Study On Probability Model Of Relay Protection For Power Systems Reliability Assessment

Relay protection as the first line of defense to prevent the effect of fault and disturbance to power system is an indispensable part of power system, which is of extreme importance to ensure power system secure operation and the quality of power supply, prevent faults to expand and prevent from accidents. Along with the network and capacity of interconnected system augmenting and voltage grade increasing, the zone and consumer number which are affected by faults are increasing. How to ensure power network to operate normally, to make relay protection system operating high-speedy, accurately, reliably is an important issue which power workers need face. Meanwhile, the system reform of electric power is expanded deeply, and the request of power supply's quality is increasing for consumers, the reliability assessment of power system has aroused broadly people's attention and research. But now the reliability assessment of power system refers to protection system's reliability rarely, the reliability assessment which refers to relay protection always deal with the relay protection system as a component, or reflects the influence of relay protection through adjust the failure rate of component protected, thus, it can not reflect the influence of relay protection system to reliability assessment of power system truly and accurately. According to the actuating logic of relay protection system, this paper uses Markov process theory to research the relay protection system's reliability model in the reliability assessment of power network.Markov state space is widely applied to the reliability of repairable system, because the field of Markov state space is abroad, which is a very effective method. Relay protection system of power system is repairable, failure rateλand repair rateμare constant, the reliability of relay protection system is suitable to use Markov state space to evaluate.The paper analyzes the operation characteristic of relay protection system, and summarizes the characteristic value of relay protection system's reliability. According to the actuating logic of relay protective unit and different relay protection system configurations, this paper uses Markov state space to analyze and evaluate the reliability of protection system in detail, and proposes the corresponding reliability model of protection system.Considering the effect of major protection and backup protection, the model can evaluate the reliability of protection system with different configurations, and can reflect the reliability of protection system truly. Using practical statistic data, the cases indicate the validity of the model; the results are valuable for the reliability assessment of power system.