Calculation of current distribution in a lightning stroked metal structure considering the nonlinear ground impedance

This paper presents a circuit approach to compute the transient current distributions induced by a direct lightning on a metal structure such as oil containers in presence of a nonlinear ground impedance. The metal structure is simulated by means of an equivalent network formed by resistances, capacitances and inductances having all the branches coupled to each other. A nonlinear current-dependent electrical model, function of the electrode shape and the ground resistivity, represents the ionization phenomena in the soil. The analysis of the equivalent lumped-constants network is carried out by means of SPICE. The influence of the nonlinear ground impedance upon the distribution of the currents is put in evidence. The transient responses and the current distributions due to the stroke on a point of the structure are reported.