Synchronous motors

11. In a synchronous motor, the armature current has large values for

high excitation only
low excitation only
both high and low excitation
none of the above

Detailed SolutionIn a synchronous motor, the armature current has large values for

12. Riunting in a synchronous motor takes place

When supply voltage fluctuates
When load varies
When power factor is unity
Motor is under loaded

Detailed SolutionRiunting in a synchronous motor takes place

13. In a synchronous motor which loss varies with load ?

Windage loss
Bearing friction loss
Copper loss
Core loss

Detailed SolutionIn a synchronous motor which loss varies with load ?

14. Exciters of synchronous machines are

d.c. shunt machines
d.c. series machines
d.c. compound machines
any of the above

Detailed SolutionExciters of synchronous machines are

15. A synchronous motor can operate at

lagging power factor only
leading power factor only
unity power factor only
lagging, leading and unity power factors

Detailed SolutionA synchronous motor can operate at

16. The shaft of synchronous motor is made of

mild steel
chrome steel
alnico
stainless steel

Detailed SolutionThe shaft of synchronous motor is made of

17. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?

Phase to phase winding resistance
Stator winding to earthed frame
Rotor winding to earthed shaft
All of the above

Detailed SolutionWhich of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?

18. An over excited synchronous motor is used for

Fluctuating loads
Variable speed loads
Low torque loads
Power factor corrections

Detailed SolutionAn over excited synchronous motor is used for

19. The operating speed of a synchronous motor can be changed to new fixed value by

changing the load
changing the supply voltage
changing frequency
using brakes

Detailed SolutionThe operating speed of a synchronous motor can be changed to new fixed value by

20. 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

Detailed SolutionAn important advantage of a synchronous motor over wound round induction motor is that

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