electrical machines mcq

DC Machines MCQ

1. The armature of DC machine is laminated in order to reduce
  1. hysteresis losses
  2. copper losses
  3. frictional losses
  4. eddy current losses
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Answer: 4

2. The yoke of a DC machine is generally made of
  1. silicon steel
  2. cast steel
  3. soft iron
  4. cast steel

Answer: 4

3. If field current is decreased in shunt dc motor, the speed of the motor
  1. increases
  2. decreases
  3. remain same
  4. none of the above

Answer: 1
As a shunt field current If decreases, φ also decreases and the speed rises as speed is inversely proportional to flux

4. In Ward-Leonard system, the lower limit of the speed imposed by
  1. armature resistance
  2. field resistance
  3. residual magnetism of the generator
  4. none of the above

Answer: 3
In Ward-Leonard method of speed control, the lower limit of speed is imposed by residual magnetism of the generator.

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5. Ward-Leonard control is basically a _________________________ control method.
  1. armature resistance control
  2. field control
  3. armature voltage control
  4. field diverter control

Answer: 3
Ward-Leonard speed control method consists a motor with a constant excitation and applying a variable voltage to its armature to provide the required speed. Hence it is armature voltage control method.

6. In a DC Machine, the current flow in a armature circuit is
  1. pulsating DC
  2. pure DC
  3. AC
  4. none of the above

Answer: 3

7. As the armature reaction effect increases, the main flux of DC machine is
  1. increases
  2. decreases
  3. remain same
  4. none of the above

Answer: 2

8. In DC machines, slot wedges are generally made of
  1. cotton
  2. fibre
  3. impregnated paper
  4. silicon steel

Answer: 2

9. Eddy current loss will depends on
  1. flux density
  2. frequency
  3. thickness
  4. all of the above

Answer: 4

10. Hysteresis loss will depends on
  1. f
  2. f1.6

Answer: 1

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