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

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

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Electrical Machines
Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will

  rotate in the same direction as before maintenance.
  not start at all.
  get heated and damaged.
  rotate in direction opposite to that before maintenance.

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Electrical Machines
If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)

 changes to 1.5 times the original value
 changes to three times the original value
 changes to 0.5 times the original value
 remain the same as the original

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