Synchronous Motors Quiz practies questions test1

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1. Synchronous motors are generally not self-starting because ______.
the direction of rotation is not fixed	the direction of instantaneous torque reverses after half cycle
startes cannot be used on these machines	starting winding is not provided on the machines

2. In case one phase of a three-phase synchronous motor is short-circuited the motor will ______.
not start	run at 2/3 of synchronous speed
run with excessive vibrations	take less than the rated load

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

4. A synchronous motor can develop synchronous torque _____.
when under loaded	while over-excited
only at synchronous speed	below or above synchronous speed

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

6. A three-phase synchronous motor will have _____.
no slip-rings	one slip-ring
two slip-rings	three slip-rings

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

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

9. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as _____.
V	V312
V2	1/V

10. The power developed by a synchronous motor will be maximum when the load angle is _____.
zero	45°
90°	120°

11. A synchronous motor can be used as a synchronous capacitor when it is ______.
under-loaded	over-loaded
under-excited	over-excited

12. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased _____.
power factor as well as armature current will decrease	power factor as well as armature current will increase
power factor will increase but armature current will decrease	power factor will decrease and armature current will increase

13. Mostly, synchronous motors are of _____.
alternator type machines	induction type machines
salient pole type machines	smooth cylindrical type machines

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

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

16. Synchronous motor always runs at _____.
the synchronous speed	less than synchronous speed
more than synchronous speed	none of the above

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

18. The working of a synchronous motor is similar to _____.
gear train arrangement	transmission of mechancial power by shaft
distribution transformer	turbine

19. The minimum armature current of the synchronous motor corresponds to operation at _____.
zero power factor leading	unity power factor
0.707 power factor lagging	0.707 power factor leading

20. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on _____.
d.c. excitation only	speed of the motor
load on the motor	both the speed and rotor flux