Resonance phenomena on line-to-ground fault current harmonics in MV networks

High levels of harmonic components measured on MV line fault currents have prompted a detailed investigation of the phenomena in order to develop models to accurately reproduce the observed harmonic currents and clarify the resonance characteristics of the system under line-to-ground fault conditions. A procedure which can predict the fault current wave-form of a whatsoever complex distribution system supplying a variety of loads, enabling identification of potentially harmonic resonance conditions, is presented. It may be applied, for instance, to verify the performance of networks adopting suppressing coil (which is normally tuned on the fundamental frequency) or zero-sequence protection relays. A parametric analysis on typical MV distribution systems shows how it is possible to identify critical fault locations which may give rise to very high harmonic currents