###### Abstract  
This paper presents a comparative analysis of different earthing designs' performances, with particular interest on the use of earthing enhancing compound (EEC) for a selected earthing design of 500 kV transmission towers in a rocky soil, using the SESCAD tool of the Current distribution, electromagnetic field grounding and soil structure analysis (CDEGS) software. The simulation included the interpretation of soil profile and comparison between designs A, B and C, which are currently used for the 500 kV tower footing resistance (TFR) improvement. Results showed each design had reduced the TFR by 66%, 54.7% and 63.2% for the towers T42, T48 and T50, respectively. In some cases, further improvement of TFR is required, especially in the rocky area where the soil resistivity (SR) value is of more than 500 \(\Omega\)-m. In this case, EEC was used in Design C, encasing both the vertical and horizontal electrodes, and it reduced the TFR further by 16% to 20%. The characteristics of the soil and earthing arrangement design play an important role in achieving a low TFR value, which is directly proportional to the backflashover occurrence and thus to the transmission line performance.  
earthing design; tower footing resistance (TFR); EEC; CDEGS 20 May 2021 13 June 2 earthing structure was usually installed based on the location of the transmission tower and surrounding soil conditions. When the soil resistivity exceeds 100 \(\Omega\cdot\)m, an additional earth electrode should be added, i.e., a rectangular or square horizontal electrode. However, if the soil resistivity is over 4000 \(\Omega\cdot\)m, the use of a horizontal electrode along the tower and connection of an earth electrode to each tower are two measures found to be more effective and recommended [10; 11; 12; 13]. Table 1 shows some of the current practices of earthing designs available and used in several Asian countries.  
\begin{table}
\begin{tabular}{c c c} \hline
**Countries** & **Earthing Design** & **References** & **Remarks** \\ \hline \hline China & \(S\) & [11; 12] & Earthing design \\ China & \(S\) & [11; 12] & a: 4 m \\  & & S: 8 to 10 m \\  & & _l:_ 0 to 50 m \\ \end{tabular}
\end{table}
Table 1: Current practice of earthing design and arrangement in several Asian countries.  
Another method to reduce tower footing resistance is the counterpoise approach. It is perceived as practical and efficient for high voltage transmission earthing systems [15; 16]. There are two types of counterpoises that have been widely used for towers located in high soil resistivity areas, such as rocky and sandy soils: the continuous and the radial type [3; 4]. Other aspects important in earthing design include soil resistivity, number of soil layers and soil thickness in each layer [17; 18].  
Thus, a convenient way to reduce the value of soil resistivity and earthing resistance is to use an earthing enhancement compound (EEC), which has recently become popular in electric power systems, particularly for mitigating the issue of earthing systems [19; 20] by replacing inappropriate soil content to minimise footing resistance caused by high cost and space constraints [21; 22; 23]. Hence, in this paper, we intended to present an improvement of an earthing system with different earthing designs and applications of EEC on a selected design to achieve the requirement limit for tower footing resistance of a 500 kV tower, i.e., less than or equal to 5 \(\Omega\). We also interpreted the soil structure and evaluated several earthing designs based on the soil resistivity measurements carried out on selected 500 kV towers.