The article presents the essentials of reactance compensation of unbalanced loads in three-phase four-wire systems powered by a sinusoidal and asymmetrical voltage source. The whole of compensation and symmetrization is based on the Currents’ Physical Components (CPC) theory. Reactance compensation, i.e. compensation based solely on inductors and capacitors, in four-wire systems requires the device to be included in a star (Y) structure in order to compensate for the reactive current (reactive power) and the current at the neutral conductor caused by zero sequence asymmetry, and for the device in a delta (∆) structure to allow compensation of the reactive current (reactive power) and current, causing asymmetry of the negative sequence.

The proper description of circuits supplied from an asymmetrical and sinusoidal voltage source, in which line parameters are included, requires an adequate mathematical concept or theory. The authors of the publication present the mathematical concept of the currents’ asymmetrical components for three-phase four-wire systems, taking into account the impedance of the neutral conductor and the impedance of power transmission lines. In the new approach, four orthogonal current components were proposed in charge of its flow between the source and the load. The introduced distribution shows, regardless of the type of the voltage asymmetry (amplitude or phase), it is possible to set down the symmetrical active current and other components, i.e. reactive current, negative current and zero current, which will allow determining the reference current of the active filter.

This article aims to explain the capability of describing three-phase systems powered from the source with asymmetrical nonsinusoidal voltage waveforms. Indicating the physical components of the currents associated closely with specific physical phenomena facilitates separating the unbalanced components from the active and reactive ones. All those currents, excluding the active current and the scattered current, contribute to the existing unbalanced and reactive power. This article presents the decomposition of currents based on the Currents’ Physical Components Theory. When decomposing currents, it is assumed that the load is linear and unchanging in time, and the voltage supply is asymmetrical and nonsinusoidal.