A site electrician observes that a capacitor bank for power factor correction is frequently tripping its associated overcurrent protective device. Upon further investigation, the electrician measures significant harmonic distortion downstream from a new variable frequency drive (VFD). How might the harmonics be contributing to the capacitor bank trips?

Question: A site electrician observes that a capacitor bank for power factor correction is frequently tripping its associated overcurrent protective device. Upon further investigation, the electrician measures significant harmonic distortion downstream from a new variable frequency drive (VFD). How might the harmonics be contributing to the capacitor bank trips?

Answer options:

• Harmonics are causing the capacitors to draw excessive leading current at fundamental frequency. ✅ Harmonics can create resonant conditions with the capacitor bank, leading to dangerously high currents and voltages.
• Harmonics directly increase the capacitive reactance, leading to higher current flow.
• The VFD is causing a lagging power factor that the capacitors cannot correct.

Correct answer: Harmonics can create resonant conditions with the capacitor bank, leading to dangerously high currents and voltages.

Explanation: Capacitors inherently present a lower impedance to higher frequencies. The presence of significant harmonics from non-linear loads like VFDs can create resonant circuits with the capacitor bank, leading to dangerously high harmonic currents and voltages flowing through the capacitors, often causing overcurrent protection to trip.