Research On The Method Of Analyzing Danger Level Of Cascading Trips In Power System Based On Nodal Injection

The main reason of power outages is cascading failure,and the chief form of the beginning of cascading failure is cascading trips.Therefore,it is extremely important to study the matter of cascading trips to prevent cascading failure.Starting from the critical state of cascading trips and combining with the action of relay protection and nodal injection of the grid,this paper studied the danger level of cascading trips after initial fault disturbances,analysed and calculated it.Firstly,a mathematical model expressed by nodal injection for measuring the danger level of cascading trips was presented.In view of the widely equipped distance protection in transmission network,this paper discussed critical state of cascading trips in a way that separately analyzed the manifestation of cascading trips from the level of branch and grid and combined with the third section of distance protection in case of the action equation.On this basis,combined with various inherent physical constraints in the power system,an indicator for quantifying the possibility of cascading trips was proposed.That was the danger level of cascading trips,and then a mathematical model was built.The objective function of the computational model was defined as the danger distance of cascading trips,which is the reciprocal of the danger level of cascading trips.And danger distance is the minimum Euclidean distance between critcal state of cascading trips and normal state.The smaller of the value of danger distance,the bigger of the value of danger level.And the greater the possibility of cascading trips.Then,this paper solved the mathematical model for danger level by using optimization algorithm and provided detailed procedures.Combined with the optimization theory and the mathematical model,the constraints ware expressed in the form of penalty terms.Considering the danger distance function,the unconstrained expression of the mathematical model of danger level is given,which is the penalty function of the mathematical model of danger level of cascading trips.Aiming at the penalty function,this paper established the fitness function,and used the particle swarm algorithm and genetic algorithm to calculate the mathematical model.Finally,after case studies,the mathematical model of danger level and the solution for it were further explained and demonstrated in the simulation environment of MATLAB2017 b.And the program of the mathematical model was compiled according to particle swarm algorithm and genetic algorithm.After that,this paper analyzed the cases in the IEEE-14 node system and the IEEE-39 node system.The results of the cases showed that the improved adaptive genetic optimization algorithm is the most suitable one for solving the mathematical model of danger level.It also showed that the mathematical model of danger level proposed in this paper is feasible and effective.Therefore,the mathematical model of danger level can provide theoretical support for further research on preventing cascading trips and cascading failures and technical support for power scheduling.