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

 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.
 The accuracy in speed control is required.

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Electrical Machines
Flashing the field of DC generator means

  creating residual magnetism by a DC source.
  making the magnetic losses forces parallel.
  neutralising residual magnetism.
 increasing flux density by adding extra turns of winding.

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