Electrical Machines
Compensating windings are used in DC generators

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

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Electrical Machines
Flashing the field of DC generator means

  making the magnetic losses forces parallel.
  neutralising residual magnetism.
 increasing flux density by adding extra turns of winding.
  creating residual magnetism by a DC source.

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