Tricky Synchronous Motors Multiple choice Questions and Answers pdf

101.    In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
(a)    the motor is said to be fully loaded
(b)    the torque generated is maximum
(c)    the excitation is said to be zero per cent
(d)    the excitation is said to be hundred per cent
Ans: d

102.    In a synchronous motor, the damping winding is generally used to
(a)    prevent hunting and provide the starting torque
(b)    reduce the eddy currents
(c)    provide starting torque only
(d)    reduce noise level
(e)    none of the above
Ans: a

103.    If the field of a synchronous motor is underexcited, the power factor will be
(a) zero 
(b) unity
(c) lagging 
(d) leading
Ans: c

104.    The back e.m.f. in the stator of a synchronous motor depends on
(a)    number of poles
(b)    flux density    
(c)     rotor speed
(d)    rotor excitation
(e)    none of the above
Ans: d

105.   The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as
(a)     slip torque 
(b)     pull-out torque
(c)    breaking torque
(d)    synchronising torque
Ans: d

106.    In a synchronous motor, the armature current has large values for
(a)    high excitation only
(b)    low excitation only
(c)    both high and low excitation
(d)    none of the above
Ans: c

107.    Which of the following losses, in a synchronous motor, does not vary with load?
(a) Windage loss 
(b) Copper losses
(c) Any of the above
(d) None of the above
Ans: a

108.    The size of a synchronous motor decreases with the increase in
(a)    flux density
(b)    horse power rating
(c)    speed
(d)    all of the above
Ans: a

109.    Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
(a)    Eddy current losses in the conductors
(b)    Iron losses in the stator
(c)    Copper losses in the slot portion of the conductors
(d)    Windage losses
(e)    None of the above
Ans: d

110.    The duration of sudden snort-circuit test on a synchronous motor is usually about
(a)     one hour 
(b)     one minute
(c)    one second
(d)    none of the above
Ans: c

Read More Questions:
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