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
Cogging and crawling are phenomena associated with

 any of the above.
 cage induction machines and they are essentially the same.
 the former at a fraction of its rate speed and the latter during starting.
 the former during starting and the latter at a fraction of its rated speed.

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