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

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Electrical Machines
An ideal synchronous motor has no starting torque because

 rotor winding is highly reactive.
  relative velocity between stator and rotor mmf’s is not zero.
 rotor is made up of salient poles.
 relative velocity between the stator and rotor mmf’s is zero.

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Electrical Machines
In a DC generator, the armature reaction results in

  demagnetization of leading & magnetization of trailing pole tip.
 magnetization of leading and demagnetization of trailing pole tip.
  magnetization of inter poles.
 demagnetization of centers of poles.

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Electrical Machines
Compensating windings are used in DC generators

  to neutralize the cross magnetizing effect of the armature reaction.
None of these
  to provide path for the circulation of cooling air.
  mainly to reduce the eddy currents by providing local short circuit.

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