The operating speed of a synchronous motor can be changed to new fixed value by___________?

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. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?

   A. By changing the supply frequency
   B. By interchanging any two phases
   C. By changing the applied voltage
   D. By changing the load

3. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop_________________?

   A. inductor motor torque
   B. induction generator torque
   C. synchronous motor torque
   D. d.c. motor toque
   E. none of the above

4. 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

5. 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

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. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

   A. synchronous motor has no slip
   B. stator supply is not required to produce magnetic field
   C. mechanical load on the rotor remains constant
   D. synchronous motor has large airgap

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. 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