| In the environment of power market, the huge power demand and economic operation of assetsmake stability margin of power system much smaller, and the incorrect operation of the relayprotection system is becoming one of the most important factors that triggers and spreads thedisturbance of system. The research indicates that in certain conditions hidden failures of protectionsystem may cause their incorrect operations that lead to cascading failures. Supported by theNational Natural Science Foundation, this paper gives a deep research of protection systemreliability model containing hidden failures under circumstance of CBM (Condition-basedMaintenance) and the following is the major work:In view of digital relay protection system, the paper redefines the concept of protection systemhidden failures under CBM circumstances, presents a reliability model of hidden failures in theprotection system containing hidden failures of circuit breaker(considering each state of thecomponents to be protected, digital protection devices and circuit breaker divided by hidden failures),compares that with reliability model of protection system without hidden failures, demonstrates theinevitability of existence of hidden failures and its effect on system reliability, and discusses theimpact of common cause failures and human errors on system reliability.In view of digital relay protection system, Markov method, fault tree and event tree method areused for reliability modeling with a comparison of their advantages and disadvantages, and it isproved that the Markov method has unparalleled advantages over fault tree and event tree methodsreferring to hidden failures reliability model for the protection system.Aiming at four possible failure reasons for the multi-function digital protection system—thedevice hardware failure, configuration issues of protection scheme (principle), software defects, aswell as incorrect setting value or its inappropriate application, a detailed analysis of the impact of avariety of redundancy methods on protection system reliability is made, and redundancy measures toimprove reliability of protection systems are put forward.Further studying the reliability of relay protection system in terms of hidden failures underCBM circumstances and considering the effect of common cause failure and human error on doubleprotection, main and backup protection and a single main protection respectively, the paper gives aresearch on protection system reliability model in detail, defines reliability indices of relayprotection system, discusses effect of different redundant method on probabilistic index of protectionhidden failures and analyzes the effect of common cause failure and human error on reliability ofprotection system, thus offers guidance for reliability assessment of protection system andimplementation of CBM. By analyzing the mechanism of hidden failures of protection in terms of protection hardwareand software failures and mismatched settings, protection hidden failure mode is given andvulnerability zone is analyzed quantitatively taking distance protection for example, and N-k secureanalysis of power system is carried out based on initial failure and protection hidden failure, risk ofdouble（triple）failure incident of line is evaluated, risk index is defined accordingly, improvingmeasures for high risk scenarios are proposed, thus offers guidance for operation personnel.Monitoring and controlling system structure of hidden failures based on Multi-Agent System isestablished, namely the wide-area adaptive protection scheme to guard against cascading failures.Concrete implementation strategies for CBM of protection system are introduced. |
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