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

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

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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, 3, 5
 1, 4, 6
 1, 2, 6
 1, 2, 5

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