Research On Power Grid Security Level Based On Cascading Failure Triggering Scenario

With the continuous expansion of power grid scale,China’s mainland has formed a national regional interconnected power grid.The number of users of power grid is increasing year by year.In case of failure in small area,the load will be redistributed in local power grid.With the rapid spread of power grid structure to regional power grid,large-scale cascading failures will occur,which will lead to blackout and bring great losses to people’s social production and economy.According to previous studies,blackouts are usually accompanied by cascading failures.The triggering stage of cascading failures in power grid is generally characterized by cascading trips.Therefore,the study of Cascading Trips is helpful to prevent the occurrence of blackouts.In this paper,starting from the phenomenon of cascading trip,the electrical quantity after power flow redistribution and the action behavior of backup protection,the security level of power grid under the scenario of cascading fault triggering is studied.(1)According to the action characteristics of relay protection,this paper takes the minimum Euclidean distance between any critical state of cascading trip and normal operation state of power grid under the action of initial fault as the safety index under the condition that the backup protection of cascading trip is distance III Protection and overload protection,The index is expressed by the distance between the injection power of the node in the critical state and the normal operation state.Combined with the power flow constraints,generator output constraints and node voltage constraints,a power grid security level calculation model is designed,which takes the security index as the objective function and the node injection power as the variable,considering the scenario of cascading failure triggering.The smaller the safety level is,the greater the possibility of cascading trip is.(2)The security level model of power grid is solved by particle swarm optimization algorithm,improved particle swarm optimization algorithm based on learning factor and improved particle swarm optimization algorithm based on adaptive inertia weight.The simulation results show that PSO can solve the security level of power grid,and the improved PSO can find a better security level than the basic PSO.(3)From the perspective of power grid vulnerability,the initial fault branch is selected,and a method combining node degree and weighted dielectric number is proposed to identify the vulnerable branch.The vulnerable branch is selected as the initial fault branch to analyze the security level of power grid,and the security level of power grid is obtained by particle swarm optimization algorithm and improved particle swarm optimization model.Through the research of this paper,using particle swarm optimization algorithm can solve the power grid security level of cascading failure trigger scenario,which can provide theoretical and technical support for further research of cascading trip and even cascading failure.