新版轮机英语unit28-paralleling-operation-of-alternators

Lesson28Paralleloperationofgenerators•(发电机的并联运行)Threephasesalternatorsarrangedforparalleloperationrequireaconsiderableamountofinstrumentations(仪表）.Thiswillincludeammeters,wattmeter,voltmeter,frequencymeterandasynchronizingdevice(同步装置).Reversepowerprotection(逆功率保护)isprovidedtoalternatorssincecurrentprotectioncannotbeused.Alternativelyvarioustrips(跳闸机构)maybeprovidedintheeventofprimemoverfailuretoensurethatthealternatordoesnotactasamotor.Theoperationofparallelingtwoalternatorsrequiresthevoltagestobeequalandalsoinphase（同相）.Thealternatingcurrentoutputofanymachineisalwayschanging,sofortwomachinestooperatetogethertheirvoltagesmustbechangingatthesamerateorfrequency,mustbereachingtheirmaximum(oranyothervalue)together.Theyarethensaidtobe‘inphase’.（同相）Useisnowadaysmadeofasynchroscope(同步指示器)whenparallelingtwoa.c.machines.Thesynchroscopehastwowindings(绕组)whichareconnectedonetoeachsideoftheparallelingswitch（联络开关）.Apointer(指针)isfreetorotateandismovedbythemagneticeffect(磁效应）ofthetwowindings.Whenthetwovoltagesuppliesareinphasethepointerisstationary（固定的，静止的）inthe12o’clockposition.Ifthepointerisrotatingthenafrequencydifferenceexistsandandthedial（表盘，刻度盘）ismarkedforclockwiserotationFASTandanti-clockwiserotationSLOW,thereferencebeingtotheincomingmachinefrequency.Toparallelanincomingmachinetoarunningmachinethereforeitisnecessarytoensurefirstlythatbothvoltagesareequal.Voltmetersareprovidedforthispurpose.Secondlythefrequenciesmustbebroughtintophase.InpracticethesynchroscopeusuallymovesslowlyintheFASTdirectionandparallelingswitchisclosed（合闸）asthepointerreachesthe11o’clockposition.Thisresultsintheincomingmachineimmediatelyacceptingasmallamountofload.Asetofthreelampsmayalsobeprovidedtoenablesynchronizing（同步操作）.Thesequencemethodoflampconnectionhasakeylampconnectedacrossonephasewiththetwootherlampscrossconnectedovertheothertwophases.Ifthefrequenciesofthemachinesaredifferentthelampswillbrightenanddarkeninrotation,dependingupontheincomingfrequencybeingFASTorSLOW.Thecorrectmomentforsynchronizingiswhenthekeylampisdarkandtheothertwoareequallybright.Theprocedureforparallelinga440-volt3phaseA.C.generatorwithanothergeneratoronthelinewasasfollows:1.Seethatthegeneratorcircuitbreaker(发电机断路器）andfieldswitch(励磁开关iffurnished)areopen（断开）.2.Seethatfieldrheostathandle（磁场电阻手柄）issettocutinallthefieldresistance.rheostat（可变电阻器）3.Makesurethatthevoltageregulatorcontrolswitch(iffinished)isturnedtothemanualposition.4.Makesurethatthemanualvoltagecontrolissetatthepositionthatgivesthelowestgeneratorvoltage.5.Makesurethatbothprimemoverandelectricalendsareexaminedforevidenceofobstruction（阻碍物）tomovingparts.6.Seethattheoilreservoirforoilringlubricatedbearings（油环润滑的轴承）containstherightamountofoilasindicatedbytheoilsightglass（观察镜）.7.Seethattheunitisstartedandbroughtuptospeedinaccordancewiththeinstructionsforthetypeofprimemoverused.Besurethattheoverspeedgovernorandtrip（断路器）andallothersafetydevicesaretestedandfunctioningasrequiredbytheseinstructions.8.Checkthelubricationofbearings,checkoilandbearingtemperatures.9.Seethatthecollectrings（汇流环）runtrue,thatallbrushesridefreely（安放良好）inthebrushholders,andthatthereisnochattering（咔嗒声）ofbrushes.10.Fortotallyenclosedmachineswithcoolers,seethatthewaterisflowingthroughthecooler,anddeterminethatthereisnoleakageofwater.Shuttheheatersoff(iffurnished)11.Bringthegeneratoruptoapproximatelynormalspeed.Closethefieldswitch（励磁开关）andbringthevoltageuptoapproximatelynormalandplacethevoltageregulatorincontrol.12.Turnthevoltmeterswitchontheincominggeneratortoindicatethegeneratorvoltageonthevoltmeter.13.Turnthevoltmeterswitchontheadjacentgeneratorpaneltoindicatethebusvoltage.14.Turnthevoltageadjustingrheostatofthevoltageregulatoruntiltheincominggeneratorvoltageisequaltothebusvoltage.15.Comparethefrequencyoftheincominggeneratorwiththatofthebusandadjusttocorrespondwiththebusfrequency.16.Turnthesynchroscope（同步表）switchtotheONposition.Thesynchroscopewillrotateinonedirectionortheother.Adjustthespeedofthegeneratorbymeansofthegovernormotorcontrolswitchuntilthesynchroscoperotatesveryslowlyintheclockwisedirection.17.Becertainthatthevoltagesofthebusandtheincominggeneratorarestillequal,andclosethegeneratorcircuitbreaker（合闸）justbeforethesynchroscopepointerpassesveryslowlythroughthezeroposition(pointingverticallyupwards).Whenthesynchronizinglampsareusedinsteadofthesynchroscope,closethecircuitbreakerjustbeforethemidpoint（中点，正中央）ofthedarkperiodofthelampsisreached.Themidpointofthedarkperiodcorrespondstotheverticalpositionofthesynchroscopepointer.18.TurnthesynchronizingswitchtotheOFFposition.19.AdjustthegeneratorssothatthekilowattandthereactiveKVAload（无功功率）isdividedevenly（均匀的）betweenthem.