Synchronous motors Archives - Page 3 of 10 - MCQ and Quiz for Exams

21. If load (or torque) angle of a 4-pole synchronous motor is 6Â° electrical, its value in mechanical degrees is

2

3

4

6

Detailed SolutionIf load (or torque) angle of a 4-pole synchronous motor is 6Â° electrical, its value in mechanical degrees is

22. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on

load on the motor

d.c. excitation only

both the speed and rotor flux

none of the above

Detailed SolutionIn a synchronous motor, the magnitude of stator back e.m.f. Eb depends on

23. 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

Detailed SolutionThe mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of

24. When the field of a synchronous motor is under-excited, the power factor will be

leading

lagging

unity

zero

Detailed SolutionWhen the field of a synchronous motor is under-excited, the power factor will be

25. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

the motor is said to be fully loaded

the torque generated is maximum

the excitation is said to be zero per cent

the excitation is said to be hundred per cent

Detailed SolutionIn a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

26. 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

Detailed SolutionWhich of the following methods is used to start a synchronous motor ?

27. Slip-rings in a synchronous motor carry

direct current

alternating current

no current

all of the above

Detailed SolutionSlip-rings in a synchronous motor carry

28. A synchronous motor develops maximum power when load angle is

45Â°

60Â°

90Â°

120Â°

Detailed SolutionA synchronous motor develops maximum power when load angle is

29. 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

Detailed SolutionWhen the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected

30. 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

Detailed SolutionThe minimum armature current of the synchronous motor corresponds to operation at

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