Important Multiple choice questions For competitive Exams on Three Phase Induction motor
20 Most Important 3-phase Induction Motor Multiple Choice Questions with explanation
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1. The Outer frame of an induction motor is usually made of
Cast iron
Aluminum
Bronze
Silicon steel
Correct Answer
Wrong Answer
2. In an induction motor, no-load the slip is generally
5%
Less than 1%
2%
4%
Correct Answer
Wrong Answer
3. The shaft of an induction motor is made of
Stainless steel
Carbon steel
Aluminium
Cast iron
Correct Answer
Wrong Answer
4. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be
50 Hz
5 Hz
25 Hz
2 Hz
Correct Answer
Wrong Answer
5. The starting torque of a squirrel-cage induction motor is
Full-load torque
Negligible
Slightly more than full-load torque
Low
Correct Answer
Wrong Answer
6. The efficiency of an induction motor is about
80-90%
100%
50-60%
Less than 50%
Correct Answer
Wrong Answer
7. A double squirrel-cage induction motor has
Two series winding in stator
Two parallel windings in stator
Two parallel winding in Rotor
Two rotors moving in opposite direction
Correct Answer
Wrong Answer
8. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as
Humming
Hunting
Cogging
Crawling
Correct Answer
Wrong Answer
9. In a three-phase induction motor, the number of poles in the rotor winding is always
Equal to the number of poles in the stator
Less than the number of poles in the stator
More than the number of poles in the stator
Zero
Correct Answer
Wrong Answer
10. Which of the following motor has high starting torque?
Squirrel cage induction motor
Slip ring Induction motor
Both 1 & 2
None of the above
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Correct Answer
Wrong Answer
11. At standstill condition the value of slip is
Infinity
0
One
None of the above
Correct Answer
Wrong Answer
12. The condition for maximum running torque is
R= S × X/2
R = X/2
R =X
R =X × S
Correct Answer
Wrong Answer
13. The condition for maximum starting torque is
R = S × X/2
R = X/2
R = X × S
R = X
Correct Answer
Wrong Answer
14. Rotor resistance speed control method is not applicable in
Slip Ring induction motor
Squirrel cage induction motor
Synchronous motor
None of the above
Correct Answer
Wrong Answer
15. As compared to DOL starting method the star delta starting method should have
High torque
Low starting current
High starting current
Smooth acceleration
Correct Answer
Wrong Answer
16. If the terminal voltage of an induction motor is decreased then current
Decreased
Increased
Remain same
None of the above
Correct Answer
Wrong Answer
17. The maximum EMF is induced in the rotor of a 3-phase induction motor when it
No-Load
Full-load
Half-load
is blocked
Correct Answer
Wrong Answer
18. The power supplied to a three-phase induction motor is 32 kW and the stator losses are 1200 Watt. If the slip is 5 percent. determine the rotor copper loss
2.8 kW
1.54 kW
3.5 kW
4 kW
Correct Answer
Wrong Answer
19. The reactance of the rotor circuit of a 3-phase induction motor is maximum at
Full load
Half Load
Half Full load
Starting
Correct Answer
Wrong Answer
20. At no-load, the Iron loss of a 3-phase induction motor is
Practically Zero
Large
Small
None of the above
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