1. Synchronous motors generally have
(A) salient pole rotor
(B) either the salient pole rotor or smooth cylindrical rotor
(C) smooth cylindrical rotor
(D) none of the above
2. Number of slip rings in a 3-phase synchronous motor will be
(A) 0
(B) 1
(C) 3 or 4
(D) 2
3. The direction of rotation of a synchronous motor can be reversed by reversing
(A) current to the field winding
(B) polarity of rotor poles
(C) supply phase sequence
(D) none of the above
4. In a synchronous motor, the magnitude of stator back e.m.f. depends on
(A) speed of the motor
(B) d.c. excitation only
(C) both the speed and rotor flux
(D) load on the motor
5. Damper winding is provided in synchronous motor to
(A) both (ii) and (iii)
(B) suppress rotor oscillations
(C) develop necessary starting torque
(D) stabilize rotor motion
6. The V-curves of a synchronous motor show relationship between
(A) excitation current and back e.m.f.
(B) field current and armature current
(C) field current and supply voltage
(D) armature current and supply voltage
7. The angle between the synchronously-rotating stator flux and rotor poles of a synchronous motor is called _______ angle.
(A) short
(B) power factor
(C) torque
(D) slip
8. The maximum value of torque angle α in a synchronous motor is
(A) 45°
(B) less than 60°
(C) between 45° and 90°
(D) 90°
9. Which of the following is most commonly used technique for starting synchronous motor?
(A) Using an induction motor
(B) By using a dc machine
(C) By using slip ring induction motor
(D) Using damper windings
10. Which of the following is an application of synchronous motor?
(A) Synchronous capacitor
(B) Voltage regulation
(C) Constant speed applications
(D) All of the above
11. If the field of a synchronous motor is under excited, the power factor will be
(A) lagging
(B) zero
(C) leading
(D) unity
12. When load on a normally-excited synchronous motor is increased, its power factor tends to
(A) become increasingly lagging
(B) remain unchanged
(C) become increasingly leading
(D) approach unity
13. In a synchronous machine when the rotor speed becomes more than the synchronous speed during hunting, the damping bars develop
(A) synchronous motor torque
(B) d.c. motor torque
(C) induction generator torque
(D) induction motor torque
14. The V-curves of a synchronous motor show relationship between
(A) Excitation current and back e.m.f
(B) Field current and p.f.
(C) Armature current and supply voltage
(D) D.C. field current and A.C. armature current
15. 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 a lower speed
(C) It runs as a reluctance motor at the same speed
(D) None of the above
16. An over-excited synchronous motor is used for
(A) Fluctuating loads
(B) Variable speed loads/span
(C) Power factor corrections
(D) Low torque loads
17. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in its
(A) Power factor
(B) Torque angle
(C) Back e.m.f.
(D) Armature current
18. An over-excited synchronous motor takes
(A) Both (A) and (B)
(B) Lagging current
(C) Leading current
(D) None of the above
19. A synchronous motor can be started by
(A) Pony Motor
(B) D.C. machine
(C) All of these
(D) Providing damper winding
20. Synchronous motor always runs at
(A) More than synchronous speed
(B) Less than synchronous speed
(C) The synchronous speed
(D) None of the above