Polyphase Induction Motors Mcqs
This set of Electrical engineering Multiple Choice Questions & Answers (MCQs) focuses on “Polyphase Induction Motors”. These questions are chosen from a collection of most authoritative and best reference books on Electrical engineering. Our aim is to prepare an individual for competitive exams like NTS, GAT, ECAT, University and College entrance exams, Jobs and interviews. One should practice our MCQS to assimilate Polyphase Induction Motors Mcqs comprehensively.
17. In induction motor, percentage slip depends on__________?
Supply frequency
Supply voltage
Copper losses in motor
None of the above
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18. When /?2 is the rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running conditions will be_____________?
SR2X2 = 1
SR2 = X2
R2 = sX2
R2 = s2X2
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19. In case of a double cage induction motor, the inner cage has__________?
High inductance arid low resistance
Low inductance and high resistance
Low inductance and low resistance
High inductance and high resistance
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20. In an induction motor if air-gap is increased__________?
The power factor will be low
Windage losses will be more
Bearing friction will reduce
Copper loss will reduce In an induction motor
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21. The torque developed by a 3-phase induction motor least depends on__________?
Rotor current
Rotor power factor
Rotor e.m.f.
Shaft diameter
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22. Which motor is preferred for use in mines where explosive gases exist ?
Air motor
Induction motor
D.C. shunt motor
Synchronous motor
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23. Lubricant used for ball bearing is usually___________?
Graphite
Grease
Mineral oil
Molasses
24. The circle diagram for an induction motor cannot be used to determine____________?
Efficiency
Power factor
Frequency
Output
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25. 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
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26. 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
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27. 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
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28. 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
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29. 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
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30. 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
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