Estimation of lightning current wave front duration by the lightning performance of Japanese EHV transmission lines

In the analysis of back-flashover of transmission lines, the wave-front time of the lightning current is assumed to be 2~4 μs. The results of a lightning investigation at the tops of isolated towers show that the front time is closely related to the current amplitude, and is longer than 8 μs in 70~120 kA range. The author estimates the wave-front time from the lightning performance of EHV (extra-high-voltage) double circuit transmission lines, and finds that it is about 4 μs in the 70~150 kA range. The author predicts that lightning currents measured at the tops of isolated tall towers will be different in shape because of the large predischarge current