Assessment and analysis of indirect lightning performance of overhead lines

Abstract

This paper presents an efficient method for the assessment of the indirect lightning performance of overhead power lines and analyses the influence of some relevant parameters on the flashover rate. The method is based on a formula to calculate the peak value of lightning-induced voltages in overhead lines over a lossy ground, which considers the front-time of the channel-base current. The results of the method are validated by comparison with results available in the literature. The method is then used to investigate the effect of subsequent strokes on the line flashover rate, leading to the conclusion that their contribution is negligible, as long as no correlation is assumed between front-time and peak value of the strokes (first and subsequent). In the following, the method is used to analyze the influence of some parameters on the lightning performance of overhead lines. The results show that the stroke current front-time influence decreases as the soil resistivity increases, and that a higher front-time leads to a lower flashover rate. It is shown that the use of a fixed front-time T=5.63μs for the first strokes leads to results that match well the results obtained from Cigré’s front-time probabilistic distribution. Regarding the return stroke velocity, the results show that, for soils with resistivity higher than 100Ωm, the flashover rate increases as the return stroke velocity increases. The results also show that a relative velocity vr=0.4 leads to flashover rates that match well the results obtained considering some correlations between return stroke velocity and peak current proposed in the literature. The influence of the correlation between current peak value and front-time for first strokes is also analyzed and it is shown that the correlation reduces the flashover rate. It is also shown that considering this correlation for first strokes and not for subsequent strokes increases the contribution of the latter to the flashover rate, especially for good conducting soils.