Most recently Synchronous Motors Multiple choice Questions and Answers pdf

41.    Synchronous motors are
(a)     not-self starting
(b)    self-starting
(c)    essentially self-starting
(d)    none of the above
Ans: a

42.    The  standard full-load power factor ratings for synchronous motors are
(a)     zero or 0.8 leading
(b)     unity or 0.8 lagging
(c)    unity or 0.8 leading
(d)    unity or zero
Ans: c

43.    A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
(a) back e.m.f.
(b) armature current
(c) power factor   
(d) torque angle
Ans: b

44.    A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
(a)    synchronous motor has no slip
(b)    stator supply is not required to produce magnetic field
(c)    mechanical load on the rotor remains constant
(d)    synchronous motor has large airgap
Ans: b

45.    A synchronous motor working at leading power factor can be used as
(a)     voltage booster
(b)     phase advancer
(c)    noise generator
(d)    mechanical synchronizer
Ans: b

46.    Slip rings are usually made of
(a)    carbon or graphite
(b)    brass or steel
(c)    silver or gold
(d)    copper or aluminium
Ans: b

47.    An over excited synchronous motor is used for
(a)    fluctuating loads
(b)    variable speed loads
(c)    low torque loads
(d)      power factor corrections
Ans: d

48.    When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
(a)     Stator flux 
(b)     Pull in torque
(c)    Both (a) and (b)
(d)    None of the above
 Ans: d

49.    The efficiency of a properly designed synchronous motor will usually fall in range
(a) 60 to 70% 
(6) 75 to 80%
(c) 85 to 95% 
(d) 99 to 99.5%
Ans: c

50.    To limit the operating temperature an electrical machine should have proper
(a) voltage rating
(b) current rating
(c) power factor   
(d) speed
Ans: b

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