The lightning stroke

IN RECENT YEARS renewed interest has developed in the effect of lightning on electrical transmission lines. The most vital characteristic of lightning in most methods of calculating its effect is the current measured at the ground terminal. A large amount of data is available about the stroke current crest magnitude and a considerable amount of data is available which covers the time-to-crest of the stroke current. Despite these data there is still controversy over the time-to-crest. Measurements in the region of a microsecond are admittedly difficult. The industry is still seeking new data. In approaching this problem, it was felt that it might be conducive of results to analyze the mechanism of the return stroke and then, from the factors governing the mechanism, try to synthesize the stroke. Perhaps certain limits to the rate of rise could be ascertained. Some of the characteristics of the component factors could be obtained in the laboratory, others by computation. It was with this in mind that the present investigation was undertaken.