Electrical Machines
The basic function of a transformer is to change

 the power level
 the power factor
 the frequency
 the level of the voltage

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

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

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