Power factor correction formula
The capacitor reactive power required for power factor correction can be estimated from real power and the difference between the tangent of the existing and target phase angles.
Here, Qc is the required correction in kVAR, P is real power in kW, φ1 is the existing phase angle and φ2 is the target phase angle.
Worked example
Consider a 100 kW load with an existing power factor of 0.80 and a target power factor of 0.95.
The existing reactive power is 75 kVAR. At 0.95 power factor, the remaining reactive power is approximately 32.868 kVAR. The required correction is therefore approximately 42.132 kVAR.
Apparent power before and after
Apparent power is related to real power and power factor by:
For the 100 kW example, the apparent power falls from 125 kVA at 0.80 PF to about 105.263 kVA at 0.95 PF.
Current reduction
Improving power factor reduces the apparent power required for the same real power. With the same supply voltage, this also reduces line current.
For single-phase AC:
For balanced three-phase AC using line-to-line voltage:
Existing and target power factor
The target power factor must be higher than the existing power factor for this correction calculation. Both values must be greater than zero and no more than 1.
A target close to unity reduces reactive demand further, but real installations should not simply be corrected as far as possible without considering operating conditions.
What power factor correction changes
Power factor correction reduces reactive power drawn from the supply and reduces apparent power and current for the same real-power load.
The real power in kW does not decrease simply because a capacitor bank is added. The correction changes the reactive component and therefore the overall power factor.
Single-phase vs. three-phase
The required correction kVAR is determined by the real power and the two power factors. The selected system type and voltage are used to estimate current before and after correction.
For the three-phase option, this calculator assumes a balanced load and uses line-to-line voltage.
Power factor correction and capacitor-bank sizing
The calculated kVAR is an engineering estimate of the reactive correction required. It is not by itself a complete capacitor-bank specification.
Real installations may require stepped banks, contactors, controllers, detuning reactors, fuses, discharge resistors and equipment selected for the system voltage and fault level.
Harmonic-producing loads such as variable-frequency drives and other nonlinear equipment can also affect capacitor-bank selection because of resonance and harmonic-current concerns.
Related electrical calculations
To calculate an existing power factor from kW and kVA, use the Power Factor Calculator.
For voltage, current and resistance relationships, use the Ohm's Law Calculator.
For electrical energy cost, use the Electricity Cost Calculator.
This calculator provides a preliminary power-factor correction estimate. It does not evaluate harmonics, resonance, switching transients, utility rules, protection requirements or final capacitor-bank equipment selection.
Frequently asked questions
How do I calculate required capacitor kVAR?
Multiply real power by the difference between the tangent of the existing phase angle and the tangent of the target phase angle.
Does power factor correction reduce kW?
Not directly. It reduces reactive power, apparent power and current while the real-power load remains the same.
Why does current decrease after correction?
A higher power factor means less apparent power is required to deliver the same real power at the same voltage.
Can I target power factor 1.0?
The calculator allows a target up to 1, but actual capacitor-bank design should account for changing loads and avoid unwanted overcorrection.
Is the calculated kVAR enough to buy a capacitor bank?
No. The result is a sizing estimate. Final equipment selection should consider voltage, harmonics, resonance, switching, protection and applicable engineering requirements.
Using this calculator effectively
The Power Factor Correction Calculator estimates the capacitor kVAR required to raise an AC load from its existing power factor to a higher target. It also compares reactive power, apparent power and current before and after correction.
Common uses
- Estimating correction kVAR from real power and existing and target power factor.
- Comparing kVA and line current before and after power factor improvement.
- Screening a correction requirement before detailed capacitor-bank engineering.
Tips for a better estimate
- Use measured or representative operating kW and power factor values from the same load condition.
- For three-phase current calculations, enter line-to-line voltage and use the result only for a balanced-load estimate.
- Treat the calculated kVAR as preliminary because harmonics, resonance, switching and protection can affect final capacitor-bank selection.
Related calculations
Power Factor Calculator · Amps to Watts Calculator · Ohm's Law Calculator