Harmonic analysis and power quality studies – MCQs – EE

1. Harmonics in power systems are caused by:
(A) Purely resistive loads
(B) Nonlinear loads
(C) Ideal transformers
(D) Synchronous generators

2. Total Harmonic Distortion (THD) measures:
(A) Only voltage magnitude
(B) Ratio of harmonic content to fundamental
(C) Load current
(D) Step response only

3. Harmonics can cause:
(A) Overheating of transformers and motors
(B) Only reactive power improvement
(C) Load shedding
(D) Improved system efficiency

4. Power quality issues include:
(A) Only frequency deviation
(B) Voltage sags, swells, flicker, and harmonics
(C) Step response plots only
(D) RMS voltage measurement

5. A passive filter is used to:
(A) Block specific harmonic frequencies
(B) Improve generator efficiency
(C) Step response only
(D) Measure THD

6. Active filters are used for:
(A) Harmonic mitigation
(B) Voltage measurement only
(C) Transformer protection
(D) Step response

7. Single-tuned filters are designed for:
(A) Specific harmonic frequency
(B) All frequencies
(C) Voltage only
(D) Load current only

8. Interharmonics are:
(A) Multiples of the fundamental frequency
(B) Non-integer multiples of the fundamental frequency
(C) Pure DC components
(D) Step response only

9. Sources of harmonics include:
(A) Linear loads
(B) Nonlinear devices like rectifiers and inverters
(C) Ideal voltage sources
(D) Step response blocks

10. Harmonics can cause:
(A) Reduced losses
(B) Resonance, overheating, and misoperation of protective devices
(C) Improved voltage stability
(D) Load balancing

11. Power factor is affected by:
(A) Only resistance
(B) Harmonics and reactive power
(C) Step response only
(D) Transformer tap

12. THD is expressed as:
(A) A percentage of fundamental frequency
(B) Absolute voltage
(C) Load current only
(D) Step response time

13. Harmonic resonance occurs when:
(A) Filter reactance matches system impedance at a harmonic frequency
(B) Voltage drops to zero
(C) Step response only
(D) Current is balanced

14. Voltage sag is defined as:
(A) Momentary decrease in RMS voltage
(B) Increase in frequency
(C) Step response only
(D) DC offset

15. Voltage swell is:
(A) Momentary increase in RMS voltage
(B) Decrease in current
(C) Step response only
(D) Harmonic injection

16. Flicker is caused by:
(A) Rapid voltage fluctuations
(B) Harmonic resonance
(C) Load balancing
(D) Step response only

17. Harmonic distortion can be minimized by:
(A) Using nonlinear loads
(B) Passive or active filters
(C) Step response only
(D) Reducing transformer ratings

18. Power quality monitoring includes:
(A) Voltage, current, frequency, harmonics
(B) Step response only
(C) Load flow only
(D) Transformer tap positions

19. 5th and 7th harmonics are usually caused by:
(A) Linear resistive loads
(B) Three-phase rectifiers
(C) Step response only
(D) Ideal voltage sources

20. Harmonic currents can cause:
(A) Transformer overheating and neutral conductor overload
(B) Step response only
(C) Improved efficiency
(D) Voltage regulation improvement

21. Power factor correction capacitors can:
(A) Reduce harmonics if properly designed
(B) Increase step response
(C) Reduce load only
(D) Measure THD

22. Interharmonics may lead to:
(A) Equipment malfunction
(B) Load balancing
(C) Step response only
(D) Improved harmonic filtering

23. Current THD is calculated as:
(A) RMS value of all harmonic currents divided by fundamental current
(B) Step response only
(C) Absolute voltage
(D) Only fundamental current

24. Harmonic voltage distortion affects:
(A) Sensitive loads and power electronics
(B) Step response only
(C) Load shedding
(D) Transformer rating only

25. Mitigation of harmonics improves:
(A) System efficiency, equipment life, and voltage quality
(B) Step response only
(C) Load flow only
(D) Current unbalance

26. Nonlinear loads include:
(A) Resistive heaters
(B) Rectifiers, variable speed drives, UPS systems
(C) Step response blocks
(D) Ideal generators

27. THD for voltage is normally limited to:
(A) 10–15%
(B) Step response only
(C) 50%
(D) 100%

28. Harmonics can be represented by:
(A) Fourier series
(B) Step response only
(C) Load flow only
(D) RMS measurement only

29. Active harmonic filters inject:
(A) Currents to cancel harmonics
(B) Step response only
(C) Only voltage
(D) Only reactive power

30. Poor power quality can cause:
(A) Malfunction of sensitive equipment and increased losses
(B) Step response only
(C) Improved efficiency
(D) Reduced losses