Electrical Machines
For P pole machine relation between electrical degrees and mechanical degrees is

 θelec = 4/P*θmech
 θelec = P/2*θmech
 θelec = θmech
 θelec = 2/P*θmech

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Electrical Machines
Compensating windings are used in DC generators

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

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