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MCQs

Total Questions : 395 | Page 2 of 40 pages
Question 11. Power factor of a synchronous motor is unity when
  1.    the armature current is maximum
  2.    the armature current is minimum
  3.    the armature current is zero
  4.    none of the above
 Discuss Question
Answer: Option B. -> the armature current is minimum
Question 12. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
  1.    3000 r.p.m.
  2.    1500 r.p.m.
  3.    750 r.p.m.
  4.    none of the above
 Discuss Question
Answer: Option B. -> 1500 r.p.m.
Question 13. Which of the following motors is non-self starting ?
  1.    D.C. series motor
  2.    synchronous motor
  3.    Squirrel cage induction motor
  4.    Wound round induction motor
 Discuss Question
Answer: Option B. -> synchronous motor
Question 14. Which of the following losses, in a synchronous motor, does not vary with load?
  1.    Windage loss
  2.    Copper losses
  3.    Any of the above
  4.    None of the above
 Discuss Question
Answer: Option A. -> Windage loss
Question 15. Stability of a synchronous machine
  1.    decreases with increase in its excitation
  2.    increases with increase in its excitation
  3.    remains unaffected with increase in excitation
  4.    any of the above
 Discuss Question
Answer: Option B. -> increases with increase in its excitation
Question 16. Which of the following methods is used to start a synchronous motor ?
  1.    Damper winding
  2.    Star-delta starter
  3.    Damper winding in conjunction with star-delta starter
  4.    Resistance starter in the armature circuit
 Discuss Question
Answer: Option C. -> Damper winding in conjunction with star-delta starter
Question 17. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
  1.    Eddy current losses in the conductors
  2.    Iron losses in the stator
  3.    Copper losses in the slot portion of the conductors
  4.    Windage losses
 Discuss Question
Answer: Option D. -> Windage losses
Question 18. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
  1.    Phase to phase winding resistance
  2.    Stator winding to earthed frame
  3.    Rotor winding to earthed shaft
  4.    All of the above
 Discuss Question
Answer: Option D. -> All of the above
Question 19. A synchronous motor working at leading power factor can be used as
  1.    voltage booster
  2.    phase advancer
  3.    noise generator
  4.    mechanical synchronizer
 Discuss Question
Answer: Option B. -> phase advancer
Question 20. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of
  1.    zero degree
  2.    two degrees
  3.    five degrees
  4.    ten degrees
 Discuss Question
Answer: Option C. -> five degrees

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