Synchronous motors Archives - Page 6 of 10 - MCQ and Quiz for Exams

51. A pony motor is basically a

small induction motor

D.

series motor C.

double winding A.C./D.C. motor

Detailed SolutionA pony motor is basically a

52. If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then

it runs at a slower speed

the motor stops

it continues to run at the same speed

it runs at a very high speed

Detailed SolutionIf the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then

53. 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

Detailed SolutionUnder which of the following conditions hunting of synchronous motor is likely to occur ?

54. Which of the following motors will be used in electric clocks ?

D.C. shunt motor

D.

shunt motor B.

A.C. synchronous motor

Detailed SolutionWhich of the following motors will be used in electric clocks ?

55. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have

no change of power factor

lagging power factor with over-excitation

leading power factor with under-excitation

leading power factor with over-excitation

Detailed SolutionA synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have

56. The maximum power developed in a synchronous motor will depend on

the rotor excitation only

the supply voltage only

the rotor excitation and supply volt-age both

the rotor excitation, supply voltage and maximum value of coupling angle (90Â°)

Detailed SolutionThe maximum power developed in a synchronous motor will depend on

57. In a synchronous motor, the damping winding is generally used to

prevent hunting and provide the starting torque

reduce the eddy currents

provide starting torque only

reduce noise level

Detailed SolutionIn a synchronous motor, the damping winding is generally used to

58. If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor

become more

become less

remain constant

none of the above

Detailed SolutionIf in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor

59. In case one phase of a three-phase synchronous motor is short-circuited the motor will

Not start

Run at $$rac{2}{3}$$ of synchronous speed

Run with excessive vibrations

Take less than the rated load

Detailed SolutionIn case one phase of a three-phase synchronous motor is short-circuited the motor will

60. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

Speed of the motor is reduced

Power factor is decreased

Eb (back e.m.f.) becomes less than V (applied voltage)

Er (net resultant voltage) in armature is increased

Detailed SolutionA synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

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