Electrical Machines
The residual magnetism of a self-excited dc generator is lost. To build up its emf again

 field winding must be excited by low voltage dc supply
 the armature connection must be reversed
 the field winding connection must be reversed
 the field winding must be replaced

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

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