Enter the real power of the load, the present and the target power factor, voltage and frequency. The calculator gives the kVAR of capacitors to add and what that does to current and kVA.
Capacitor bank needed
kVAR
Capacitance per phase
µF
Current before
A
Current after
A
Apparent power after (before)
How power factor correction is calculated
Inductive loads such as motors and transformers draw reactive power that does no work but still flows in the cables. Capacitors supply that reactive power locally. The kVAR needed is the difference between the reactive power now and at the target power factor:
QC = P · (tan φ1 − tan φ2)
Three-phase, delta: C = QC ÷ (3 · 2πf · V²)
Single-phase: C = QC ÷ (2πf · V²)
P
real power of the load in kW
φ1, φ2
angles of the present and target power factor, φ = arccos(PF)
V
voltage across the capacitor (line voltage in delta)
f
frequency, 50 or 60 Hz
Worked example
A plant draws 100 kW at a power factor of 0.75 from 480 V, 60 Hz. To reach 0.95 it needs 100 × (0.882 − 0.329) = 55.3 kVAR. In delta that is 212 µF per phase. The current falls from 160 A to 127 A, and the apparent power from 133 to 105 kVA.
Capacitor kVAR = kW × (tan φ1 − tan φ2), where φ1 = arccos of the present power factor and φ2 = arccos of the target. For 100 kW from 0.75 to 0.95: 100 × (0.882 − 0.329) = 55.3 kVAR.
How do I convert kVAR to microfarads?
Single-phase: C = Q ÷ (2π × f × V²). Three-phase delta, per capacitor: C = Q ÷ (3 × 2π × f × V²) with V the line voltage. 55 kVAR at 480 V, 60 Hz is about 211 µF per phase in delta.
Why correct the power factor?
A low power factor means more current for the same real power. That raises cable and transformer losses, uses up capacity and on many commercial tariffs adds a reactive power or demand charge. Raising it to 0.95 typically cuts the current by 15 to 25%.
Can I correct to a power factor of 1.0?
It is not recommended. At light load the capacitors would push the system into a leading power factor, and the bank can resonate with harmonics from drives. Most designs aim for 0.95 to 0.98 and use detuned or automatic banks where drives are present.