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

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

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Electrical Machines
Interpoles in a DC motor must be

 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.

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