Statistical Analysis of Lightning Performance of Distribution Lines Based on Observation in Fields

Abstract

Because of the lower insulation level than is for transmission line, in this study on lightning protection design of distribution line, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. So it is necessary to grasp the frequency of occurrence on lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO’s distribution lines in use had been continuously observed for 6 years (1996-2001). Through this observation, new interesting statistical data, that can be useful basis for rationalization of lightning protection design of distribution lines was obtained. 204 lightning was observed through six years observation in all. Probability of occurrence of direct stroke was 22% (45 data of direct stroke was obtained). The fact that in 47% case of direct stroke the electric outage didn’t occur is very interesting. Moreover, the value of surge discharge current of arrester in case of nearby stroke is basis for conventional theory of grounding system. Therefore statistical analysis of ZnO discharging current in case of nearby strokes was carried out. As a result, in case of nearby strokes, 5% value of cumulative frequency of discharging current is 0.5kA. This value is half of conventional data.