The Effect of Wide Band Modeling of Tower-Footing Grounding System on the Lightning Performance of Transmission Lines A Probabilistic Evaluation

Abstract

This paper presents a probabilistic evaluation, based on Monte-Carlo method, to estimate back flashover rate (BFR) and shielding failure flashover rate (SFFOR) of overhead transmission lines (TLs). In the proposed approach, as opposed to the conventional methods, a wide band model of the tower-footing grounding system is adopted assuming the soil electrical parameters to be either constant or frequency dependent. The statistical parameters affecting the TLs’ outage rate are taken into account in the probabilistic studies. Simulations are done for a typical 400-kV transmission line which is modeled in EMTP.RV. From the simulation results, it is found that the BFR of transmission lines is markedly affected by the tower footing grounding system model. This effect is more pronounced when the soil electrical parameters are frequency dependent. It is also found that the SFFOR of the transmission lines is not significantly affected by the wide-band model of the tower-footing grounding system.