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 approximately 4 mu s. 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 mu s in 70 approximately 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 mu s in the 70 approximately 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.<
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