TOP Synchronous Motors Multiple choice Questions and Answers pdf

11.    A synchronous motor can be used as a synchronous capacitor when it is
(a) under-loaded 
(b) over-loaded
(c) under-excited 
(d) over-excited
Ans: d

12.    A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
(a) power factor as well as armature current will decrease
(b) power factor as well as armature current will increase
(c) power factor will increase but armature current will decrease
(d) power factor will decrease and armature current will increase
Ans: d

13.    Mostly, synchronous motors are of
(a) alternator type machines
(6) induction type machines
(c) salient pole type machines
(d) smooth cylindrical type machines
Ans: c

14.    The synchronous motor is not inherently self-starting because
(a) the force required to accelerate the rotor to the synchronous speed in an instant is absent
(b) the starting device to accelerate the rotor to near synchronous speed is absent
(c) a rotating magnetic field does not have enough poles
(d) the rotating magnetic field is produced by only 50 Hz frequency currents
Ans: a

15.    As the load is applied to a synchronous motor, the motor takes more armature current because
(a)     the increased load has to take more current
(b)     the rotor by shifting its phase backward causes motor to take more current
(c)    the back e.m.f. decreases causing an increase in motor current
(d)    the rotor strengthens the rotating field casuing more motor current
Ans: b

16.    Synchronous motor always runs at
(a)     the synchronous speed
(b)     less than synchronous speed
(c)    more than synchronous speed
(d)    none of the above
Ans: a

17.    An over-excited synchronous motor takes
(a)    leading current
(b)    lagging current
(c)    both (a) and (b)
(d)     none of the above
 Ans: a

18. The working of a synchronous motor is similar to
(a)    gear train arrangement
(b)    transmission of mechancial power by shaft
(c)    distribution transformer
(d)    turbine
(e)    none of the above
Ans: b

19. The minimum armature current of the synchronous motor corresponds to operation at
(a)    zero power factor leading
(b)    unity power factor
(c)    0.707 power factor lagging
(d)    0.707 power factor leading
Ans: b

20. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on
(a)    d.c. excitation only
(b)    speed of the motor
(c)    load on the motor
(d)    both the speed and rotor flux
Ans: a

Read More Questions:
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