Abstract
In chemical and nuclear power plants, protective systems are used for risk reduction. Now, with rapid development of microprocessor technology, the protective system with self-diagnosis function has spread. This paper studies the effect of self-diagnosis on protective systems consisting of k-out-of-n: G systems. Considering selfdiagnosis, scheduled and unscheduled maintenances, expected numbers of normal trips, failure detection trips, spurious trips and hazards caused by protective system failure are derived. We discuss how the variation of expected number of failures are influenced by the failure detection ratio. Moreover, the total expected loss caused by protective system failures is analyzed mathematically as the sum of unscheduled maintenance cost and loss cost. The optimal failure detection ratio that can minimize the total expected loss is also discussed. Illustrative examples are given.
