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This article introduces a method by which the power grid's security level can be observed in advance based on the expected initial failure. Firstly, based on the general form of cascading trip, this paper gives a mathematical expression of grid tripping based on cascading trip relay protection action behavior. According to the mathematical expression, the relationship between grid tripping and grid node injection power is discussed. According to this relationship, the distance between the node injection power under the current operation state and the nearest critical state node injection power is taken as the index to measure the power grid's security for cascading trip. According to this index, combined with various power grid constraints before and after the initial fault, a mathematical model for obtaining this safety index is given. This model is an optimized mathematical model. For the model, this paper gives a solution idea based on particle swarm. Finally, a few cases are performed in the IEEE-14 node system, and the calculations of the cases proved the accuracy of the proposed model and method.

In the case of power grid cascading trip, this study puts forward a strategy to prevent cascading trip by changing the output of generator set. Firstly, according to the specific performance of the power grid under the cascade tripping, combined with the action behavior of the line current-type backup protection, and an expression equation for measuring the safety level index between the power grid and the cascading trip failure is given. Secondly, the vulnerable branch is found out through the safety level index, the output of the key power generation nodes on the branch is taken as the optimization variable, and the optimization model is established to improve the safety level index under the chain trip of the power grid. Finally, a combination of sensitivity analysis and particle swarm optimization(PSO) was used to analyze an example on the IEEE-39 node system. The results demonstrate the feasibility and effectiveness of the model and method, and provide a reference for preventing chain trip accidents.

View of preventing cascading trips, this paper mainly studies the security level model of how to effectively prevent cascading failures in the system is studied. First of all, from the point of view of relay protection, we consider the case of backup protection for current protection, by judging the electrical distance between the operating parameters of the branch and the relay protection fixed value after the initial fault of the system, it can be judged whether the branch will undergo cascading trips or not. Then, considering the critical state of cascading trips in branch grids, a safety index is proposed to measure the shortest distance between the critical state of power grids and the current operation state, and the specific calculation method is given. Finally, an optimization model is given, which aims to find the nearest state on the boundary from the current operation state. Aiming at this model, this paper presents a solution method based on PSO algorithm, which is verified by simulation through an example analysis.

With the continuous development of the smart wireless communications, the importance of electric energy becomes increasingly evident. Intricately interconnected power grids will also suffer from the threats of blackouts caused by grid cascading failure while bringing convenience to the masses. The grid cascading trip is closely related to cascading failure. Generally, the cascading failure shows a cascading trip at early stage. Hence, the avoidance of occurrence of cascading trip at an early stage may restrain the occurrence of complex cascading failure, thereby avoiding the occurrence of the blackout. In this paper, the occurrence principle of the cascading trip is firstly analyzed from the perspective of relay protection. The output of the generator is taken as the optimization variable, and the optimization model for restraining the grid trip is presented. Finally, the example of IEEE14 node system is analyzed in this paper in combination with the particle swarm algorithm, which verifies the rationality of the proposed method.

In this paper, a grid security index considering cascade tripping is proposed, and an algorithm is proposed for this index combination with the operating behavior of relay protection so as to solve the cascading tripping problem of the power system. Firstly, according to the current behavior of branch cascading tripping and the action of line current-mode backup protection, the critical state of grid cascading trip is analyzed, and it is proved that the input power of grid nodes can be used to describe the security of grid. Then, based on the relationship between the input power of nodes and the security level of power grid, a model is presented to represent the security level of power system without cascading failures under the impact of initial faults, and the model is solved by particle swarm optimization. An example proves the validity of the algorithm.