Electrical Machines
In DC machines, the interpoles are provided

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

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Electrical Machines
A dc shunt generator, when commissioned after a major repair of the field system, failed to build Up voltage. It was because

 field winding was wrongly connected
 field system lost residual magnetism
 there was a break in the armature circuit
 field resistance was higher than critical resistance

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Electrical Machines
An inverted V curve of synchronous motor shows variation of

 power factor and supply voltage during hunting.
 supply voltage and excitation current at constant load.
  power factor and DC excitation at constant load.
 supply voltage and field current at constant excitation.

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