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Electrical Engineering Objective Questions { Induction Motors }

57. 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

58. 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

59. 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

60. 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

61. In an induction increased
A. the power factor will be low
B. windage losses will be more
C. bearing friction will reduce
D. copper loss will reduce

62. When R2 is the rotor resistance, X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under runing condition will be
A. sR2X2 = 1
B. sR2 = X2
C. R2 = sX2
D. R2 = S2X2

63.  The low power factor of induction motor is :him to
A. rotor leakage reactances
B. stator reactance
C. the reactive lagging current necessary to magnetic flux
D. all of the above

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