Reliability and profit analysis of a water process system considering none switching of redundant units and proper/improper repairs of minor faults

A water process system in a Thermal Power Plant comprises of several redundant and non-redundant subsystems wherein the redundant subsystems are of two types, namely 1-out-of-2 (Type-I) and 2-out-of-3 (Type-II). On occurrence of a minor fault, the system goes to partial failure whereas on occurrence of a major fault the system goes to complete failure. Further on partial failure of the system, the available single repairman first inspects the subsystems to judge which subsystem has the minor fault and accordingly carries out the online repair of the infected subsystem, i.e. without halting the operation of the system, to avoid losses including loss of power generation etc. Even when a fault occurs in a redundant subsystem, switching of a redundant unit, being non-instantaneous and costly, is not done. However improper online repair of the infected subsystem sometimes results in to complete failure of the system. The present paper investigates a stochastic model developed for the system for the above practical situations. Various measures of system effectiveness for the model are obtained using Markov process and regenerative point technique. Using these measures, profit incurred to the system is also computed. The reliability and cost analyses of the system is presented through graphs for a particular case.