MarineEngineeringEnglish《輪機英語》APracticalCourseforEngineersWorkingonBoardShips

MarineElectricalSystemandAutomatizationLesson24ACGenerator

第24課交流發(fā)電機LearningObjectives:1.Graspsomeusefulwordsandexpressionsinthewholetext.2.Afterstudyingthelesson,heorshewillhaveabetterunderstandingofConstruction&PrincipleofACGenerator.3

4part1

NewWordsandExpressions5part2

TextAnalysisLesson24ACGeneratorAlternatingcurrenthasnowallbutreplaceddirectcurrentasthestandardsupplyforallmarineinstallations.#交流電現(xiàn)在幾乎取代了直流電，成為所有海上設施的標準電源。Lesson24ACGeneratorTheuseofalternatingcurrenthasanumberofimportantadvantages:forexample,reducedfirstcost,lessweight,lessspacerequiredandareductioninmaintenancerequirements.#使用交流電有許多重要的優(yōu)點：例如，降低了初始成本、重量、所需空間和維護要求。Lesson24ACGeneratorDirectcurrentdoes,however,offeradvantagesinmotorcontrolusing,forexample,theWard-Leonardsystemwhichprovidesawiderangeofspeed.#然而，直流電確實在電機控制方面具有優(yōu)勢，例如，沃德·倫納德系統(tǒng)提供了廣泛的速度范圍。Directingcurrentgenerator直流發(fā)電機工作原理9Alternatingcurrentgenerator交流發(fā)電機工作原理Lesson24ACGeneratorAcoilofwirerotatinginamagneticfieldproducesacurrent.#線圈在磁場中旋轉(zhuǎn)產(chǎn)生電流。Lesson24ACGeneratorThecurrentcanbebroughtouttotwoslipringswhichareinsulatedfromtheshaft.#電流可由與軸絕緣的滑環(huán)輸出。Lesson24ACGeneratorCarbonbushesrestontheseringsastheyrotateandcollectthecurrentforuseinanexternalcircuit.#碳刷停靠在旋轉(zhuǎn)的滑環(huán)上，匯集電流供外電路使用。Lesson24ACGeneratorCurrentcollectedinthiswaywillbealternating,thatis,changingindirectionandrisingandfallinginvalue.#以這種方式匯集的電流是交變的，即方向變化且數(shù)值升降。Lesson24ACGeneratorToincreasethecurrentproduced,additionalsetsofpolesmaybeintroduced.#為了增加輸出的電流可以采用多組磁極。Lesson24ACGeneratorThemagneticfieldisprovidedbyelectromagnetssoarrangedthatadjacentpoleshaveoppositepolarity.#磁場是由電磁鐵產(chǎn)生，電磁鐵布置成相鄰的磁極磁性相反。Lesson24ACGeneratorThese“fieldcoils”,astheyarecalled,areconnectedinseriestoanexternalsourceorthemachineoutput.#這些“勵磁線圈”，正如其所稱的那樣串聯(lián)在外電源上，或發(fā)電機的輸出端上。Lesson24ACGeneratorIfseparatecoilsorconductorsareusedthenseveraloutputscanbeobtained.#如果使用單獨的線圈或?qū)Ь€，就可獲得多個輸出。Lesson24ACGeneratorThreeoutputsareusuallyarrangedwithaphaseseparationof120°,toproduceathreephasesupply.#三個輸出通常布置成相位間隔120°，以產(chǎn)生三相電。Lesson24ACGeneratorThethreephasesystemismoreefficientinthatforthesamemechanicalpoweragreatertotalelectricaloutputisobtained.#三相制的效率較高，對于相同的(輸入)機械功，可獲得較大的電力輸出。Lesson24ACGeneratorEachofthethreeoutputsmaybeusedinsinglephasesuppliesorinconjunctionforathreephasesupply.#三個輸出中的每一個可作單相電源使用或在三相電源中聯(lián)合使用。Lesson24ACGeneratorTheseparatesuppliesareconnectedineitherstarordeltaformation.#各相輸出可接成星形或三角形。2324starformationdeltaformation25deltaformationLesson24ACGeneratorThestarformationismostcommonlyusedandrequiresfourslipringsonthealternator.#星形接法最常見，它要求交流發(fā)電機上有四個滑環(huán)。Lesson24ACGeneratorThethreeconductorsarejoinedatacommonslipringandalsohavetheirindividualslipring.#三根導線連在一個共用的滑環(huán)上，同時又各有各自的滑環(huán)。Lesson24ACGeneratorThecentralorneutrallineiscommontoeachphase.#中性線各相共用。Lesson24ACGeneratorThedeltaarrangementhastwophasesjoinedateachofthethreeslipringsonthealternator.#三角形接線法中，交流發(fā)電機的三個滑環(huán)，各滑環(huán)接有兩相線。Lesson24ACGeneratorAsinglephasesupplycanbetakenfromanytwosliprings.#單相電可以從任何兩個滑環(huán)上獲取。Lesson24ACGeneratorSofar,alternatorconstructionhasconsideredthearmaturerotatingandthefieldcoilsstationary.#至今，發(fā)電機結(jié)構均采用電樞旋轉(zhuǎn)而磁場不動。Lesson24ACGeneratorThesameelectricitygeneratingeffectisproducedifthereverseoccurs,thatis,thefieldcoilsrotateandthearmatureisstationary.#反之，若磁場旋轉(zhuǎn)而電樞不動，也會產(chǎn)生同樣的效果。Lesson24ACGeneratorThisisinfactthearrangementadoptedforlarge,heavydutyalternators.#這種設計實際上已被承擔重要任務的大型發(fā)電機采用。Lesson24ACGeneratorThefieldcurrentsupplyinoldermachinescomesfromalowvoltagedirectcurrentgeneratororexciteronthesameshaftasthealternator.#老式發(fā)電機，勵磁電流來自低壓直流發(fā)電機或與交流發(fā)電機同軸的勵磁器。Lesson24ACGeneratorModernmachineshoweverareeitherstaticallyexcitedorofthehighspeedbrushlesstype.#然而，現(xiàn)代發(fā)電機不是靜態(tài)勵磁型的就是高速無刷型的。Lesson24ACGeneratorTheexciterisrequiredtooperatetocountertheeffectsofpowerfactorforagivenload.#要求勵磁機在運行時能抵消給定負荷下的功率因數(shù)的影響。Lesson24ACGeneratorThepowerfactorisameasureofthephase,differencebetweenvoltageandcurrentandisexpressedasthecosineofthephaseangle.#功率因數(shù)是對電壓和電流間的相位差的衡量，以相位角的余弦表示。Lesson24ACGeneratorWithapurelyresistanceloadthevoltageandcurrentareinphase,givingapowerfactorofone.#對于純電阻負荷，電壓和電流同相，功率因素為1。Lesson24ACGeneratorThepowerconsumedisthereforetheproductofvoltageandcurrent.#所消耗的功率為電壓和電流的乘積。Lesson24ACGeneratorInductiveorcapacitiveloads,combinedwithresistanceloads,producelaggingorleadingpowerfactorswhichhaveavaluelessthanone.#電感性或電容性負荷與電阻相結(jié)合，產(chǎn)生滯后或超前的功率因數(shù)，其值小于1。Lesson24ACGeneratorThepowerconsumedistheproductofcurrent,voltageandpowerfactor.#所消耗的功率為電壓、電流和功率因數(shù)的乘積。Lesson24ACGeneratorThealternatingcurrentgeneratorsupplyingaloadhasavoltagedropresultingfromtileload.#帶負載的發(fā)電機因負載而產(chǎn)生壓降。Lesson24ACGeneratorWhentheloadhasalaggingpowerfactorthisvoltagedropisconsiderable.#當負載具有滯后功率因數(shù)時，此壓降是相當大的。Lesson24ACGeneratorThereforetheexciter,inmaintainingthealternatorvoltage,mustvarywiththeloadcurrentandalsothepowerfactor.#因此，勵磁器在保持發(fā)電機電壓的過程中，(其勵磁電流)必須隨著負載電流和功率因數(shù)的變化而變化。Lesson24ACGeneratorThespeedchangeoftheprimemovermustalsobetakenintoaccount.#還需考慮原動機轉(zhuǎn)速變化。Lesson24ACGeneratorHandcontrolofexcitationisdifficultsouseismadeofanautomaticvoltageregulator(AVR).#手控勵磁較難，因此采用自動電壓調(diào)節(jié)器。Lesson24ACGeneratorTheAVRconsistsbasicallyofacircuitfedfromthealternatoroutputvoltagewhichdetectssmallchangesinvoltageandfeedsasignaltoanamplifierwhichchangestheexcitationtocorrectthevoltage.#自動電壓調(diào)節(jié)器基本上由一個經(jīng)發(fā)電機輸出電壓供電的電路組成，該電路能檢測電壓的微小變化，輸出一個信號給放大器以改變勵磁，調(diào)整電壓。Lesson24ACGeneratorStabilizingfeaturesarealsoincorporatedinthecircuitstoavoid“hunting”

(constantvoltagefluctuations)orovercorrecting.#穩(wěn)壓部件連結(jié)于電路中，以避免“振蕩”(不斷的電壓波動)或過調(diào)現(xiàn)象。Lesson24ACGeneratorVariousdesignsofAVRareinusewhichcanbebroadlydividedintoclassessuchascarbonpiletypes,magneticamplifiers,electronictypes,etc.Lesson24ACGeneratorThestaticallyexcitedalternatorhasastaticexcitationsysteminsteadofaDCexciter.#靜止勵磁交流發(fā)電機有靜止勵磁系統(tǒng)，代替直流勵磁機。Lesson24ACGeneratorThistypeofalternatorwillmorereadilyacceptthesuddenloadingbydirecton-linestartingoflargesquirrelcagemotors.#這種類型的交流發(fā)電機能較好地承受由大型鼠籠式電機直接帶載起動而造成的沖擊負荷。Lesson24ACGeneratorThestaticexcitationsystemusestransformersandrectifierstoprovideseriesandshuntcomponentsforthealternatorfield,thatis,itiscompounded.#靜止勵磁系統(tǒng)使用變壓器和整流器，為交流發(fā)電機磁場產(chǎn)生一個串勵和并勵分量，也就是說，它是復勵的。53他勵：他勵發(fā)電機的勵磁電流fieldcurrent

是由獨立的電源供給，不受發(fā)電機的

電壓和電流的影響。自勵：自勵發(fā)電機的勵磁電流是由發(fā)電機的

電樞armature電路供給，因而勵磁電流

受電樞電流和電壓的影響。自勵又分為：并勵shunt串勵series

復勵compoundLesson24ACGeneratorBrushesandslip-ringsareusedtotransferthecurrenttothefieldcoilswhicharemountedontherotor.#使用電刷和滑環(huán)把電流傳遞到裝在轉(zhuǎn)子上的勵磁線圈上。Lesson24ACGeneratorTheterminalvoltagefromthealternatorthusgivestheno-loadvoltageandtheloadcurrentprovidestheextraexcitationtogiveasteadyvoltageunderanyloadcondition.#交流發(fā)電機的端電壓提供空載電壓，負載電流提供一個額外勵磁以便在任何負荷下輸出穩(wěn)定的電壓。Lesson24ACGeneratorThecarefulmatchingofcomponentsprovidesasystemwhichfunctionsasaselfregulatorofvoltage.#部件的仔細匹配提供了一個系統(tǒng)，該系統(tǒng)起到電壓自調(diào)節(jié)器的作用。Lesson24ACGeneratorCertainpracticalelectricalproblemsandthecompensationnecessaryforspeedvariationrequirethatavoltageregulatorisalsobuiltintothesystem.#某些實際電氣問題，以及為了對速度變化進行必要的補償，要求發(fā)電機系統(tǒng)中裝有電壓調(diào)節(jié)器。Lesson24ACGeneratorThebrushlesshighspeedalternatorwasalsodevelopedtoeliminateDCexciterswiththeirassociatedcommutatorsandbrushgear.#無刷高速交流發(fā)電機的開發(fā)，廢除了直流發(fā)電機及與其配套的整流子和電刷機構。Lesson24ACGeneratorThealternatorandexciterrotorsareonacommonshaft,whichalsocarriestherectifiers.#交流發(fā)電機和勵磁器轉(zhuǎn)子同軸，軸上還帶有整流器。Lesson24ACGeneratorTheexciteroutputisfedtotherectifiersandthenthroughconductorsinthehollowshafttothealternatorfieldcoils.#勵磁器輸出饋電到整流器上，然后通過空心軸里的導線連到交流發(fā)電機勵磁線圈上。Lesson24ACGeneratorAnautomaticvoltageregulatorisusedwiththistypeofalternator.#這種發(fā)電機使用自動電壓調(diào)節(jié)器。Lesson24ACGeneratorTheconstructionofanalternatorcanbeseeninFig.24-3.Therotor

housesthepoleswhichprovidethefieldcurrent,andtheseareusuallyofthesalientorprojecting-poletype.#交流發(fā)電機的結(jié)構如圖24-3所示。轉(zhuǎn)子包含提供磁場電流的磁極，通常為凸極式。Lesson24ACGeneratorSlipringsandafanarealsomountedontherotorshaft,whichisdrivenbytheauxiliaryengine.Thestatorcoresurroundstherotorandsupportsthethreeseparatephasewindings.#滑環(huán)和風扇也安裝在由副機驅(qū)動的轉(zhuǎn)子軸上。定子鐵芯包圍轉(zhuǎn)子并支撐三個獨立的相繞組。Lesson24ACGeneratorHeatisproducedinthevariouswindingsand

mustberemovedbycooling.Theshaftfandrivesairoverawater-cooledheatexchanger.#各種繞組產(chǎn)生熱量，必須通過冷卻來消除。軸流式風扇驅(qū)動空氣通過水冷式熱交換器。Lesson24ACGeneratorElectricheatersareusedtopreventcondensationonthewindingswhenthealternatorisnotinuse.#當交流發(fā)電機不使用時，電加熱器用于防止繞組上冷凝。Lesson24ACGeneratorInadditiontoauxiliary-engine-drivenalternatorsashipmayhaveashaft-drivenalternator.#除副機驅(qū)動的交流發(fā)電機外，船舶還可配備軸驅(qū)動交流發(fā)電機。Lesson24ACGeneratorInthisarrangementadriveistakenfromthemainengineorthepropellershaftandusedtorotatethealternator.#在這種布置中，驅(qū)動力來自主機或傳動軸，用于旋轉(zhuǎn)交流發(fā)電機。Lesson24ACGeneratorThevariousoperatingconditionsoftheenginewillinevitablyresultinvariationsofthealternatordrivingspeed.#發(fā)動機的各種工作條件將不可避免地導致交流發(fā)電機驅(qū)動速度的變化。Lesson24ACGeneratorAhydraulicpumpandgearboxarrangementmaybeusedtoprovideaconstant-speeddrive,orthealternatoroutputmaybefedtoastaticfrequencyconverter.#液壓泵和齒輪箱配置可用于提供恒速驅(qū)動，或者交流發(fā)電機輸出可饋送至靜態(tài)變頻器。Lesson24ACGeneratorInthestaticfrequencyconvertertheACoutputisfirstrectifiedintoavariableDCvoltageandtheninvertedbackintoathree-phaseACvoltage.#在靜態(tài)變頻器中，交流輸出首先被整流為可變直流電壓，然后再逆變回三相交流電壓。Lesson24ACGeneratorAfeedbacksystemintheoscillatorinverterproducesaconstant-outputACvoltageandfrequency.#振蕩器逆變器中的反饋系統(tǒng)產(chǎn)生恒定的輸出交流電壓和頻率。part3

Exercise&ExaminationTheamountofvoltageinducedinthewindingsofanACgeneratordependson_____.A.thenumberofco