When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is___________?

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 in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

   A. will become more
   B. will become less
   C. will remain unchanged
   D. none of the above.

3. If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________?

   A. become more
   B. become less
   C. remain constant
   D. none of the above

4. 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

5. When the field of a synchronous motor is under-excited, the power factor will be____________?

   A. leading
   B. lagging
   C. unity
   D. zero

6. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

   A. speed of the motor is reduced
   B. power factor is decreased
   C. Eb (back e.m.f.) becomes less than V (applied voltage)
   D. Er (net resultant voltage) in armature is increased
   E. none of the above

7. As the load is applied to a synchronous motor, the motor takes more armature current because

   A. the increased load has to take more current
   B. the rotor by shifting its phase backward causes motor to take more current
   C. the back e.m.f. decreases causing an increase in motor current
   D. the rotor strengthens the rotating field casuing more motor current

8. 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

9. 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

10. 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