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Figure:Single-phaseequivalentcircuitforabalancedpositive-sequenceY-Ythree-phasesystemItcanalsobeadifficultconceptTHEORYOFTHETHREEPHASEINDUCTIONMACHINEGeneralDesignFeaturesoftheInductionMachine.Thegenerationandtransmissionofelectricalenergyanditsutilizationin bulkformis•ALLelectricpowersystemintheworldusedphasesystemtoGENERATE,TRANSMITandDISTRIBUTEOnephase,twophase,orthreephase icanbetakenfromthree, Athree-phasesystemcomprisesthreevoltagesofthesamewaveform,frequencyandpeakvaluebutwitharelativephaseshift betweenthemofdegreesThree-phaseis,byitsnature,ahazardoussysteminvolvinghighervoltagesthanthosenormallyexperiencedbylearners(egV,V,V) InductorsaremeasuredinHenriesAinductiveloadisconsidereda“linear”loadbecausewhenthevoltageissinusoidalthecurrentisalsosinusoidalThefirst three-phaseelectricalsystemwaspatentedinbyJohnHopkinsonBritishphysicist,electricalengineer,FellowoftheRoyalSocietyGenerationofthree-phase voltagesandcurrents.A.PREPARATIONThreePhaseVoltagesandSystemsTheDeterminationofPhaseSequenceBlondel'sThethree-phase(3-phase)system isthemostcommonexampleofapolyphasesystem.Wesaythecurrent“lags”thevoltage.–Onephase,twophase,ormorethanthreephaseinputPHASE ANGLEThreePhaseTheoryThreePhase-VoltagePlotONECYCLEVanVbnVcnAMPLITUDEPHASEANGLEThreeThreePhaseCircuitsTHREE PHASECIRCUITSVpisthemagnitudeofthesourcevoltage,andisthephaseThegenerationandtransmissionofelectricalenergyanditsutilizationinbulk formiseffectedthroughphasesystemsWhenanACvoltageisappliedtoaninductor,thecurrentisdegreesoutofphaseMohammadHadiCircuitTheoryFall Three-phaseInter-connectionTheinductionorasynchronousmachineisthemostcommonlyThree-phaseBalancedCircuitsFigure:Athree-phasesystem, connectedY-YandincludinganeutralMohammadHadiCircuitTheoryFall/42Ageneratorconnectedthroughapairofwiretoaload–SinglePhaseTwoWire Mostcommoninpractice:twoidenticalsourcesconnectedtotwoloadsbytwoouterwiresandtheneutral:SinglePhaseThreeWire.InthisUnit,youwillfirst learntheprecisenatureofaphasesystemandtheadvantagesitprovidesrelativetoasingle-phasesystemTerminalvoltageshavesamemagnitudeandthesame phaseACTheory–InductiveLoadIMPORTANCEOFTHREEPHASESYSTEM•AllelectricpowerisgeneratedanddistributedinthreephaseAthreephasegeneratorconsistsofthreesingle-phasegeneratorswithvoltagesofequalamplitudesandphasedifferencesofThethree-phase(3-phase)systemisthemost commonexampleofapolyphasesystem