How to handle Harmonic Issues in Pure Capacitor Reactive Power Compensation?
Feb 10, 2026| As nonlinear loads are increasingly used in power distribution systems, the resulting harmonic pollution has become increasingly severe. Reactive power compensation capacitors are among the distribution equipment most vulnerable to harmonic damage. Harmonics not only cause capacitor overload, reduce capacitance, and shorten service life but may also lead to grid resonance, resulting in serious electrical accidents. Additionally, incorrect compensation type selection can amplify harmonics, further exacerbating harmonic pollution in the distribution network. Therefore, it is essential to select the appropriate reactive power compensation type based on the level of harmonic pollution.
When high-order harmonics are present in the system, using conventional pure capacitors for reactive power compensation poses the following issues:
(1) Since the capacitive reactance of a capacitor is inversely proportional to frequency, higher frequencies result in lower capacitive reactance. As a result, more harmonics flow through the capacitor, causing overload and damage.
(2) Pure capacitor compensation amplifies harmonic currents on the system side. The amplified currents flowing through the capacitor can overload it. Additionally, when the amplified harmonic currents flow into the system side, they generate greater harmonic voltage distortion under the influence of these amplified currents, posing risks to both power supply and consumption equipment in the entire system.
(3) The presence of harmonic currents generates corresponding harmonic voltages in the system. When harmonic voltages superimpose on the fundamental voltage, the total voltage may exceed the capacitor's withstand voltage level. Furthermore, high-order harmonics in the system may induce resonance, producing high resonant overvoltages that can damage the capacitor. For capacitors, every 10% increase in voltage reduces their service life by half.
(4) When the terminal voltage of the capacitor is non-sinusoidal, additional active losses occur in the capacitor's dielectric, generating extra heat and raising the capacitor's temperature. This accelerates dielectric aging, with every 8%–10% increase in temperature reducing the service life by half.
Conventional pure capacitor compensation is unsuitable for distribution systems with a high proportion of nonlinear loads. To address this, adding a detuned harmonic filter reactor in series with the capacitor in the reactive power compensation circuit alters its impedance characteristics under harmonic conditions. This ensures that the compensation circuit does not exhibit capacitive behavior in the presence of harmonics, thereby avoiding harmonic amplification and resonance.