Voltage Sag, Swell, and Flicker — MCQs – EE

1. A voltage sag (dip) is defined as:
(A) A short-duration reduction in RMS voltage
(B) A permanent voltage reduction
(C) An increase in voltage magnitude
(D) A zero-voltage condition lasting hours

2. A voltage swell is:
(A) A short-duration increase in RMS voltage
(B) A long-term decrease in voltage
(C) A sustained overcurrent
(D) A frequency deviation

3. The typical duration of voltage sags and swells is:
(A) 0.5 cycles to 1 minute
(B) Several hours
(C) Microseconds only
(D) More than 1 day

4. The main causes of voltage sags are:
(A) Short circuits and starting of large motors
(B) Overvoltage
(C) Capacitor switching
(D) Lightning strikes only

5. Voltage swells are usually caused by:
(A) Sudden load reduction or switching off large loads
(B) Motor starting
(C) Ground faults
(D) Short circuits

6. The magnitude of a voltage sag is typically:
(A) 10% to 90% of nominal voltage
(B) 100% of nominal voltage
(C) Zero volts only
(D) Greater than 200% of nominal voltage

7. The magnitude of a voltage swell is usually:
(A) 110% to 180% of nominal voltage
(B) 50% to 90%
(C) Zero volts
(D) More than 300%

8. Flicker is caused by:
(A) Rapid and repetitive voltage fluctuations
(B) Harmonics only
(C) Sustained overvoltage
(D) Frequency deviations

9. Voltage flicker mainly affects:
(A) Lighting systems
(B) Transformers
(C) Capacitors
(D) Heaters

10. The standard limits for voltage sags and swells are defined by:
(A) IEC 61000-2-2 and IEEE 1159
(B) IEEE 519 only
(C) IEC 60034
(D) NEMA MG1

11. The duration of flicker that causes noticeable light intensity variations is typically:
(A) 0.5 to 30 Hz
(B) 50–60 Hz
(C) Less than 0.1 Hz
(D) More than 100 Hz

12. The short-term flicker severity is measured by:
(A) Plt
(B) THD
(C) RMS voltage
(D) Power factor

13. The long-term flicker severity is measured by:
(A) Pst
(B) Plt
(C) THD
(D) RMS current

14. The main sources of voltage flicker include:
(A) Arc furnaces, large motor starting, welding machines
(B) Lighting loads only
(C) Transformers
(D) Resistive heaters only

15. Voltage sag duration is classified as:
16. A swell lasting more than 3 minutes is considered:
(A) Sustained overvoltage
(B) Momentary swell
(C) Voltage flicker
(D) Sag

17. Voltage sag mitigation can be achieved using:
(A) Uninterruptible Power Supplies (UPS) and voltage regulators
(B) Harmonic filters only
(C) Transformers only
(D) Reactors only

18. Voltage swell mitigation includes:
(A) Tap-changing transformers and surge protection
(B) Reducing load
(C) Capacitor switching
(D) Induction motors

19. Flicker reduction methods include:
(A) Load balancing, static VAR compensators, and smoothing reactors
(B) Increasing voltage
(C) Removing transformers
(D) Reducing frequency

20. Momentary voltage dips are mostly caused by:
(A) Faults on the transmission system
(B) Capacitor switching
(C) Reactive power compensation
(D) Resistive loads

21. Voltage sags can cause:
(A) Tripping of motors and sensitive electronic equipment
(B) Reduced heating losses
(C) Reduced harmonic currents
(D) Improved insulation life

22. Voltage swell can cause:
(A) Insulation stress and equipment damage
(B) Reduced transformer losses
(C) Motor startup improvement
(D) Harmonic reduction

23. Flicker severity is evaluated by:
(A) Measuring voltage fluctuations and perceptible light variations
(B) RMS voltage only
(C) Current harmonics
(D) System frequency

24. The IEEE Standard 1453 deals with:
(A) Measurement and assessment of voltage flicker
(B) Harmonic limits
(C) Surge protection
(D) Power factor correction

25. Voltage sag and swell monitoring uses:
(A) RMS voltage monitoring instruments
(B) Power factor meters only
(C) Frequency counters
(D) Thermal sensors

26. Dynamic voltage restorers (DVRs) are used to:
(A) Mitigate voltage sags and swells in real-time
(B) Correct frequency deviations only
(C) Reduce harmonic currents
(D) Increase load power factor

27. The main impact of voltage flicker is:
(A) Visible light intensity fluctuations causing annoyance
(B) Motor overheating
(C) Capacitor failure
(D) Reduced THD

28. Power electronic converters can cause:
(A) Both voltage sags and flicker
(B) Only overvoltage
(C) Frequency drift only
(D) Reduced load current

29. Industrial arc furnaces are a major source of:
(A) Voltage flicker
(B) Steady voltage
(C) Reduced harmonic distortion
(D) Overvoltage protection

30. The main goal of addressing voltage sags, swells, and flicker is to:
(A) Ensure reliable, stable, and disturbance-free operation of electrical equipment
(B) Reduce system frequency only
(C) Increase load current
(D) Improve reactive power only