Electrical Drives MCQs Quiz Multiple Choice Questions & Answers

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

16. The basic elements of a electric drive are

1. electrical motor and control system
2. electric motor
3. control system
4. None of these

17. The concept of V/f control of inverters driving induction motors resuls in

1. reduced magnetic loss
2. constant torque operation
3. speed reversal
4. hormonic elimination

18. The heating time constant of an electrical machine gives an induction of its

1. overload capacity
2. rating
3. cooling
4. short time rating

19. The power input to a 3 - F induction motor is 60 kW and stator loss is 1 kW the rotor cu loss per phase is

1. slip × 69 / 3
2. slip × 50 / 3
3. slip × 59 / 3
4. 1

20. The slip of an induction motor during DC rheostatic braking is

1. 2 + s
2. 2 - s
3. 1 - s
4. s

21. What are the constituents in speed time curve of train?

1. Constant speed
2. Coasting
3. Initial acceleration
4. All of the above

22. What type electric drive is used in cranes?

1. Individual
2. Multimotor
3. Group
4. Both A and C

23. Which braking is not possible in series motor?

1. Counter current braking
2. Regenerative braking
3. Dynamic braking
4. Rheostat braking

24. Which of the following are electrical braking methods ?

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

25. Which speed control method preferred for constant torque drive?

1. Mechanical loading system
2. Field control
3. Armature voltage control
4. None of these

26. While operating on variable frequency supplies, the AC motor requires variable voltage in order to

1. improve the capabilities of the inverter
2. protect the insulation
3. avoid effect of saturation
4. protect thyristor from dV / dt