Latest Synchronous Motors Multiple choice Questions and Answers pdf

51.    A synchronous motor develops maximum power when load angle is
(a) 45° 
(b) 60°
(c) 90° 
(d) 120°
Ans: c

52.    In a synchronous motor, the breakdown torque is
(a)    directly proportional to applied voltage
(b)    directly proportional to the square of the applied voltage
(c)    inversely proportional to applied voltage
(d)    none of the above
Ans: a

53.    Slip-rings in a synchronous motor carry
(a)    direct current
(b)    alternating current
(c)    no current
(d)    all of the above
Ans: a

54.    A synchronous machine with large air gap has
(a)     a higher value of stability limit
(6)     a small value of inherent regulation
(c)    a higher synchronizing power which makes the machine less sensitive to load variations
(d)    all of the above
Ans: d

55.    The armature current of the synchronous motor has higher values for
(a)     high excitation only
(b)     low excitation only
(c)    both (a) and (b)
(d)    none of the above
Ans: c

56.    In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
(a) one-third 
(b) twice
(c) thrice 
(d) six times
(e) nine times
Ans: c

57.    The angle between the rotating stator flux and rotor poles is called _____ angle.
(a) torque
(b) obtuse
(c) synchronizing
(d) power factor
Ans: a

58.    Which of the following methods is used to start a synchronous motor ?
(a)    Damper winding
(b)    Star-delta starter
(c)    Damper winding in conjunction with star-delta starter
(d)    Resistance starter in the armature circuit
Ans: c

59.    When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop
(a)     inductor motor torque
(b)     induction generator torque
(c)    synchronous motor torque
(d)    d.c. motor toque
(e)    none of the above
Ans: b

60.    An important advantage of a synchronous motor over wound round induction motor is that
(a)    its power factor may be varied at will
(b)    its speed is independent of supply frequency
(c)    its speed may be controlled more easily
(d)    none of the above
Ans: a

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