Electrical Machines
The mmf produced by rotor currents of a 3 - Φ induction motor

  rotates at synchronous speed with respect to rotor.
  rotates at slip speed with respect to stator mmf.
  is at standstill with respect to stator mmf.
  rotates at the speed of rotor in the air gap.

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Electrical Machines
In DC machines, the interpoles are provided

  both (B) and (C).
  to make commutation spark less.
 to counteract demagnetizing effect of armature mmf in commutating zone.
 to counteract the reactance voltage and the cross-magnetizi

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