What is a Detuned Power Factor (PF) Capacitor? PQM-104

Since power factor capacitors have capacitance reactance (ohms) that decrease as frequency increases, they will naturally offer a low impedance path to harmonics. If the power system voltage is distorted, then current will be driven into the capacitor, at each of the frequencies that are present in the harmonic voltage spectrum. Additionally, the capacitance (Farads) will combine with upstream circuit inductance (Henries) to form a parallel tuned circuit and a series tuned circuit, each with their respective natural resonant frequency. If harmonic voltage is present at one of these frequencies, then harmonic resonance can cause amplification of harmonic voltage (parallel resonance) or harmonic current (series resonance).  A detuning reactor is used to prevent harmonic resonance, by purposefully shifting the capacitor circuit resonant frequency beneath the lowest harmonic that is present. It also restricts the flow of harmonic current into the capacitor by increasing the capacitor circuit impedance relative to harmonic frequencies.  Power factor capacitor systems that use detuning reactors are sometimes referred to as anti-resonant capacitors, capacitors with harmonic blocking reactors, or simply detuned capacitors.