Calculation of Lightning Flashover Rates of Overhead Distribution Lines Considering Direct and Indirect Strokes

This paper presents a procedure for evaluation of lightning performance of overhead distribution lines. Because both voltages from direct strokes and nearby strokes may cause flashovers in distribution lines, flashover rates due to them need to be analyzed. The procedure is implemented in electromagnetic transient program, and the Monte Carlo method is used to take into account the random nature of lightning parameters. The lightning-induced voltages are calculated with an equivalent circuit derived from Agrawal formula. The influence of insulation level and spacing between surge arresters on lightning flashover rates is analyzed with the procedure. For a line with low-insulation level about 150 kV above high conductivity ground or with high-insulation level about 300 kV above low conductivity ground, the spacing between arresters is best less than 400 m. But for a line with low-insulation level above low conductivity ground, it is better to reduce the spacing to 200 m.