Advanced Electrical Machines MCQs

1. Which of the following machines operates on the principle of electromagnetic induction?
A) DC Generator
B) Synchronous Motor
C) Induction Motor
D) Transformer
Answer: D) Transformer

2. The armature current in a DC motor is maximum when:
A) The motor is running at no load
B) The motor is running at full load
C) The motor is starting
D) The motor is decelerating
Answer: B) The motor is running at full load

3. Slip in an induction motor is defined as:
A) Difference between synchronous speed and rotor speed
B) Difference between rotor speed and stator speed
C) Ratio of rotor speed to synchronous speed
D) Ratio of synchronous speed to rotor speed
Answer: A) Difference between synchronous speed and rotor speed

4. In a synchronous machine, hunting refers to:
A) Oscillations in speed when load changes
B) Over-excitation of the field winding
C) Vibrations due to unbalanced rotor
D) Overheating of the stator winding
Answer: A) Oscillations in speed when load changes

5. The starting torque of a single-phase induction motor is:
A) High
B) Low
C) Moderate
D) Zero
Answer: B) Low

6. The main advantage of a switched reluctance motor is:
A) High efficiency at all loads
B) High starting torque
C) Low cost and simple construction
D) High speed operation
Answer: C) Low cost and simple construction

7. The back emf in a DC motor:
A) Increases with increase in speed
B) Decreases with increase in speed
C) Is independent of speed
D) Depends on armature current
Answer: A) Increases with increase in speed

8. The speed of a three-phase induction motor can be controlled by:
A) Changing the supply voltage
B) Changing the number of stator poles
C) Changing the rotor resistance
D) All of the above
Answer: D) All of the above

9. The power factor of an induction motor under no-load conditions is typically:
A) Leading
B) Lagging
C) Unity
D) Zero
Answer: A) Leading

10. The term ‘cogging’ in a permanent magnet synchronous motor refers to:
A) Starting torque
B) Rotor position errors
C) Uncontrolled movements
D) Reluctance torque
Answer: B) Rotor position errors

11. Which type of rotor is used in a squirrel cage induction motor?
A) Salient pole rotor
B) Wound rotor
C) Smooth cylindrical rotor
D) None of the above
Answer: C) Smooth cylindrical rotor

12. The efficiency of a transformer is maximum when:
A) The transformer is lightly loaded
B) The transformer is fully loaded
C) The transformer is operating at half load
D) The transformer is at no load
Answer: B) The transformer is fully loaded

13. In a synchronous generator, the armature reaction affects:
A) Voltage regulation
B) Power factor
C) Speed regulation
D) Excitation voltage
Answer: A) Voltage regulation

14. The inrush current in a transformer is higher than normal operating current because of:
A) Core losses
B) Hysteresis losses
C) Eddy current losses
D) Magnetizing current
Answer: D) Magnetizing current

15. Which motor has the highest power factor at full load?
A) DC shunt motor
B) Induction motor
C) Synchronous motor
D) Switched reluctance motor
Answer: C) Synchronous motor

16. The speed-torque characteristic of a DC series motor is:
A) High starting torque, variable speed
B) High starting torque, constant speed
C) Low starting torque, variable speed
D) Low starting torque, constant speed
Answer: A) High starting torque, variable speed

17. The slip rings in an induction motor are used for:
A) Starting torque
B) Speed control
C) Supplying power to the rotor windings
D) Providing a path for stator flux
Answer: C) Supplying power to the rotor windings

18. The efficiency of a transformer is approximately:
A) 100%
B) 99%
C) 98%
D) 97%
Answer: C) 98%

19. The armature reaction in a DC motor affects:
A) Speed regulation
B) Torque
C) Efficiency
D) Voltage regulation
Answer: D) Voltage regulation

20. The starting torque of a synchronous motor is:
A) Zero
B) High
C) Low
D) Moderate
Answer: A) Zero

21. A universal motor operates on:
A) DC supply only
B) AC supply only
C) Both AC and DC supply
D) None of the above
Answer: C) Both AC and DC supply

22. The direction of rotation of a split-phase induction motor can be reversed by:
A) Interchanging the supply terminals
B) Changing the supply frequency
C) Changing the rotor resistance
D) None of the above
Answer: A) Interchanging the supply terminals

23. The function of a commutator in a DC machine is to:
A) Control the armature current
B) Reverse the direction of current in the armature
C) Control the field winding current
D) Provide mechanical support to the armature
Answer: B) Reverse the direction of current in the armature

24. The power factor of a synchronous motor can be adjusted by varying the:
A) Armature resistance
B) Field excitation
C) Rotor resistance
D) Supply voltage
Answer: B) Field excitation

25. The starting current of a squirrel cage induction motor is typically:
A) Equal to full-load current
B) Less than full-load current
C) Greater than full-load current
D) Zero
Answer: C) Greater than full-load current

26. The direction of rotation of a three-phase induction motor can be reversed by:
A) Interchanging any two supply lines
B) Changing the supply frequency
C) Changing the rotor resistance
D) None of the above
Answer: A) Interchanging any two supply lines

27. The armature winding in a DC machine is:
A) Concentrated
B) Distributed
C) Both concentrated and distributed
D) None of the above
Answer: B) Distributed

28. The speed of a DC shunt motor can be controlled by:
A) Changing the supply voltage
B) Changing the field current
C) Changing the armature resistance
D) All of the above
Answer: D) All of the above

29. Which of the following losses occur in a transformer?
A) Eddy current losses
B) Hysteresis losses
C) Copper losses
D) All of the above
Answer: D) All of the above

30. The efficiency of a DC generator is maximum when:
A) The generator is lightly loaded
B) The generator is fully loaded
C) The generator is operating at half load
D) The generator is at no load
Answer: B) The generator is fully loaded

31. The emf induced in the armature of a DC generator depends on:
A) Armature speed
B) Field current
C) Both armature speed and field current
D) None of the above
Answer: C) Both armature speed and field current

32. Which motor does not require a starting mechanism?
A) Synchronous motor
B) Induction motor
C) DC series motor
D) Universal motor
Answer: A) Synchronous motor

33. The speed of a synchronous motor is:
A) Constant
B) Variable
C) Zero
D) Indeterminate
Answer: A) Constant

34. The no-load current in a transformer is mainly due to:
A) Core losses
B) Eddy current losses
C) Magnetizing current
D) Copper losses
Answer: C) Magnetizing current

35. Which motor has the highest starting torque?
A) Induction motor
B) DC shunt motor
C) Synchronous motor
D) Switched reluctance motor
Answer: D) Switched reluctance motor

36. The torque in an induction motor is maximum when:
A) Slip is zero
B) Slip is one
C) Slip is 0.5
D) Slip is indeterminate
Answer: A) Slip is zero

37. The power factor of a capacitor-run induction motor is:
A) Leading
B) Lagging
C) Unity
D) Zero
Answer: A) Leading

38. In a wound rotor induction motor, external resistances are used to:
A) Control speed
B) Control torque
C) Control power factor
D) All of the above
Answer: D) All of the above

39. The function of laminations in the core of a transformer is to reduce:
A) Eddy currents
B) Hysteresis losses
C) Copper losses
D) All of the above
Answer: A) Eddy currents

40. The armature reaction in a synchronous machine affects:
A) Voltage regulation
B) Power factor
C) Speed regulation
D) Efficiency
Answer: A) Voltage regulation

41. The speed of a DC series motor decreases with increasing:
A) Armature resistance
B) Field current
C) Load torque
D) Supply voltage
Answer: C) Load torque

42. A transformer with a primary winding connected to a sinusoidal AC supply will induce:
A) An AC voltage in the secondary winding
B) A DC voltage in the secondary winding
C) No voltage in the secondary winding
D) None of the above
Answer: A) An AC voltage in the secondary winding

43. The slip rings in a wound rotor induction motor are used to connect:
A) The rotor windings to the stator windings
B) The rotor windings to the external resistances
C) The rotor windings to the DC supply
D) None of the above
Answer: B) The rotor windings to the external resistances

44. The eddy current loss in a transformer core depends on:
A) The frequency of the supply
B) The thickness of the laminations
C) The material of the core
D) All of the above
Answer: D) All of the above

45. The power factor of a synchronous generator is typically:
A) Leading
B) Lagging
C) Unity
D) Zero
Answer: A) Leading

46. The starting torque of a shaded-pole induction motor is:
A) High
B) Low
C) Moderate
D) Zero
Answer: B) Low

47. The torque developed in an induction motor is proportional to:
A) Slip
B) Speed
C) Supply voltage
D) Both slip and speed
Answer: D) Both slip and speed

48. The regulation of an alternator is defined as:
A) The difference between no-load and full-load terminal voltage
B) The difference between synchronous speed and actual speed
C) The difference between excitation voltage and terminal voltage
D) None of the above
Answer: A) The difference between no-load and full-load terminal voltage

49. The power factor of an induction motor decreases with:
A) Increasing load
B) Decreasing load
C) Increasing supply voltage
D) Increasing rotor resistance
Answer: B) Decreasing load

50. The torque-speed characteristic of a universal motor is similar to that of a:
A) DC series motor
B) Synchronous motor
C) Induction motor
D) None of the above
Answer: A) DC series motor

Advanced Electrical Machines MCQs

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