Synchronous Motors(Electrical Engineering Questions ) Questions and Answers

Question 1. A synchronous motor can develop synchronous torque:
  1.    when under loaded
  2.    while over-excited
  3.    only at synchronous speed
  4.    below or above synchronous speed
Explanation:-
Answer: Option C. -> only at synchronous speed
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 2. In a synchronous motor, the breakdown torque is__________?
  1.    directly proportional to the square of the applied voltage
  2.    directly proportional to applied voltage
  3.    inversely proportional to applied voltage
  4.    none of the above
Explanation:-
Answer: Option B. -> directly proportional to applied voltage
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 3. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as_________?
  1.    static condenser
  2.    condenser
  3.    synchronous condenser
  4.    none of the above
Explanation:-
Answer: Option C. -> synchronous condenser
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 4. The maximum power developed in a synchronous motor will depend on__________?
  1.    the rotor excitation only
  2.    the supply voltage only
  3.    the rotor excitation and supply volt-age both
  4.    the rotor excitation, supply voltage and maximum value of coupling angle (90°)
  5.    none of the above
Explanation:-
Answer: Option D. -> the rotor excitation, supply voltage and maximum value of coupling angle (90°)
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 5. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then_____________?
  1.    the stator current will be zero
  2.    the stator current will be very small
  3.    the stator current will be very high
  4.    the back e.m.f. will be more than the supply voltage
  5.    none of the above
Explanation:-
Answer: Option A. -> the stator current will be zero
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 6. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as__________?
  1.    locked-rotor torque
  2.    synchronous torque
  3.    pull up torque
  4.    reluctance torque
Explanation:-
Answer: Option A. -> locked-rotor torque
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 7. The coupling angle or load angle of synchronous motor is defined as the angle between the__________?
  1.    rotor and stator teeth
  2.    rotor and the stator poles of opposite polarity
  3.    rotor and the stator poles of the same polarity
  4.    none of the above
Explanation:-
Answer: Option B. -> rotor and the stator poles of opposite polarity
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 8. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will__________?
  1.    stop
  2.    run as induction motor
  3.    function as static condenser
  4.    burn with dense smoke
Explanation:-
Answer: Option A. -> stop
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 9. A synchronous machine with low value of short-circuit ratio has___________?
  1.    lower stability limit
  2.    high stability limit
  3.    good speed regulation
  4.    good voltage regulation
  5.    none of the above
Explanation:-
Answer: Option A. -> lower stability limit
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
Question 10. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as___________?
  1.    pull-up torque
  2.    pull-in torque
  3.    pull-out torque
  4.    none of the above
Explanation:-
Answer: Option B. -> pull-in torque
NO EXPLANATION IS AVAILABLE FOR THIS QUESTION!
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