# Design, Modeling, and Analysis of IEEE Std 80 Earth Grid Design Refinement Methods Using ETAP
## 3 Earth Grid Design Criteria
Figure 3 shows the short-circuit study results and Figure 4 shows the dialogue plane of the fault current value being exported to the earth grid study parameters. Figure 3: Short-circuit study results. Figure 2: Earth grid superimposed onto a power system with solidly earthed transformers. Using the imported fault current and the predetermined input parameters of the substation under study, the input date was tabulated as shown in Table 2. Amongst other parameters, the earth grid consists of an 80 m \(\times\) 70 m surface area, 50 \(\Omega\)m soil resistivity, 12 \(\times\) 10 earth grid conductors laying in the \(x\)-axis and \(y\)-axis, respectively, and 12 earth electrodes buried 3 m deep into the earth mass. \begin{table}
\begin{tabular}{c l c} \hline
**No.** & **Design Parameters Description** & **Value** \\ \hline
1 & Maximum fault current generated by the power system, \(3I_{0}\) & 22.759 kA \\
2 & Shock duration, \(t_{s}\) & 0.4 s \\
3 & Earth grid conductor sizing fault current duration, \(t_{c}\) & 0.4 s \\
4 & Decrement factor fault current duration, \(t_{f}\) & 0.4 s \\
5 & The resistivity of the surface layer, \(\rho_{s}\) & 4267.2 \(\Omega\)m \\
6 & The thickness of the surface layer, \(h_{s}\) & 0.2 m \\
7 & Earth grid depth, \(h_{o}\) & 5 m \\
8 & Soil resistivity of the studied area, \(\rho\) & 50 \(\Omega\)m \\
9 & Depth at which the earth grid conductors are buried, \(h\) & 1 m \\
10 & The sum of earth grid conductor lengths in the \(x\)-axis, \(L_{x}\) & 960 m \\
11 & The sum of earth grid conductor lengths in the \(y\)-axis, \(L_{y}\) & 700 m \\
12 & The spacing between the parallel conductor (\(x\)-axis/\(y\)-axis), \(D\) & 8.9 m/6.4 m \\
13 & The length of each earth electrode, \(L_{r}\) & 3 m \\
14 & The sum of earth electrodes, \(n_{R}\) & 12 \\
15 & The sum of earth grid conductors in the \(x\)-axis, \(N_{x}\) & 12 \\
16 & The sum of earth grid conductors in the \(y\)-axis, \(N_{y}\) & 10 \\
17 & The calculated size of the earth grid conductors & 120 m\({}^{2}\) \\
18 & The earth grid’s surface area (80 m \(\times\) 70 m), \(A\) & 5600 m\({}^{2}\) \\
19 & The combined length of all buried earth grid conductors (\(x\)-axis/\(y\)-axis) (960 m + 700 m), \(L_{c}\) & 1660 m \\
20 & The combined length of all earth electrodes installed (3 m \(\times\) 12 m), \(L_{R}\) & 36 m \\
21 & The combined length of the earth grid conductors and earth electrodes, \(L_{T}\) & 1696 m \\ \hline \end{tabular}
\end{table} 
Table 2: Earth grid design input parameters. Figure 4: Exporting the short-circuit study results to the earth grid design interface. Using the input data tabulated in Table 2, the earth grid was modeled and simulated in ETAP's Ground Grid interface, and the isometric earth grid design is shown in Figure 5. The design was then simulated, and the results are shown in Figure 6, with the values of the safety limits of touch voltage, step voltage, and ground potential rise calculated. Using this earth grid, the refinement methods that are discussed in Section 2: Literature Review were assessed to evaluate their impact and effectiveness on the substation earth grids.