Electrical Machines
A 500 V, 55 kVA single phase alternator has an effective resistance of 0.5 Ω. An excitation current of 10 A produces 200 A armature current on short circuit and an emf of 450 V on per circuit. The synchronous reactance will be

  2.241 Ω.
 2.781 Ω.
 2.74 Ω.
 25.564 Ω.

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

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

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Electrical Machines
The armature mmf of a DC machine has

  triangular space distribution and rotates at the speed of armature.
 stepped distribution and rotates at the speed of armature.
  triangular space distribution and is stationary in space.
  trapezoidal space distribution and is stationary in space.

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