Capacitor Bank Calculator Formula
Understand the math behind the capacitor bank calculator. Each variable explained with a worked example.
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_existingApparent Power After
kva_after = real_power / pf_targetVariables
| Variable | Description | Default |
|---|---|---|
real_power | Real Power (P)(kW) | 200 |
pf_existing | Existing Power Factor | 0.75 |
pf_target | Target Power Factor | 0.95 |
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.
- 01tan(phi_1) = sqrt(1/0.75^2 - 1) = sqrt(0.778) = 0.882
- 02tan(phi_2) = sqrt(1/0.95^2 - 1) = sqrt(0.108) = 0.329
- 03Q_c = 200 x (0.882 - 0.329) = 200 x 0.553 = 110.6 kVAR
- 04Select 120 kVAR capacitor bank (next standard size).
Frequently Asked Questions
Should I correct to unity power factor?
Generally no. Correcting to exactly 1.0 is expensive and can cause leading power factor during light load conditions, which may create voltage rise issues. Target 0.92-0.97 for best economics.
What types of capacitor banks are available?
Fixed banks provide constant correction. Automatic (switched) banks use a controller to switch capacitor stages in and out as load varies. Automatic banks are preferred for varying loads to avoid over-correction.
Can capacitors cause harmonic problems?
Yes. Capacitors can resonate with system inductance at harmonic frequencies, amplifying harmonics. In systems with significant harmonic content (VFDs, rectifiers), use detuned capacitor banks with series reactors.
Ready to run the numbers?
Open Capacitor Bank Calculator