Polyphase Induction Motors(Engineering > Electrical Engineering ) Questions and Answers

Question 1. The complete circle diagram of induction motor can be drawn with the help of data found from
  1.    No-load test
  2.    Blocked rotor test
  3.    Stator resistance test
  4.    All of the above
Explanation:-
Answer: Option D. -> All of the above
Question 2. An induction motor with 1000 r.p.m. speed will have
  1.    8 poles
  2.    6 poles
  3.    4 poles
  4.    2 poles
Explanation:-
Answer: Option B. -> 6 poles
Question 3. Less maintenance troubles are experienced in case of
  1.    Slip ring induction motor
  2.    Squirrel cage induction motor
  3.    Both (A) and (B)
  4.    None of the above
Explanation:-
Answer: Option B. -> Squirrel cage induction motor
Question 4. As load on an induction motor goes on increasing
  1.    Its power factor goes on decreasing
  2.    Its power factor remains constant
  3.    Its power factor goes on increasing even after full load
  4.    Its power factor goes on increasing up to full load and then it falls again
Explanation:-
Answer: Option D. -> Its power factor goes on increasing up to full load and then it falls again
Question 5. The frame of an induction motor is usually made of
  1.    Silicon steel
  2.    Cast iron
  3.    Aluminium
  4.    Bronze
Explanation:-
Answer: Option B. -> Cast iron
Question 6. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be
  1.    200 Hz
  2.    50 Hz
  3.    2 Hz
  4.    0.2 Hz
Explanation:-
Answer: Option C. -> 2 Hz
Question 7. DOL starting of induction motors is usually restricted to
  1.    Low horsepower motors
  2.    Variable speed motors
  3.    High horsepower motors
  4.    High speed motors
Explanation:-
Answer: Option A. -> Low horsepower motors
Question 8. In induction motor, percentage slip depends on
  1.    Supply frequency
  2.    Supply voltage
  3.    Copper losses in motor
  4.    None of the above
Explanation:-
Answer: Option C. -> Copper losses in motor
Question 9. The speed of a squirrel-cage induction motor can be controlled by all of the following except
  1.    Changing supply frequency
  2.    Changing number of poles
  3.    Changing winding resistance
  4.    Reducing supply voltage
Explanation:-
Answer: Option C. -> Changing winding resistance
Question 10. Reduced voltage starter can be used with
  1.    Slip ring motor only but not with squirrel cage induction motor
  2.    Squirrel cage induction motor only but not with slip ring motor
  3.    Squirrel cage as well as slip ring induction motor
  4.    None of the above
Explanation:-
Answer: Option C. -> Squirrel cage as well as slip ring induction motor
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