Condition-based Maintenance with Imperfect Inspections for the GIL Subject to Continuous Degradation and Random Shocks

In recent decades, the gas insulated transmission line (GIL) has been developed as a reliable technology for electric power transmission. The GIL are subject to degradation-shock-based competing failure modes of SF6 gas leakage and partial discharge. To maintain the high reliability of the GIL in its long lifetime, condition-based maintenance (CBM) can be designed based on inspected degradation levels. However, due to the complex inner structures and limited inspection environment of the GIL, the SF6 leakage rate cannot always be perfectly inspected. Therefore, this paper proposes a new CBM strategy with imperfect inspections for the GIL. Based on the concepts of false positive (FP) and false negative (FN) incurred by imperfect inspections, long run cost rate is computed under three different scenarios of maintenance actions, i.e., ending up with corrective maintenance (CM) for soft failure, CM for hard failure, and preventive maintenance (PM). The optimal inspection interval and preventive maintenance threshold are obtained by minimizing the long run cost rate. A numerical example illustrates the effectiveness of the proposed strategy, and sensitivity analysis is conducted to study the effects of imperfect inspection cost and inspection error.