Electrical Machines
Compensating windings are used in DC generators

  to neutralize the cross magnetizing effect of the armature reaction.
None of these
  to provide path for the circulation of cooling air.
  mainly to reduce the eddy currents by providing local short circuit.

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

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

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