Power Factor Correction (kVAr) Calculator
Size the capacitor bank your facility needs to reach its target power factor and stay out of the penalty band.
Your facility load in kilowatts
Typically 0.98 to stay clear of the penalty band
Result
What is power factor correction and why do you need it?
Inductive loads (motors, transformers, ballasts) draw reactive power from the grid while running. This power does no useful work but burdens the grid and lowers your power factor (cosφ). As power factor drops, the distribution company applies a reactive penalty. Power factor correction (compensation) uses an on-site capacitor bank to supply that reactive power locally, so the reactive power drawn from the grid falls, cosφ rises and the penalty disappears.
How is the required kVAr calculated?
The formula is Q = P × (tan φ1 − tan φ2), where P is your active power (kW), φ1 the angle of your current power factor and φ2 that of the target. For example, with a 250 kW load, current cosφ 0.75 and target 0.98: tan(arccos 0.75) = 0.882, tan(arccos 0.98) = 0.203. Required kVAr = 250 × (0.882 − 0.203) = ≈ 170 kVAr. The tool above does this for you.
Choosing the right target power factor
A common target is 0.98. It keeps you safely clear of the inductive penalty band without pushing you into capacitive penalties. Aiming for exactly 1.0 is risky: when the facility goes idle (night, weekend), the capacitors left engaged push capacitive power back onto the grid, causing a capacitive penalty. So the target is kept in the 0.98–0.99 range.
Steps, not one big bank
Installing your total kVAr as a single large capacitor is wrong. Load varies through the day; a fixed bank over-compensates at low load. The right approach is to split the total capacity into steps and use a reactive power relay to engage and disengage them as load changes. This keeps you balanced on both the inductive and capacitive side.
Monitor compensation with SolarTools
Capacitors age and lose capacity over time; relay settings can drift. The SolarTools compensation module monitors the health of each step, the power factor and reactive consumption in real time, and alerts you when compensation falls short. So a system you sized correctly once stays effective for years. Do your calculation above, then try monitoring free for 14 days.
Related solution
Compensation Tracking Module →Frequently Asked Questions
How is the required kVAr calculated?
Q = P × (tan(arccos φ1) − tan(arccos φ2)), where P is active power, φ1 the current power factor and φ2 the target. The tool applies this formula automatically.
What target power factor should I choose?
A target of 0.98 keeps you comfortably clear of the inductive penalty band (which starts when the ratio pushes power factor below ~0.98). Going to exactly 1.0 risks capacitive penalties at low load.
Should I install one big capacitor bank?
No. Split the total kVAr into steps controlled by a reactive power relay, so compensation follows the changing load and you avoid capacitive overshoot when the facility is idle.
Does compensation alone prevent penalties?
It reduces inductive penalties, but capacitor health, relay settings and harmonics matter too. Continuous monitoring keeps the system effective over time.
Stop penalties before they hit your bill
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