# Maintenance Management of a Transmission Substation with Optimization
## 5 Results of Optimal RCM Maintenance
### Postprocessing of the Results  
A comparison analysis of maintenance costs with the existing time-based maintenance and with the new RCM maintenance concept (Table 6) showed that the costs of the existing maintenance method amount to EUR 568,423, to which inspections contributed the main share. The optimization also influenced the revision activities in the three-year period. Figure 8: (**a**) \(c-i_{\text{avg}}\) diagram after optimization; (**b**) \(c-i_{\text{avg}}\) diagram with changed maintenance areas. The savings were the highest in the first year, and amounted to 90.96% of the anticipated revision costs, or 25.53% of the total maintenance budget for the observed TS. In the second year, the savings were lower, and amounted to 66.83% of the anticipated revision costs, or 18.76% of the total maintenance budget for the observed TS. In the last year of the three-year period, the savings were the lowest, amounting to 24.13% of the anticipated revision costs, or 6.77% of the total maintenance budget for the observed TS. The costs and savings shown above depend on the selection of weights \(\gamma_{1}\), \(\gamma_{2}\), and \(\gamma_{3}\) in the objective function. The selection of weights can provide more importance, either to the introduction of RCM maintenance or costs, i.e., reliability, or savings. The TSO needs to decide which aspect is more important. Table 6 shows the costs and savings for the selection of weights, described in Section 4.1 (\(\gamma_{1}\) = 0.25, \(\gamma_{2}\) = 0.25, and \(\gamma_{3}\) = 0.5), where higher importance is given to RCM maintenance, i.e., reliability. For comparison, Table 7 shows costs and savings for the following selection of weights: \(\gamma_{1}\) = 0.5, \(\gamma_{2}\) = 0.25, and \(\gamma_{3}\) = 0.25. The selection of weights in Table 7 brings in the first year a 95.50% saving of predicted revision costs and 26.78% of the total maintenance budget of the substation. In the second year, the savings were lower, amounting to 82.13% of the predicted revision costs and 23.06% of the total maintenance budget. In the third year, the savings were the lowest, amounting to 17.87% of the predicted revision costs and 5.02% of the total maintenance budget. The maximum difference between savings in the revision costs from Tables 6 and 7 was 15.3%. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Maintenance Tasks**} & \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**Without**} & \multicolumn{2}{c}{**With**} & \multirow{2}{*}{\begin{tabular}{c} **Saving** \\ **(EUR/Year)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Saving** \\ **(EUR/Year)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Saving** \\ **(EUR/Year)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **(\%)** \\ **(\%)** \\ \end{tabular} } \\ \hline \multirow{3}{*}{Revisions} & \(x\) & 159,574 & 14,429 & 145,145 & 90.96 \\  & \(x+1\) & 159,574 & 52,933 & 106,641 & 66.83 \\  & \(x+2\) & 159,574 & 121,069 & 38,505 & 24.13 \\ \hline Inspections & & 405,935 & 405,935 & colspan=”2” & – \\ \hline Replacements & & 2914 & 2914 & – & – \\ \hline \multirow{3}{*}{Total} & \(x\) & **568,423** & **423,278** & **145,145** & **25.53** \\  & \(x+1\) & **568,423** & **461,782** & **106,641** & **18.76** \\  & \(x+2\) & **568,423** & **529,918** & **38,505** & **6.77** \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Revision and total costs with and without optimization.