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Electrical Engineering Objective Questions { Induction Motors }

330.  For an induction motor, operating at a slip s, the ratio of gross power output to air gap power is equal to
A. ( I ? s)2
B.(1 ?s)
C.I -7s7)
D. (I+s)
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331.  Under no load condition, if the applied voltage to an induction motor is reduced from the rated voltage to half the rated value,
A. the speed decreases and the stator current increases
B. both the speed and the stator current descrease
C. the speed and the stator current remain practically constant
D. there is negligible change in the speed but the stator current decreases
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332.  A three-phase cage induction motor is started by direct-on-line (DOL) switching at the rated voltage. If the starting current drawn is 6 times the full load current, and the full load slip is 4%, the ratio of the starting developed torque to the full load torque is approximately equal to
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333. In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve
A. low starting torque
B. quick acceleration
C. high efficiency
D. reduced size
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334.  In a normal 3-phase slip-ring induction motor, the developed starting torque will
A. increase with the increase in the value of the rotor resistance
B. decrease with the increase in the value of the rotor resistance
C. not depend upon the value of the rotor resistance
D. increase with increase in the value of the rotor resistance upto a certain value and then decrease with further increase in rotor resistance
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335.  A 3-phase induction machine operates on 3-phase fixed frequency ac mains at a per unit slip of 1.5. Consider the following statements regarding the operating condition of the machine 1. It drawn electrical power from the mains. 2. It draws mechanical power through the shaft. 3. It delivers electrical power to the mains. 4. It delivers mechanical power through the shaft. Of these statements :
A. 1 and 2 are correct
B. 1 and 4 are correct
C. 2 and 3 are correct
D. 3 and 4 correct
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336. The magnetising current component of the noload current of an induction motor is much larger than a corresponding transformer because of
A. additional friction and windage loss in motor
B. different winding configurations on stator and rotor
C. increased flux requirement
D. an air-gap in the magnetic circuit
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