The effect of wide band modeling of tower-footing grounding system on the lightning performance of transmission lines: A probabilistic evaluation

• The wide-band modeling of grounding system alters the maximum overvoltage across the insulators and estimated LFOR of transmission line.
• The maximum value of overvoltage associated with the Static model is higher than the case of wide-band modeling of grounding system.
• The difference between calculated BFR by wide-band and static model of grounding system increases as the soil resistivity increases.
• The maximum variation in the calculated LFOR by FD wide-band model than to static model is seen for the rod-shape grounding system.

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.