherthanlinear.Theresistanceofthemetal-filamentlampincreases,andthatofthecarbon-filamentlampdecreaseswithincreaseofcurrent.,Fig.1.4,Electriccircuitscontainingcomponentswithnon-linearcharacteristic（含有非线性特性元件的）arecallednon-linear.,.,13,Ifthee.m.f.andinternalresistancesofsourcesandassociatedloadresistancesareassumedtobeindependentofthecurrentandvoltage,respectively,theexternalcharacteristicV(I)ofthesourcesandthevolt-amperecharacteristicV1(I)oftheloadswillbelinear.Electriccircuitscontainingonlyelementswithlinearcharacteristicarecalledlinear.,Fig.1.5,Mostpracticalcircuitsmaybeclassedaslinear.Therefore,astudyintothepropertiesandanalysisoflinearcircuitsisofboththeoreticalandappliedinterest.,ofinterest=interesting,.,14,Unit2SpecializedEnglishWords,idealsource理想电源seriesandparallelequivalentcircuit串并联等值电路internalresistance内阻doublesubscript双下标idealvoltagesource理想电压源activecircuitelements有源电路元件passivecircuitelements无源电路元件powertransmissionline输电线sendingend发送端receivingend接收端leakagecurrent漏电流idealcurrentsource理想电流源,.,15,Unit2IdealSourcesSeriesandParallelEquivalentCircuits,Consideranelementarycircuitcontainingasinglesourceofe.m.f.EandofinternalresistanceRS,andasingleloadR(Fig.2.1).Theresistanceoftheconductorsofthistypeofcircuitmaybeneglected.Intheexternalportionofthecircuit,thatis,intheloadR,thecurrentisassumedtoflowfromthejunctiona(whichisatahigherpotentialsuchthata=1)tothejunctionb(whichisatalowerpotentialsuchthatb=2).Thedirectionofcurrentflowmaybeshowneitherbyahollowarrowheadorbysupplyingthecurrentsymbolwithadoublesubscriptwhosefirstdigitidentifiesthejunctionatahigherpotentialandthesecond(省略了identifies)thejunctionatalowerpotential.ThusforthecircuitofFig.2.1,thecurrentI=Iab.,.,16,WeshallshowthatthecircuitofFig.2.1containingasourceofknowne.m.f.EandsourceresistanceRmayberepresentedbytwotypesofequivalentcircuits.Asalreadystarted,theterminalvoltageofaloadedsourceislowerthanthesourcee.m.f.byanamountequaltothevoltagedropacrossthesourceresistanceV=12=EVS=ERSI(2.1)Ontheotherhand,thevoltageacrosstheloadresistanceRis,Fig.2.1,Since1=aand2=b,fromEqs.(2.1)and(2.2)itfollowsthatE-RsI=RI,orE=RSI+RI(2.3)AndI=E/(RS+R),V=ab=RI(2.2),.,17,Fromthelastequationweconcludethatthecurrentthroughthesourceiscontrolledbyboththeloadresistanceandthesourceresistance.Therefore,inanequivalentcircuitdiagramthesourceresistanceRmaybeshownconnectedinserieswith（与-串联）theloadresistanceR.Thisconfigurationmaybecalledtheseriesequivalentcircuit(usuallyknownastheTheveninequivalentsource-戴维宁等效电源).DependingontherelativemagnitudeofthevoltagesacrossRsandR,wecandeveloptwomodificationsoftheseriesequivalentcircuit（串联等效电路）.,Fig.2.2,.,18,IntheequivalentcircuitofFig.2.2(a),Viscontrolledbytheloadcurrentandisdecidedbythedifferencebetweenthesourcee.m.f.EandthevoltagedropV.IfRSRand,forthesamecurrent,VSRand,forthesamevoltagesacrossRSandR,thecurrentIS0andi0.ThesegmentsofthecurvebetweenpointsaandborOandccoveracompletecycleofcurrentalternationsoveroneperiod.,Fig.4.1,Thenumberofcyclesorperiodspersecondisthefrequencyofaperiodiccurrent.Itisreciprocalofitsperiodf=1/TItisusuallytospecifythefrequencyofanyperiodicquantityincyclespersecond（每秒周数）.Thusthefrequencyofaperiodiccurrentwillbe1cyclepersecond,ifitsperiodis1second,or1cycle/sec.,.,31,Adirectcurrentmayberegardedasaspecialcaseofaperiodiccurrentwhoseperiodisinfinitelylong（无穷大）andthefrequencyisthuszero.Theterm（术语）alternatingcurrentisoftenusedinthenarrowsenseofaperiodiccurrentwhoseconstant(direct-current)componentiszero,orThefrequenciesofalternatingcurrentencounteredinpractice（在实际中遇到的）rangeover（涉及）verywidevalues.Themainsfrequencyis50HzintheSovietUnionandEurope,and60HzintheUnitedStates.Someindustrialprocessesusefrequenciesfrom10Hzto2.5109Hz.inradiopractice（在无线电应用中）,frequenciesupto31010Hzareemployed.,.,32,Thedefinitionsforcurrentsjustintroduced(and,indeed,thosethatwillbeintroducedshortly)fullyapplytoperiodicvoltages,e.m.f.s,magneticfluxesandanyotherelectricalandmagneticquantities.Someadditionalremarksareonlyneededwithregardtothesignofalternatingvoltagesande.m.f.s.AnalternatingvoltagebetweentwopointsAandB,determinedalongaspecifiedpathl,periodicallychangessign,sothatifitisassumedtobepositiveinthedirectionfromAtoB（沿A到B的方向）,itwillbenegativeinthedirectionfromBtoAatthesameinstantoftime【1】.Thisiswhyitisimportanttolabelwhichofthetwodirectionsisassumedpositive.Indiagrams,suchadirectionislabeledeitherbyarrowsorsubscriptsinthesymbolsforvoltagesandisregardedtobethepositivereferencedirectionofavoltage(orofane.m.f.).,.,33,Electricalengineeringusesthesimplestandcommonesttypeofalternatingcurrent,theonewhichvariessinusoidallywithtime;(按正弦规律变化）hencetheterm（iscalled/termed）aharmonicorasinusoidalcurrent.Thepreferenceforsinusoidalcurrentsisexplainedbythefactthatnon-sinusoidalcurrentsentailincreasedenergylosses,inducedover-voltages,andexcessiveinterferencewith（对-的干扰）communicationscircuits.Thetransmissionofinformationoveradistance(wireorradiocommunicationscircuits,remotecontrol,etc.)alsousessinusoidalcurrentsmodulatedbythesignalinamplitude,frequencyorphase.Periodicnon-sinusoidalcurrentsmaylikewisebetreatedascomposedofsinusoidalcurrentsatavarietyoffrequenciesoccurringsimultaneously.Thisiswhythoroughofsinusoidal-currentcircuitsisofprimaryimportance.,.,34,TheA.C.GeneratorAnA.C.generatorconsistsofastationarypart,thestator,andarevolvingpart,therotor.Asaruletherotorcarriesmagneticpoleswithcoilsaroundthem.Thesearethefieldcoilsofthegenerator,becausetheyestablishamagneticfieldinthemachine.Theyareenergizedwithdirectcurrentthroughslipringsandbrushes.Theslotsofthestatorstackedupfromelectrical-sheetsteelpunchingsreceivethecoilsofthestatorwinding【2】.Thestatorcoilsareconnectedinseries,asshownbythefullanddottedlinesinthedrawing.Thee.m.f.inducedinastatorconductorisgivenbyE=BlvwhereBmagneticinductionofthefieldmovingrelativetotheconductor;lactivelengthoftheconductor;vspeedwithwhichthemagneticfieldmovesrelativetotheconductor.,.,35,Sincelandvareconstant,theinducede.m.f.willvaryexactlyasBvaries.Iftheinducede.m.f.istobesinusoidal(whichisusuallysought),thedistributionofBaroundthecircumferenceofthestatorshouldbeasclosetosinusoidalaspracticable.Withppole-pairsontherotor,thee.m.f.willundergopcyclesofchangeseveryrevolution.Ifthespeedoftherotorisrevolutionsperminute(r/min),thisworksouttopncyclesperminute,andthefrequencyoftheinducede.m.f.isf=pn/60,.,36,Forf=50Hz,therotorofageneratorwithonepairofpolesshouldrunat3000r/min.andwithtwopole-pairs,at1500r/min.Withspeedslikethis,rotorsareusuallyfabricatedwithnon-salientpilesforgreatermechanicalstrength.High-frequencygeneratorsoperatingat800to8000Hzareallofspecialdesigns.Theirusesareintheheat-treatmentandinduction-heatingfield.Stillhigherfrequenciesaregeneratedbyvalveandsemiconductoroscillators.,.,37,SinusoidalCurrentTheinstantaneousvalueofasinusoidalcurrentisgivenby(4.1)whereImisthepeakvalueoramplitudeofthecurrent,andisthephaseofthecurrent.Thequantityistheinitialphaseofthecurrent(fort=0)andistermedtheepochangle.Thephaseofacurrentcontinuouslyincreaseswithtime.Whenithasincrea