Double-Exponential Expression of Lightning Current Waveforms

A lightning waveform is usually defined by the rise time t_f , pulse length t_p and peak value I. In order to represent lightning current waveforms in an analytic manner, the double-exponential formula is employed to fit with the lightning current waveforms. This paper describes the relationship between the waveform parameters t_f, t_p, I and the formula constants alpha, beta and A. An effective algorithm is proposed to calculate alpha, beta and A. The algorithm gives a reasonable expression for alpha, beta and A from the data points of lightning current waveforms. Numerical examples are derived from the algorithm for a few types of lightning current waveforms that are commonly used in lightning protection design. A better agreement appears between calculated and standard waveforms