Reliability and availability analysis of three-state device systems.

Abstract

This study presents the reliability and availability analysis of three-state device systems with common-cause failures. The effect of common-cause failures on different systems is discussed. Different configurations are compared in order to obtain higher standby system reliability. Mathematical expressions are developed for the system reliability, the mean time to failure, the steady state availability and the time dependent availability of cold standby system, warm standby system, series system and parallel system. For system with constant common-cause failure rates, the Markov State Space approach is used to perform reliability analysis. The Method of Stages approach is used to investigate systems with non-constant common cause failure rates. Selected plots demonstrate the effect of the varying common cause failure rate on system reliability mean time to failure, steady state availability and time dependent availability. This study clearly shows that the occurrence of common-cause failure has a negative effect on standby system reliability parameters. However the system reliability, the mean time to failure, the steady state availability and the time dependent availability increase as the number of standby devices in the three-state device standby system increases.