Quiz-3 based on Three phase Induction machines ,Electrical Engineering ( Subject -ELECTRICAL MACHINES)
Hello students,this is the practice Quiz -3 for You Related with Electrical Machines Subject Hope this is beneficial for your practice work.
Manisha tyagi
1
154
1. In squirrel cage rotor, bars are usually brazed to the end rings. The end rings are used to
Prevent rotor leakage current
Give reduced starting torque
Provide good mechanical strength
All of these
Correct Answer
Wrong Answer
2. Slots of squirrel cage rotor are generally skewed to
Reduce magnetic hum
Reduce magnetic locking
Make motor operation smooth
All of these
Correct Answer
Wrong Answer
3. The wound rotor induction motor gives
high stating torque
moderate starting torque
reduced starting torque
all of these
Correct Answer
Wrong Answer
4. The slip ring or wound rotor induction motor find its applications in
lifts, cranes
lathes
drilling machines
printing machines
Correct Answer
Wrong Answer
5. For the speed control of squirrel cage induction motor, the most suitable method is
Rotor resistance control
Rotor reactance control
Stator resistance control
Stator reactance control
Correct Answer
Wrong Answer
6. “The direction of induced current in the rotor is so as to oppose the cause producing it”. This is given by
Faraday’s law
Lenz’s law
Electromagnetic law
Ampere’s law
Correct Answer
Wrong Answer
7. If the rotor of the machine catches the speed of the rotating magnetic field, then the motor will
Rotate at the speed of rotating magnetic field
Rotate at double the speed of the rotating magnetic field
Eventually stop
None of these
Correct Answer
Wrong Answer
8. Slip speed of the motor decides the magnitude of the induced emf and the rotor current, which in turn decides the torque produced. If Ns is the synchronous speed and N is the motor speed in rpm, then the slip speed is given by
Ns
Ns – N
Ns + N
N – Ns
Correct Answer
Wrong Answer
9. At start, the slip of the induction motor is
1
0
0.5
None of these
Correct Answer
Wrong Answer
10. Slip of a induction motor will be zero,
At start
When machine is rotating at its maximum speed
When it is rotating at half of the maximum speed
Cannot be zero
Correct Answer
Wrong Answer
11. A 4 pole, 3 phase, 50 Hz star connected induction motor has a full load slip of 5%. Then full load speed of the motor is
1500
1400
1405
1425
Correct Answer
Wrong Answer
12. The rotor frequency of a three phase induction motor is
Slip times the supply frequency
1 / slip times the supply frequency
Equal to the supply frequency
None of these
Correct Answer
Wrong Answer
13. Nature of the rotor power factor in running condition is always
Leading
Lagging
Both (a) and (b)
None of these
Correct Answer
Wrong Answer
14. In terms of slip, the actual speed (N) of the induction motor can be expressed as
Ns (1-s)
Ns (s-1)
Ns / (1-s)
Ns / (s-1)
Correct Answer
Wrong Answer
15. For a three phase induction motor, the two rotor frequencies are given by
sf, (1 – s) f
sf, (2 – s) f
(1 – s) f, (2 – s) f
Sf , sf
Correct Answer
Wrong Answer
16. The torque produced in a three phase induction motor is
Directly proportional to the square of the induced emf in rotor
Directly proportional to the induced emf in rotor
Inversely proportional to the square of the induced emf in rotor
Inversely proportional to the induced emf in rotor
Correct Answer
Wrong Answer
17. When the torque produced by the induction motor is at its maximum, the slip is given by
X2 / R2
(R2 + X2) / X2
R2 / X2
R2 / (R2 + X2)
Correct Answer
Wrong Answer
18. When an induction motor is loaded from no load to full load, its speed and slip
Increases, decreases
Decreases, increases
Both increases
Both decreases
Correct Answer
Wrong Answer
19. If an induction motor is operating at a point in the high slip region, then the motor will be
Stable
Unstable
Either stable or unstable depending on the torque
None of these
Correct Answer
Wrong Answer
20. When the slip of an induction machine is negative, it is running as a
Motor
Generator
Synchronous machine
None of these
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