Computer simulation of lightning flashes to transmission lines

A special transmission line lightning simulation program developed by the authors was used to examine the factors involved in the approach of a lightning leader toward a line. Three different methods were used to model the development of the final upward leader: critical charge criteria; a critical gradient between the leader tip and the wire; and simple strike distance equations. The results suggest that standard strike distance equations-when used with straight vertical leaders-can create substantial error and may not predict shielding failures that may actually occur