Ground terminations of lightning protective systems

In a lightning protective system, the ground terminations must be designed to keep within fixed values the step voltage both inside and outside the protected structure and the maximum total voltage. Design criteria shall take into account that the behavior of ground systems is affected by their length, by soil resistivity, by amplitude and wave shapes of lightning currents. In this paper, investigations carried out on ground terminations when subjected to impulse currents are presented and typical phenomena which characterize their behavior are summarized. Theoretical analysis of the transient phenomenon and new experimental results on each electrode are presented. On the basis of maximum step voltage and of the statistical variation of lightning currents, the design of ground terminations is analyzed and curves for their practical sizing are given. Provisions to avoid discharges into the soil between ground conductors and buried cables or pipes are given, together with computation methods to evaluate overvoltage amplitudes between live conductors and ground in shielded cables.