Reliability Assessment of Cross-Strapped Redundant Systems Considering Unit Level Failure Propagation

SUMMARY & CONCLUSIONSStandard reliability model assumes independence between upstream and downstream units in a cross-strapped redundant system. In case unit design possesses potential propagating failure modes, this assumption may not be valid. This paper presents a novel method of assessing reliability of such redundant systems by considering dependency of the reliability characteristics of downstream units on failure of upstream units. A new set of generalized reliability models are developed, covering two common types of concerned failure modes applicable to electrical stresses like voltage or current. Results from examples provide a validation and verification of the models since they converge to prediction by standard reliability models when the stress ratio becomes 1. The results also demonstrate that system level reliability could be significantly degraded (e.g., by 14% as shown in the example), in case the propagating failure modes have potential to impose high level of stresses on downstream units. Limitations and proposed paths-forward are also outlined at the end of the paper.