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Electrical Engineering Objective Questions { Induction Motors }

316.  A 3 phase squirrel cage induction motor has a full load efficiency of 0.8 and a maximum efficiency of 0.9. It is operated at a slip of 0.6 by applying a reduced voltage. The efficiency of the motor at this operating point is
A. less than 0.4
B. greater than 0.6
C. in the range of 0.8 + 0.1
D. none of the above
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317. A 3-phase, 4-pole squirrel cage induction motor has 36 stator and 28 rotor slots. The number of phases in the rotor is
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318. The power input to a 415V, 50Hz, 6 pole, 3-phase induction motor running at 975 rpm is 40 kW. The stator losses are 1 kW and friction and windage losses total 2 kW. The efficiency of the motor is
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319.  A three phase, wound rotor induction motor is to be operated with slip energy recovery in the constant torque mode, when it delivers an output power Po at slip s. Then theoretically, the maximum power that is available for recovery at the rotor terminals, is equal to '
A. 1 HP
B. 2 HP
C. 4 HP
D. 10 HP
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320. 1f a 400V, 50Hz, star connected, 3 phase squirrel cage induction motor is operated from a 400V, 75iiz Fupply, the torque that the motor can now provide while drawing rated current from the supply?
A. reduces
B. increases
C. remains the same
D. increase or reduces depending upon the rotor resistance
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321. The rotor of a three phase, 5 kW, 400V, 50Hz, slip ring induction motor is wound for 6 poles while its stator is wound for 4 poles. The approximate average no load steady state speed when this motor is connected to 400V, 50Hz supply is
A. 1500 rpm
B. 500 rpm
C. 0 rpm
D. 1000 rpm
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322.  Group I lists different applications and Group II lists the motors for these applications. Match the application with the most suitable motor and choose the right combination among the choices given thereafter P Food mixer I. Permanent magnet dc motor Q Cassette tape 2. Single-phase induction recorder motor R Domestic water 3. Universal motor pump S Escalator 4. Three-phase induction motor 5. DC series motor 6. Stepper motor
A. P-3, Q-6, R-4, S-5
B. P-1, Q-3, R-2, S-4
C. P-3, Q-1, R-2, S-4
D. P-3, Q-2, R-1, S-4
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