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MCQs 1: The torque developed by a 3-phase induction motor least depends on__________?

rotor current rotor power factor rotor e.m.f. shaft diameter
Answer Explanation

MCQs 2: Which motor is preferred for use in mines where explosive gases exist ?

Air motor Induction motor D.C. shunt motor Synchronous motor
Answer Explanation

MCQs 3: Lubricant used for ball bearing is usually___________?

graphite grease mineral oil molasses
Answer Explanation

MCQs 4: The circle diagram for an induction motor cannot be used to determine____________?

efficiency power factor frequency output
Answer Explanation

MCQs 5: Blocked rotor test on induction motors is used to find out?

leakage reactance power factor on short circuit short-circuit current under rated voltage all of the above
Answer Explanation

MCQs 6: The complete circle diagram of induetion motor can be drawn with the help of data found from__________?

noload test blocked rotor test stator resistance test all of the above
Answer Explanation

MCQs 7: In the squirrel-cage induction motor the rotor slots are usually given slight skew__________?

to reduce the magnetic hum and locking tendency of the rotor to increase the tensile strength of the rotor bars to ensure easy fabrication none of the above
Answer Explanation

MCQs 8: The torque of a rotor in an induction motor under running condition is maximum__________?

at the unit value of slip at the zero value of slip at the value of the slip which makes rotor reactance per phase equal to the resistance per phase at the value of the slip which makes the rotor reactance half of the rotor
Answer Explanation

MCQs 9: What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero ?

The slip of the motor will be 5% The rotor will not run The rotor will run at very high speed The torque produced will be very large
Answer Explanation

MCQs 10: The stating torque of the slip ring induction motor can be increased by adding__________?

external inductance to the rotor external resistance to the rotor external capacitance to the rotor both resistance and inductance to rotor
Answer Explanation

MCQs 11: 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__________?

0.01 0.02 0.03 0.04
Answer Explanation

MCQs 12: The power scale of circle diagram of an induction motor can be found from__________?

stator resistance test no-load test only short-circuit test only none of the above
Answer Explanation

MCQs 13: A change of 4% of supply voltage to an induction motor will produce a change of approximately ________?

4% in the rotor torque 8% in the rotor torque 12% in the rotor torque 16% in the rotor torque
Answer Explanation

MCQs 14: The shape of the torque/slip curve of induction motor is__________?

parabola hyperbola rectangular parabola straigth line
Answer Explanation

MCQs 15: The vafcie of transformation ratio of an induction motor can be found by__________?

open-circuit test only short-circuit test only stator resistance test none of the above
Answer Explanation

MCQs 16: In a three-phase induction motor__________?

power factor at starting is high as compared to that while running power factor at starting is low as compared to that while running power factor at starting in the same as that while running
Answer Explanation

MCQs 17: In three-phase induction motors sometimes copper bars are placed deep in the rotor to___________?

improve starting torque reduce copper losses improve efficiency improve power factor
Answer Explanation

MCQs 18: Which is of the following data is required to draw the circle diagram for an induction motor ?

Block rotor test only No load test only Block rotor test and no-load test Block rotor test, no-load test and stator resistance test
Answer Explanation

MCQs 19: In case of 3-phase induction motors, plugging means__________?

pulling the motor directly on line without a starter locking of rotor due to harmonics starting the motor on load which is more than the rated load interchanging two supply phases for quick stopping
Answer Explanation

MCQs 20: In a three-phase induction motor_______________?

iron losses in stator will be negligible as compared to that in rotor iron losses in motor will be neg¬ligible as compared to that in rotor iron losses in stator will be less than that in rotor iron losses in stator will be more than that in rotor
Answer Explanation

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