Observational results of lightning current on transmission towers

Lightning parameters, particularly the amplitude and the front duration of lightning stroke current, are the basic requirements for lightning protection design, and identifying lightning stroke current waveforms in detail is essential for rational lightning protection design. Between 1994 and 2004, Tokyo Electric Power Company directly measured the current waveforms of lightning strokes on 60 transmission towers (mainly 500-kV transmission lines) and obtained 120 data sets, including waveforms exceeding 100 kA. This paper quantitatively evaluates the characteristics of each lightning waveform parameter calculated from the observed waveforms as well as correlations between parameters, together with comparisons with previous data. In terms of the correlation between the current amplitude and the front duration, the front duration corresponding to the maximum rate of rise is defined, and the relationship that greater current amplitude results in a longer, front duration is formulated for the first time. Quantifying the relationship of the current amplitude and the front duration is very useful to rationalize lightning protection design.