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Engineering
Electrical Engineering
Equivalent circuit of an Induction Motor
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[QUOTE="Babadag, post: 5418974, member: 407262"] The stator currents are regular a.c. currents produced by supplying Vst voltage in stator circuit. This current will produce an “in time variable” magnetic field and then an EMF opposing the supplying voltage. The total variable- static- a.c. magnetic fields produced in each of three phases’ windings behaves as a rotated pole wheel. This common three_ phase rotating field will induce emf in the rotor. The rotor current frequency is direct proportionally with the slip frot=fstator*s. The rotor resistance- never-the-less depends on rotor current frequency as skin effect and thermal effect ,heated by rotor current-could be considered constant. The rotor leakage field reactance depends directly on rotor frequency : Xrots=2*pi()*frot*Lroto=2*pi*f*s*Lroto Lroto=Lrot at s=1 [at start].[It is also an approximation since L depends also on s- for squirrel cage rotor mainly.] In order to simplify the motor diagram, in the rotor circuit we may multiply the rotor resistance and rotor reactance by rotor winding to stator winding factors k^2 where k= kw2/kw1*n2/n1 and to divide the rotor resistance by s and so you can consider the rotor as stator extension and EMFrot/k =EMFst and V'r=Vr/k we get the current I'rot=Irot*k. If we should neglect Rfe and Xm- as easier may consider at a transformer where the no-load current is about 2-3% of the rated but here the no-load current could be 20-30% -we could state Vst=Ist*[(Rs+R'r/s)+j*(Xs+X'r)]. [/QUOTE]
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Engineering
Electrical Engineering
Equivalent circuit of an Induction Motor
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