Change of D.C. excitation of a synchronous motor changes:

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. 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

3. 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

4. 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

5. The effect of increasing the load on a synchronous motor running with normal excitation is to___________?

   A. decrease both armature current and power factor
   B. decrease armature current but increase power factor
   C. increase armature current but decrease power factor
   D. increase both its armature current and power factor

6. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in______________?

   A. back e.m.f.
   B. armature current
   C. power factor
   D. torque angle

7. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected______________?

   A. the motor stops
   B. it runs as a reluctance motor at the same speed
   C. it runs as a reluctance motor at a lower speed
   D. none of the above

8. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately

   A. one-third
   B. twice
   C. thrice
   D. six times
   E. nine times

9. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to____________?

   A. increase in both armature current and power factor angle
   B. increase in back e.m.f. but decrease in armature current
   C. increase in both armature current and power factor which is lagging
   D. increase in torque angle but decrease in back e.m.f.

10. 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.