## 3 Case Study
### Reliability Assessment
Importance measures for some selected components are given in Table 4. When revised importance measures are compared with the originals, some important changes with the integration of priority factor ocurr. It should be noted that the revised importance measures for the important components are increasing, and the different levels of increase cause a different ranking of the components. With larger weights given to the loads with higher priorities, the results lay more emphasis on the important loads in the local framework. The important components are highlighted, which in reality reflects the users' concerns incarnated in load priorities. \begin{table}
\begin{tabular}{c c c c} \hline
**Load point** & **Reliability** & **Compound weight** & **Unreliability contribution** \\ \hline Load 1 & 99.9550\% & 0.1667 & \(7.50\times 10^{-5}\) \\ Load 2 & 99.9518\% & 0.0875 & \(4.22\times 10^{-5}\) \\ Load 3 & 99.9139\% & 0.1250 & \(1.08\times 10^{-4}\) \\ Load 4 & 99.4451\% & 0.1042 & \(5.78\times 10^{-4}\) \\ Load 5 & 99.3837\% & 0.0333 & \(2.05\times 10^{-4}\) \\ Load 6 & 99.3311\% & 0.0313 & \(2.09\times 10^{-4}\) \\ Load 7 & 86.4229\% & 0.0417 & \(5.66\times 10^{-3}\) \\ Load 8 & 85.9354\% & 0.0104 & \(1.47\times 10^{-3}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Assessment results in a year for load points in the local framework. Components with the highest value of NRAW\({}_{+}\) are the IEM devices, the 12 kV AC bus and communication components. These components should be maintained well, so the reliability of the system is not reduced significantly. In consequence, the maintenance priority for those components should be set high. The important components with the highest values of NRRW\({}_{+}\) are the two diesel generators. It should also be noted that the values for the wind turbine and the PV array are notably large. It is worth increasing the reliability of these respective components, so the system reliability can be increased significantly. The failure rates for the IEM devices, IFM devices and communication components are set manually. However, these components, especially IEM and communication components, are among the most important parts in the local framework of the FREEDM system according to their importance \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Component** & **NRAW\({}_{+}\)** & **NRAW** & **Component** & **NRRW\({}_{+}\)** & **NRRW** \\ \hline IEM & 71.9406 & 27.3848 & Diesel generator 1 & 1.2327 & 1.2198 \\
12 kV AC bus & 71.9406 & 27.3848 & Diesel generator 2 & 1.2324 & 1.2196 \\ Local communication & 71.9406 & 27.3848 & Wind turbine & 1.0320 & 1.0275 \\ Cross-system communication & 71.9406 & 27.3848 & PV array & 1.0254 & 1.0225 \\ PV array & 71.6585 & 64.4566 & IEM & 1.0067 & 1.0024 \\ Wind turbine & 56.4163 & 49.7676 & Local communication & 1.0066 & 1.0024 \\
120 V AC bus 1 & 37.7093 & 14.0423 & 12 kV AC bus & 1.0065 & 1.0024 \\
400 V DC bus 1 & 33.9686 & 16.6568 & Cross-system communication & 1.0061 & 1.0022 \\ Circuit breaker 1 & 22.7390 & 10.7413 & 120 V AC bus 1 & 1.0031 & 1.0011 \\ Diesel generator 2 & 21.9213 & 21.2917 & 120 V AC bus 2 & 1.0014 & 1.0006 \\ Diesel generator 1 & 21.7725 & 21.2584 & 120 V AC bus 3 & 1.0013 & 1.0005 \\
120 V AC bus 3 & 19.6982 & 7.8285 & IFM & 1.0003 & 1.0001 \\
120 V AC bus 2 & 16.5330 & 7.5141 & 400 V DC bus 1 & 1.0001 & 1.0000 \\ IFM & 4.1946 & 1.8846 & Circuit breaker 1 & 1.0000 & 0.9962 \\ Battery 1 & 2.6618 & 1.8156 & 400 V DC bus 3 & 1.0000 & 1.0000 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Importance measures for selected components in the local framework. Figure 8: Unreliability curves in a year of different loads in the local framework. measures in Table 4. Sensitivity analysis should be carried out for these components, in order to analyze the influence of failure data for the reliability assessment result. In Table 5, the failure rates for IEM devices, communication components and IFM devices are set respectively with increasing order of magnitude from 1.00 \(\times\) 10\({}^{-8}\) to 1.00 \(\times\) 10\({}^{-6}\).