Electrical machine MCQ #8

1) Function of _____ is to collect current from the commutator and supply it to the external load.

      (a) Brushes

      (b) Armature

      (c) Field magnet

      (d) Yoke

2) The brushes are ____ in shape.

      (a) Triangular

      (b) Rectangular

      (c) Square

      (d) Cylindrical

3) Shaft torque equals to

      (a) Net torque

      (b) Net torque – (Friction torque + Torque lost)

      (c) Net torque + Friction torque + Torque lost

      (d) Friction torque

4) The mechanical losses are about _____ % of full load losses.

      (a) 0 to 10

      (b) 30 to 40

      (c) 20 to 30

      (d) 10 to 20

ANSWER: | 1-a | 2-b | 3-b | 4-d |

5) The armature winding of repulsion motor is excited

      (a) Inductively

      (b) Conductively

      (c) Resistively

      (d) None of the above

6) Which of the following parameters contributes to the friction loss in the alternators?

      (a) Temperature

      (b) Lubrication of bearings

      (c) Load variation

      (d) All above parameters

7) Eddy current losses in the alternator are

      (a) Dependent on the load

      (b) Dependent on the excitation

      (c) Independent of the load

      (d) (b) and (c) both

8) The skewing of the rotor bars of the induction motor

      (a) Will increase the induced voltage in each bar to a value more than if the bars were unscrewed

      (b) Will reduce the induced voltage in each bar to a value less than if the base were unscrewed

      (c) Increases the cogging

      (d) Increases the motor noise

ANSWER: | 5-a | 6-d | 7-d | 8-b |

9) If the source voltage of a DC motor is increased, which of the following will decrease?
      (a) Full load current.
      (b) Starting torque
      (c) Starting torque, operating speed, full load current.
      (d) Operating speed.

10) The equation of output voltage of a DC generator is
      (a) E = V + IaRa.
      (b) E = V – IaRa.
      (c) E = V + Ia.
      (d) E = V + Ra.

11) In a DC generator the emf generated by the armature is maximum when
      (a) rate of change of flux is maximum.
      (b) induced voltage is high.
      (c) rate of change of flux is minimum.
      (d) shaft rotation is high.

12) What is the effect of armature reaction?

      (a) Armature flux weakens the main field flux.
      (b) Armature flux distorts the main field flux.
      (c) Both option (a) and (b).
      (d) None of the options.

ANSWER: | 9-c | 10-a | 11-a | 12-c |

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