## 5 Case Study
### Calculation Results for the Circuit Breaker and Comparison of the Technical Condition Calculations  
Figure 6a presents the progression of the \(c\)-curves calculated using the new model, which incorporates a multiplicative criterion in combination with the additive criteria from Table 4, aligning with the actual maintenance outcomes. In contrast, Figure 6b illustrates the procedure based solely on additive criteria, representing the existing model for assessing the technical condition of devices defined in Table 4. The procedure is designed such that year 0 represents the year of the device's installation, with the current year marking the end of the calculation period. This approach allows for a direct comparison of CBs of a particular type. The blue curve represents the \(c\)-curve for a selected CB from the subset \(SCB_{1}\), which is detailed further in Figure 7 for both models. In Figure 6a, the state declines for CBs with detected DIDs are shown for the entire selected subset of CBs. The depth of the decline depends on the _RDID_ level. The density of the technical state decline indicates the trend of detected DIDs during a specific period of operation for the CB type under consideration. The upper band reflects the impact of multiplicative criteria on the state of decline. Conversely, the density of these declines offers insight into the effectiveness of TSO's maintenance implementation. In comparison, Figure 6b shows the condition progression using only additive criteria for the same CB subset. In this case, it is not possible to determine the severity of detected DIDs directly. The decline is influenced solely by the cumulative number of DIDs rather than the _RDID_ rate. As a result, the additive state does not reflect improvements, and it offers limited sensitivity to maintenance effectiveness. Figure 6: (**a**) Longitudinal technical state plot of circuit breakers assessed using multiplicative criteria; (**b**) longitudinal technical state plot of circuit breakers assessed using additive criteria. \begin{table}
\begin{tabular}{l r} \hline \hline _SELSB_ & \(\mathbf{N_{\text{dev}}}\) \\ \hline \(SCB_{1}\) (chosen CB SF\({}_{6}\)) & 122 \\ \(SD_{1}\) (bus disconnectors) & 1552 \\ _SITCOMB_ (combined ITs) & 186 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Population of devices in HV SB for the calculation of the technical state. Figure 6a presents a longitudinal chart of the multiplicative technical state \(c\) for 122 breakers of subtype \(SCB_{1}\). The red line illustrates the idealized technical state of a device that has experienced no defects, with its only decline in the technical state due to aging. For most devices, the aging trend similarly dominates their condition curves, as defect data were not collected during the early years following installation. However, data on deficiencies and internal defects (DIDs) have been collected systematically for the past 10 years. This more recent period is reflected in deviations from the red aging curve, where the technical condition declines corresponding to the recorded defects. Figure 7 illustrates the longitudinal technical state of a circuit breaker over a 21.75-year period leading up to the date of analysis. At the time of assessment, the CB's multiplicative technical condition was 0.7917, while its additive condition was 0.5092. In the following descriptions, the multiplicative technical condition is listed first, with the corresponding additive value in parentheses. The observed device exhibited aging and was classified as such until it reached an operational age of 13.31 years, at which point its technical state was 0.9542 (0.9084). Shortly after, at an age of 13.74, a second regular revision increased the number of operations under nominal loads to two. This triggered a reduction in the relevant criterion, resulting in a technical state drop to 0.9398 (0.8797).