Electrical machine MCQ #10

1) stray losses are sum of

      (a) copper and mechanical loss

      (b) copper and iron loss

      (c) iron and mechanical loss

      (d) none of these

2) Laminated yoke is DC motor can reduce

      (a) temperature rise

      (b) iron loss

      (c) speed regulation

      (d) sparking on load

3) Which of the following is not a part of DC machine.

      (a) field winding

      (b) commutator

      (c) armature

      (d) damper winding

4) the field coils of DC generator are usually made of

      (a) cast iron

      (b) copper

      (c) mica

      (d) carbon

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

5) the commutator of a DC motor serves the purpose of

      (a) converting DC into AC

      (b) changing AC to DC

      (c) reducing friction

      (d) avoiding arc at the brushes

6) Wave winding is employed in a DC machine of _____ current and _____ voltage rating.

      (a) high, low

      (b) low, high

      (c) high, high

      (d) low, low

7) the basic function of transformer is to change

      (a) the level of the voltage

      (b) the frequency

      (c) the power factor

      (d) the power level

8) the efficiency of power transformer is around

      (a) 50%

      (b) 60%

      (c) 80%

      (d) 95%

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

9) the damper winding is used in synchronous machine to

      (a) help in starting as a motor

      (b) run it as an induction motor

      (c) increase efficiency

      (d) help in starting as a motor and to reduce hunting

10) the effect of armature reaction in synchronous machine depends on

      (a) load current

      (b) power factor of the load

      (c) speed of the machine

      (d) both a and b

11) the iron core in transformer provides a ____ path to the main flux.

      (a) low resistance

      (b) high reluctance

      (c) low reluctance

      (d) high resistance

12) A three phase synchronous motor hunts due to

      (a) fluctuating load

      (b) fluctuating supply voltage

      (c) excessive field current

      (d) either fluctuating load or fluctuating supply voltage

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

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