Approximately Optimal Testing Policy for Two-Unit Parallel Standby Systems

Due to the impact of time-dependent unit unavailability, the testing strategies (e.g., simultaneous or staggered testing) have significant effect on the system unavailability for complex standby systems. Several testing strategies have been studied to minimize average system unavailability for certain systems. For example, uniformly staggered testing has been shown to be the best for two identical units in parallel with and without common cause failure between units. However, this result may not be suitable for parallel systems with nonidentical units. This study provides a discussion to obtain the optimal testing strategy for parallel systems for the case in which units are not necessary to be identical. Moreover, a maintenance manager who is aware of the importance of each system in the plant should establish a testing schedule based on plant-level, not on system- or component-level. That is, the manager should set up testing schedule for each system based on its contribution to the plant. Therefore, a good testing schedule should consider the balance between the maintenance cost and risk (or unavailability) coming with the maintenance task for each system. This study provides a cost-effective model taking both cost and risk into account to establish a good testing policy (including testing strategy and test interval) for two-unit parallel systems.