Harmonics and Filters — MCQs – EE

1. Harmonics in power systems are:
(A) Voltages or currents at frequencies that are integer multiples of the fundamental frequency
(B) Random noise signals
(C) DC components only
(D) Frequency deviations

2. The fundamental frequency in most power systems is:
(A) 50 Hz or 60 Hz
(B) 100 Hz
(C) 25 Hz
(D) 400 Hz

3. Total Harmonic Distortion (THD) quantifies:
(A) The ratio of the RMS value of all harmonic components to the RMS value of the fundamental
(B) Only the 3rd harmonic
(C) Peak voltage of the fundamental
(D) Load current

4. The most common odd harmonics in power systems are:
(A) 3rd, 5th, 7th
(B) 2nd, 4th, 6th
(C) 1st, 2nd, 3rd
(D) 6th, 12th, 18th

5. The 3rd harmonic is also called:
(A) Triplen harmonic
(B) Quadratic harmonic
(C) Fundamental
(D) Non-integer harmonic

6. Non-linear loads that produce harmonics include:
(A) Rectifiers, variable frequency drives, and fluorescent lamps
(B) Resistive heaters only
(C) Synchronous motors only
(D) Transformers under no-load

7. Effects of harmonics include:
(A) Heating of transformers, cables, and capacitors
(B) Improved voltage regulation
(C) Lower losses
(D) Reduced current

8. Harmonics can cause:
(A) Misoperation of protective relays and malfunctioning of sensitive electronics
(B) Higher efficiency
(C) Lower neutral currents in three-phase systems
(D) Constant torque in motors

9. Voltage harmonics can result in:
(A) Overvoltage stress on insulation
(B) Reduced RMS voltage
(C) Lower frequency
(D) Reduced efficiency only in resistive loads

10. The most significant harmonic in a six-pulse rectifier is:
(A) 5th and 7th
(B) 3rd only
(C) 2nd only
(D) 11th only

11. Active power filters (APFs) are used to:
(A) Inject currents to cancel harmonics
(B) Increase voltage sag
(C) Reduce load power factor
(D) Improve grounding

12. Passive filters are composed of:
(A) Inductors, capacitors, and resistors
(B) Only resistors
(C) Only capacitors
(D) Only inductors

13. A tuned passive filter is designed to:
(A) Eliminate specific harmonic frequencies
(B) Increase system frequency
(C) Reduce load power factor
(D) Eliminate DC components

14. High-pass filters are used to:
(A) Block low frequencies and pass high-frequency harmonics
(B) Block high frequencies
(C) Only pass fundamental
(D) Reduce voltage sag

15. Low-pass filters are used to:
(A) Pass fundamental frequency and block high-frequency harmonics
(B) Pass harmonics only
(C) Increase THD
(D) Increase reactive power

16. Detuned filters prevent:
(A) Resonance between capacitor banks and system inductance
(B) Voltage sags
(C) Motor overheating
(D) Frequency deviation

17. Resonance in power systems occurs when:
(A) System inductive reactance equals capacitive reactance at a harmonic frequency
(B) Voltage exceeds rated value
(C) Current exceeds rated value
(D) Frequency drops below nominal

18. Effects of triplen harmonics in three-phase systems include:
(A) High neutral currents in star-connected systems
(B) Reduced copper losses
(C) Improved power factor
(D) Reduced harmonic distortion

19. Total demand distortion (TDD) is:
(A) The RMS of harmonics divided by rated load current
(B) The fundamental current
(C) Voltage sag magnitude
(D) Frequency deviation

20. Harmonic distortion can lead to:
(A) Increased capacitor heating
(B) Reduced power factor
(C) Higher torque in motors
(D) Improved insulation life

21. IEEE Standard 519 sets limits for:
(A) Harmonic distortion in power systems
(B) Voltage sag only
(C) Frequency stability
(D) Power factor correction

22. Harmonics can cause electromagnetic interference (EMI) in:
(A) Sensitive electronic devices
(B) Induction motors only
(C) Transformers only
(D) Lighting loads only

23. Active filters are preferable over passive filters because:
(A) They can adapt to changing harmonic levels
(B) They are cheaper
(C) They require no power supply
(D) They produce reactive power only

24. Single-tuned filters are designed for:
(A) One specific harmonic frequency
(B) All harmonic frequencies
(C) Fundamental frequency only
(D) DC components

25. Multi-tuned filters are used to:
(A) Eliminate multiple harmonic frequencies simultaneously
(B) Reduce fundamental voltage
(C) Increase frequency
(D) Improve mechanical stability

26. Passive filters can also provide:
(A) Reactive power compensation
(B) Voltage stabilization
(C) Frequency correction
(D) Surge protection

27. Harmonics in motors can lead to:
(A) Excessive heating and vibration
(B) Reduced copper losses only
(C) Higher efficiency
(D) Reduced speed

28. Harmonics increase eddy current losses in:
(A) Transformer cores
(B) Mechanical shafts
(C) Insulation
(D) Capacitors

29. Harmonic mitigation is necessary for:
(A) Protecting equipment, reducing losses, and improving power quality
(B) Increasing frequency
(C) Reducing insulation class
(D) Decreasing system voltage

30. The main goal of harmonic filters is to:
(A) Reduce total harmonic distortion and improve overall power quality
(B) Increase THD
(C) Increase neutral currents
(D) Reduce system efficiency