Power Quality MCQs

1. What is the acceptable voltage variation limit for sensitive electronic equipment as per IEEE standards?
A. ±5%
B. ±10%
C. ±15%
D. ±20%
Answer: B

2. Harmonics in power systems are primarily caused by:
A. Unbalanced loads
B. Non-linear loads
C. Overloaded transformers
D. Voltage sags
Answer: B

3. The total harmonic distortion (THD) is a measure of:
A. Voltage stability
B. Frequency stability
C. Power factor
D. Harmonic content
Answer: D

4. Which power quality issue is characterized by a brief reduction in voltage?
A. Surge
B. Sag
C. Swell
D. Interruption
Answer: B

5. A voltage sag lasting from a few milliseconds to a few seconds is typically caused by:
A. Lightning strikes
B. Transformer faults
C. Motor starting
D. Capacitor switching
Answer: C

6. What type of power quality issue results in a sudden increase in voltage?
A. Sag
B. Swell
C. Interruption
D. Harmonic distortion
Answer: B

7. A power quality issue that can be caused by lightning strikes or switching operations is:
A. Sag
B. Swell
C. Interruption
D. Surge
Answer: D

8. Which of the following devices is commonly used to mitigate voltage sags?
A. Surge protector
B. Voltage regulator
C. Capacitor bank
D. Uninterruptible power supply (UPS)
Answer: B

9. The main purpose of a UPS (Uninterruptible Power Supply) in relation to power quality is to:
A. Reduce harmonics
B. Regulate voltage
C. Provide backup power during interruptions
D. Correct power factor
Answer: C

10. Which parameter is measured to evaluate the quality of AC power?
A. Voltage only
B. Current only
C. Voltage and current
D. Power factor only
Answer: C

11. A power quality problem that can result from rapid changes in load currents is:
A. Harmonic distortion
B. Voltage sag
C. Voltage swell
D. Transient
Answer: D

12. The flicker effect in lighting systems is primarily caused by:
A. Harmonic distortion
B. Voltage sag
C. Voltage swell
D. Rapid voltage fluctuations
Answer: D

13. The rapid change in voltage lasting for a few microseconds to milliseconds is called:
A. Sag
B. Swell
C. Transient
D. Interruption
Answer: C

14. Which type of device is used to suppress or mitigate transients in power systems?
A. Surge protector
B. Voltage stabilizer
C. UPS
D. Inverter
Answer: A

15. The phenomenon where the waveform of the current does not follow the voltage waveform is known as:
A. Voltage sag
B. Voltage swell
C. Current harmonics
D. Power factor
Answer: C

16. What is the typical frequency range for power system harmonics?
A. 50-60 Hz
B. 100-120 Hz
C. 200-240 Hz
D. 400-480 Hz
Answer: A

17. A sudden loss of voltage for a short duration is known as a:
A. Sag
B. Swell
C. Surge
D. Interruption
Answer: D

18. The presence of which of the following is a common cause of harmonic distortion?
A. Resistive loads
B. Inductive loads
C. Capacitive loads
D. Non-linear loads
Answer: D

19. The ratio of the real power to the apparent power in a power system is known as:
A. Voltage sag
B. Power factor
C. Voltage swell
D. Harmonic distortion
Answer: B

20. A prolonged increase in voltage beyond the normal level is known as:
A. Sag
B. Swell
C. Surge
D. Flicker
Answer: B

21. In a power quality context, what does “EMI” stand for?
A. Electrical Maintenance Issue
B. Electromagnetic Interference
C. Electrical Measurement Instrument
D. Energy Management Interface
Answer: B

22. A device that can help reduce voltage variations and regulate the voltage supplied to sensitive equipment is called a:
A. Surge protector
B. Voltage regulator
C. Harmonic filter
D. Transformer
Answer: B

23. A sudden, short-duration increase in voltage is known as a:
A. Sag
B. Swell
C. Surge
D. Flicker
Answer: C

24. Which power quality issue is most likely to cause overheating and premature failure of electrical equipment?
A. Voltage sag
B. Voltage swell
C. Harmonic distortion
D. Transient
Answer: C

25. The measure of how effectively power is being used in a system is indicated by:
A. Voltage
B. Current
C. Power factor
D. Harmonic content
Answer: C

26. A device used to smooth out voltage fluctuations and protect sensitive equipment from power surges is called a:
A. Transformer
B. Capacitor
C. Surge protector
D. Circuit breaker
Answer: C

27. In a power system, the term “brownout” refers to:
A. A complete loss of voltage
B. A slight decrease in voltage
C. A rapid increase in voltage
D. A momentary interruption of voltage
Answer: B

28. Which of the following is not a typical cause of voltage sags?
A. Faults in power lines
B. Lightning strikes
C. Starting large motors
D. Faulty transformers
Answer: B

29. The term “crest factor” in power quality refers to the ratio of:
A. Peak value to RMS value
B. Maximum to minimum voltage
C. Maximum to minimum current
D. Active power to apparent power
Answer: A

30. A device that can help mitigate flicker in lighting systems is called a:
A. Surge protector
B. Voltage stabilizer
C. Power conditioner
D. Harmonic filter
Answer: C

31. What is the main purpose of a harmonic filter in a power system?
A. To reduce voltage sags
B. To eliminate voltage surges
C. To mitigate harmonic distortion
D. To stabilize power factor
Answer: C

32. A sudden increase in voltage above normal levels that lasts for a short duration is known as a:
A. Sag
B. Swell
C. Surge
D. Flicker
Answer: C

33. A power quality issue characterized by a steady-state overvoltage condition is known as a:
A. Sag
B. Swell
C. Surge
D. Interruption
Answer: B

34. What type of load is typically responsible for generating harmonic currents in a power system?
A. Purely resistive
B. Purely inductive
C. Purely capacitive
D. Non-linear
Answer: D

35. The effect of harmonic distortion on power systems can include:
A. Overheating of transformers
B. Increased power factor
C. Improved voltage regulation
D. Decreased current
Answer: A

36. The term “power factor” indicates the:
A. Ratio of real power to reactive power
B. Ratio of apparent power to real power
C. Ratio of active power to reactive power
D. Ratio of apparent power to reactive power
Answer: B

37. A power quality issue that can cause visible fluctuations in lighting brightness is:
A. Harmonic distortion
B. Voltage sag
C. Voltage swell
D. Transient
Answer: A

38. In power systems, harmonic currents can result in:
A. Increased energy efficiency
B. Reduced losses
C. Voltage distortion
D. Improved power factor
Answer: C

39. A device that maintains a constant output voltage despite fluctuations in input voltage is called a:
A. Surge protector
B. Voltage regulator
C. Capacitor bank
D. UPS
Answer: B

40. The phenomenon where there is a sudden, complete loss of voltage for a short duration is known as a:
A. Sag
B. Swell
C. Surge
D. Interruption
Answer: D

41. Which type of power quality issue is characterized by a continuous overvoltage condition?
A. Sag
B. Swell
C. Surge
D. Flicker
Answer: B

42. A device that can provide temporary power during a mains power failure is:
A. Inverter
B. Transformer
C. Generator
D. Surge protector
Answer: C

43. The term “power quality” refers to the:
A. Efficiency of power generation
B. Stability of power supply
C. Cleanliness of electrical signals
D. Safety of electrical installations
Answer: C

44. A device that can help maintain a stable voltage supply to sensitive equipment during fluctuations is called a:
A. Capacitor bank
B. Surge protector
C. Voltage regulator
D. Harmonic filter
Answer: C

45. A transient voltage surge suppressor is designed to protect against:
A. Harmonic distortion
B. Voltage sag
C. Voltage swell
D. Power surges
Answer: D

46. The term “flicker” in power quality refers to:
A. Sudden voltage increases
B. Rapid changes in voltage
C. Oscillating voltage levels
D. High-frequency harmonics
Answer: B

47. A device used to correct power factor in industrial applications is called a:
A. Transformer
B. Capacitor bank
C. Surge protector
D. Inverter
Answer: B

48. The presence of which of the following can indicate poor power quality?
A. High power factor
B. Low current harmonics
C. Low crest factor
D. High THD (Total Harmonic Distortion)
Answer: D

49. A device that converts DC power into AC power during a mains power failure is called a:
A. Capacitor
B. Inverter
C. Transformer
D. Generator
Answer: B

50. Which parameter indicates the efficiency with which electrical power is converted into useful work?
A. Power factor
B. Crest factor
C. Efficiency factor
D. Harmonic factor
Answer: A

Power Quality MCQs

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