Errors in availability estimation by 2-state models of 3-state systems

Abstract

Errors in steady-state availability estimation by 2-state models of one-unit systems which can be represented by 3-state Markovian models are evaluated. It is found that, except for very specific cases, the 2-state models result in unacceptably large error for the case in which degraded systems are not repaired; hence, multistate models should be used. On the other hand, the 2-state models can present a reasonable accuracy for the cases in which degraded systems are repaired. It is recommended that analyst select better models (2-state or 3-state models) by first estimating the model errors as well as the error due to data uncertainty.