Synchronous Motor Multiple Choice Questions And Answers In English -01

1. The operating speed of a synchronous motor can be changed to a new fixed value by
(A) changing the load
(B) changing the supply voltage
(C) changing frequency
(D) using brakes
Ans: C

2. A synchronous motor will always stop when
(A) supply voltage fluctuates
(B) load in motor varies
(C) excitation winding gets disconnected
(D) supply voltage frequency changes
Ans: C

3.Hunting in a synchronous motor takes place
(A) when supply voltage fluctuates
(B) when load varies
(C) when power factor is unity
(D) motor is under loaded
Ans: B

4. In a synchronous motor which loss varies with load ?
(A) Windage loss
(B) Bearing friction loss
(C) Copper loss
(D) Core loss
Ans: C

5. 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

6. 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

7. 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

8. An over-excited synchronous motor takes
(A) leading current
(B) lagging current
(C) both (A) and (B)
(D) none of the above
Ans: A

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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
Ans: A

15. 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
Ans: C

16. A synchronous motor can be started by
(A) pony motor
(B) D.C. compound motor
(C) providing damper winding
(D) any of the above
Ans: D

17. Synchronous motors are generally not self-starting because
(A) the direction of rotation is not fixed
(B) the direction of instantaneous torque reverses after half cycle
(C) starter cannot be used on these machines
(D) starting winding is not provided on the machines
Ans: B

18. In case one phase of a three-phase synchronous motor is short-circuited the motor will
(A) not start
(B) run at 2/3 of synchronous speed
(C) run with excessive vibrations
(D) take less than the rated load
Ans: A

19. A three-phase synchronous motor will have
(A) no slip-rings
(B) one slip-ring
(C) two slip-rings
(D) three slip-rings
Ans: C

20. 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
Ans: A