Study On The Distance Of Safety Of Cascading Trips

Now with the rapid development of economy and science and technology,human beings are becoming more and more dependent on electricity in terms of study,production,lives and other aspects,the demand for the adequate and reliable supply of electricity is also becoming more prominent.The operation mode of the large power grid has become the general tone of power grid construction and development due to its unique economic and technological advantages.In recent years,major power outages that have occurred around the world have brought huge negative impacts and have also attracted the attention of researchers.Related research is increasing day by day.In the face of the huge economic losses caused by major power outages,the significance of relevant research is becoming increasingly important.Cascading trips are often the prelude to major blackouts.In promoting the development of vicious blackouts,cascading trips usually play an extremely important role.The major blackouts in the world in recent years have fully demonstrated this.Strengthened the analysis and research of the cascading trips events is of great significance to the safe operation of the power system.This paper first analyzes the characteristics of cascading trips from two levels of branches and grid.Aiming at the current-type backup protection in the grid,combined with the action equation of relay protection,a mathematical expression that reflects the cascading trips is constructed,and the grid is given accordingly.According to this,the judgment of whether the power grid is in the critical state of cascading trips is given.On this basis,based on the premise of the constraints of the power system,with the nodal injection as the entry point,using the optimization theory to give a model of distance of safety to measure the critical state of cascading trips of the grid distance after the initial fault disturbance.Then two methods for solving the distance of safety are proposed.One is a distance of safety direct solution method(referred to as the direct method),which is based on the distance of safety,combined with the physical constraints of the power grid and the critical criterion of the cascading trips of the power grid as a penalty term.An indirect solution method for the distance of safety of the overall load level of the power grid(referred to as the indirect method).Considering that vulnerable branches are more susceptible to the nodal injection of sensitive nodes,an improved particle swarm optimization algorithm based on "excitation" sensitive nodes is proposed(referred to as the incentive method).In the end,the paper analyzes and compares the corresponding calculation examples,and gives further explanations and demonstrations for the given distance of safety analysis model and different solving methods.According to the particle swarm optimization algorithm,the program is compiled under the MATLAB simulation environment.the IEEE-14 node system and IEEE-39 node system were analyzed and compared.The results of the examples show that the indirect method solution model is superior to the direct method solution model in terms of distance of safety and CPU time.the improved particle swarm optimization algorithm is better than the elementary particle swarm optimization algorithm in solving value of the distance of safety.At the same time,it shows that the distance of safety model and solution method proposed for the cascading trips of the power grid are feasible and can provide reference for the operation of the power grid and further research.