Power Factor Correction Calculator
The capacitor bank needed to raise power factor, and what it saves.
Fundamental-frequency correction for a balanced, sinusoidal system. Sites with substantial harmonic content need a detuned or filtered bank, designed with the harmonic spectrum measured rather than assumed.
How it works
Power factor is the cosine of the angle between voltage and current. Any inductive load — motors, transformers, fluorescent ballasts, welders — pulls current that lags the voltage, and the lagging component does no work while still having to be carried by every cable, breaker and transformer between the load and the generator.
Correction adds capacitance, whose current leads by the same 90° the inductor's lags, so the two cancel locally. The reactive power to add is
Qc = P × (tan φ₁ − tan φ₂)
and the capacitance follows from Qc = 2πf C V², adjusted for how the bank is connected. Delta needs a third the capacitance of star for the same kVAR, because each capacitor sees the full line voltage rather than the line-to-neutral one — which is why delta is the normal choice.
The saving comes in three separate forms. Reactive charges disappear directly if your tariff bills them. Cable and transformer losses fall with the square of current, so correcting from 0.75 to 0.95 cuts current by 21% and I²R losses by about 38%. And released capacity is often the largest benefit of all: the same transformer that was full at 133 kVA now carries the same 100 kW at 105 kVA, leaving room to add load without an upgrade that would have cost far more than the capacitors.
Do not correct to unity. Aim for 0.95, occasionally 0.98. Overcorrection makes the system capacitive, which raises voltage, and a fixed capacitor bank left connected at light load will do exactly that. It can also resonate with the supply inductance at a harmonic frequency, and harmonic resonance destroys capacitors — which is why any installation with significant drive or rectifier load wants detuned reactors in series with the bank.
Common questions
Why not correct all the way to 1.0?
Because loads vary and a fixed bank sized for full load overcorrects at light load, making the system capacitive and pushing voltage up. 0.95 is the usual target — it captures nearly all the benefit with margin. Automatic banks that switch steps can go higher safely.
Does correction reduce my kWh bill?
Only indirectly. Real energy consumption is unchanged; you save on reactive charges if your tariff has them, on demand charges measured in kVA, and on the cable and transformer losses that fall with the square of current. On a domestic tariff billed purely in kWh there is essentially nothing to gain.
Delta or star?
Delta, normally. Each capacitor sees the full line voltage, so delta gives three times the kVAR from the same capacitance — a third of the capacitance for the same correction. Star is used at higher voltages where capacitor voltage rating becomes the constraint.
What are detuned reactors for?
A capacitor bank and the supply transformer's inductance form a resonant circuit. If that resonance lands near a harmonic the drives are producing — the fifth at 250 Hz is the usual suspect — currents amplify and destroy the capacitors. A series reactor moves the resonance below the fifth harmonic, out of harm's way.