Electrical Machines
Compensating windings are used in DC generators

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

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Electrical Machines
Ward-Leonard system for controlling the speed of a DC motor is used where

 The speed in both the direction is required.
 Very fine speed control over the whole range from zero to normal speed is required.
 All of above.
 The accuracy in speed control is required.

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