Realtime Synchronous Motors Multiple choice Questions and Answers pdf

21. If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is
(a) 2 
(b) 3
(c) 4 
(d) 6
Ans: b

22. For V-curves for a synchronous motor the graph is drawn between
(a)    field current and armature current
(b)    terminal voltage and load factor
(c)    power factor and field current
(d)     armature current and power factor
Ans: a

23. The back e.m.f. of a synchronous motor depends on
(a) speed 
(b) load
(c) load angle 
(d) all of the above
Ans: c

24. A synchronous motor can operate at
(a) lagging power factor only
(6) leading power factor only
(c) unity power factor only
(d) lagging, leading and unity power factors
Ans: d

25. In a synchronous motor which loss varies with load ?
(a) Windage loss
(b) Bearing friction loss
(c) Copper loss    
(d) Core loss
Ans: c

26.    A synchronous motor can be made self starting by providing
(a)    damper winding on rotor poles
(b)    damper winding on stator
(c)    damper winding on stator as well as rotor poles
(d)    none of the above
Ans: d

27.    The oscillations in a synchronous motor can be damped out by
(a)     maintaining constant excitation
(b)     running the motor on leading power factors
(c)    providing damper bars in the rotor pole faces
(d)    oscillations cannot be damped
Ans: c

28.    The shaft of synchronous motor is made of
(a) mild steel 
(b) chrome steel
(c) alnico 
(d) stainless steel
Ans: a

29.    When the field of a synchronous motor is under-excited, the power factor will be
(a) leading 
(b) lagging
(c) unity 
(d) zero
Ans: b

30.    The speed regulation of a synchronous motor is always
(a) 1% 
(b) 0.5%
(c) positive 
(d) zero
Ans: d

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