Why size a power factor correction capacitor?
Inductive loads such as motors and transformers cause current to lag voltage, lowering the power factor and increasing the apparent power (kVA) a supply must deliver for the same useful work. Adding a correctly sized capacitor bank supplies the reactive power the load needs locally, raising the power factor closer to 1.0 and reducing wasted current in the supply wiring.
How this calculator works
The reactive power to add is Qc = P × (tan(cos⁻¹(PF_current)) − tan(cos⁻¹(PF_target))), where P is the real power in kW. The required capacitance is then found from C = Qc / (2π·f·V²), using the appropriate voltage (phase voltage for single-phase, line voltage for a delta-connected three-phase bank). For three-phase systems, the total capacitance is split evenly across the three capacitors in the bank.
This tool gives a general engineering estimate for planning purposes. Capacitor voltage rating, switching, and protection must be selected by a qualified electrical engineer, and over-correction (power factor above unity, or leading) should be avoided.