Hiried Synchronous Motors Multiple choice Questions and Answers pdf

31.    The percentage slip in case of a synchronous motor is
(a) 1%
(b) 100%
(c) 0.5%
(d) zero
Ans: d

32.    The operating speed of a synchronous motor can be changed to new fixed value by
(a) changing the load
(b) changing the supply voltage
(c) changing frequency
(d) using brakes
Ans: c

33.    A synchronous motor will always stop when
(a) supply voltage fluctuates
(b) load in motor varies
(c) excitation winding gets disconnected
(d) supply voltage frequency changes
Ans: c

34.    riunting in a synchronous motor takes place
(a)    when supply voltage fluctuates
(b)    when load varies
(c)    when power factor is unity
(d)    motor is under loaded
Ans: b

35.    When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is
(a) more
(b) less
(c) equal
(d) twice
Ans: b

36.    The rotor copper losses, in a synchronous motor, are met by
(a) d.c. source
(b) armature input
(c) motor input   
(d) supply lines
Ans: a

37.    The maximum power developed in a synchronous motor occurs at a coupling angle of
(a) 30°
(b) 60°
(c) 90°
(d) 180°
Ans: c

38.    When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor
(a)    remains same as the original value
(b)    decreases to half the original value
(c)    tends to becomes zero
(d)     increases to two times the original value
Ans: d

39.    In which of the following motors the stator and rotor magnetic field rotate at the same speed ?
(a)    Universal motor
(b)    Synchronous motor
(c)     Induction motor
(d)    Reluctance motor
Ans: b

40.    Synchronsizingpower of a synchronous machine is
(a) direcly proportional to the synchronous reactance
(6) inversely proportional to the synchronous reactance
(a) equal to the synchronous reactance
(d) none of the above
Ans: b

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