Preliminary study of the effect of dispersive ground parameters on transferred lightning surges

This paper presents a preliminary study on the effect of dispersive ground parameters on surges transferred from medium-voltage to low-voltage distribution lines located in rural areas. In this study, a direct lightning strike is assumed at different points of a distribution line terminated at a 10 kVA 7.967 kV/240-120 V single-phase transformer with center-tapped secondary. The distribution line is modeled using the JMarti model modified to include the variation with frequency of the ground resistivity and permittivity. The transformer is represented as a two-port model valid in a wide frequency range. Insulation breakdown is modeled using the disruptive effect method and for simplicity the grounding impedances are represented as simple resistances. Voltages transferred to the transformer secondary are calculated for different conditions. It is shown that considering dispersive ground parameters does not have a significant influence on phase-to-neutral voltages transferred through the transformer to its low-voltage side in the investigated cases.