Reliability Assessment Of Power System Protection

When power system is failed and protection devices do not correctly clear fault which willlead to expansion of the accident. The relay is a sentinel to protect the primary equipment, and itsfast, reliable action will effectively curb the system to be worse, which plays the role in ensuringnetwork security and reliable operation. Protection should meet the requirements of the celerity,reliability, selectivity and sensitivity and how to improve the reliability of protective relayssystem has become an important growing concerned issue. This paper is mainly discussing theMarkov state space method and then introduces the fault tree analysis. The main research resultsand the specific contents are as follows:Firstly, according to the basic concepts of reliability, this paper introduces the indicators ofprotection reliability assessment and the relationship between these indicators, then analysis thefactors that affecting the reliability of protection. Combining the Markov state space method andthe fault tree analysis method, steps for solving the component failure rate and the state-spacedivision methods for microcomputer protection system are presented. Secondly, this paperestablish the Markov model to assess the reliability of a single set protective relaying thatconsiders the software, hardware, TA/TV, circuit breakers and other primary equipment. Andthen a study case is used to verify the reliability of protection system and to calculate theavailability of the protection system. Finally, different Markov state transition diagram areestablished for different protection scheme to assess the reliability of protection system, such astwo main protection, two main protection with an additional set of near backup protection, twomain protection with a near backup protection and a remote backup protection. The result showthat with the increase of protection redundancy the protection malfunction probability increasesand the protection tripping probability decreases. This is significant to choose protection schemefor different devices and different voltage levels.