Synchronous Motors free Model online Quiz Test2

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1. Synchronous motors are _____.
not-self starting	self-starting
essentially self-starting	none of the above

2. The standard full-load power factor ratings for synchronous motors are ______.
zero or 0.8 leading	unity or 0.8 lagging
unity or 0.8 leading	unity or zero

3. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in ______.
back e.m.f.	armature current
power factor	torque angle

4. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because _____.
synchronous motor has no slip	stator supply is not required to produce magnetic field
mechanical load on the rotor remains constant	synchronous motor has large airgap

5. A synchronous motor working at leading power factor can be used as ______.
voltage booster	phase advancer
noise generator	mechanical synchronizer

6. Slip rings are usually made of _____.
carbon or graphite	brass or steel
silver or gold	copper or aluminium

7. An over excited synchronous motor is used for _____.
fluctuating loads	variable speed loads
low torque loads	power factor corrections

8. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
Stator flux	Pull in torque
Both (a) and (b)	None of the above

9. The efficiency of a properly designed synchronous motor will usually fall in range
60 to 70%	75 to 80%
85 to 95%	99 to 99.5%

10. To limit the operating temperature an electrical machine should have proper ______.
voltage rating	current rating
power factor	speed

11. Slip-rings in a synchronous motor carry _____.
direct current	alternating current
no current	all of the above

12. A synchronous machine with large air gap has _____.
a higher value of stability limit	a small value of inherent regulation
a higher synchronizing power which makes the machine less sensitive to load variations	all of the above

13. The armature current of the synchronous motor has higher values for ______.
high excitation only	low excitation only
both (a) and (b)	none of the above

14. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately ______.
one-third	twice
thrice	six times

15. The angle between the rotating stator flux and rotor poles is called _____ angle.
torque	obtuse
synchronizing	power factor

16. Which of the following methods is used to start a synchronous motor ?
Damper winding	Star-delta starter
Damper winding in conjunction with star-delta starter	Resistance starter in the armature circuit

17. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop _____.
inductor motor torque	induction generator torque
synchronous motor torque	d.c. motor toque

18. An important advantage of a synchronous motor over wound round induction motor is that _______.
its power factor may be varied at will	its speed is independent of supply frequency
its speed may be controlled more easily	none of the above

19. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of ______.
zero degree	two degrees
five degrees	ten degrees

20. Power factor of a synchronous motor is unity when ______.
the armature current is maximum	the armature current is minimum
the armature current is zero	none of the above

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