## 4 Case Study
### Case 2 (\(\text{STO}=\text{27,28,29}\))
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\boldsymbol{STO_{27}}\) & \(\boldsymbol{t=27}\) & \(\boldsymbol{t=28}\) & \(\boldsymbol{t=29}\) & \(\boldsymbol{t=30}\) \\ \hline with preparation & 10 MW & 15 MW & 16 MW & 16 MW \\ \(w/o\) preparation & 4 MW & 6 MW & 11 MW & 14 MW \\ \hline \(\boldsymbol{STO_{28}}\) & \(\boldsymbol{t=28}\) & \(\boldsymbol{t=29}\) & \(\boldsymbol{t=30}\) & \(\boldsymbol{t=31}\) \\ \hline with preparation & 11 MW & 16 MW & 16 MW & 16 MW \\ \(w/o\) preparation & 6 MW & 11 MW & 14 MW & 16 MW \\ \hline \(\boldsymbol{STO_{29}}\) & \(\boldsymbol{t=29}\) & \(\boldsymbol{t=30}\) & \(\boldsymbol{t=31}\) & \(\boldsymbol{t=32}\) \\ \hline with preparation & 14 MW & 16 MW & 16 MW & 16 MW \\ \(w/o\) preparation & 9 MW & 14 MW & 16 MW & 16 MW \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Total available power of CGs at each \(STO_{l}\). Figure 8: Pre-event MG operation without and with preparation in Case 2. In Case 1, the SoC continued to decline over time, where the load was relatively high. However, in Case 2, the SoC increased at times when the load was very low. This means that, at \(t=31\), \(t=32\), and \(t=33\), the surplus available power required to guarantee the survivability of the increased load was adequately stored. An increase in SoC at \(t=31\), \(t=32\), and \(t=33\) is observed in emergency MG operations with preparation because the total available power of CGs can quickly reach its maximum with preparation. The differences in load survivability between the two modes during the event periods are caused by the SoC and total available power of CG at the pre-event time. The mean values of load A survivability are 98.31% and 95.91% with and without preparation, respectively. The mean values of load B survivability are 92.83% and 82.36% with and without preparation, respectively. Load A survivability is greater than the setting value of \(\alpha\)%, which is equal to 95% regardless of preparation because the load is relatively low. Further, the difference in load B survivability is low. However, a low difference in load survivability significantly affects emergency MG operation costs. These costs without preparation are USD 5037, USD 5905, and USD 9901, and those with preparation are USD 2407, USD 3580, and USD 6312. Although available power difference is the most at \(STO_{27}\), since loads increase significantly over time, the maximum values for the emergency-mode operation costs and the maximum difference in the emergency-mode operation costs are shown at \(STO_{29}\). When comparing normal mode operating cost, an additional cost of USD 318 is incurred during normal mode to operate in preparation mode. However, even without preparation in Case 2, the critical load's survivability is above \(\alpha\)% during the event periods due to the low load. Thus, the resilience-enhancement effect of the proposed method is lower than that of Case 1. However, in event periods, there are differences in normal load survivability, and operation costs for all \(STO_{l}\) are higher than those of MG operation with preparation. The simulation results in Case 2 show that the proposed method employs proactive actions to ensure the survivability of normal loads and lower the total operation cost, which includes the ECLS. Table 5 shows the total MG operation costs in Case 2 according to \(STO_{l}\). \begin{table}
\begin{tabular}{c c c c} \hline  & \(STO_{27}\) & \(STO_{28}\) & \(STO_{29}\) \\ \hline with preparation & USD 24,988 & USD 26,161 & USD 28,893 \\ \(w/o\) preparation & USD 27,300 & USD 28,168 & USD 32,164 \\ \hline Cost improvement & 8.47\% & 7.13\% & 10.17\% \\ \hline \end{tabular}
\end{table} 
Table 5: Total MG operation costs according to \(STO_{l}\) in Case 2. Figure 9: Different components (SoC, load A survivability, load B survivability, and operating costs) of MG operation based on the proactive action at each event period in Case 2.