Lightning Performance of Transmission Lines: Requirements of Tower-Footing Electrodes Consisting of Long Counterpoise Wires

This paper addresses the requirements of tower-footing electrodes for ensuring improved lightning performance of transmission lines. The response of typical arrangements of electrodes subjected to lightning currents is simulated using an electromagnetic model and their influent parameters are calculated. Simple expressions are provided for their estimation. Lightning overvoltages across insulators due to direct strikes to real lines are determined, and backflashover occurrence is assessed using the Disruptive Effect model. Concise representations of tower-footing electrodes are tested. Two original results ensued: 1) the ascertainment that the effective length of counterpoise wires is longer than that of horizontal and four-star electrodes and 2) the finding that using the impulse impedance for a concise representation of tower-footing electrodes in the assessment of the lightning performance of lines yields practically the same result obtained under their physical representation.