Polyphase Induction Motors(Electrical Engineering ) Questions and Answers

Question 1. Which is of the following data is required to draw the circle diagram for an induction motor?
  1.    Block rotor test only
  2.    No load test only
  3.    Block rotor test and no-load test
  4.    Block rotor test, no-load test and stator resistance test
Explanation:-
Answer: Option D. -> Block rotor test, no-load test and stator resistance test
Question 2. The stating torque of the slip ring induction motor can be increased by adding
  1.    External inductance to the rotor
  2.    External resistance to the rotor
  3.    External capacitance to the rotor
  4.    Both resistance and inductance to rotor
Explanation:-
Answer: Option B. -> External resistance to the rotor
Question 3. The starting torque of a three phase induction motor can be increased by
  1.    Increasing slip
  2.    Increasing current
  3.    Both (A) and (B)
  4.    None of the above
Explanation:-
Answer: Option C. -> Both (A) and (B)
Question 4. Slip rings are usually made of
  1.    Copper
  2.    Carbon
  3.    Phosphor bronze
  4.    Aluminium
Explanation:-
Answer: Option C. -> Phosphor bronze
Question 5. Rotor rheostat control method of speed control is used for
  1.    Squirrel-cage induction motors only
  2.    Slip ring induction motors only
  3.    Both (A) and (B)
  4.    None of the above
Explanation:-
Answer: Option B. -> Slip ring induction motors only
Question 6. 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 7. 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 8. 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 9. 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 10. 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
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