高职电气自动化技术专业英语2

Chapter1ElectricandElectronicTechnologyFundamentalsUnit2NetworkAnalysisTextNewWordsandExpressionsExercisesEndTranslationStandardUnit2NetworkAnalysisIntroductionAnetwork,inthecontextofelectronics,isacollectionofinterconnectedcomponents.Networkanalysisistheprocessoffindingthevoltagesacross,andthecurrentsthrough,everycomponentinthenetwork.Thereareanumberofdifferenttechniquesforachievingthis.However,forthemostpart,theyassumethatthecomponentsofthenetworkarealllinear.Themethodsdescribedinthisarticleareonlyapplicabletolinearnetworkanalysisexceptwhereexplicitlystated.Unit2NetworkAnalysisDefinitionsComponent:Adevicewithtwoormoreterminalsintowhich,oroutofwhich,chargemayflow.Node:Apointatwhichterminalsofmorethantwocomponentsarejoined.Aconductorwithasubstantiallyzeroresistanceisconsideredtobeanodeforthepurposeofanalysis.Branch:Thecomponent(s)joiningtwonodes.Mesh:Agroupofbrancheswithinanetworkjoinedsoastoformacompleteloop.Port:Twoterminalswherethecurrentintooneisidenticaltothecurrentoutoftheother.Unit2NetworkAnalysisEquivalentcircuitsAusefulprocedureinnetworkanalysisistosimplifythenetworkbyreducingthenumberofcomponents.Thiscanbedonebyreplacingtheactualcomponentswithothernotionalcomponentsthathavethesameeffect.Aparticulartechniquemightdirectlyreducethenumberofcomponents,forinstancebycombiningimpedancesinseries.Ontheotherhanditmightmerelychangetheformintooneinwhichthecomponentscanbereducedinalateroperation.Forinstance,onemighttransformavoltagegeneratorintoacurrentgeneratorusingNorton'stheoreminordertobeabletolatercombinetheinternalresistanceofthegeneratorwithaparallelimpedanceload.Aresistivecircuitisacircuitcontainingonlyresistors,idealcurrentsources,andidealvoltagesources.Ifthesourcesareconstant(DC)sources,theresultisaDCcircuit.Theanalysisofacircuitreferstotheprocessofsolvingforthevoltagesandcurrentspresentinthecircuit.ThesolutionprinciplesoutlinedherealsoapplytophasoranalysisofACcircuits.Twocircuitsaresaidtobeequivalentwithrespecttoapairofterminalsifthevoltageacrosstheterminalsandcurrentthroughtheterminalsforonenetworkhavethesamerelationshipasthevoltageandcurrentattheterminalsoftheothernetwork.Unit2NetworkAnalysisUnit2NetworkAnalysisIfimpliesforall(real)valuesof,thenwithrespecttoterminalsabandxy,circuit1andcircuit2areequivalent.Theaboveisasufficientdefinitionforaone-portnetwork.Formorethanoneport,thenitmustbedefinedthatthecurrentsandvoltagesbetweenallpairsofcorrespondingportsmustbearthesamerelationship.Forinstance,staranddeltanetworksareeffectivelythreeportnetworksandhencerequirethreesimultaneousequationstofullyspecifytheirequivalence.ImpedancesinseriesandinparallelAnytwoterminalnetworkofimpedancescaneventuallybereducedtoasingleimpedancebysuccessiveapplicationsofimpendancesinseriesorimpendancesinparallel.Impedancesinseries:Impedancesinparallel:Theabovesimplifiedforonlytwoimpedancesinparallel:Unit2NetworkAnalysis321ZZZZeqneqZZZZ1111212121ZZZZZeqUnit2NetworkAnalysisDelta-wyetransformationAnetworkofimpedanceswithmorethantwoterminalscannotbereducedtoasingleimpedanceequivalentcircuit.Ann-terminalnetworkcan,atbest,bereducedtonimpedances.Forathreeterminalnetwork,thethreeimpedancescanbeexpressedasathreenodedelta(Δ)networkorafournodestar(Y)network.Thesetwonetworksareequivalentandthetransformationsbetweenthemaregivenbelow.Ageneralnetworkwithanarbitrarynumberofterminalscannotbereducedtotheminimumnumberofimpedancesusingonlyseriesandparallelcombinations.Ingeneral,Y-ΔandΔ-Ytransformationsmustalsobeused.Itcanbeshownthatthisissufficienttofindtheminimalnetworkforanyarbitrarynetworkwithsuccessiveapplicationsofseries,parallel,Y-ΔandΔ-Y;nomorecomplextransformationsarerequired.Unit2NetworkAnalysisForequivalence,theimpedancesbetweenanypairofterminalsmustbethesameforbothnetworks,resultinginasetofthreesimultaneousequations.Theequationsbelowareexpressedasresistancesbutapplyequallytothegeneralcasewithimpedances.Unit2NetworkAnalysisSourcetransformationAgeneratorwithaninternalimpedance(ienon-idealgenerator)canberepresentedaseitheranidealvoltagegeneratororanidealcurrentgeneratorplustheimpedance.Thesetwoformsareequivalentandthetransformationsaregivenbelow.Ifthetwonetworksareequivalentwithrespecttoterminalsab,thenVandImustbeidenticalforbothnetworks.Thus,Norton'stheoremstatesthatanytwo-terminalnetworkcanbereducedtoanidealcurrentgeneratorandaparallelimpedance.Thévenin'stheoremstatesthatanytwo-terminalnetworkcanbereducedtoanidealvoltagegeneratorplusaseriesimpedance.Unit2NetworkAnalysisReturnorNewWordsandExpressionslinearnetwork线性网络componentn.元件,组件terminaln.终端explicitlyadv.明白地,明确地noden.节点，结点meshn.网孔portn.端口Equivalentcircuit等值电路Norton'stheorem诺顿定理resistivecircuit电阻性电路phasoranalysis相量分析staranddeltanetworks星三角网络simultaneousadj.同时发生的impendancen.阻抗seriesn.串联paralleln.并联delta-wyetransformation三角星变换arbitraryadj.任意的successiveadj.连续的equivalencen.同等,等价sourcetransformation电源变换identicaladj.同一的,同样的Thévenin'stheorem戴维南定理ReturnTranslationStandard准确明白通顺严密简练全面专业英语翻译是对原文的一种再创作，其标准为TranslationStandard掌握英语语法知识具有一定深度的专业知识和较为广博的科学知识有较高的汉语修养为达到以上翻译标准，必须做