Capacitor Bank Calculator Formula

Understand the math behind the capacitor bank calculator. Each variable explained with a worked example.

Use the Capacitor Bank Calculator

Formulas Used

Required Capacitor Bank

kvar_required = real_power * (sqrt(1 / pow(pf_existing, 2) - 1) - sqrt(1 / pow(pf_target, 2) - 1))

Apparent Power Before

kva_before = real_power / pf_existing

Apparent Power After

kva_after = real_power / pf_target

Variables

VariableDescriptionDefault
real_powerReal Power (P)(kW)200
pf_existingExisting Power Factor0.75
pf_targetTarget Power Factor0.95

How It Works

Power Factor Correction with Capacitors

Capacitor banks supply reactive power locally, reducing the reactive current drawn from the supply.

Formula

Q_c = P (tan(phi_1) - tan(phi_2))

where P is real power, phi_1 = arccos(PF_old), phi_2 = arccos(PF_new). Equivalently: tan(phi) = sqrt(1/PF^2 - 1).

Worked Example

Improve power factor from 0.75 to 0.95 on a 200 kW load.

real_power = 200pf_existing = 0.75pf_target = 0.95
  1. 01tan(phi_1) = sqrt(1/0.75^2 - 1) = sqrt(0.778) = 0.882
  2. 02tan(phi_2) = sqrt(1/0.95^2 - 1) = sqrt(0.108) = 0.329
  3. 03Q_c = 200 x (0.882 - 0.329) = 200 x 0.553 = 110.6 kVAR
  4. 04Select 120 kVAR capacitor bank (next standard size).

Ready to run the numbers?

Open Capacitor Bank Calculator