轮机英语课件

MarineEngineeringEnglish《轮机英语》APracticalCourseforEngineersWorkingonBoardShips

MarineElectricalSystemandAutomatizationLesson24ACGenerator

第24课交流发电机LearningObjectives:1.Graspsomeusefulwordsandexpressionsinthewholetext.2.Afterstudyingthelesson,heorshewillhaveabetterunderstandingofConstruction&PrincipleofACGenerator.3

4part1

NewWordsandExpressions5part2

TextAnalysisLesson24ACGeneratorAlternatingcurrenthasnowallbutreplaceddirectcurrentasthestandardsupplyforallmarineinstallations.#交流电现在几乎取代了直流电，成为所有海上设施的标准电源。Lesson24ACGeneratorTheuseofalternatingcurrenthasanumberofimportantadvantages:forexample,reducedfirstcost,lessweight,lessspacerequiredandareductioninmaintenancerequirements.#使用交流电有许多重要的优点：例如，降低了初始成本、重量、所需空间和维护要求。Lesson24ACGeneratorDirectcurrentdoes,however,offeradvantagesinmotorcontrolusing,forexample,theWard-Leonardsystemwhichprovidesawiderangeofspeed.#然而，直流电确实在电机控制方面具有优势，例如，沃德·伦纳德系统提供了广泛的速度范围。Directingcurrentgenerator直流发电机工作原理9Alternatingcurrentgenerator交流发电机工作原理Lesson24ACGeneratorAcoilofwirerotatinginamagneticfieldproducesacurrent.#线圈在磁场中旋转产生电流。Lesson24ACGeneratorThecurrentcanbebroughtouttotwoslipringswhichareinsulatedfromtheshaft.#电流可由与轴绝缘的滑环输出。Lesson24ACGeneratorCarbonbushesrestontheseringsastheyrotateandcollectthecurrentforuseinanexternalcircuit.#碳刷停靠在旋转的滑环上，汇集电流供外电路使用。Lesson24ACGeneratorCurrentcollectedinthiswaywillbealternating,thatis,changingindirectionandrisingandfallinginvalue.#以这种方式汇集的电流是交变的，即方向变化且数值升降。Lesson24ACGeneratorToincreasethecurrentproduced,additionalsetsofpolesmaybeintroduced.#为了增加输出的电流可以采用多组磁极。Lesson24ACGeneratorThemagneticfieldisprovidedbyelectromagnetssoarrangedthatadjacentpoleshaveoppositepolarity.#磁场是由电磁铁产生，电磁铁布置成相邻的磁极磁性相反。Lesson24ACGeneratorThese“fieldcoils”,astheyarecalled,areconnectedinseriestoanexternalsourceorthemachineoutput.#这些“励磁线圈”，正如其所称的那样串联在外电源上，或发电机的输出端上。Lesson24ACGeneratorIfseparatecoilsorconductorsareusedthenseveraloutputscanbeobtained.#如果使用单独的线圈或导线，就可获得多个输出。Lesson24ACGeneratorThreeoutputsareusuallyarrangedwithaphaseseparationof120°,toproduceathreephasesupply.#三个输出通常布置成相位间隔120°，以产生三相电。Lesson24ACGeneratorThethreephasesystemismoreefficientinthatforthesamemechanicalpoweragreatertotalelectricaloutputisobtained.#三相制的效率较高，对于相同的(输入)机械功，可获得较大的电力输出。Lesson24ACGeneratorEachofthethreeoutputsmaybeusedinsinglephasesuppliesorinconjunctionforathreephasesupply.#三个输出中的每一个可作单相电源使用或在三相电源中联合使用。Lesson24ACGeneratorTheseparatesuppliesareconnectedineitherstarordeltaformation.#各相输出可接成星形或三角形。2324starformationdeltaformation25deltaformationLesson24ACGeneratorThestarformationismostcommonlyusedandrequiresfourslipringsonthealternator.#星形接法最常见，它要求交流发电机上有四个滑环。Lesson24ACGeneratorThethreeconductorsarejoinedatacommonslipringandalsohavetheirindividualslipring.#三根导线连在一个共用的滑环上，同时又各有各自的滑环。Lesson24ACGeneratorThecentralorneutrallineiscommontoeachphase.#中性线各相共用。Lesson24ACGeneratorThedeltaarrangementhastwophasesjoinedateachofthethreeslipringsonthealternator.#三角形接线法中，交流发电机的三个滑环，各滑环接有两相线。Lesson24ACGeneratorAsinglephasesupplycanbetakenfromanytwosliprings.#单相电可以从任何两个滑环上获取。Lesson24ACGeneratorSofar,alternatorconstructionhasconsideredthearmaturerotatingandthefieldcoilsstationary.#至今，发电机结构均采用电枢旋转而磁场不动。Lesson24ACGeneratorThesameelectricitygeneratingeffectisproducedifthereverseoccurs,thatis,thefieldcoilsrotateandthearmatureisstationary.#反之，若磁场旋转而电枢不动，也会产生同样的效果。Lesson24ACGeneratorThisisinfactthearrangementadoptedforlarge,heavydutyalternators.#这种设计实际上已被承担重要任务的大型发电机采用。Lesson24ACGeneratorThefieldcurrentsupplyinoldermachinescomesfromalowvoltagedirectcurrentgeneratororexciteronthesameshaftasthealternator.#老式发电机，励磁电流来自低压直流发电机或与交流发电机同轴的励磁器。Lesson24ACGeneratorModernmachineshoweverareeitherstaticallyexcitedorofthehighspeedbrushlesstype.#然而，现代发电机不是静态励磁型的就是高速无刷型的。Lesson24ACGeneratorTheexciterisrequiredtooperatetocountertheeffectsofpowerfactorforagivenload.#要求励磁机在运行时能抵消给定负荷下的功率因数的影响。Lesson24ACGeneratorThepowerfactorisameasureofthephase,differencebetweenvoltageandcurrentandisexpressedasthecosineofthephaseangle.#功率因数是对电压和电流间的相位差的衡量，以相位角的余弦表示。Lesson24ACGeneratorWithapurelyresistanceloadthevoltageandcurrentareinphase,givingapowerfactorofone.#对于纯电阻负荷，电压和电流同相，功率因素为1。Lesson24ACGeneratorThepowerconsumedisthereforetheproductofvoltageandcurrent.#所消耗的功率为电压和电流的乘积。Lesson24ACGeneratorInductiveorcapacitiveloads,combinedwithresistanceloads,producelaggingorleadingpowerfactorswhichhaveavaluelessthanone.#电感性或电容性负荷与电阻相结合，产生滞后或超前的功率因数，其值小于1。Lesson24ACGeneratorThepowerconsumedistheproductofcurrent,voltageandpowerfactor.#所消耗的功率为电压、电流和功率因数的乘积。Lesson24ACGeneratorThealternatingcurrentgeneratorsupplyingaloadhasavoltagedropresultingfromtileload.#带负载的发电机因负载而产生压降。Lesson24ACGeneratorWhentheloadhasalaggingpowerfactorthisvoltagedropisconsiderable.#当负载具有滞后功率因数时，此压降是相当大的。Lesson24ACGeneratorThereforetheexciter,inmaintainingthealternatorvoltage,mustvarywiththeloadcurrentandalsothepowerfactor.#因此，励磁器在保持发电机电压的过程中，(其励磁电流)必须随着负载电流和功率因数的变化而变化。Lesson24ACGeneratorThespeedchangeoftheprimemovermustalsobetakenintoaccount.#还需考虑原动机转速变化。Lesson24ACGeneratorHandcontrolofexcitationisdifficultsouseismadeofanautomaticvoltageregulator(AVR).#手控励磁较难，因此采用自动电压调节器。Lesson24ACGeneratorTheAVRconsistsbasicallyofacircuitfedfromthealternatoroutputvoltagewhichdetectssmallchangesinvoltageandfeedsasignaltoanamplifierwhichchangestheexcitationtocorrectthevoltage.#自动电压调节器基本上由一个经发电机输出电压供电的电路组成，该电路能检测电压的微小变化，输出一个信号给放大器以改变励磁，调整电压。Lesson24ACGeneratorStabilizingfeaturesarealsoincorporatedinthecircuitstoavoid“hunting”

(constantvoltagefluctuations)orovercorrecting.#稳压部件连结于电路中，以避免“振荡”(不断的电压波动)或过调现象。Lesson24ACGeneratorVariousdesignsofAVRareinusewhichcanbebroadlydividedintoclassessuchascarbonpiletypes,magneticamplifiers,electronictypes,etc.Lesson24ACGeneratorThestaticallyexcitedalternatorhasastaticexcitationsysteminsteadofaDCexciter.#静止励磁交流发电机有静止励磁系统，代替直流励磁机。Lesson24ACGeneratorThistypeofalternatorwillmorereadilyacceptthesuddenloadingbydirecton-linestartingoflargesquirrelcagemotors.#这种类型的交流发电机能较好地承受由大型鼠笼式电机直接带载起动而造成的冲击负荷。Lesson24ACGeneratorThestaticexcitationsystemusestransformersandrectifierstoprovideseriesandshuntcomponentsforthealternatorfield,thatis,itiscompounded.#静止励磁系统使用变压器和整流器，为交流发电机磁场产生一个串励和并励分量，也就是说，它是复励的。53他励：他励发电机的励磁电流fieldcurrent

是由独立的电源供给，不受发电机的

电压和电流的影响。自励：自励发电机的励磁电流是由发电机的

电枢armature电路供给，因而励磁电流

受电枢电流和电压的影响。自励又分为：并励shunt串励series

复励compoundLesson24ACGeneratorBrushesandslip-ringsareusedtotransferthecurrenttothefieldcoilswhicharemountedontherotor.#使用电刷和滑环把电流传递到装在转子上的励磁线圈上。Lesson24ACGeneratorTheterminalvoltagefromthealternatorthusgivestheno-loadvoltageandtheloadcurrentprovidestheextraexcitationtogiveasteadyvoltageunderanyloadcondition.#交流发电机的端电压提供空载电压，负载电流提供一个额外励磁以便在任何负荷下输出稳定的电压。Lesson24ACGeneratorThecarefulmatchingofcomponentsprovidesasystemwhichfunctionsasaselfregulatorofvoltage.#部件的仔细匹配提供了一个系统，该系统起到电压自调节器的作用。Lesson24ACGeneratorCertainpracticalelectricalproblemsandthecompensationnecessaryforspeedvariationrequirethatavoltageregulatorisalsobuiltintothesystem.#某些实际电气问题，以及为了对速度变化进行必要的补偿，要求发电机系统中装有电压调节器。Lesson24ACGeneratorThebrushlesshighspeedalternatorwasalsodevelopedtoeliminateDCexciterswiththeirassociatedcommutatorsandbrushgear.#无刷高速交流发电机的开发，废除了直流发电机及与其配套的整流子和电刷机构。Lesson24ACGeneratorThealternatorandexciterrotorsareonacommonshaft,whichalsocarriestherectifiers.#交流发电机和励磁器转子同轴，轴上还带有整流器。Lesson24ACGeneratorTheexciteroutputisfedtotherectifiersandthenthroughconductorsinthehollowshafttothealternatorfieldcoils.#励磁器输出馈电到整流器上，然后通过空心轴里的导线连到交流发电机励磁线圈上。Lesson24ACGeneratorAnautomaticvoltageregulatorisusedwiththistypeofalternator.#这种发电机使用自动电压调节器。Lesson24ACGeneratorTheconstructionofanalternatorcanbeseeninFig.24-3.Therotor

housesthepoleswhichprovidethefieldcurrent,andtheseareusuallyofthesalientorprojecting-poletype.#交流发电机的结构如图24-3所示。转子包含提供磁场电流的磁极，通常为凸极式。Lesson24ACGeneratorSlipringsandafanarealsomountedontherotorshaft,whichisdrivenbytheauxiliaryengine.Thestatorcoresurroundstherotorandsupportsthethreeseparatephasewindings.#滑环和风扇也安装在由副机驱动的转子轴上。定子铁芯包围转子并支撑三个独立的相绕组。Lesson24ACGeneratorHeatisproducedinthevariouswindingsand

mustberemovedbycooling.Theshaftfandrivesairoverawater-cooledheatexchanger.#各种绕组产生热量，必须通过冷却来消除。轴流式风扇驱动空气通过水冷式热交换器。Lesson24ACGeneratorElectricheatersareusedtopreventcondensationonthewindingswhenthealternatorisnotinuse.#当交流发电机不使用时，电加热器用于防止绕组上冷凝。Lesson24ACGeneratorInadditiontoauxiliary-engine-drivenalternatorsashipmayhaveashaft-drivenalternator.#除副机驱动的交流发电机外，船舶还可配备轴驱动交流发电机。Lesson24ACGeneratorInthisarrangementadriveistakenfromthemainengineorthepropellershaftandusedtorotatethealternator.#在这种布置中，驱动力来自主机或传动轴，用于旋转交流发电机。Lesson24ACGeneratorThevariousoperatingconditionsoftheenginewillinevitablyresultinvariationsofthealternatordrivingspeed.#发动机的各种工作条件将不可避免地导致交流发电机驱动速度的变化。Lesson24ACGeneratorAhydraulicpumpandgearboxarrangementmaybeusedtoprovideaconstant-speeddrive,orthealternatoroutputmaybefedtoastaticfrequencyconverter.#液压泵和齿轮箱配置可用于提供恒速驱动，或者交流发电机输出可馈送至静态变频器。Lesson24ACGeneratorInthestaticfrequencyconvertertheACoutputisfirstrectifiedintoavariableDCvoltageandtheninvertedbackintoathree-phaseACvoltage.#在静态变频器中，交流输出首先被整流为可变直流电压，然后再逆变回三相交流电压。Lesson24ACGeneratorAfeedbacksystemintheoscillatorinverterproducesaconstant-outputACvoltageandfrequency.#振荡器逆变器中的反馈系统产生恒定的输出交流电压和频率。part3

Exercise&ExaminationTheamountofvoltageinducedinthewindingsofanACgeneratordependson_____.A.thenumberofco