Clarifying the conditions under which the LEMP significantly affects lightning flashover rates of medium-voltage distribution lines

Abstract

Lightning strikes on distribution lines can disrupt the operation of electric power systems, and hence it is crucial to accurately estimate the lightning performance by comparing various protection strategies. Recent studies have shown that the lightning electromagnetic pulses (LEMPs), which generate lightning-induced voltages in distribution lines, have a significant impact on the overvoltages generated even by direct strikes. This study aimed to clarify the conditions under which the LEMP significantly affects flashover rates (FORs) because considering the LEMP for direct lightning surge analysis requires additional calculations for electromagnetic transient analysis. We evaluated the LEMP impact on the FORs by considering the parameters as follows: soil resistivity (grounding resistance), intervals of surge arresters (SAs), and critical flashover voltages (CFOs). The analyses clarified that the LEMP impact is significant for lines with a coarse interval of SAs and low soil resistivity; this trend is emphasized by a high CFO. The impact is insignificant for lines with a close interval of SAs or a high resistivity. Although considering the LEMP impact is important for performing an accurate analysis, it can be neglected in the latter conditions, facilitating an efficient lightning performance assessment of distribution lines taking account of various protection strategies.