电气工程及其自动化专业英语.ppt

电气工程及其自动化专业英语.ppt

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电气工程及其自动化专业英语电气工程及其自动化专业英语SpecializedEnglishforElectricalEngineeringItsAutomation戴文进戴文进主主编编杨植新杨植新副主编副主编ContentsPart1ElectricsandElectronicsPart2ElectricMachineryPart3ElectricalEngineeringPart4ModernComputerControlTechniquesUnit1SpecializedEnglishWordscircuitcomponents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Unit1CircuitElementsandParametersAnelectriccircuit（ornetwork）isaninterconnectionofphysicalelectricaldevices.Thepurposeofelectriccircuitsistodistributeandconvertenergyintosomeotherforms.Accordingly,thebasiccircuitcomponentsareanenergysource（orsources）,anenergyconverter（orconverters）andconductorsconnectingthem（连接它们的）（连接它们的）.Anenergysource（aprimaryorsecondarycell,ageneratorandthelike）convertschemical,mechanical,thermalorsomeotherformsofenergyinto（将（将-转换成转换成-）electricenergy.Anenergyconverter,alsocalledload（suchasalamp,heatingapplianceorelectricmotor）,convertselectricenergyintolight,heat,mechanicalworkandsoon.Eventsinacircuitcanbedefinedintermsof（用（用-，根据，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）（自感或互感）appearinD.C.circuits,norarethere（倒装结构）（倒装结构）anydisplacementcurrents（位移电流）（位移电流）inthedielectricsurroundingtheconductors（导体周围的电介导体周围的电介质质）.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）（按不同方式连接的）.Tosimplifyanalysisofactualcircuits,itisusualtoshowthemsymbolicallyinadiagramcalledacircuitdiagram,whichisinfactafictitiousor,rather,idealizedmodelofanactualcircuitofnetwork.Suchadiagramconsistsofinterconnectedsymbolscalledcircuitelementsorcircuitparameters.TwoelementsarenecessarytorepresentprocessesinaD.C.circuit.Theseareasourceofe.m.f.Eandofinternal（orsource）resistanceRS,andtheloadresistance（whichincludestheresistanceoftheconductors）R（Fig.1.2）Fig.1.2Whateveritsorigin（thermal,contact,etc.）,thesourcee.m.f.E（Fig.1.2（a）isnumericallyequaltothepotentialdifferencebetweenterminals1and2withtheexternalcircuitopen,thatis,whenthereisnocurrentflowingthroughthesourceE=12=V12（1.1）Thesourcee.m.f.isdirectedfromtheterminalatalowerpotentialtothat（代替代替terminal）atahigherone（代替代替potential）.Ondiagram,thisisshownbyarrows（箭箭头）.Whenaloadisconnectedtothesourceterminals（thecircuitisthensaidtobeloaded）andthecircuitisclosed,acurrentbeginstoflowroundit.Nowthevoltagebetweensourceterminals1and2（calledtheterminalvoltage）isnotequaltoitse.m.f.becauseofthevoltagedropVSinsidethesource,thatis,acrossthesourceresistanceRSVS=RSIFig.1.3showsatypicalso-calledexternalcharacteristicV=12=V（I）ofaloadedsource（henceanothernameistheloadcharacteristicofasource）.Asisseen,increaseofcurrentfromzerotoII1causestheterminalvoltageofthesourcetodecreaselinearlyV12=V=EVS=ERSIFig.1.3Inotherwords,thevoltagedropVSacrossthesourceresistancerisesinproportiontothecurrent.Thisgoesonuntilacertainlimitisreached.Thenasthecurrentkeepsrising,theproportionalitybetweenitsvalueandthevoltagedropacrossthesourceisupset,andtheexternalcharacteristicceasestobe（不再是）（不再是）linear.Thisdecreaseinvoltagemaybecausedbyareductioninthesourcevoltage,byanincreaseintheinternalresistance,orboth.The