The main advantage of synchronous motor over induction motor is

 

1. The speed of a synchronous motor is
   A) Proportional to load
   B) Constant at all loads
   C) Proportional to supply voltage
   D) Proportional to supply frequency

B

2. The synchronous speed depends on
   A) Supply voltage only
   B) Supply frequency and number of poles
   C) Load
   D) Armature resistance

B

3. A synchronous motor runs at
   A) Less than synchronous speed
   B) Synchronous speed
   C) More than synchronous speed
   D) Variable speed

B

4. The torque in a synchronous motor is developed by
   A) Induction principle
   B) Interaction of stator and rotor magnetic fields
   C) Eddy currents
   D) Friction

B

5. Synchronous motors are not self-starting because
   A) High starting current
   B) No starting torque at standstill
   C) Poor power factor
   D) Rotor inertia is high

B

6. The excitation in a synchronous motor is supplied to
   A) Stator
   B) Rotor
   C) Both
   D) None

B

7. The field winding of a synchronous motor is excited with
   A) AC
   B) DC
   C) Both AC and DC
   D) No excitation

B

8. A synchronous motor can operate at
   A) Unity power factor only
   B) Lagging power factor only
   C) Leading, lagging, or unity power factor
   D) Lagging or unity only

C

9. A synchronous motor can be used for
   A) Voltage regulation
   B) Power factor correction
   C) Frequency control
   D) Speed control

B

10. The stator of a synchronous motor is similar to that of
    A) DC motor
    B) Induction motor
    C) Stepper motor
    D) Universal motor

B

11. The rotor of a synchronous motor has
    A) Squirrel cage
    B) Salient poles or cylindrical poles
    C) Permanent magnets only
    D) None of these

B

12. Hunting in a synchronous motor is
    A) Load fluctuation
    B) Speed oscillation about synchronous speed
    C) Torque pulsation
    D) Voltage variation

B

13. Damper windings in a synchronous motor are used to
    A) Improve efficiency
    B) Prevent hunting and assist starting
    C) Reduce speed
    D) Increase torque

B

14. The synchronous motor can be started by
    A) Direct-on-line
    B) Damper winding
    C) Induction motor starting
    D) All of the above

D

15. The main disadvantage of synchronous motor is
    A) High maintenance
    B) Not self-starting
    C) Low efficiency
    D) High noise

B

16. V-curves of a synchronous motor show relation between
    A) Voltage and current
    B) Field current and armature current
    C) Speed and torque
    D) Power and frequency

B

17. When over-excited, a synchronous motor operates at
    A) Lagging power factor
    B) Leading power factor
    C) Unity power factor
    D) Zero power factor

B

18. When under-excited, a synchronous motor operates at
    A) Lagging power factor
    B) Leading power factor
    C) Unity power factor
    D) Zero power factor

A

19. For constant load, if excitation is increased, armature current
    A) Increases
    B) Decreases
    C) Remains constant
    D) Becomes zero

B

20. The phasor diagram of synchronous motor resembles that of
    A) Transformer
    B) DC motor
    C) Induction generator
    D) Induction motor

A

21. The efficiency of a synchronous motor is usually
    A) 60–70%
    B) 70–80%
    C) 85–95%
    D) 50–60%

C

22. Synchronous motors are generally preferred for
    A) Variable speed drives
    B) Constant speed drives
    C) High starting torque drives
    D) None

B

23. Pull-out torque of a synchronous motor occurs when
    A) Load torque exceeds maximum torque
    B) Field current is zero
    C) Supply frequency decreases
    D) Armature current is zero

A

24. The mechanical power developed by a synchronous motor depends on
    A) Supply voltage only
    B) Load angle
    C) Frequency
    D) Armature resistance

B

25. The load angle of a synchronous motor is the angle between
    A) Rotor and stator magnetic fields
    B) Supply voltage and current
    C) Current and flux
    D) Torque and speed

A

26. The synchronous condenser operates at
    A) Leading power factor
    B) Lagging power factor
    C) Unity power factor
    D) Zero power factor

A

27. Synchronous condensers are used to
    A) Improve efficiency
    B) Improve power factor
    C) Control voltage
    D) Control frequency

B

28. The main losses in a synchronous motor are
    A) Iron and friction losses
    B) Copper and core losses
    C) Copper, friction, and iron losses
    D) Armature only

C

29. The excitation of a synchronous motor is adjusted to get
    A) Desired power factor
    B) Maximum efficiency
    C) Minimum voltage
    D) Constant torque

A

30. The synchronous motor can be started as
    A) Induction motor
    B) DC motor
    C) Stepper motor
    D) Reluctance motor

A

31. The torque angle of a synchronous motor is
    A) Always zero
    B) 0°–90° under normal operation
    C) 90°–180° under normal operation
    D) 180°

B

32. A synchronous motor will fall out of step when
    A) Load increases beyond pull-out torque
    B) Voltage increases
    C) Frequency decreases
    D) Speed increases

A

33. The reactive power of a synchronous motor is controlled by
    A) Load torque
    B) Field excitation
    C) Supply voltage
    D) Armature resistance

B

34. In synchronous motor, maximum torque is developed when load angle is
    A) 0°
    B) 45°
    C) 90°
    D) 180°

C

35. The armature reaction in a synchronous motor is
    A) Cross-magnetizing
    B) Demagnetizing or magnetizing depending on excitation
    C) Only demagnetizing
    D) None

B

36. Which of the following is not an application of synchronous motor?
    A) Power factor improvement
    B) Constant speed drives
    C) Variable frequency drives
    D) Voltage regulation

C

37. The field poles in a salient pole rotor are
    A) Smooth and cylindrical
    B) Projected and laminated
    C) Non-laminated
    D) Round shaped

B

38. The slip of a synchronous motor is
    A) Zero
    B) One
    C) Depends on load
    D) Variable

A

39. The rotor current frequency in synchronous motor is
    A) Zero
    B) 50 Hz
    C) Depends on speed
    D) 100 Hz

A

40. For a 4-pole, 50 Hz supply, the synchronous speed is
    A) 750 rpm
    B) 1000 rpm
    C) 1500 rpm
    D) 3000 rpm

C

41. The starting torque of a synchronous motor is
    A) Zero
    B) High
    C) Moderate
    D) Depends on field current

A

42. The direction of rotation of a synchronous motor can be reversed by
    A) Reversing supply
    B) Reversing field current polarity
    C) Both A and B
    D) None

C

43. A synchronous motor can run as a generator when
    A) Load is reversed
    B) Supply is removed
    C) Driven above synchronous speed
    D) Field is reduced

C

44. The function of the damper winding is
    A) Reduce noise
    B) Reduce oscillations and assist starting
    C) Increase efficiency
    D) Reduce current

B

45. A synchronous motor draws leading current when
    A) Over-excited
    B) Under-excited
    C) At unity excitation
    D) None

A

46. The excitation control of a synchronous motor is used to control
    A) Speed
    B) Power factor
    C) Torque
    D) Frequency

B

47. The main advantage of synchronous motor over induction motor is
    A) Constant speed and power factor control
    B) Low cost
    C) High starting torque
    D) Light weight

A

48. In a synchronous motor, the armature current is minimum at
    A) Unity power factor
    B) Leading power factor
    C) Lagging power factor
    D) Zero power factor

A

49. When a synchronous motor is running as a synchronous condenser, its shaft load is
    A) Zero
    B) Full-load
    C) Half-load
    D) Variable

A

50. The relation between electrical degrees and mechanical degrees in a synchronous motor is
    A) Equal
    B) Electrical degrees = (P/2) × mechanical degrees
    C) Electrical degrees = (2/P) × mechanical degrees
    D) None

B