Synchronous Motors PART 6
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Attempt Free Synchronous Motors PART 6 Here. Read The Important Electrical MCQ From Below.
76. The curve for 20 k W is expected to be
(A) A
(B) B
(C) C
(D) D.
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77. In a synchronous motor hunting can be minimized
(A) by using damper bars
(B) by using a flywheel
(C) by designing the motor for adequate synchronizing power
(D) by any of the above methods.
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Synchronous Motors PART 6
78. A three phase 400 V, 50 Hz synchronous motor is working at 50 percent load. In case an increase in the field current of the motor causes a reduction in the armature current, it can be concluded that
(A) the motor is delivering reactive power to the mains
(B) the motor is absorbing reactive power to the mains
(C) the motor is neither absorbing nor delivering reactive power.
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79. Inverted V-curves for a synchronous motor show
(A) Variation of power factor with dc field current when load on the motor remains constant
(B) Variation of field current and supply voltage when excitation remains constant
(C) Variation of power factor and supply voltage when motor is hunting
(D) none of the above.
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80. The armature current of the synchronous motor has large values for
(A) low excitation only
(B) high excitation only
(C) both low and high excitation.
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81. In which range the cost of a synchronous motor can be comparable to the cost of a induction motor ?
(A) Low HP high speed
(B) High HP low speed
(C) High HP high speed
(D) Low HP low speed.
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82. Insulation resistance test on synchronous motor can be conducted to measure which of the following resistances?
(A) Stator winding to earthed frame
(B) Rotor winding to earthed shaft
(C) Phase to phase winding resistance
(D) All of the above.
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Synchronous Motors PART 6
83. Which curve represents the open circuit characteristic of a synchronous motor
(A) Curve A
(B) Curve B
(C) Curve C
(D) Curve D.
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84. During short circuit test which of the following is short circuited ?
(A) Armature terminals
(B) One of the phase windings of stator
(C) AH phase windings of stator
(D) All phase windings of stator and armature.
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85. The duration of sudden short circuit test on a synchronous motor is usually
(A) about one second
(B) about one minute
(C) about one hour
(D) 40 minutes.
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Synchronous Motors PART 6
86. The maximum torque which a synchronous will develop at rest for any angular positions of the rotor, at rated stator supply voltage and frequency, is known as
(A) Reluctance torque
(B) Synchronous torque
(C) Locked-rotor torque
(D) Pull up torque.
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87. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
(A) Synchronous torque
(B) Pull in torque
(C) Pull up torque
(D) Pull out torque.
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88. The maximum sustained torque which a synchronous motor will develop at synchronous
speed for 1 mm with rated frequency and rated field current is known as
(A) Pull out torque
(B) Reluctance torque
(C) Synchronous torque
(D) Average torque.
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Synchronous Motors PART 6
89. The total steady state to drive synchronous motor and the load at synchronous speed is known as
(A) Synchronous torque
(B) Asynchronous torque
(C) Reluctance torque
(D) Pull-up torque.
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90. The space angle between the axis of the stator revolving magnetic field and the rotor-pole axis, both looked and
running at synchronous speed, is known as
(A) angle of lead
(B) power angle
(C) power factor angle
(D) reactive power angle.
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