A three-phase synchronous motor will have_____________?

Related Mcqs:

1. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?

   A. remain same
   B. go down
   C. improve
   D. none of the above

2. In case one phase of a three-phase synchronous motor is short-circuited the motor will____________?

   A. not start
   B. run at 2/3 of synchronous speed
   C. run with excessive vibrations
   D. take less than the rated load

3. If one-phase of a 3-phase synchronous motor is short-circuited, motor will ______________?

   A. will refuse to start
   B. will overheat in spots
   C. will not come upto speed
   D. will fail to pull into step

4. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is_______________?

   A. supplied with unbalanced voltage
   B. under-loaded
   C. over-loaded
   D. none of the above

5. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?

   A. no change of power factor
   B. lagging power factor with over-excitation
   C. leading power factor with under-excitation
   D. leading power factor with over-excitation

6. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________?

   A. 3000 r.p.m.
   B. 1500 r.p.m.
   C. 750 r.p.m.
   D. none of the above

7. A synchronous motor can be used as a synchronous capacitor when it is____________?

   A. under-loaded
   B. over-loaded
   C. under-excited
   D. over-excited

8. A synchronous motor can develop synchronous torque:

   A. when under loaded
   B. while over-excited
   C. only at synchronous speed
   D. below or above synchronous speed

9. The maximum speed variation in a 3-phase synchronous motor is____________?

   A. 10 per cent
   B. 6 per cent
   C. 4 per cent
   D. 2. per cent
   E. zero

10. A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed

    A. the motor will stop
    B. the motor continue to run in the same direction
    C. the winding of the motor will burn
    D. the motor will run in the reverse direction
    E. none of the above