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_____________?

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. 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.

5. 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

6. 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

7. 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___________?

   A. more
   B. less
   C. equal
   D. twice

8. 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

9. Power factor of a synchronous motor is unity when_____________?

   A. the armature current is maximum
   B. the armature current is minimum
   C. the armature current is zero
   D. none of the above

10. 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