Research And Development Of Zero-sequence Filter Using Zig-zag Transformer

The load unbalance and the nonlinear loads result in a significant neutral current in the three-phase four-wire distribution power system.The zero-sequence harmonic current pile up in neutral line and make it overload.It will make transformer overheat,burn the neutral line, debase the efficiency of the electric equipment.So it is necessary to find a way to eliminate the zero-sequence harmonic in neutral line.The Zig-Zag transformer has been proposed to attenuate the zero-sequence harmonic current in neutral line in this paper.There is no capacitor in it,so resonance will not happen in it.The filter will not be influenced by the system factor,so the mistuned phenomenon is avoided.The paper introduces the main circuit topo,working theory and installing spot of the filter.The paper also proposes an approach to eliminate the infection of unbalance system voltage.The simulation under PSCAD and experiments results show that the filter can effectively attenuate the neutral current and zero-sequence harmonic currents on the utility side.It improves the quality and reliability of the power.