Electric Drives and Motors MCQ Part-3

1. Speed control by variation of field flux results in__________.

a. Variable power drive 

b. Variable torque drive

c. Constant torque drive

d. Constant power drive

 

2. In variable speed dc motor drive the armature voltage controls leads to_________.

a. Variable torque operation 

b. Randomly varying power operation

c. Constant torque operation 

d. Constant power operation

3. Speed of an induction motor is controlled by injecting voltage into the rotor winding. Frequency of the injected voltage should be _________.

a. Slip frequency

b. Frequency corresponding to rotor speed 

c. Frequency corresponding to required speed

d. Main frequency

4. The slip power recovery scheme is used in induction motor for speed control in the range__________.

a. Above synchronous speed

b. Below synchronous speed

c. Both above and below synchronous speed

d. None of the above

5. The electric braking system commonly employed in rolling mills, elevators and printing presses is ___________.

a. Regenerative 

b. Dynamic

c. Rheostatic 

d. Plugging

 

6. For rheostatic braking of two series motor connected in parallel_______.

a. Equaliser is better

b. Cross-connection is better

c. Both are equally good

d. None of the two is required

7. Dynamic braking is employed to brake__________.

a. Reversing drive

b. Non-reversing drive

c. In both (a) and (b)

 

8. The condition of regenerative braking can be achieved by________.

a. Increasing the excitation while supply voltage remains constant

b. Speed higher than no-load speed of overhauling load

c. Increasing current at high speed

d. Either (a) or (b)

 

9. In a dc shunt motor, regenerative braking is limited by________.

a. Saturation of flux at low speed 

b. Saturation of flux at high speed 

c. Armature current at high speed 

d. Either (a) or (b) 

10. Foe regeneratively braking with dc series motors, its field windings are_________ excited.

a. Separately

b. Shunt 

c. Series

d. Either (b) or (c)

11. The most economical method of electric braking is_________.

a. Regenerative braking

b. Plugging

c. Dynamic braking with self excitation

d. Dynamic braking with separate excitation

12. The plugging provides _________ braking torque in comparison to rheostatic and regenerative braking systems.

a. Highest

b. Negligible 

c. Small

13. Rheostatic braking may be applied to an induction motor provided________.

a. Variable external resistance is available

b. Separate dc source for field excitation is available

c. It is a squirrel cage type

d. It is a wound type

14. The motor enclosure used for collieries, chemical plants is _______.

a. Pipe ventilated type

b. Totally enclosed type

c. Splash proof type

d. Flame proof type

15. The motor enclosure used in woodworking industry is________.

a. Protected type

b. Totally enclosed fan cooled type

c. Flame-proof type

d. Splash-proof type

16. The motor enclosure used for industrial purposes is_________.

a. Drip proof type

b. Totally enclosed type

c. Protected type

d. Open type

17. Rotor of a motor is usually supported on_________.

a. Ball or roller bearing

b. Bush bearing

c. Thrust bearing 

d. Any of the above

18. Ball-bearings are___________.

a. Costlier and noisy particularly at high motor speed

b. Used up to 75 kW motors

c. Of long life and low friction loss

d. All of the above

 

19. Sleeve bearings_________.

a. Are used where noise is to be avoided

b. Have self-lubricating properties

c. Are normally of bronze

d. All of the above

 

20. Hot bearings of a dc motor may be caused by__________.

a. Incorrect voltage

b. Poor ventilation

c. Lack of or dirty lubricant

d. Loose coupling

21. Excessive motor vibration is caused by________.

a. Excessive brush tension

b. Bent shaft

c. Open armature coil

d. Worn bearings

 

22. Excessive sparking at the brushes may be caused due to_________.

a. Open armature coil

b. Worn bearings

c. Loose coupling

d. Dirt on commutator

 

23.  Intermittent sparking at the brushes of a dc motor may be caused due to_________.

a. Incorrect voltage

b. Loose coupling

c. Intermittent level

d. Open armature coil

 

24. The least expensive drive is_________.

a. Gear drive

b. Belt drive

c. Rope drive

d. Chain drive 

25. For very high speed ratio the indispensable drive is________.

a. Chain drive

b. Rope drive 

c. Direct drive

d. Any of the above

26. In rotating electrical machines, the insulation temperature limit for class B type is________.

a. 105*C

b. 130*C

c. 150*C

d. 180*C

• Electric Drives and Motors MCQ Part-1
• Electric Drives and motors MCQ Part-2
• Electric Drives and Motors MCQ Part-4
• Electric Drives and Motors MCQ Part-5
• Electric Drives and Motors MCQ Part-6
• Electric Drives and Motors MCQ Part-7
• Electric Drives and Motors MCQ Part-8
• Electric Drives and Motors MCQ Part-9
• Electric Drives and Motors MCQ Part-10