Research On Corrosion Diagnosis Of Grounding Grid Based On Hybrid Genetic Algorithm

Grounding grid is an important facility to grantee the reliable operation of power system and the safety of person as well as electrical equipment.Being buried underground,grounding grid is easily jeopardized due to the soil corrosion,which does harm to the stable operation of the power system and the safety of the staff as well as electrical equipment in substations.After grounding accidents,the poor grounding usually results in expansion of the failure,which brings huge economic losses and serious social impact.Excavating in large area is widely used to search the break point and corrosion section in practice,this method has blindness,the workload is enormous,and it also affects the normal operation of the power system.Therefore,it is of great practical significance to study the grounding grid corrosion detection technology without power interruption and large area excavation.This thesis mainly studied the method of grounding grid corrosion diagnosis.Currently,many scholars have studied this problem,electric network method has been commonly used.This paper made some improvements based on this method.Firstly,based on the electric network theory,optimization technology and fault diagnosis theory,we set up the mathematical model of grounding grid and its diagnosis equation,it needs to be solved by optimization method due to the nonlinearity and the characteristic of under-determined.Genetic algorithm(GA)is a kind of mature modern optimization algorithm which has excellent global optimization ability,however,its deficiency lies in the time-consuming process and the slow convergence velocity.Sequential quadratic programming(SQP)algorithm shows good astringency with convergence rate of the second order,but it makes high demands of the initial values.Therefore,this paper proposes an improved hybrid genetic algorithm(hybridGA)based on the genetic algorithm.This algorithm introduces the SQP algorithm as a child-operator in the basic GA,which effectively combines the advantages of the two algorithms.Based on the hybrid GA,we wrote the program of the grounding grid corrosion diagnosis by MATLAB to obtain the optimal solution of the corrosion diagnosis equation.Then we use ATP-Draw software to build the equivalent model of the grounding grid to simulate its corrosion circumstance.By measuring the resistance between the accessible node and substituting it into the corrosion diagnostic program,We are able to obtain the resistance values of each branch after solving the equation,which gave birth to the grounding grid corrosion diagnosis by judging the variation of resistance value among different branches.The diagnostic results under basic GA and hybrid GA are compared by the examples of experimental grounding grid and actual substation grounding grid.Finally,considering the possible interference factors in the field test of grounding grid corrosion diagnosis,simulation analysis for an 110 kV actual substation grounding grid was carried out,we proposed some corresponding improvement measures on the influence by different factors according to the diagnosis results,some suggestions for the field detection and its future expansion and reconstruction were also put forward.According to a lot of simulated results of grounding grid corrosion diagnosis,it is proved that the hybrid GA proposed in this paper is superior to the basic GA both in calculation speed and accuracy,and it also verified the engineering practicability of the hybrid genetic algorithm.The improvement measures and suggestions on engineering construction for the field test of grounding grid corrosion diagnosis also have reference value.