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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Electrical Machines
Compensating windings are used in DC generators

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

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Electrical Machines
For satisfactory parallel operation of two transformers which of the following conditions is most essential,

 voltage ratio of all transformers must be same.
  polarities of all transformers must be same.
 percentage impedance of all transformers must be same.
 MVA rating of all transformer inversely proportional to impedance.

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