Empirical Formulas of Surge Impedance for Grounding Lead Conductors in Distribution Lines

Abstract

When lightning strikes an overhead distribution line, an overvoltage is induced across an insulator due to the lightning current flowing into the system. In analyzing the lightning overvoltage in a distribution system, the surge characteristic of a grounding vertical conductor should be taken into account if the lightning current has a steep front. In the present paper, an experiment on a reduced-scale model is carried out to evaluate the surge characteristic of a grounding lead conductor with circular and flat shapes. On the basis of the experimental result, an empirical formula of the surge impedance of the grounding vertical conductor is proposed. This formula includes the effect of a reinforced concrete pole close to the grounding vertical conductor. The developed formula agrees well with measured results. The formula of the surge impedance of the grounding lead conductor is effective for an accurate lightning surge analysis in an overhead distribution line.