Availability, Reliability, and Component Importance Evaluation of Various Repairable Substation Automation Systems

Due to the fact that repair plays a vital role in the reliability modeling, this paper investigates the effects of component repair on the availability, reliability, and component importance analyses of various four substation automation systems (SASs). For this purpose, some explicit expressions are derived for the steady-state availability, mean time to failure, mean time to first failure (MTTF¹), and repair rate regarding a repairable SAS. Then, some numerical results are presented and are accompanied by detailed descriptions of how much increase in the reliability and availability indices of SASs can take place with component repair. Besides, for the repairable model, the results obtained demonstrate the most reliable SAS in comparison with the others. Then, different sensitivity analyses have been carried out for the repairable and the nonrepairable SAS. Finally, some suitable measures of importance are selected and used, thereby knowing which components of a repairable SAS are the most important and how much they can improve the system performance. The results calculated by importance measures can be informative to guide the designers when trying to enhance the performance of a repairable SAS.