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外文翻译——交流电.doc

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外文翻译——交流电.doc

附录附录A外文翻译原文部分ALTERNATINGCURRENTANALTERNATINGCURRENTISONEWHICHVARIESINTHECIRCUITWITHTIMETHEVALUEOFTHECURRENTATANYGIVENINSTANTOFTIMEISTHEINSTANTANEOUSVALUEOFCURRENT,SYMBOLIZEDBYITHEINSTANTANEOUSVALUEOFCURRENTIISDEEMEDPOSITIVEFORONEDIRECTIONOFFLOWTHOUGHTHECROSSSECTIONOFACONDUCTOR,ANDNEGATIVEFORTHEOPPOSITEDIRECTIONTHEDIRECTIONOFCURRENTFLOWINWHICHINSTANTANEOUSVALUESAREPOSITIVEISCALLEDPOSITIVEACURRENTISFULLYSPECIFIED,IFONEKNOWSITSINSTANTANEOUSVALUEASAFUNCTIONOFTIME,IFT,ANDITSPOSITIVEDIRECTIONCURRENTWHOSEVALUERECURFOREQUALINCREMENTSOFTIMEARECALLEDPERIODIC,ANDTHELEASTINCREMENTOFTIMEFORWHICHTHISRECURRENTTAKESPLACEISCALLEDTHEPERIODTFORAPERIODICCURRENTIFTFTTFIG41SHOWSANEXAMPLEOFTHERELATIONSHIPIFTFORAPERIODICCURRENTTHEARROWINTHEDIAGRAMINDICATESTHEPOSITIVEDIRECTIONOFCURRENTFLOWTHEDOTTEDARROWSSHOWTHEACTUALDIRECTIONOFCURRENTFLOWATTHEINSTANTSOFTIMEWHENI0ANDI0THESEGMENTSOFTHECURVEBETWEENPOINTSAANDBOROANDCCOVERACOMPLETECYCLEOFCURRENTALTERNATIONSOVERONEPERIODTHENUMBEROFCYCLEORPERIODPERSECONDISTHEFREQUENCYOFAPERIODICCURRENTITISRECIPROCALOFITSPERIODTF/1ITISUSUALLYTOSPECIFYTHEFREQUENCYOFANYPERIODICQUANTITYINCYCLEPERSECONDTHUSTHEFREQUENCYOFAPERIODICCURRENTWILLBE1CYCLEPERSECOND,IFITSPERIODISSECOND,OR1CYCLE/SECADIRECTCURRENTMAYBEREGARDEDASASPECIALCASEOFAPERIODICCURRENTWHOSEPERIODISINFINITELYLONGANDTHEFREQUENCYISTHUSZEROTHETERMALTERNATINGCURRENTISOFTENUSEDINTHENARROWSENSEOFAPERIODICCURRENTWHOSECONSTANTDIRECTIONCURRENTCOMPONENTISZERO,OR010TIDTTTHEFREQUENCIESOFALTERNATINGCURRENTENCOUNTEREDINPRACTICERANGEOVERWIDEVALUESTHEMAINSFREQUENCYIS50HZINTHESOVIETUNIONANDEUROPE,AND60HZINTHEUNITEDSTATESSOMEINDUSTRIALPROCESSESUSEFREQUENCIESFROM10HZTO91052HZINRADIOPRACTICE,FREQUENCIESUPTO10103HZAREEMPLOYEDTHEDEFINITIONSFORCURRENTJUSTINTRODUCEDAND,INDEED,THOSETHATWILLBEINTRODUCEDSHORTLYFULLYAPPLYTOPERIODICVOLTAGES,EMFS,MAGNETICFLUXESANDANYOTHERELECTRICALANDMAGNETICQUANTITIESSOMEADDITIONALREMARKSAREONLYNEEDEDWITHREGARDTOTHESIGNOFALTERNATINGVOLTAGEANDEMFSANALTERNATINGVOLTAGEBETWEENTWOPOINTAANDB,DETERMINEDALONGASPECIFIEDPATH1,PERIODICALLYCHANGESSIGN,SOTHATIFITISASSUMEDTOBEPOSITIVEINTHEDIRECTIONFROMATOBITWILLBENEGATIVEINDIRECTIONFROMBTOAATTHESAMEINSTANTOFTIMETHISISWHYITISIMPORTANTTOLABELWHICHOFTHETWODIRECTIONSISASSUMEDPOSITIVEINDIAGRAMS,SUCHADIRECTIONISLABELEDEITHERBYARROWSORSUBSCRIPTSINTHESYMBOLSFORVOLTAGEANDISREGARDEDTOBETHEPOSITIVEREFERENCEDIRECTIONOFAVOLTAGEOROFANEMFSELECTRICALENGINEERINGUSESTHESIMPLESTANDCOMMONESTTYPEOFALTERNATINGCURRENT,THEONEWHICHVARIESSINUSOIDALLYWITHTIME;HENCETHETERMAHARMONICORASINUSOIDALCURRENTTHEPREFERENCEFORSINUSOIDALCURRENTSISEXPLAINEDMODULATEDBYTHESIGNALINAMPLITUDE,FREQUENCYORPHASEPERIODICNONSINUSOIDALCURRENTMAYLIKEWISEBETREATEDASCOMPOSEDOFSINUSOIDALCURRENTATAVARIETYOFFREQUENCIESOCCURRINGSIMULTANEOUSLYTHISISWHYTHOROUGHOFSINUSOIDALCURRENTCIRCUITSISOFPRIMARYIMPORTANCETHEACGENERATORANACGENERATORCONSISTSOFASTATIONARYPART,THESTATOR,ANDAREVOLVINGPART,THEROTORASARULETHEROTORCARRIESMAGNETICPOLESWITHCOILSAROUNDTHEMTHESEARETHEFILEDCOILSOFTHEGENERATOR,BECAUSETHEYESTABLISHAMAGNETICFILEDINTHEMACHINETHEYAREENERGIZEDWITHDIRECTCURRENTTHROUGHSLIPRINGSANDBRUSHESTHESLOTSOFTHESTATORSTAKEDUPFROMELECTRICALSHEETSTEELPUNCHINGSRECEIVETHECOILSOFTHESTATORWINDINGTHESTATORCOILSARECONNECTEDINSERIES,ASSHOWNBYTHEFULLYANDDOTTEDLINESINTHEDRAWINGTHEEMFINDUCEDINASTATORCONDUCTORISGIVENBYBLVEWHEREBMAGNETICINDUCTIONOFTHEFIELDMOVINGRELATIVETOTHECONDUCTOR;LACTIVELENGTHOFTHECONDUCTOR;VSPEEDWITHWHICHTHEMAGNETICFIELDMOVESRELATIVETOTHECONDUCTORSINCELANDVARECONSTANT,THEINDUCEDEMFWILLVARYEXACTLYASBVARIESIFTHEINDUCEDEMFISTOBESINUSOIDALWHICHISUSUALLYSOUGHT,THEDISTRIBUTIONOFBAROUNDTHECIRCUMFERENCEOFTHESTATORSHOULDBEASCLOSETOSINUSOIDALASPRACTICABLEWITHPPOLEPAIRSONTHEROTOR,THEEMFWILLUNDERGOPCYCLESOFCHANGESEVERYREVOLUTIONIFTHESPEEDOFTHEROTORISREVOLUTIONSPERMINUTESR/MIN,THISWORKSOUTTOPNCYCLESPERMINUTE,ANDTHEFREQUENCYOFTHEINDUCEDEMFIS60/PNFFORF50HZ,THEROTOROFAGENERATORWITHONEPAIROFPOLESSHOULDRUNAT3000R/MINANDWITHTWOPOLEPAIRS,AT1500R/MINWITHSPEEDSLIKETHIS,ROTORSAREUSUALLYFABRICATEDWITHNONSALIENTPILESFORGREATERMECHANICALSTRENGTHHIGHFREQUENCYGENERATORSOPERATINGAT800TO8000HZAREALLOFSPECIALDESIGNSTHEIRUSESAREINTHEHEATTREATMENTANDINDUCTIONHEATINGFIELDSTILLHIGHERFREQUENCIESAREGENERATEDBYVALVEANDSEMICONDUCTOROSCILLATORSSINUSOIDALCURRENTTHEINSTANTANEOUSVALUEOFASINUSOIDALCURRENTISGIVENBY2SINTTIIMWHEREMIISTHEPEAKVALUEORAMPLITUDEOFTHECURRENT,AND2TTISTHEPHASEOFTHECURRENTTHEQUANTITYISTHEINITIALPHASEOFTHECURRENTFORT0ANDISTERMEDTHEEPOCHANGLETHEPHASEOFACURRENTCONTINUOUSLYINCREASESWITHTIMEWHENITHASINCREASEBY2,THEWHOLECYCLEOFCHANGESISREPEATEDEXACTLYALLOVERAGAINTHEREFORE,SPEAKINGOFTHEPHASEOFACURRENT,ITISCUSTOMARYTODROPTHEINTEGER2ANDTOCONSIDERTHEPHASEWITHINORBETWEENZEROAND2THEABOVECHANGEOFPHASEBY2OCCURSDURINGTHEPERIODTTHEREFORE,THERATEOFCHANGEOFTHEPHASEISGIVENBYT/2ITISSYMBOLIZEDBYTHEGREEKLETTEROMEGAANDISCALLEDTHEPULSATANCENOTINGTHATTF/1,WEMAYWRITEFT2/2THEABOVEEXPRESSION,RELATINGANDF,HASBEENRESPONSIBLEFORTHEFACTTHATTHEPULSTANCEISALSOTERMEDTHEANGULARVELOCITYORFREQUENCYITISEXPRESSEDINRADIANSPERSECONDTHUS,FORHZF50,SRAD/314INTRODUCEINEQ41WEOBTAINSINTIIMSINUSOIDALCURRENTOFTHESAMEFREQUENCY,BUTDIFFERINGINAMPLITUDEANDEPOCHANGLES,ARESHOWNINFIG42THEIRINSTANTANEOUSVALUESARESIN111TIIMSIN222TIIMTHETIMETORTHEPRODUCTT,PROPORTIONALTOTIME,ISLAIDOFFASABSCISSATHEEPOCHANGLEISALWAYSMEASUREDBETWEENTHEORIGINOFCOORDINATES,WHICHCORRESPONDSTOTHEREFERENCETIMET0,ANDTHEINSTANTWHENAGIVENSINUSOIDALJUSTPASSESTHROUGHZEROFROMNEGATIVETOPOSITIVEVALUESFOR10,THESTARTORZEROPOINTOFTHESINUSOID1IISSHIFTEDTOTHELEFT,ANDFOR20ITISSHIFTEDTOTHERIGHTOFTHEORIGINOFCOORDINATESALTERNATIVELY,THEINSTANTANEOUSVALUEOFASINUSOIDALCURRENTMAYBEREPRESENTEDBYACOSINUSOIDALFUNCTIONOFTHEFORMTIIMCOSWHERE2/WHENTWOORMORESINUSOIDALFUNCTIONDIFFERINTIMEPHASEASRECKONEDFROMSIMILARPOINTS,THEYARESAIDTOBESHIFTEDORDISPLACEDINPHASEWITHRESPECTTOONEANOTHERTHISPHASESHIFT,ORTHEPHASEDISPLACEMENT,ISMEASUREDBETWEENTHEIRRESPECTIVEZEROS,ANDOBVIOUSLYISTHEDIFFERENCEINEPOCHANGLESREFERRINGTOFIG43,021,ANDTHECURRENT1IISSAIDTOLEADTHECURRENT2IINPHASEBY21,OR,WHICHISTHESAME,THECURRENT2ILAGSINPHASEBEHINDTHECURRENT1IBY21TWOSINUSOIDALFUNCTIONSOFTHESAMEFREQUENCYARESAIDTOBEINPHASEIFTHEYHAVESAMEEPOCHANGLE,ANDARESAIDTOBEINANTIPHASEWHENTHEIRPHASEDISPLACEMENTISFINALLY,THEYARESAIDTOBEINQUADRATUREIFTHEIRDIFFERENCEIS2/附录B外文翻译译文部分交流电交流电在电路中是一个随时间变化的值。电流值在任何给定的时间上都是一个瞬态值,用符号I表示。当瞬态电流值I从用正号标记的导体的端流进时为正值,而从相反的方向流动时为负值。当电流的任一瞬态值为正时,它流进导体的方向就为正极。假如知道瞬态值与时间的关系式TFI以及它的正方向,那么瞬时电流值就是一个定值。电流值随时间T进行周期性变化的这种现象叫做交流电的周期性,能满足这个条件的最小T值我们把它叫做周期。周期电流的公式为IFTFTT

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