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1、Electrical MachineryEMF of AC winding EMF of AC winding4.3 EMF of AC winding Rotating magnetic field is base of AC electric machines work,there are two types of rotating magnetic fields in AC electric machine theory.(1)Mechanically rotating magnetic field(2)Electrical rotating magnetic fieldMechanic
2、ally rotating magnetic field can be produced when the prime mover drives the magnetic pole to rotate.Electrical rotating magnetic field can be produced in the space of air gap of the electric machine when alternating current goes through the three phases of AC windings.When the AC winding is in the
3、alternating magnetic field and cuts the rotating field,induced EMF is produced.Analysis of induced EMF in sine magnetic field-take AC generator for instance1.Waveform2.Effective value3.FrequencyConductorCoilCoil assemblyPhase winding4.3 EMF of AC winding 4.3 EMF of AC winding 1.WaveformI.Conductor E
4、MF sectionWhen the number of pole pairs is one,When the number of pole pairs is two,Relation among the number of magnetic pole pairs(p),revolving speed of electric machine(n)and the frequency of induced EMF(f).When the number of pole pairs is p,4.3 EMF of AC winding 2.Electromotive force frequencyI.
5、Conductor EMFConclusion:EMF of a piece of conductor is-fundamental-wave magnetic flux of each pole 4.3 EMF of AC winding 3.Effective valueI.Conductor EMFEffective value of EMF for full-pitch wire turn4.3 EMF of AC winding 1.Full-pitch coilII.Coil EMF4.3 EMF of AC winding 2.short pitch coilI.Conducto
6、r EMF4.3 EMF of AC winding Use electrical angle expressing the pitch of short-pitch coilEffective value of EMF for short-pitch wire turn is fundamental-wave short pitch coefficient of the coil,expressing the decrement rate of induced EMF for the short-pitch coil compared to that for full pitch.Concl
7、usion:for the coil whose turns number is Nc,the effective value of EMF is:I.Conductor EMFEach coil assembly consists of q units of coils,EMF of coil assembly is equal to the sum of EMF vectors of q units of adjacent coils.4.3 EMF of AC winding III.Coil assembly EMF 4.3 EMF of AC winding III.Coil ass
8、embly EMF In the formula,-the algebraic sum of coil EMFs;-Fundamental distribution factor of winding Meaning of Kq1:because windings are laid in different slots,so that the resultant EMF of number q units of distributed coils Eq1 is smaller than the resultant EMF of number q units of centralized coi
9、ls,Et1.So this decrement rate is caused.4.3 EMF of AC winding III.Coil assembly EMF Conclusion:EMF of a coil assembly isIn the formula:qNc-the number of turns of number q units of coils-Fundamental wave distribution factor of windingMeaning of KN1:the total decrement rate required for the resultant
10、EMF of whole the winding when consider short pitch of the winding and also consider winding distribution.4.3 EMF of AC winding For single-layer winding,there is a coil assembly under each pair of poles,the electric machine of p pairs of poles has number p units of coil assemblies in series or parall
11、el.The phase winding composes number a pieces of parallel branches,and EMF of one phase of winding is:IV.Phase EMF and line EMF 4.3 EMF of AC winding For two-layer winding,one coil assembly under each pole,the electric machine of p pairs of poles has 2p coil assemblies in series or parallel.Phase wi
12、nding composes number a parallel branches,and electromotive force of one phase of winding is:IV.Phase EMF and line EMF 4.3 EMF of AC winding Conclusion:for a single-phase winding,the effective value of fundamental EMF is:For single-layer winding:For two-layer winding:Line EMF(Y，)4.3 EMF of AC winding THANKS FOR WATCHING!
