33 Power Quality & Harmonics questions from the Electrical Design bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
Free to start: the 2-minute EE readiness check — six questions and a result.
A.drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
B.parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
C.short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
D.ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
Answer + AI explanation with Pro
2. Which term means: "ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current"?
Junior
A.Triplen harmonics
B.12-pulse rectifier
C.Voltage sag
D.Total harmonic distortion
Answer + AI explanation with Pro
3. Which statement is correct?
Junior
A.Total harmonic distortion — required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
B.Total harmonic distortion — voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
C.Total harmonic distortion — short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
D.Total harmonic distortion — ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
Answer + AI explanation with Pro
4. What is Displacement vs true power factor?
Junior
A.voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
B.drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
C.series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.displacement PF is cos φ of the fundamental only; true PF includes distortion, so a VFD can show 0.95 displacement but 0.7 true
Answer + AI explanation with Pro
5. Which term means: "displacement PF is cos φ of the fundamental only; true PF includes distortion, so a VFD can show 0.95 displacement but 0.7 true"?
Junior
A.IEEE 519 voltage limits
B.Displacement vs true power factor
C.Triplen harmonics
D.Harmonic resonance
Answer + AI explanation with Pro
6. Which statement is correct?
Junior
A.Displacement vs true power factor — short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
B.Displacement vs true power factor — displacement PF is cos φ of the fundamental only; true PF includes distortion, so a VFD can show 0.95 displacement but 0.7 true
C.Displacement vs true power factor — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.Displacement vs true power factor — drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
Answer + AI explanation with Pro
7. What is Voltage sag?
Junior
A.required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
B.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
C.displacement PF is cos φ of the fundamental only; true PF includes distortion, so a VFD can show 0.95 displacement but 0.7 true
D.drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
Answer + AI explanation with Pro
8. Which term means: "drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159"?
Junior
A.Total harmonic distortion
B.Detuned filter reactor
C.12-pulse rectifier
D.Voltage sag
Answer + AI explanation with Pro
9. Which statement is correct?
Junior
A.Voltage sag — two 6-pulse bridges fed by delta and star secondaries cancel the 5th and 7th, leaving the 11th and 13th as the lowest characteristic harmonics
B.Voltage sag — ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
C.Voltage sag — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.Voltage sag — drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
Answer + AI explanation with Pro
10. What is IEEE 519 voltage limits?
Mid
A.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
B.two 6-pulse bridges fed by delta and star secondaries cancel the 5th and 7th, leaving the 11th and 13th as the lowest characteristic harmonics
C.current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
D.voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
Answer + AI explanation with Pro
11. Which term means: "voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling"?
Mid
A.IEEE 519 voltage limits
B.Detuned filter reactor
C.Total harmonic distortion
D.Capacitor bank sizing
Answer + AI explanation with Pro
12. Which statement is correct?
Mid
A.IEEE 519 voltage limits — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
B.IEEE 519 voltage limits — 3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
C.IEEE 519 voltage limits — voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
D.IEEE 519 voltage limits — ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
Answer + AI explanation with Pro
13. What is IEEE 519 current TDD?
Mid
A.required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
B.parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
C.current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
D.series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
Answer + AI explanation with Pro
14. Which term means: "current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000"?
Mid
A.Flicker Pst
B.Voltage sag
C.IEEE 519 current TDD
D.Triplen harmonics
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.IEEE 519 current TDD — current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
B.IEEE 519 current TDD — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
C.IEEE 519 current TDD — ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
D.IEEE 519 current TDD — voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
Answer + AI explanation with Pro
16. What is Capacitor bank sizing?
Mid
A.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
B.voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
C.required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
D.short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
Answer + AI explanation with Pro
17. Which term means: "required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor"?
Mid
A.Flicker Pst
B.12-pulse rectifier
C.Detuned filter reactor
D.Capacitor bank sizing
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
A.Capacitor bank sizing — required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
B.Capacitor bank sizing — drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
C.Capacitor bank sizing — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.Capacitor bank sizing — voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
Answer + AI explanation with Pro
19. What is Detuned filter reactor?
Mid
A.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
B.series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
C.drop to 10–90% of nominal rms lasting half a cycle to one minute, usually from remote faults or large motor starting, per IEEE 1159
D.ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
Answer + AI explanation with Pro
20. Which term means: "series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply"?
Mid
A.Voltage sag
B.Total harmonic distortion
C.Detuned filter reactor
D.IEEE 519 voltage limits
Answer + AI explanation with Pro
21. Which statement is correct?
Mid
A.Detuned filter reactor — ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
B.Detuned filter reactor — required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
C.Detuned filter reactor — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.Detuned filter reactor — parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
Answer + AI explanation with Pro
22. What is Harmonic resonance?
Mid
A.parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
B.series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
C.ratio of the rms of all harmonic components to the fundamental, expressed as a percentage, for either voltage or current
D.displacement PF is cos φ of the fundamental only; true PF includes distortion, so a VFD can show 0.95 displacement but 0.7 true
Answer + AI explanation with Pro
23. Which term means: "parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses"?
Mid
A.Harmonic resonance
B.Triplen harmonics
C.Capacitor bank sizing
D.Displacement vs true power factor
Answer + AI explanation with Pro
24. Which statement is correct?
Mid
A.Harmonic resonance — 3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
B.Harmonic resonance — parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
C.Harmonic resonance — two 6-pulse bridges fed by delta and star secondaries cancel the 5th and 7th, leaving the 11th and 13th as the lowest characteristic harmonics
D.Harmonic resonance — short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
Answer + AI explanation with Pro
25. What is Flicker Pst?
Mid
A.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
B.current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
C.parallel resonance between PF capacitors and source inductance near f1·√(Ssc/Qc), amplifying a nearby harmonic and blowing capacitor fuses
D.short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
Answer + AI explanation with Pro
26. Which term means: "short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold"?
Mid
A.Detuned filter reactor
B.Flicker Pst
C.12-pulse rectifier
D.IEEE 519 voltage limits
Answer + AI explanation with Pro
27. Which statement is correct?
Mid
A.Flicker Pst — two 6-pulse bridges fed by delta and star secondaries cancel the 5th and 7th, leaving the 11th and 13th as the lowest characteristic harmonics
B.Flicker Pst — current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
C.Flicker Pst — series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
D.Flicker Pst — short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
Answer + AI explanation with Pro
28. What is Triplen harmonics?
Senior
A.series reactor of 7% (189 Hz tuning) makes the capacitor bank inductive at the 5th harmonic so it cannot resonate with the supply
B.voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
C.required kVAr equals kW times (tan φ1 − tan φ2) to move from the existing to the target power factor
D.3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
Answer + AI explanation with Pro
29. Which term means: "3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current"?
Senior
A.Capacitor bank sizing
B.Triplen harmonics
C.Flicker Pst
D.Total harmonic distortion
Answer + AI explanation with Pro
30. Which statement is correct?
Senior
A.Triplen harmonics — short-term flicker severity from a 10-minute measurement per IEC 61000-4-15, where Pst = 1 is the conventional irritation threshold
B.Triplen harmonics — voltage THD limited to 8% at 1 kV and below, 5% for 1–69 kV and 2.5% for 69–161 kV at the point of common coupling
C.Triplen harmonics — current distortion limit depends on the Isc/IL ratio at the PCC, from 5% for a stiff ratio below 20 up to 20% above 1000
D.Triplen harmonics — 3rd, 9th and 15th order zero-sequence harmonics that add in the neutral of a four-wire system and can load the neutral above phase current
Answer + AI explanation with Pro
Showing 30 of 33 Power Quality & Harmonics questions — the full set, with answers, explanations and an AI tutor on every question, is inside.
Free to start
Start with a free readiness check
Sign up free for the 2-minute EE readiness check and a scored result. Answers, explanations and the AI tutor on every Power Quality & Harmonics question come with Pro.