Synchronous motors

41. The oscillations in a synchronous motor can be damped out by

maintaining constant excitation
running the motor on leading power factors
providing damper bars in the rotor pole faces
oscillations cannot be damped

Detailed SolutionThe oscillations in a synchronous motor can be damped out by

42. In a synchronous motor, V-curves represent relation between

armature current and field current
power factor and speed
field current and speed
field current and power factor

Detailed SolutionIn a synchronous motor, V-curves represent relation between

43. 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

Detailed SolutionPower factor of a synchronous motor is unity when

44. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as

locked-rotor torque
synchronous torque
pull up torque
reluctance torque

Detailed SolutionThe maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as

45. The induced e.m.f. in a synchronous motor working on leading power factor will be

more than the supply voltage
less than the supply voltage
equal to the supply voltage
none of the above

Detailed SolutionThe induced e.m.f. in a synchronous motor working on leading power factor will be

46. 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

Detailed SolutionThe armature current of the synchronous motor has higher values for

47. A synchronous machine with low value of short-circuit ratio has

lower stability limit
high stability limit
good speed regulation
good voltage regulation

Detailed SolutionA synchronous machine with low value of short-circuit ratio has

48. The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as

slip torque
pull-out torque
breaking torque
synchronising torque

Detailed SolutionThe maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as

49. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be

3000 r.p.m.
1500 r.p.m.
750 r.p.m.
none of the above

Detailed SolutionIn a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be

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