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

Nur Alia Farina Mohamad Nasir,Nik Hakimi Nik Ali,Miszaina Osman,Mohd Solehin Mohd Nasir,Nur Hazirah Zaini,Ungku Anisa Ungku Amirulddin,Mohd Zainal Abidin Ab Kadir,Muhamad Safwan Abd Rahman

doi:10.3390/en14164736

Abstract

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.

Highlights

Minimizing the earthing impedance is the correct alternative to refinements of the transmission line (TL) performance caused by the back flashover (BFO) phenomena
This paper has provided detail comparative analyses of tower footing resistance (TFR) before and after the improvement of an earthing system design was carried out under steady-state and lightning conditions
The analysis demonstrated that at least more than 70% of TFR can be reduced by a diamond ‘crowfoot’ design

Summary

Introduction

Minimizing the earthing impedance is the correct alternative to refinements of the TL performance caused by the back flashover (BFO) phenomena. The BFO occurs when the potential exceeds the insulation strength along the string of an insulator. The impulse potential will be highly detrimental and will subsequently affect the tower and the earthing device efficiency [1,2,3,4,5,6]. The system failure due to BFO is measured as a back-flashover rate (BFR) that is typically related to high tower footing impedance and soil resistivity. The tower footing impedance associated with soil resistivity is known to have a significant effect on transmission system failure [7,8,9].

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Results

Conclusion