1. If the field of a synchronous motor is underexcited, the power factor will be
Correct : C. lagging
2. The back e.m.f. in the stator of a synchronous motor depends on
Correct : D. rotor excitation
3. The maximum value of torque that a synchronous motor can develop without losing
its synchronism, is known as
Correct : D. synchronising torque
4. In a synchronous motor, the armature current has large values for
Correct : C. both high and low excitation
5. Which of the following losses, in a synchronous motor, does not vary with load?
Correct : A. Windage loss
6. The size of a synchronous motor decreases with the increase in
Correct : A. flux density
7. Which of the following losses is not dissipated by the stator core surface in a
synchronous motor ?
Correct : D. Windage losses
8. The duration of sudden snort-circuit test on a synchronous motor is usually about
Correct : C. one second
9. A synchronous machine with low value of short-circuit ratio has
Correct : A. lower stability limit
10. The construction of a synchronous motor resembles
Correct : C. an alternator
11. If the field winding of an unloaded salient pole synchronous motor is open circuited,
the motor will
Correct : A. stop
12. For power factor correction, synchronous motors operate at
Correct : A. no-load and greatly over-excited fields
13. The maximum torque which a synchronous motor will develop at rest for any
angular position of the rotor, at rated stator supply voltage and frequency, is known as
Correct : A. locked-rotor torque
14. Exciters of synchronous machines are
Correct : A. d.c. shunt machines
15. The coupling angle or load angle of synchronous motor is defined as the angle
between the
Correct : B. rotor and the stator poles of opposite polarity
16. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
Correct : A. the stator current will be zero
17. The armature current of the synchronous motor
Correct : C. has large values for low and high excitation
18. The maximum power developed in a synchronous motor will depend on
Correct : D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)
19. A synchronous motor which works on a leading power factor and does not drive a
mechanical load is called as
Correct : C. synchronous condenser
20. A synchronous motor develops maximum power when load angle is
Correct : C. 90°
21. In a synchronous motor, the breakdown torque is
Correct : A. directly proportional to applied voltage