Electrical Machines
Compensating windings are used in DC generators

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

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Electrical Machines
In a loaded DC generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

 improve with rise in terminal voltage.
 improve with fall of terminal voltage.
 deteriorate with rise in terminal voltage.
 deteriorate with fall of terminal voltage.

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