Reliability modeling of protection system based on phase-type distribution

For a long time, power system reliability studies assume that the state transition functions should follow exponential distribution, but the preventive maintenance interval and repair time are typically non-exponential. Therefore, the assumption is bound to seriously affect the credibility of analysis results. For this reason, this paper proceeds from the fundamental theory of reliability in mathematics, and with relay protection system as an example and taking into account the preventive maintenance, a model for system reliability with multi-outage modes and its analytical solution based on PH distributions are studied and developed. The proposed model and its solution is not only universal, which can analytical solve system reliability indices with state transition functions of arbitrary distributions, but also in strong readability and calculability, which can profoundly reveal the mechanism of system reliability evaluation. With the actual relay protection operation statistical data as the basic data on reliability, by comparing with numerical results based on sequential Monte-Carlo simulation, the proposed reliability model and its analytical solution are fully proved to be of engineering application value in power system reliability evaluation.