small induction motor
D.
series motor C.
double winding A.C./D.C. motor
Answer is Right!
Answer is Wrong!
Synchronous motors
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
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Answer is Wrong!
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
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Answer is Wrong!
54. Which of the following motors will be used in electric clocks ?
D.C. shunt motor
D.
shunt motor B.
A.C. synchronous motor
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Answer is Wrong!
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
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Answer is Wrong!
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 (90°)
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Answer is Wrong!
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
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Answer is Wrong!
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
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Answer is Wrong!
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
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Answer is Wrong!
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
Answer is Right!
Answer is Wrong!