## 5 Case Study
### Calculation Results for the Circuit Breaker and Comparison of the Technical Condition Calculations
A subsequent planned revision at an age of 14.69 introduced two switching operations, reducing the value of criterion \(CR_{7}\) to 0, further resulting in a decline in the technical state to 0.9172 (0.8344). Due to accessibility constraints in servicing, the grade for the criterion is \(GCR_{9}=10\). Planned maintenance events involving shutdown at ages 15.06, 15.21, 15.72, 16.01, 16.11, 16.14, 16.23, 16.28, 16.31, 16.70, and 16.81 no longer affect the evaluation criteria, resulting in a technical condition decrease driven solely by aging. At an age of 16.92, a nearby lightning strike occurred (grid disturbance), which caused an unplanned overvoltage event with a backflashover, triggering the short-circuit operation of the CBs in the overhead line system unit, followed by automatic reconnection. This incident reduced the value of criterion \(CR_{6}\) to 6, resulting in a technical condition of 0.8829 (0.7658). No subsequent planned maintenance events impacted the condition criteria until the age of 20.77, when the first DIDs were identified and logged. This caused the technical state to drop sharply from the aging-based value of 0.8689 (0.7377) to 0.1896 (0.5166), reflecting the presence of multiple DIDs. The detected deficiencies were \(DID_{32}\)\({}^{\text{M}}\), \(DID_{33}\)\({}^{\text{M}}\), and \(DID_{1,1}\)\({}^{1}\) from Table 1. In this case, the number of DIDs is \(NDID=3\) and \(SETDID=\max\{1,\,2,\,1\}=2\), resulting in a calculated grade of \(GCR_{-1}=0.125\). Remedial action was performed the same  
Figure 7: Comparison of the longitudinal technical state plot estimated with multiplicative (orange) and purely additive assessment criteria (blue). day, restoring the multiplicative technical state to 0.7583. However, the additive model did not reflect this improvement and retained the prior value. From that point until the end of the observation period, only a single planned maintenance event was recorded. The final technical state, determined at the age of 21.73, was 0.7545 (0.5092), with the last change attributable solely to aging. The new model reflects the current state of the CB, with DIDs detected using maintenance processes (multiplicative criteria). The degree of DIDs is included in the calculation results, reflecting the priorities for eliminating the detected DIDs. In the additive-criteria-only model, the progression of the \(c\)-curve between maintenance interventions is governed solely by the additive criteria, ensuring continuity in the device's state curve. The operation of the CB indicates an impact on the decline of the device's state, but this is only a penalty and an indication of possible hidden defects. However, the main impact is exerted by the detected DIDs. After their elimination, the multiplicative model's assessed state improved. In contrast, when using the additive-only model, the technical state of CB declined monotonically and remained unchanged after defect resolution. This is because DIDs are counted cumulatively, without regard for severity or whether corrective actions have been taken. As a result, the \(c\)-curve lacks clarity in depicting the impact of DIDs, and the decline in the technical state is generally more severe than in the multiplicative model. In the old model, the CB's technical state cannot reach zero, whereas the new model allows it to drop to zero when the device requires replacement. For additive-only models, the detected DIDs only represent statistical discrete data. Each DID is cumulatively added to previous DIDs for the selected criteria. The decline in the calculated technical condition is permanent. For these reasons, the technical condition of a normally operating device with several DIDs that were fixed could be the lowest compared to a device that has just experienced its first defect, and it needs to be urgently addressed as the device is not functioning. Therefore, the additive formula for technical conditions does not reflect the priority of action for the device.