Electric Drives MCQs

1. Which of the following is not a type of electric drive?
A) Hydraulic drive
B) DC drive
C) AC drive
D) Servo drive
Answer: A) Hydraulic drive

2. In an electric drive system, the function of the controller is to:
A) Generate electric power
B) Convert DC to AC
C) Regulate speed and torque
D) Transmit mechanical power
Answer: C) Regulate speed and torque

3. The speed-torque characteristic of a DC motor is typically:
A) Parabolic
B) Linear
C) Exponential
D) Hyperbolic
Answer: B) Linear

4. 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

5. The speed of a synchronous motor is:
A) Directly proportional to the supply voltage
B) Inversely proportional to the supply frequency
C) Directly proportional to the supply frequency
D) Independent of both voltage and frequency
Answer: C) Directly proportional to the supply frequency

6. Which of the following is not a method of speed control for DC motors?
A) Armature resistance control
B) Field flux control
C) Stator voltage control
D) Rotor resistance control
Answer: C) Stator voltage control

7. In an electric drive system, PID control is used for:
A) Speed control
B) Voltage control
C) Power factor correction
D) Frequency control
Answer: A) Speed control

8. The power factor of an electric drive system can be improved by using:
A) Synchronous motors
B) Induction motors
C) DC motors
D) Servo motors
Answer: A) Synchronous motors

9. Which of the following motors is most suitable for applications requiring precise position and speed control?
A) Induction motor
B) Synchronous motor
C) DC motor
D) Single-phase motor
Answer: C) DC motor

10. The starting torque of a synchronous motor is:
A) Very high
B) Very low
C) Moderate
D) Zero
Answer: A) Very high

11. Which motor is preferred for traction applications such as electric trains?
A) DC series motor
B) Squirrel cage induction motor
C) Permanent magnet synchronous motor
D) Slip ring induction motor
Answer: C) Permanent magnet synchronous motor

12. A VFD (Variable Frequency Drive) is used to control the speed of:
A) DC motors only
B) Induction motors only
C) Synchronous motors only
D) Both induction and synchronous motors
Answer: D) Both induction and synchronous motors

13. The braking of a DC motor can be achieved by:
A) Regenerative braking
B) Dynamic braking
C) Plugging
D) All of the above
Answer: D) All of the above

14. In a Ward Leonard control system, the motor-generator set is used for:
A) Voltage regulation
B) Current regulation
C) Speed control
D) Torque control
Answer: C) Speed control

15. Which of the following is not a method of improving the efficiency of electric drives?
A) Using energy-efficient motors
B) Implementing regenerative braking
C) Decreasing power factor
D) Minimizing losses in power electronics
Answer: C) Decreasing power factor

16. The torque developed by a DC motor is proportional to:
A) Armature current
B) Field current
C) Both armature and field currents
D) Speed of the motor
Answer: C) Both armature and field currents

17. A cycloconverter is used to convert:
A) DC to AC
B) AC to DC
C) AC to variable frequency AC
D) DC to variable frequency AC
Answer: C) AC to variable frequency AC

18. The speed of a DC shunt motor is approximately proportional to:
A) Supply voltage
B) Supply frequency
C) Armature current
D) Field current
Answer: A) Supply voltage

19. In a vector control method for AC motors, the control variables are:
A) Voltage and frequency
B) Stator and rotor currents
C) Armature and field currents
D) Speed and torque
Answer: B) Stator and rotor currents

20. A regenerative braking system is used to:
A) Increase the speed of the motor
B) Reduce the speed of the motor
C) Recover energy during braking
D) None of the above
Answer: C) Recover energy during braking

21. The speed of an induction motor can be controlled by varying the:
A) Stator voltage
B) Rotor resistance
C) Supply frequency
D) All of the above
Answer: D) All of the above

22. Which motor is most commonly used in household appliances like fans and pumps?
A) Induction motor
B) DC shunt motor
C) Synchronous motor
D) Universal motor
Answer: A) Induction motor

23. A buck-boost converter is used to:
A) Step up voltage
B) Step down voltage
C) Step up or step down voltage
D) Convert AC to DC
Answer: C) Step up or step down voltage

24. The rotor of a synchronous motor is rotated at:
A) Synchronous speed
B) Sub-synchronous speed
C) Supra-synchronous speed
D) None of the above
Answer: A) Synchronous speed

25. The efficiency of an electric drive system is highest when:
A) Power factor is low
B) Power factor is high
C) Speed is low
D) Speed is high
Answer: B) Power factor is high

26. The speed of a permanent magnet synchronous motor is controlled by varying the:
A) Stator voltage
B) Rotor resistance
C) Supply frequency
D) Permanent magnet strength
Answer: C) Supply frequency

27. Which motor is used in cranes and hoists for its high starting torque?
A) Squirrel cage induction motor
B) Slip ring induction motor
C) DC series motor
D) DC shunt motor
Answer: C) DC series motor

28. A Cycloconverter is used for:
A) Speed control of DC motor
B) Variable voltage and variable frequency AC output
C) Speed control of induction motor
D) Variable voltage DC output
Answer: B) Variable voltage and variable frequency AC output

29. The direction of rotation of a DC motor can be reversed by reversing:
A) The armature current
B) The field current
C) Both armature and field currents
D) The direction of the supply voltage
Answer: D) The direction of the supply voltage

30. The efficiency of an electric drive is defined as:
A) Output power / Input power
B) Input power / Output power
C) Speed / Torque
D) Voltage / Current
Answer: A) Output power / Input power

31. The duty cycle in PWM control of motors refers to:
A) On-time of the motor
B) Off-time of the motor
C) Ratio of on-time to off-time
D) None of the above
Answer: C) Ratio of on-time to off-time

32. Which of the following is not a method of speed control in AC motors?
A) Pole changing
B) Slip power recovery
C) Rotor resistance control
D) Commutation control
Answer: D) Commutation control

33. The braking torque in an electric drive is proportional to:
A) Supply voltage
B) Square of supply voltage
C) Square of speed
D) Square of torque
Answer: B) Square of supply voltage

34. A sensorless control technique for motors uses:
A) Hall sensors
B) Encoders
C) Back EMF
D) Thermistors
Answer: C) Back EMF

35. The torque developed by an induction motor is approximately proportional to:
A) Stator voltage
B) Rotor resistance
C) Slip
D) Rotor current
Answer: C) Slip

36. The efficiency of an electric motor can be improved by:
A) Increasing losses in the motor
B) Decreasing losses in the motor
C) Using a smaller motor
D) Running the motor at high speed
Answer: B) Decreasing losses in the motor

37. Which motor type is preferred for applications requiring high starting torque?
A) Synchronous motor
B) Induction motor
C) DC shunt motor
D) Universal motor
Answer: D) Universal motor

38. The power factor of an electric motor can be improved by:
A) Using large capacitors
B) Using large inductors
C) Using synchronous motors
D) Running the motor at low speed
Answer: C) Using synchronous motors

39. A DC chopper is used for:
A) Rectification
B) Inversion
C) Speed control of DC motors
D) Starting of DC motors
Answer: C) Speed control of DC motors

40. Which motor is not suitable for applications requiring constant speed operation?
A) DC series motor
B) Synchronous motor
C) Induction motor
D) DC shunt motor
Answer: A) DC series motor

41. A four-quadrant operation of a DC motor is possible with:
A) PWM control
B) H-bridge inverter
C) Cycloconverter
D) Ward Leonard control
Answer: B) H-bridge inverter

42. In a VFD, the DC link voltage is:
A) Fixed
B) Variable
C) AC
D) Zero
Answer: B) Variable

43. The starting torque of a single-phase induction motor is:
A) High
B) Low
C) Zero
D) Depends on the supply voltage
Answer: B) Low

44. In a servo motor, feedback is typically provided by:
A) Potentiometer
B) Encoder
C) Thermistor
D) Transformer
Answer: B) Encoder

45. Which motor type has the highest efficiency among the following?
A) DC motor
B) Induction motor
C) Synchronous motor
D) Universal motor
Answer: C) Synchronous motor

46. The torque developed by a permanent magnet DC motor is proportional to:
A) Armature current
B) Field current
C) Speed
D) Supply voltage
Answer: A) Armature current

47. A VFD converts:
A) DC to AC
B) AC to DC
C) AC to variable frequency AC
D) DC to variable frequency AC
Answer: D) DC to variable frequency AC

48. In a DC series motor, speed regulation is:
A) Good
B) Poor
C) Very poor
D) Zero
Answer: B) Poor

49. The main advantage of a brushless DC motor (BLDC) over a brushed DC motor is:
A) Higher efficiency
B) Lower cost
C) Simplicity
D) Higher torque
Answer: A) Higher efficiency

50. The power rating of an electric drive system is typically measured in:
A) Amperes
B) Volts
C) Watts
D) Hertz
Answer: C) Watts

Electric Drives MCQs

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