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____________?

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. If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is__________?

   A. 2
   B. 3
   C. 4
   D. 6

3. 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

4. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as___________?

   A. pull-up torque
   B. pull-in torque
   C. pull-out torque
   D. none of the above

5. The ratio of starting torque to running torque in a synchronous motor is____________?

   A. zero
   B. one
   C. two
   D. infinity

6. 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

7. 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

8. 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

9. 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

10. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

    A. power factor as well as armature current will decrease
    B. power factor as well as armature current will increase
    C. power factor will increase but armature current will decrease
    D. power factor will decrease and armature current will increase