Oklahoma client has me stumped. They installed a 600 kVAR capacitor bank six months ago to correct power factor on their OG&E Schedule LPS service. PF actually got worse, dropping from 0.81 to 0.76, and now they're getting penalties. Power quality meter shows the caps are energizing properly but there's significant harmonic distortion - THD went from 3% to 12%. Could the harmonics be making the utility's PF measurements read incorrectly? Never seen this before in 15 years of doing this work.
OG&E capacitor bank causing harmonics - making PF worse?
Susan, you've got harmonic resonance. The capacitors are resonating with system inductance at probably the 5th or 7th harmonic. This actually makes power factor worse because the utility meter sees the distorted current waveform. You need harmonic analysis and likely tuned reactors to detune the capacitor bank. PG&E sees this all the time here in Silicon Valley with tech companies adding capacitors without harmonic studies.
Pete's right about the resonance issue. Had the exact same problem in Atlanta with a Georgia Power industrial customer. The capacitors were amplifying harmonics from their VFD loads. Solution was adding 5.67% series reactors to detune the bank away from the predominant harmonics. Cost about $8K but eliminated both the harmonic problems and the power factor penalties. Your client needs a full harmonic analysis before adding more correction.
I've dealt with similar issues with Westar Energy here in Kansas. The key is measuring true power factor vs displacement power factor. With harmonics present, the utility meter measures true PF which includes the distortion component. Even if your displacement PF looks good, the harmonic currents kill your true PF. OG&E probably measures true PF for billing purposes. Get an IEEE 519 compliant harmonic study done before spending more money on capacitors.