The magnitude of field flux in a 3-phase synchronous motor?

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. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?

   A. induction motor torque in field winding
   B. induction motor torque in damper winding
   C. eddy current and hysteresis torque in pole faces
   D. reHetance motor torque due to saliency of the rotor
   E. all of the above methods

3. 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

4. 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

5. 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

6. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way

   A. augments it directly
   B. directly opposes it
   C. cross-magnetises it
   D. none of the above

7. 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

8. While starting a synchronous motor by induction motor action, field winding is usually_____________?

   A. connected to D.C. supply
   B. short-circuited by low resistance
   C. kept open-circuited
   D. none of the above

9. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will__________?

   A. stop
   B. run as induction motor
   C. function as static condenser
   D. burn with dense smoke

10. 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