DESIGN OF TRANSFORMER

1 DESIGN OF INDUCTION MOTOR1 Construction of Induction MotorTheACinductionmotorcomprisestwoelec tromagneticparts: Stationarypartcalledthestator RotatingpartcalledtherotorThestatorandth erotorareeachmadeupof Anelectriccircuit,usuallymadeofinsulated copperoraluminiumwinding,tocarrycurrent Amagneticcircuit,usuallymadefromlaminate dsiliconsteel,tocarrymagneticflux23 StatorThestatoristheouterstationaryparto fthemotor,whichconsistsof: Theoutercylindricalframeofthemotororyoke ,whichismadeeitherofweldedsheetsteel,cas tironorcastaluminiumalloy. Themagneticpath, ,reducinglossesandheating. Asetofinsulatedelectricalwindings, ,3setsofwindingsarerequired, , squirrelcage .Aluminiumrotorbarsareusuallydie-castint otherotorslots, , ,are: Twoend-flangestosupportthetwobearings,on eatthedriving-endandtheotheratthenondriv ing-end,wherethedrivingendwillhavethesha ftextension.

2 Twosetsofbearingstosupporttherotatingsha ft, Steelshaftfortransmittingthemechanicalpo wertotheload. Coolingfanlocatedatthenondrivingendtopro videforcedcoolingforthestatorandrotor Terminalboxontopoftheyokeoronsidetorecei vetheexternalelectricalconnections8 Cut sectional view of the induction motor9 Introduction to :Thearmaturediameter(statorbore) :TotalMagneticLoading:thetotalfluxaround thearmature(orstator) TotalElectricLoading:thetotalnumberofamp ereconductorsaroundthearmature(orstator) : :thenumberofarmature(orstator)amperecond uctorspermeterofarmature(orstator) EquationLetVph=phasevoltage;Iph=phasecur rentZph=noofconductors/phase;Tph=nooftur ns/phaseNs=Synchronousspeedinrpm;ns=sync hronousspeedinrpsp=noofpoles;ac=Specific electricloadingФ=airgapflux/pole;Bav=Ave ragefluxdensityKw=windingfactor; =efficiencyD=Diameterofthestator.

3 L=GrosscorelengthCo=Outputcoefficient;co s =powerfactor14 Consideran m phasemachine,withusualnotationsOutputQin kW=InputxefficiencyInputtomotor=mVphIphc os *10-3kWFora3 machinem=3 Inputtomotor=3 VphIphcos *10-3kWAssumingVph=Eph,Vph=Eph= ФTphKw= ФZphKwf=PNS/120=P*ns/215PФ=Bav DL,and3 IphZph/ D=acOutputtomotor= *Bav DL* Dac*nsKw cos *10-3kWQ=( 2 BavacKw cos *10-3)D2 LnskWQ=(11 BavacKw cos *10-3)D2 LnskWThereforeOutputQ=CoD2 LnskWwhereCo=(11 BavacKw cos *10-3)= :overloadcapacityincreasewithincreaseinf luxdensityLimitations:Fluxdensityinteeth < Sizeofthemachinereduced Costofthemachinedecreases of ,voltageofstatorwinding, (L/ ) ) ) ) ) ( D/p)/L= ( D/p) :ingeneraltwotypesofstatorslotsareemploy edininductionmotorsviz, (i) , (ii)Semiclosedslots.

4 Insuchtypeofslots, (iii)Taperedslots:Inthistypeofslotsalso, Design21 Selectionofnumberofstatorslots:Numberofs tatorslotsmustbeproperlyselectedatthedes ignstageassuchthisnumberaffectstheweight , , :(i)Reducedleakagereactance.(ii)Reducedt oothpulsationlosses.(iii) :(i)Increasedcost(ii)Increasedweight(iii )Increasedmagnetizingcurrent(iv)Increase dironlosses(v)Poorcooling(vi)Increasedte mperaturerise(vii)ReductioninefficiencyT henumberofslots/ ss= D/SsswhereSssisthenumberofstatorslots23 Turnsperphase:EMFequationofaninductionmo torisgivenbyEph= ФTphKwHenceturnsperphasecanbeobtainedfro memfequationTph= ФmKwGenerallytheinducedemfcanbeassumedto beequaltotheappliedvoltageperphaseFlux/p ole,Фm=Bav* DL/p, ,Zph=2xTph,andhenceTotalnumberofstatorco nductorsZ=6*Tphandconductors/slotZs=Z/Ss or6*Tph/Ss24 swhere sisthecurrentdensityinstatorwindingsStat orcurrentperphaseIs=Q/(3 Vphcos ) :(i)reductionincrosssection(ii)reduction inweight(iii)reductionincost25 Disadvantagesofhighervalueofcurrentdensi ty.

5 (i)increaseinresistance(ii)increaseincul oss(iii)increaseintemperaturerise(iv) , :Lengthofthemeanturniscalculatedusingfor mulaLmt=2L+ + Фc= ФAreaofstatorcoreAc=Фc/2 BcAreaofstatorcoreAc=LixdcsHence,depthof thecore(dcs)=Ac/Li=Фc/2Bc*LiUsingthedesi gndataobtainedsofarouterdiameterofthesta torcorecanbecalculatedasDo=D+2(depthofst atorslots+depthofcore)=D+2dss+ , ,powerfactor,overloadcapacity, , , of Air-gap29 ,theleakagefluxisreduced, :-thetoothpulsationlosses,whichisproduce dduetovariationinreactanceoftheairgap, :(i)Increasedoverloadcapacity(ii)Increas edcooling(iii)Reducedunbalancedmagneticp ull(iv)Reducedintoothpulsation(v)Reduced noiseDisadvantages(i)IncreasedMagnetisin gcurrent(ii)ReducedpowerfactorMagnetisin gcurrentandpowerfactorbeingveryimportant parametersindecidingtheperformanceofindu ctionmotors, +2 DLmm31 DESIGN of Squirrel Cage , :Therotatingmagneticfieldproducedintheai rgapwillbeusuallynonsinusoidalandgeneral lycontainsoddharmonicsoftheorder3rd, , :Thenumberofrotorslotsmaybeselectedusing thefollowingguidelines.

6 (i)Toavoidcoggingandcrawling:(a)Ss Sr(b)Ss-Sr 3P(ii)Toavoidsynchronoushooksandcuspsint orquespeedcharacteristicsSs-Sr P,2P,5P.(iii)TonoisyoperationSs-Sr 1,2,(P 1),(P 2) (statormmf)Numberofrotorbars=Nb=Sr=numbe rofrotorslotsRotorbarcurrent=IbRotormmf= ( )orIb= *(6*Is*Ts/Sr)34 bmm2 (i)Astherotorslotisclosedtherotorsurface issmoothattheairgapandhencethemotordraws lowermagnetizingcurrent.(ii)reducednoise astheairgapcharacteristicsarebetter(iii) increasedleakagereactanceand(iv)reduceds tartingcurrent.(v)Overloadcapacityisredu ced(vi) +allowanceforskewingRotorbarresistance= , , (max)=(Numberofbarsoverhalfapolepitch)Ib (av)=Sr/2P*[2/ *Ib(max)]=(Sr*Ib(max))/ PrmsvalueofbarcurrentIb=Ib(max)/ 2Ie(max)=(Sr*Ib* 2)/ PrmsvalueofendringcurrentIe=Ie(max)/ 2Ie=(Sr*Ib)/ emm2Ae=te*dewhrete=thicknessofendringand de=depthofendring37 DESIGN of wound , , , (KwrxTr)/(KwsxTs)Hencerotorturnsperphase Tr=(Er/Es)(Kws/Kwr)TsEr=opencircuitrotor voltage/phaseEs=statorvoltage/phaseKws=w indingfactorforstatorKwr=windingfactorfo rrotorTs=Numberofstatorturns/phase39 RotorCurrentandconductorsectionAssumingr otormmf= * ( ) ( ) rThecurrentdensitycouldbetakenas3to5A/mm 240 Noloadcurrent.

7 Thenoloadcurrentofaninductionmotorhastwo componentsmagnetizingcomponent,Imandiron losscomponent, (Im)2+(Iw)2 ,statorteeth,airgap, *AT60/( )wherep noofpairsofpoles,AT30 Totalampereturnsofthemagneticcircuitat60 0fromthecentreofthepole,Tph (3xphasevoltage) 0=Iw/I042 :i)Magnetizingcurrent:alargevalueofthema gnetizingcurrentindicatespoorpowerfactor ii)Idealshortcircuitcurrent(Isc) , =Im/Isci=Im/(Es/Xs)Isci=Es/Xs= , *AT60/( )WhereAT60isthetotalmmfconsumedbyfluxpat h, * *Bavl gIm P*Bavl ,machineagivenLandD,thedispersioncoeffic ientislargeforgraternumberofpoles, :AsshownincirclediagramOA=magnetizingcur rentOB=idealshortcircuitcurrentDispersio ncoefficient: =OA/OBFormaximumpowerfactorODistangentto thecircleand ODC=90o45 For = , = , :Assuming,aninductionmotorisdesignedtoha vemaximumpfatfullload, = =