A fractal model of discharge interception probability of a vertical grounded rod in the presence of a neighboring object

Abstract

An experimental investigation on the lightning discharge interception probability of a vertical grounded rod when inserted in a rod-plane gap, as affected by the presence of a neighboring grounded object (rod) is presented. The height of the two grounded rods (simulating a protective and a protected object against lightning) and their separation distance and placement with respect to the energized rod were considered as influencing parameters on breakdown voltage and time, thus also on the discharge interception probability, under negative lightning impulse voltages. The discharge interception probability of the vertical grounded rod is strongly affected by the height and position of the neighboring rod; it significantly reduces when the separation distance between rods decreases, especially as the height of the rods increases. In the presence of the neighboring rod breakdown to the vertical rod occurs sooner at higher instantaneous voltages. A fractal model describing the lightning interception probability in the evaluated electrode arrangement is developed; the electrical discharges, emanating from both energized and grounded electrodes, evolve randomly in the space where the electric field is most intense. By considering also the voltage drop along the discharge path at each evolution step a satisfactory agreement between simulation and experimental results has been achieved.