Electrical Drives MCQ Questions and Answers for Practice

1. To save energy during braking ................. braking is used?

1. regenerative
2. dynamic
3. plugging
4. All of the above

2. A 3 - F induction motor draws an electric current of 50 A from mains when starts by direct switching. If an auto transformer with 60 % tapping is used for starting the electric current drawn from the mains will be

1. 50
2. 18
3. 36
4. 80

3. A four quadrant operation requires

1. two full converter connected in back to back
2. two full converters in series
3. two full converters connected in parallel
4. two semi converters connected in back to back

4. A motor has a thermal heating time constant of 50 mm. When the motor runs continuous of full scale, its final temperature rise is 80° C, what would be the temperature rise after 1 hour, if the motor runs continuously on full load?

1. 56 degrees
2. 55.9 degrees
3. 58 degrees
4. 60 degrees

5. An elevator drive is required to operate in

1. three quadrants
2. one quadrant only
3. two quadrants
4. four quadrants

6. Electric drive is becoming more and more popular because

1. it is simple and reliable
2. it provide smooth and easy control
3. it is cheaper in cost
4. All of the below

7. For an IM to operate in braking region slip should be always

1. is equal to 1
2. less than zero
3. greater than 1
4. None of these

8. Full form of VVVF control

1. variable VAr voltage frequency
2. variable voltage VAr frequency
3. VAr variable voltage frequency
4. variable voltage variable frequency

9. High braking torque produced in

1. regenerative braking
2. plugging
3. dynamic braking
4. None of these

10. In 4 quadrant operation of a hoist 3rd quadrant represents

1. forward braking
2. reverse motoring
3. reverse braking
4. forward motoring

11. In case of kiln drives, starting torque is

1. almost equal to running torque
2. more than double of the running torque
3. more than triple of the running torque
4. less than running torque

12. In industries which electrical braking is preferred?

1. Dynamic braking
2. Regenerative braking
3. Plugging
4. None of these

13. In which braking back emf exceeds supply voltage?

1. Plugging
2. Regenerative
3. Dynamic
4. None of these

14. Polarity of supply voltage is reversed in which type of braking?

1. Plugging
2. Regenerative braking.
3. Dynamic braking
4. None of these

15. Speed control by variation of field flux results in

1. variable power drive
2. constant power drive
3. constant torque drive
4. None of these