How emf is induced in dc motor?

Answer 1

In brief,in a 3 phase SQIM,there are 3 windings per pole in the stator physically 120 degree apart,each of which is fed from per phase of a balanced 3 phase ac supply.As the magnetic field due to current in each winding varies with time as the current is alternating,the resultant field will be found to keep on changing its direction with time in a circular locus,magnitude being constant because of this setup which can be shown mathematically.Thus a rotating flux of constant mag links the rotor which induces an emf in the rotor,though initially both rotor & stator are static.

Another Answer

A three-phase induction motor is, essentially, a transformer. The 'primary' windings being the stator's field windings, and the 'secondary' winding being the bars of the rotor. For this reason, induction motors are often termed 'rotary Transformers'. So emfs are induced into the bars by 'transformer action'.

Unlike a 'static' transformer, however, the secondary voltages and the frequencies of the voltages vary with the speed of the rotor.

Answer 2

the rotating magnetic field set up in the the stator by poly phase currents is common to both stator and rotor winding. this field induces e.m.fs. in both the windings.

Answer 3

When the field windings are supplied, there is the presence of flux in the windings. The variation of this flux creates an emf that opposes the direction of the flux causing it.