Power Factor Correction

A plain capacitor bank has only capacitors and suits loads with little harmonic content. A detuned bank puts a reactor in series with each capacitor step to prevent resonance with the network and to absorb some harmonic current. Where drives, UPS or LED lighting form a large share of the load, detuned banks are the safer choice.

Use kVAr = kW x (tan of existing angle minus tan of target angle). For 200 kW going from 0.85 to 0.98 power factor, that is about 200 x (0.62 - 0.20) = 84 kVAr. Measure kW at typical and peak load, then pick standard steps. The power factor calculator on this site gives a quick estimate.

Drives draw non-sinusoidal current, so harmonics flow into the network. A capacitor lowers the system resonance frequency, and if that lands near a dominant harmonic, current and voltage amplify, overheating and damaging the capacitor. Detuned reactors, correct capacitor voltage rating and a harmonic survey prevent this.

APFC means automatic power factor correction. A controller measures the system power factor using a CT, and switches capacitor steps in or out through contactors to hold the target value as the load changes. This avoids both low power factor at high load and leading power factor at light load.

Many tariffs reward or require power factor around 0.95 or above, with some reaching up to unity incentives, but rules vary by state and DISCOM. Setting a very high target can lead to leading power factor at light load, so many users set 0.97 to 0.99. Check your tariff order and electricity bill.