Neutral earthing reactors in overhead distribution networks

Artificial Neutral Points made by oil-immersed reactors, particularly zigzag inductances, have been applied to limit earth fault currents in many MV distribution networks. ANPs can be overstressed both mechanically and thermally and a number of failures have been reported, particularly in overhead networks. A thermal analysis is performed which shows that present Standards requirements can underestimate the thermal stress due to fault conditions persisting for hours in some networks. A few approaches to this problem are reviewed and a new preventive protective solution is proposed.