Influence of Lightning Current Parameters and Earthing System Designs on Tower Footing Impedance of 500 kV Lines

This paper presents an optimum earthing system design for improving the lightning performance of a 500 kV transmission line for its sustainable operation. The study includes an interpretation of the soil profile and compares the results between default and new earthing arrangements for improving tower footing resistance and tower footing impedance. An evaluation of the tower footing resistance (TFR) and impedance (Ri) before and after earthing improvement was carried out. Moreover, the effects of TFR and Ri, also known as low and high-frequency earthing, respectively, based on a specification of TFR and soil resistivity (SR) ranges at various sites were also considered. The analysis was carried out using the SESCAD tool of Current Distribution Electromagnetic Field Grounding and Soil Structure Analysis software (CDEGS) and PSCAD/EMTDC software for low and high frequency earthing, respectively. From the analysis, the results showed that the new earthing arrangement reduced the TFR by 74.11% for Tower T40, 75.71% for Tower T41 and 80.83% for Tower T42. For Ri, the results also demonstrated that the values were significantly decreased below the TFR during a high frequency operation due to the soil ionisation phenomenon that took place during the lightning. All these improvements are now being investigated and studied in all 500 kV networks in Malaysia, where lightning is considered as a major threat in relation to power outages.