Power Factor Correction Capacitor Calculator

Inputs

Real power is P and power factor is pf. The phase angle is φ = arccos(pf). Reactive power for the load is Q = P · tan(φ).

Required correction is Qc = Q₁ − Q₂, where subscript 1 is initial and 2 is target. The bank rating is kVAR = Qc / 1000.

Capacitance uses Qc = V² · ω · C for single-phase. For three-phase star: Qc = VL² · ω · C. For delta: Qc = 3 · VL² · ω · C, where ω = 2πf.

1. Select single-phase or three-phase, then choose star or delta if needed.
2. Enter real power (kW), your initial power factor, and your target power factor.
3. Provide voltage and frequency matching your supply.
4. Optionally apply a margin percentage for tolerance and losses.
5. Click Calculate to view kVAR, microfarads, and current reduction.
6. Use Download CSV or Download PDF to export the results.

1) Why power factor correction matters

Power factor links real power (kW) to apparent power (kVA). A low value means higher current for the same kW, which increases I²R losses, voltage drop, and thermal stress in cables, transformers, and switchgear. Many utilities also apply reactive penalties or kVA-based demand charges, so improving power factor can reduce operating cost and free system capacity.

2) How capacitors reduce reactive demand

Inductive loads such as motors and magnetic ballasts draw lagging reactive power (kVAR). A capacitor bank supplies leading kVAR, offsetting a portion of the inductive kVAR so the source delivers less reactive power. The calculator uses your initial and target power factor to compute reactive power before and after, then outputs the capacitor kVAR needed to bridge that difference.

3) Typical targets and practical limits

Common design targets range from 0.90 to 0.99, with 0.95 frequently selected as a balance between savings and avoiding over-correction. Leading power factor can create overvoltage, resonance, or nuisance tripping in sensitive systems. If your required kVAR becomes negative, it indicates the chosen target shifts reactive demand in the wrong direction.

4) Single-phase and three-phase sizing

The bank kVAR is independent of how capacitors are wired, but capacitance depends on voltage and connection. For three-phase systems, the calculator assumes the voltage input is line-to-line. In star (Y), each capacitor sees phase voltage internally. In delta (Δ), each capacitor sees line voltage, so the required per-phase capacitance is lower for the same kVAR.

5) Frequency impact and microfarads conversion

Reactive power from a capacitor scales with frequency: higher frequency yields more kVAR for the same capacitance. That is why a 60 Hz system needs fewer microfarads than a 50 Hz system for identical kVAR and voltage. The calculator converts kVAR to microfarads using ω = 2πf and clearly reports bank and per-phase capacitance.

6) Current reduction and capacity release

Improving power factor reduces apparent power and line current. For a fixed kW load, current roughly follows 1/pf, so moving from 0.75 to 0.95 can cut current by about 21%. Lower current can reduce conductor heating, improve voltage regulation, and allow additional loads without upgrading feeders, provided thermal and protection limits are respected.

7) Selecting standard capacitor steps

Capacitor banks are commonly built in steps (for example 5, 10, 15, 25 kVAR) to match changing load. After the calculator produces a required kVAR, choose the nearest standard size or a stepped combination. If your site has harmonic distortion, consider detuned reactors and capacitor duty ratings suitable for harmonic environments.

8) Data you should measure before installing

For best accuracy, measure real power (kW), power factor, and line voltage at representative operating conditions. Note motor starting behavior and load variation across shifts. Record frequency, temperature, and harmonic levels if available. Use these inputs to size a bank that achieves your target without persistent leading conditions.

1) What does the required kVAR value represent?

The required kVAR is the reactive power the capacitor bank should supply to move from your initial power factor to the target, at the stated kW, voltage, and frequency.

2) Why do I get different microfarads for star and delta?

kVAR demand is the same, but each capacitor sees a different effective voltage by connection. Delta capacitors see line voltage, so they need fewer microfarads per phase than star.

3) Should I target 1.0 power factor?

Usually no. A perfect target increases over-correction risk during light load, possibly producing leading power factor. Many designs aim near 0.95 to 0.99 depending on tariff and equipment.

4) What if my required kVAR is negative?

A negative value suggests the chosen target and PF type would increase inductive reactive demand rather than reduce it. Recheck PF types, target direction, and measurement data.

5) Do harmonics affect capacitor selection?

Yes. Harmonics can raise capacitor current and create resonance. In distorted networks, use capacitors rated for harmonics and consider detuned reactors to shift resonance away from dominant harmonics.

6) Where should I install the capacitor bank?

Place correction close to the inductive load for maximum current relief, or at a bus for whole-panel correction. For variable loads, stepped or automatic banks maintain stable power factor.

7) Why is frequency required for the calculation?

Capacitor reactive power depends on ω = 2πf. For the same voltage and capacitance, 60 Hz produces more kVAR than 50 Hz, so required microfarads change with frequency.