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.

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

2. Slots of squirrel cage rotor are generally skewed to

Reduce magnetic hum
Reduce magnetic locking
Make motor operation smooth
All of these

3. The wound rotor induction motor gives

high stating torque
moderate starting torque
reduced starting torque
all of these

4. The slip ring or wound rotor induction motor find its applications in

lifts, cranes
drilling machines
printing machines

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

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

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

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 – N
Ns + N
N – Ns

9. At start, the slip of the induction motor is

None of these

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

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


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

13. Nature of the rotor power factor in running condition is always

Both (a) and (b)
None of these

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)

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

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

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)

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

19. If an induction motor is operating at a point in the high slip region, then the motor will be

Either stable or unstable depending on the torque
None of these

20. When the slip of an induction machine is negative, it is running as a

Synchronous machine
None of these