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

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

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Electrical Machines
Cogging of induction motor occurs at

 low voltage and when stator and rotor poles are equal.
 low voltage and when stator and rotor poles are not equal.
 high voltage and when stator and rotor poles are equal.
 high voltage and when stator and rotor poles are not equal.

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Electrical Machines
The compensating winding in a DC machine

 is located on commutating poles for improving commutation.
  is located on pole shoes for avoiding the flashover at the commutator.
 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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