Distortions found in supply networks are measurable and can be split into higher harmonics, that is components of voltage/current at frequencies being integer multiples of the basic frequency (50Hz). Distorted voltage/current function is defined by the sum of all constituent harmonics.

Protection of a capacitor against the impact of higher harmonics is important not only for technical, but also for economic reasons, as energy solicitation contracts contain supplier’s requirement of maintaining a particular tgφ.

This is why power factor correction has to be carried out continuously, even when there are higher harmonics in the voltage. The device that allows continuous correction in systems with distorted voltage is a filtering reactor. A circuit consisting of correctly matched capacitor and reactor makes a filter, which protects the capacitor and allows correction of power factor with higher harmoncs presence in the voltage/current.