Influence of a shield wire flashover on the indirect lightning performance assessment of distribution lines

This paper presents a new aspect of shield wire (SW) modeling for assessing the indirect lightning performance of overhead medium-voltage distribution lines: a flashover (FO) between an SW and the reinforcing bars of a distribution pole or a crossarm (SWFO). In general, an SW is periodically grounded approximately every four to ten poles and not grounded at the other poles. However, owing to lightning-induced overvoltages, the voltage difference between the SW and the distribution pole may even exceed 100 kV, and the SWFO can occur. In this paper, we evaluate the effect of the SWFO on the number of FO occurrences of phase-conductor insulators by the Monte Carlo method using a 2D finite-difference time-domain-based indirect lightning surge analysis program. The effect of the SWFO is more significant in lines with high soil resistivity (a soil resistivity of 1000 & omega;m was assumed) regardless of the installation of surge arresters: the total number of FO occurrences markedly differs by up to 50% between cases in which the SWFO is considered and not considered. The analysis presented in this paper will assist the formulation of lightning protection measures particularly, in regions with high-resistivity soils.