Joint Frequency Distributions of Stroke Current Rates of Rise and Crest Magnitude to Transmission Lines

Since strike distance is a function of stroke current magnitude, it is shown that the frequency distribution of rates of rise of stroke current to any structure can be readily determined. The most important of these is that for negative first components to transmission lines. For any realistic line configuration, the distribution is approximately log-normal with a mean of 12kA/μs. The standard deviation of the natural logarithm of the ratio of dI/dt to the mean is approximately 0.55 (i.e., 2 standard deviations from the mean, the rate of rise is 36kA/μs).