AC MOTORS

Question 1

1. What is the range of slip induction motor?
   A. 0 to 5%
   B. 0 to 2%
   C. 5 to 10%
   D. None of the above

Answer 1

A. 0 to 5%

Question 2

2. In which test the motor is rub with uncoupled load and with rated voltage supplied to stator?
   A. No load test
   B. Blocked rotor test
   C. Hopkinson’s test
   D. None of the above

Answer 2

A. No load test

Question 3

3. The condition for maximum torque under running condition is expressed by?
   A. R2 = X2
   B. R2 = sX^22
   C. R2 = sX2
   D. R2 = s/X2

Answer 3

C. R2 = sX2

Question 4

4. Rotor current frequency f ; for induction motor is expressed by?
   A. f’, =(slip)^2 × supply frequency
   B. f’, =slip/supply frequency
   C. f’ = slip × supply frequency
   D. f’, = supply frequency/ slip

Answer 4

C. f’ = slip × supply frequency

Question 5

5. In terms od rotor resistance r2, slip for maximum torque in 3phase induction motor is?
   A. Inversely proportional to r2
   B. Independent of r2
   C. Directly proportional to r2
   D. None

Answer 5

C. Directly proportional to r2

Question 6

6. At what speed does the rotor of a 3 phase induction motor always runs?
   A. At a speed less than synchronous speed
   B. At a speed more than synchronous speed
   C. At synchronous speed
   D. None

Answer 6

A. At a speed less than synchronous speed

Question 7

7. When the line voltage of an induction motor is reduced to 75% of its rated value, the starting current will reduce by?
   A. 50%
   B. 25%
   C. 75%
   D. None of the above

Answer 7

B. 25%

Question 8

8. The frequency of the induced emf in the rotor circuit is?
   A Maximum at stand still
   B. Maximum of synchronous speed
   C. Zero at stand still
   D. None of the above

Answer 8

A. Maximum at stand still

Question 9

9. What happens when a 3phase induction motor runs on single phase supply?
   A. Runs at low speed
   B. Does not run continuesly
   C. It will burn
   D. None of the above

Answer 9

C. It will burn

Question 10

10. The rotor reactance speed of 3phase induction motor?
    A. Synchronous speed × (1- slip)
    B. Synchronous speed × slip
    C. Synchronous speed
    D. 0.95 × synchronous speed

Answer 10

A. Synchronous speed × (1- slip)

Question 11

The torque of a 3 phase induction motor is proportional to?
A. √Applied voltage
B. (Applied voltage)^2
C. Applied voltage
D. Applied voltage/2

Answer 11

B. (Applied voltage)^2

Question 12

12. Synchronous motor has:
    A. Constant speed
    B. Slight drop in spred on full load
    C High speed at low torque
    D. Low speed at high torque

Answer 12

A. Constant speed

Question 13

13. Synchronous motor is capable of being operated at?
    A. Lagging power factor only
    B. Leading power factor only
    C Lagging and leading power factor
    D. None of these

Answer 13

C. Lagging and leading power factor

Question 14

14. Synchronous power of a synchronous machine is?
    A. Equal to synchronous reactance
    B. Inversely proportional to the synchronous reactance
    C. Directly proportional to the synchronous reactance
    D. None of these

Answer 14

B. Inversely proportional to the synchronous reactance

Question 15

15. Synchronous motors are?
    A. Self - starting
    B. Not self starting
    C. essentially self starting
    D. None of these

Answer 15

B. Not self starting