Electrical Machines
Commutator in DC generator is used for

 convert AC armature current in to DC
 reduce losses
 collecting of current
 increase efficiency

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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.
 All of above.
 Very fine speed control over the whole range from zero to normal speed is required.

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