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Electrical Engineering Objective Questions { Synchronous Motors }

43. In case one phase of a three-phase synchronous motor is short-circuited, the motor will
A. not start
B. run at ? of synchronous speed
C. run with excessive vibrations
D. take less than the rated load

44. A pony motor is basically a
A. small induction motor
B. D.C. series motor
C. D.C. shunt motor
D. double winding A.C./D.C. motor

45. A synchronous motor can develop synchronous torque
A. when under loaded
B. while over-excited
C. only at synchronous speed
D. below or above synchronous speed

46. A synchronous motor can be started by
A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above

47. A three-phase synchronous motor will have
A. no slip-rings
B. one slip-ring
C. two slip-rings
D. three slip-rings

48. Under which of the following conditions hunting of synchronous motor is likely to occur?
A. Periodic variation of load
B. Over-excitation
C. Over-loading for long periods
D. Small and constant load

49. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
A. the motor stops
B. it runs as a reluctance motor at the same speed
C. it runs as a reluctance motor at a lower speed
D. none of the above

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