Electrical Machines
For the speed control of polyphase squirrel cage induction motor, if frequency of operation is decreased with

None of these
 constant V, Tst increases
 constant supply voltage V, starting torque Tst decreases
 either of these

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Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 dc machines are comparatively low rating machines.
 it reduces field structure iron losses
 commutator action is not possible otherwise
 it gives more uniform air-gap flux distribution

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Electrical Machines
In DC machines, the interpoles are provided

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

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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, 2, 5
 1, 3, 5
 1, 4, 6
 1, 2, 6

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