The passive filters are used in order to protect the power system by restricting the harmonic current to enter the power system by providing a low impedance path. Passive filters consisting of tuned series L-C circuits, are the most popular, and may produce unwanted side effects, particularly in the presence capacitor which is used for power factor correction. In power systems, passive filters are used to suppress harmonic currents and decrease voltage distortion appearing in sensitive parts of the system. Passive filters work by exhibiting different impedance values at the resonant frequency. A filter connected in series should present high impedance to the harmonic frequency that needs to be blocked. Although a series configuration is possible, it is more common to connect filters in parallel. Such a shunt configuration diverts harmonic currents to ground, and simultaneously provide reactive power, which may be used to correct the power factor. We have successfully installed the passive harmonic filters for induction furnaces loads at 850VAC as system voltage.

Before installing passive harmonic filter, the detailed harmonic study should be conducted to design the right tuning of the filter product.