Research On Relay Protection And Related Stability

When power system is failed and protection devices do not correctly clear fault which will lead to expansion of the accident.The relay is a sentinel to protect the primary equipment,and its fast,reliable action will effectively curb the system to be worse,which plays the role in ensuring network security and reliable operation.Protection should meet the requirements of the celerity,reliability,selectivity and sensitivity and how to improve the reliability of protective relays system has become an important growing concerned issue.This paper is mainly discussing the Markov state space method and then introduces the fault tree analysis.The main research results and the specific contents are as follows:Firstly,according to the basic concepts of reliability,this paper introduces the indicators of protection reliability assessment and the relationship between these indicators,then analysis the factors that affecting the reliability of protection.Combining the Markov state space method and the fault tree analysis method,steps for solving the component failure rate and the state-space division methods for microcomputer protection system are presented.Secondly,this paper establish the Markov model to assess the reliability of a single set protective relaying that considers the software,hardware,TA/TV,circuit breakers and other primary equipment.And then a study case is used to verify the reliability of protection system and to calculate the availability of the protection system.Finally,different Markov state transition diagram are established for different protection scheme to assess the reliability of protection system,such as two main protection,two main protection with an additional set of near backup protection,two main protection with a near backup protection and a remote backup protection.The result show that with the increase of protection redundancy the protection malfunction probability increases and the protection tripping probability decreases.This is significant to choose protection scheme for different devices and different voltage levels.