Research On Relay Protection State Transition Model And Risk Assessment

Relay protection is the first line of defense in the power system.The relay protection device should action with selectivity,rapidity,sensitivity and reliability when the fault occurs in the power system.Among them,the reliability of protection system is one of the important factors that affect the stable operation of power system.However,in recent years,the number of catastrophic cascading failures in power systems has increased significantly,resulting in a serious large-scale power outage.The results of the analysis show that the incorrect action of relay protection device has played an important role in large-scale cascading failures.In this paper,based on the analysis of the reliability requirements of relay protection,the relay protection state transition model and risk assessment are studied.Firstly,the classification of relay protection device failure is introduced,and the reliability evaluation method of relay protection device is introduced.Then the state transition model of the relay protection device is established by using the description ability of the homogeneous continuous time Markov chain.The application model of risk assessment theory and Monte Carlo probability sampling algorithm in relay protection system is analyzed.According to the functional requirements of relay protection operation of relay protection devices are divided,and the establishment of the state space model of relay protection device,can be used to predict the future behavior of the protection device.Under the given condition,the time varying probability curve of the state space model of relay protection device is simulated.The theoretical analysis and comparative analysis show that the model is applied in the field of the application of the trend load of the relay protection device.Based on the Monte Carlo algorithm,the risk assessment system of power grid cascading failures is established,and the consequences of the action of relay protection are divided into three aspects: isolated power supply,load shedding and power grid separation.According to the probability of the protection of the hidden fault,the risk index of the relay protection device is obtained to quantify the influence of the behavior on the power grid.Finally,according to the results of risk assessment,the paper puts forward the three relay configuration of the relay protection device which is more comprehensive risk,and adopts the trip criterion of 3 to 2.