Reliability and availability analysis of three-state device redundant systems with human errors and common-cause failures

This paper presents stochastic models representing redundant three-state device systems with critical human errors and common-cause failures. The systems are analysed under two situations: without any repair and with repair. All the system transition rates, i.e., openmode and short-mode failure rates, critical human error rate, common-cause failure rate, and the repair rates are assumed constant. The Markov method is used to develop generalized expressions for system state probabilities, system reliability, and system mean time to failure. The systems analyzed incorporate commonly used redundant configurations such as parallel, kout-of-n and standby. A new kind of standby system called the k-out-of-n cold standby system is introduced and analyzed. Upon comparison of the system performance indices such as system reliability, system availability, and system mean time to failure of these systems, it is observed that cold standby has a significant effect on the performance of three-state device systems. © RAMS Consultants Printed in India.