Electrical Machines
Consider the following statements regarding the speed control of dc motors : 1. ward-leonard method is suitable forconstant-torque drives 2. Ward-leonard method is suitable for constant-power drives 3. field-control method facilitates speed control below base speed 4. Armature-resistance control method is more efficient than ward-leanard method 5. Field-control method is suitable for constant-torque drives 6. Armature-resistance control method is suitable for constant-torque drives From these, the correct answer is

 1, 4, 6
 1, 2, 5
 1, 3, 5
 1, 2, 6

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Electrical Machines
In a synchronous motor when the rotor speed exceeds the synchronous speed during hunting

  the damper bars develop induction generator torque.
  the damper bars develop synchronous motor torque.
  the damper bars develop induction motor torque.
  negative sequence currents are generated.

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Electrical Machines
In DC machines, the interpoles are provided

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

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