Synchronous Motor Objective Type Questions - Set 05 - ObjectiveBooks
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# Practice Test: Question Set - 05

1. The induced e.m.f. in a synchronous motor working on leading power factor will be
(A) More than the supply voltage
(B) Less than the supply voltage
(C) Equal to the supply voltage
(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. Which of the following losses, in a synchronous motor, does not vary with load?
(A) Windage loss
(B) Copper losses
(C) Any of the above
(D) None of the above

4. If the synchronous motor, properly synchronized to the supply is running on no load and is having negligible loss then
(A) The stator current will be zero
(B) The stator current will be very small
(C) The stator current will be very high
(D) The back e.m.f. will be more than the supply voltage

5. A synchronous motor develops maximum power when load angle is
(A) 45°
(B) 60°
(C) 90°
(D) 120°

6. In case one phase of a 3-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

7. A synchronous motor can be used as a synchronous capacitor when it is
(C) Under-excited
(D) Overexcited

8. 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

9. The operating speed of a synchronous motor can be changed to new fixed value by
(B) Changing the supply voltage
(C) Changing frequency
(D) Using brakes

10. 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

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