Power Quality and Reactive Compensation: Capacitor Banks, SVC and STATCOM

A project-level guide to reactive-power sizing, harmonic resonance, detuned capacitor banks, SVC/STATCOM response and IEC 61000-2-4 industrial compatibility lev

1. Start at the Point of Common Coupling

IEC 61000-2-4:2024 gives compatibility levels for low-frequency conducted disturbances in industrial locations up to 35 kV and includes voltage deviations, dips, imbalance, harmonics, interharmonics, DC components and transient overvoltages. Measure and model the point of common coupling (PCC) before choosing a capacitor bank, SVC or STATCOM.

2. Reactive-Power Sizing

For a load moving from power factor cosφ₁ to cosφ₂, the ideal fundamental-frequency reactive-power step is:

Qc = P · (tanφ1 - tanφ2)
EquipmentBest-fit dutyMain engineering risk
Contactor-switched capacitor bankSlowly varying, clean industrial loadResonance, inrush and overcompensation
Detuned capacitor bankPower-factor correction with harmonicsReactor loss, tuning tolerance and temperature
SVCFast reactive-power and voltage controlHarmonic emission and filter coordination
STATCOMDynamic var support, weak grids and unbalanceConverter current, cooling and control interaction

3. Harmonics and Resonance

IEC 60871-1 covers shunt capacitor units and banks above 1 kV, including power-factor correction and filter circuits. Capacitors must not be connected from a kWh estimate alone: calculate short-circuit strength, background distortion, converter spectrum, switching transients and the parallel-resonance point.

A screening estimate for a capacitor-bank resonance is:

fr ≈ f1 √((Ssc) / (Qc))

Use a frequency scan and time-domain switching study for the final design, especially where VFDs, UPS rectifiers, PV inverters or arc furnaces are present.

4. Acceptance Data

Specify PCC voltage-quality limits, step response, kvar or Mvar range, control deadband, unbalance, harmonic current, detuning frequency, discharge time, protection and bypass behaviour. Commission with before/after recordings at the PCC and at the largest nonlinear loads.

*Reference: IEC 61000-2-4:2024; IEC 60871-1:2014; IEC 61000 series; IEEE 519-2022.*