Preventive Maintenance Optimization of Electric Multiple Units Based on a Bi-Level Imperfect Maintenance Strategy

A preventive maintenance (PM) optimization policy based on a bi-level imperfect maintenance strategy was proposed for electric multiple unit equipment subject to continuous degradation, consistent with actual PM situations. As reported in preliminary studies, there is only one imperfect PM measure to choose from when the system arrives at scheduled PM time—the imperfect PM measure for the system will not change within the whole life cycle—and this is not the case in real-world applications. In practice, maintenance engineers implement various levels of PM action based on the actual condition of the system, with the goal of enhancing its performance and ensuring operational reliability. Herein, imperfect PM was divided into two levels: junior maintenance and senior maintenance, constituting the bi-level imperfect PM strategy. The specific PM measure at each interval was guided by cost-effectiveness ratio analysis. The optimal PM schedule was assumed by minimizing the total cost of the system throughout a life cycle. Example analysis revealed that the bi-level imperfect PM strategy reduced the total cost and maintained the system at a higher reliability level in its life cycle.