What is reactive power compensation?

Reactive power compensation is the process of adding capacitor banks (or synchronous condensers) to a power system to offset lagging reactive current drawn by inductive loads such as motors and transformers. This raises the power factor, reduces apparent power (kVA), and lowers line current — which cuts conductor losses and avoids utility surcharges.

Why is the formula Q_c = P × (tan φ1 − tan φ2)?

Active power P is constant. The reactive power before correction is Q1 = P × tan φ1 and after correction is Q2 = P × tan φ2. The capacitor bank must supply the difference: Q_c = Q1 − Q2 = P × (tan φ1 − tan φ2).

Should I target a power factor of exactly 1.0?

Not usually. Overcorrection causes leading power factor, which can raise voltage and cause its own penalties. Most utilities charge no surcharge above 0.90–0.95. Target 0.95–0.98 as a practical upper bound, and check your tariff before over-sizing.

Is the capacitance result per phase or total?

The result shown is per phase for a three-phase system. For a three-phase delta connection use the line voltage; for a star (wye) connection use the phase voltage (line voltage ÷ √3). The calculator uses the delta formula by default (line voltage) — label clearly when specifying to a vendor.

Does this account for harmonic distortion?

No. This calculator assumes a sinusoidal, balanced three-phase load. In the presence of significant harmonics (THD > 5%), capacitor banks may resonate with system inductance — consult a power quality engineer and consider detuned or active filters instead.

Reactive Power Compensation Calculator

Enter load power, current power factor, and target power factor to find the required capacitor bank size in kVAR.

Load Parameters

Active Load Power (kW)

Existing Power Factor (0.01 – 0.99)

Target Power Factor (0.01 – 1.00)

System Voltage (V)

Line-to-line for 3-phase

Frequency (Hz)

System Type

Compensation Results

Enter parameters and click Calculate.

Summary

Enter load power, current power factor, and target power factor to find the required capacitor bank size in kVAR.

How it works

Enter the active load power in kilowatts (kW) — the real power drawn by your equipment.
Enter the existing power factor (0.01–0.99) — check your utility bill or use a power meter.
Enter the target power factor (must be higher than existing, up to 0.99 or 1.0).
Enter system voltage (line-to-line for three-phase) and frequency (50 or 60 Hz).
The calculator applies Q_c = P × (tan(arccos(PF1)) − tan(arccos(PF2))) to find the kVAR needed.
Capacitance per phase is derived from C = Q_c / (3 × 2π × f × V²) for three-phase delta, or adjusted for star connection.

Use cases

Size capacitor banks for industrial motor loads with poor power factor.
Estimate penalty avoidance savings when correcting power factor above utility thresholds.
Plan reactive compensation for transformer and generator systems.
Verify contractor-proposed kVAR bank size against your measured load data.
Calculate individual capacitor values for single-phase correction circuits.
Determine staged compensation requirements across multiple load shifts.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu