Power Factor Correction Calculator

Calculate capacitor bank size needed to correct power factor and reduce reactive power charges on commercial electrical systems.

Results

Visualization

How It Works

Power factor is the ratio of real power (kW) to apparent power (kVA). A low power factor means your system draws more current than needed to do the same work, wasting energy as reactive power. Utilities penalize commercial customers with PF below 0.85-0.90. Capacitor banks supply reactive power locally, reducing what the utility must deliver.

The Formula

kVAR needed = kW x (tan(arccos(PFcurrent)) - tan(arccos(PFtarget)))
kVA = kW / PF

Variables

  • kW — Real power -- the actual work being done (what you pay for in energy charges)
  • kVA — Apparent power -- the total power the utility must deliver (kW + reactive component)
  • kVAR — Reactive power -- the "wasted" component that shuttles between source and load doing no work
  • PF — Power Factor -- kW / kVA (1.0 is perfect, below 0.85 is poor)

Example

A 50 kW load at 0.75 PF: kVA = 50/0.75 = 66.7 kVA, kVAR = 50 x tan(acos(0.75)) = 44.1 kVAR. To correct to 0.95 PF: kVAR needed = 50 x (tan(41.4deg) - tan(18.2deg)) = 27.7 kVAR capacitor bank.

Tips

  • Power factor penalties typically apply to commercial and industrial accounts, not residential.
  • Fixed capacitor banks are cheapest but may over-correct at light loads. Automatic switching banks adjust to varying loads.
  • Over-correction (PF > 1.0 leading) can be as problematic as under-correction -- size capacitors carefully.
  • Motors and fluorescent lighting are the biggest causes of low power factor in commercial buildings.
  • VFDs (variable frequency drives) on motors can worsen power factor due to harmonic distortion -- use harmonic-rated capacitors.