Reduction of harmonic pollution in distribution networks

The paper presents two new schemes of harmonic current reduction in distribution circuits. The first scheme aims at the reduction of harmonics generated by six pulse bridge rectifiers which are common nonlinear loads in industry. The new approach is based on injection of the third harmonic current into the transformer secondary. The current injected is generated in two passive filters connected between the outputs of the bridge and the common point of transformer secondary. The scheme is very effective, reducing harmonic distortion in the supply current from 27% to 4-5%. The second scheme presented aims at the reduction of harmonic distortion caused by fluorescent lamp systems. It assumes the installation of a series filter in the neutral conductor. A specially designed filter provides a low impedance path for the first harmonic current and high impedance for higher harmonics. Simulation and laboratory tests show significant reduction of harmonics in the neutral and phase conductors