## 5 Case Study
### Calculation Results for the Circuit Breaker and Comparison of the Technical Condition Calculations
On the other hand, the multiplicative model directly follows the implementation of the work order and accounts for the priority of action. The decline's depth depends on the detected DID rate, which is equivalent to the maximum delay until the deadline for remedial action (real maintenance decision). The details of the multiplicative criterion are set so that the resulting value reflects the maintenance action's priority, and the additive criteria reflecting the other details of the device's technical condition are only prioritized within devices with the same determined maintenance action deadline. The detected DIDs, therefore, determine the prioritization of the maintenance that is completely reflected in the multiplicative criteria and, therefore, the value returned by the model. A comparative analysis of the condition values calculated using both the conventional and proposed approaches was carried out for three selected circuit breakers (represented by the red, blue, and green curves), as shown in Figure 6a,b, at characteristic ages corresponding to changes in the device condition. The numeric values in the c-curves of the three selected CBs are given in Table 6.  
The presented values are the values on the \(c\)-curve when the technical state has been changed (breakpoint) at a certain age [year]. \(c_{\mathrm{mm}}\) represents the values of the technical state from the multiplicative method, while \(c_{\mathrm{aom}}\) represents the values from the additive-only model. CB\({}_{1}\) in red in Table 6 is already explained in detail in this subsection. In the second case, two DIDs with \(RDID=3\) and \(RDID=2\) in a short period are found on CB2 in blue at age 12.97 years with maintenance tasks, and another DID with \(RDID=2\) at age 13.73 years. After the remedial actions were taken, the device condition improved to \(c=0.7076\) according to the multiplicative model (Figure 6a) but dropped even further to \(c=0.4151\) (red in Table 6) according to the additive-only model (Figure 6b). The decline of the device condition \(c\) for the additive-only model is too significant (almost 43%). Incontrast, the decline from the multiplicative model is 14% in two years, and three DIDs were discovered. The discovered DIDs have a significant influence on the additive-only model. In the third case, CB\({}_{3}\) is green, where no DIDs were found, and the \(c\) values were only affected by the operation and aging of the device, and the trends in the \(c\) values are comparable. Each multiplicative criteria reflects the priority of the maintenance activities of the given device. On the other hand, the additive criteria do not possess this characteristic at each time stamp. The reason being that, after the DID was detected, the multiplicative criteria dropped significantly, and rose to a level slightly below the technical state before the DID was discovered. The additive criteria, on the other hand, dropped significantly after the DID was discovered and remained at a low level. The device condition \(c\), obtained by both approaches, can be utilized to adjust the intervals of selected maintenance tasks within maintenance planning. For this purpose, the TSO must define a threshold for the technical condition (Figure 6a,b). The threshold is basically different for both methods. Whether it is constant or not depends on the experience in the TSO. If the assessed technical state falls below this threshold, the maintenance interval should be shortened. In the multiplicative model, the decline in \(c\) before and after maintenance tasks, where DIDs are identified and remedial actions are taken, is minor for all three selected CBs. In contrast, the additive-only model shows a significant decline in \(c\) for CB\({}_{1}\) and CB\({}_{2}\) where DIDs were detected. This indicates that, under the additive-only model, the maintenance interval should be shortened in future to account for the greater degradation observed.