Electrical Machines
The compensating winding in a DC machine

  is located on pole shoes for avoiding the flashover at the commutator.
 is located on commutating poles for improving commutation.
 is located in armature slots for compensation of the armature reaction.
  is located on pole shoes to avoid the sparking at the brushes.

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

 The accuracy in speed control is required.
 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.

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