Monday, September 14, 2020

Chapter 8: Induction Motor-Page 6

  Chapter 8: Induction Motor

51. The stating torque of the slip ring induction motor can be increased by adding
A. external inductance to the rotor
B. external resistance to the rotor
C. external capacitance to the rotor
D. both resistance and inductance to rotor

... Answer is (B)



52. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be

... Answer is (D)


53. The complete circle diagram of induction motor can be drawn with the help of data found from
A. no-load test
B. blocked rotor test
C. stator resistance test
D. all of the above

... Answer is (D)



54. The torque of a rotor in an induction motor under runing condition is maximum
A. at the unit value of slip
B. at the zero value of slip
C. at the value of the slip which makes rotor reactance per phase
D. at the value of the slip which makes the rotor reactance half of the rotor resistance

  ... Answer is (C)


55. What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero?
A. The slip of the motor will be 5%
B. The rotor will not run
C. The rotor will run at very high specd
D. The torque produced will be be very large
Answer is (B)


56. In a three-phase induction motor
A. power factor at starting is high as compared to that while running
B. power factor at starting is low as compared to that while running
C. power factor at starting in the same as that while running
D. power factor remains through out constant

  ... Answer is (B)



57. Insertion of resistance in the rotor of an induction motor to develop a given torque
A. decreases the rotor current
B. increases the rotor current
C. rotor current becomes zero
D. rotor current reamins same

... Answer is (D)


58. For driving high inertia loads best type of induction motor suggested is
A. slip ring type
B. squirrel cage type
C. any of the above
D. none of the above

... Answer is (A)


59. Temperature of the stator winding of a three-phase induction motor is obtained by
A. resistance rise method
B. thermometer method
C. embedded temperature method
D. all above methods

  ... Answer is (D)


60. The purpose of using short-circuit gear is
A. to short circuit the rotor at slip rings
B. to short circuit the starting resistances in the starter
C. to short circuit the stator phase of motor to form star
D. none of the above

  ... Answer is (A)



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