MarineEngineeringEnglish《輪機(jī)英語(yǔ)》APracticalCourseforEngineersWorkingonBoardShips

MarineElectricalSystemandAutomatizationLesson24ACGenerator

第24課交流發(fā)電機(jī)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(shè)施的標(biāo)準(zhǔn)電源。Lesson24ACGeneratorTheuseofalternatingcurrenthasanumberofimportantadvantages:forexample,reducedfirstcost,lessweight,lessspacerequiredandareductioninmaintenancerequirements.#使用交流電有許多重要的優(yōu)點(diǎn)：例如，降低了初始成本、重量、所需空間和維護(hù)要求。Lesson24ACGeneratorDirectcurrentdoes,however,offeradvantagesinmotorcontrolusing,forexample,theWard-Leonardsystemwhichprovidesawiderangeofspeed.#然而，直流電確實(shí)在電機(jī)控制方面具有優(yōu)勢(shì)，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(jī)工作原理9Alternatingcurrentgenerator交流發(fā)電機(jī)工作原理Lesson24ACGeneratorAcoilofwirerotatinginamagneticfieldproducesacurrent.#線圈在磁場(chǎng)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?？吭谛D(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(chǎng)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(lì)磁線圈”，正如其所稱的那樣串聯(lián)在外電源上，或發(fā)電機(jī)的輸出端上。Lesson24ACGeneratorIfseparatecoilsorconductorsareusedthenseveraloutputscanbeobtained.#如果使用單獨(dú)的線圈或?qū)Ь€，就可獲得多個(gè)輸出。Lesson24ACGeneratorThreeoutputsareusuallyarrangedwithaphaseseparationof120°,toproduceathreephasesupply.#三個(gè)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(duì)于相同的(輸入)機(jī)械功，可獲得較大的電力輸出。Lesson24ACGeneratorEachofthethreeoutputsmaybeusedinsinglephasesuppliesorinconjunctionforathreephasesupply.#三個(gè)輸出中的每一個(gè)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(jī)上有四個(gè)滑環(huán)。Lesson24ACGeneratorThethreeconductorsarejoinedatacommonslipringandalsohavetheirindividualslipring.#三根導(dǎo)線連在一個(gè)共用的滑環(huán)上，同時(shí)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(jī)的三個(gè)滑環(huán)，各滑環(huán)接有兩相線。Lesson24ACGeneratorAsinglephasesupplycanbetakenfromanytwosliprings.#單相電可以從任何兩個(gè)滑環(huán)上獲取。Lesson24ACGeneratorSofar,alternatorconstructionhasconsideredthearmaturerotatingandthefieldcoilsstationary.#至今，發(fā)電機(jī)結(jié)構(gòu)均采用電樞旋轉(zhuǎn)而磁場(chǎng)不動(dòng)。Lesson24ACGeneratorThesameelectricitygeneratingeffectisproducedifthereverseoccurs,thatis,thefieldcoilsrotateandthearmatureisstationary.#反之，若磁場(chǎng)旋轉(zhuǎn)而電樞不動(dòng)，也會(huì)產(chǎn)生同樣的效果。Lesson24ACGeneratorThisisinfactthearrangementadoptedforlarge,heavydutyalternators.#這種設(shè)計(jì)實(shí)際上已被承擔(dān)重要任務(wù)的大型發(fā)電機(jī)采用。Lesson24ACGeneratorThefieldcurrentsupplyinoldermachinescomesfromalowvoltagedirectcurrentgeneratororexciteronthesameshaftasthealternator.#老式發(fā)電機(jī)，勵(lì)磁電流來自低壓直流發(fā)電機(jī)或與交流發(fā)電機(jī)同軸的勵(lì)磁器。Lesson24ACGeneratorModernmachineshoweverareeitherstaticallyexcitedorofthehighspeedbrushlesstype.#然而，現(xiàn)代發(fā)電機(jī)不是靜態(tài)勵(lì)磁型的就是高速無刷型的。Lesson24ACGeneratorTheexciterisrequiredtooperatetocountertheeffectsofpowerfactorforagivenload.#要求勵(lì)磁機(jī)在運(yùn)行時(shí)能抵消給定負(fù)荷下的功率因數(shù)的影響。Lesson24ACGeneratorThepowerfactorisameasureofthephase,differencebetweenvoltageandcurrentandisexpressedasthecosineofthephaseangle.#功率因數(shù)是對(duì)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(duì)于純電阻負(fù)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(fù)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(fù)載的發(fā)電機(jī)因負(fù)載而產(chǎn)生壓降。Lesson24ACGeneratorWhentheloadhasalaggingpowerfactorthisvoltagedropisconsiderable.#當(dāng)負(fù)載具有滯后功率因數(shù)時(shí)，此壓降是相當(dāng)大的。Lesson24ACGeneratorThereforetheexciter,inmaintainingthealternatorvoltage,mustvarywiththeloadcurrentandalsothepowerfactor.#因此，勵(lì)磁器在保持發(fā)電機(jī)電壓的過程中，(其勵(lì)磁電流)必須隨著負(fù)載電流和功率因數(shù)的變化而變化。Lesson24ACGeneratorThespeedchangeoftheprimemovermustalsobetakenintoaccount.#還需考慮原動(dòng)機(jī)轉(zhuǎn)速變化。Lesson24ACGeneratorHandcontrolofexcitationisdifficultsouseismadeofanautomaticvoltageregulator(AVR).#手控勵(lì)磁較難，因此采用自動(dòng)電壓調(diào)節(jié)器。Lesson24ACGeneratorTheAVRconsistsbasicallyofacircuitfedfromthealternatoroutputvoltagewhichdetectssmallchangesinvoltageandfeedsasignaltoanamplifierwhichchangestheexcitationtocorrectthevoltage.#自動(dòng)電壓調(diào)節(jié)器基本上由一個(gè)經(jīng)發(fā)電機(jī)輸出電壓供電的電路組成，該電路能檢測(cè)電壓的微小變化，輸出一個(gè)信號(hào)給放大器以改變勵(lì)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(dòng))或過調(diào)現(xiàn)象。Lesson24ACGeneratorVariousdesignsofAVRareinusewhichcanbebroadlydividedintoclassessuchascarbonpiletypes,magneticamplifiers,electronictypes,etc.Lesson24ACGeneratorThestaticallyexcitedalternatorhasastaticexcitationsysteminsteadofaDCexciter.#靜止勵(lì)磁交流發(fā)電機(jī)有靜止勵(lì)磁系統(tǒng)，代替直流勵(lì)磁機(jī)。Lesson24ACGeneratorThistypeofalternatorwillmorereadilyacceptthesuddenloadingbydirecton-linestartingoflargesquirrelcagemotors.#這種類型的交流發(fā)電機(jī)能較好地承受由大型鼠籠式電機(jī)直接帶載起動(dòng)而造成的沖擊負(fù)荷。Lesson24ACGeneratorThestaticexcitationsystemusestransformersandrectifierstoprovideseriesandshuntcomponentsforthealternatorfield,thatis,itiscompounded.#靜止勵(lì)磁系統(tǒng)使用變壓器和整流器，為交流發(fā)電機(jī)磁場(chǎng)產(chǎn)生一個(gè)串勵(lì)和并勵(lì)分量，也就是說，它是復(fù)勵(lì)的。53他勵(lì)：他勵(lì)發(fā)電機(jī)的勵(lì)磁電流fieldcurrent

是由獨(dú)立的電源供給，不受發(fā)電機(jī)的

電壓和電流的影響。自勵(lì)：自勵(lì)發(fā)電機(jī)的勵(lì)磁電流是由發(fā)電機(jī)的

電樞armature電路供給，因而勵(lì)磁電流

受電樞電流和電壓的影響。自勵(lì)又分為：并勵(lì)shunt串勵(lì)series

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

housesthepoleswhichprovidethefieldcurrent,andtheseareusuallyofthesalientorprojecting-poletype.#交流發(fā)電機(jī)的結(jié)構(gòu)如圖24-3所示。轉(zhuǎn)子包含提供磁場(chǎng)電流的磁極，通常為凸極式。Lesson24ACGeneratorSlipringsandafanarealsomountedontherotorshaft,whichisdrivenbytheauxiliaryengine.Thestatorcoresurroundstherotorandsupportsthethreeseparatephasewindings.#滑環(huán)和風(fēng)扇也安裝在由副機(jī)驅(qū)動(dòng)的轉(zhuǎn)子軸上。定子鐵芯包圍轉(zhuǎn)子并支撐三個(gè)獨(dú)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(fēng)扇驅(qū)動(dòng)空氣通過水冷式熱交換器。Lesson24ACGeneratorElectricheatersareusedtopreventcondensationonthewindingswhenthealternatorisnotinuse.#當(dāng)交流發(fā)電機(jī)不使用時(shí)，電加熱器用于防止繞組上冷凝。Lesson24ACGeneratorInadditiontoauxiliary-engine-drivenalternatorsashipmayhaveashaft-drivenalternator.#除副機(jī)驅(qū)動(dòng)的交流發(fā)電機(jī)外，船舶還可配備軸驅(qū)動(dòng)交流發(fā)電機(jī)。Lesson24ACGeneratorInthisarrangementadriveistakenfromthemainengineorthepropellershaftandusedtorotatethealternator.#在這種布置中，驅(qū)動(dòng)力來自主機(jī)或傳動(dòng)軸，用于旋轉(zhuǎn)交流發(fā)電機(jī)。Lesson24ACGeneratorThevariousoperatingconditionsoftheenginewillinevitablyresultinvariationsofthealternatordrivingspeed.#發(fā)動(dòng)機(jī)的各種工作條件將不可避免地導(dǎo)致交流發(fā)電機(jī)驅(qū)動(dòng)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(dòng)，或者交流發(fā)電機(jī)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