Research On Visual Diagnosis Method Of Substation Grounding Grid Corrosion

The substation grounding grid is buried deep underground all year round,and is vulnerable to chemical corrosion and electrochemical corrosion,resulting in increased branch resistance,affecting the grounding performance,and endangering the safety of equipment and personnel.At present,a large number of traction substations have been operating for more than 10 years,and the grounding grid corrosion is relatively serious.However,there is a lack of effective grounding grid corrosion diagnosis methods and devices on site,and the grounding grid fault can only be found and repaired by means of large-scale excavation,which is inefficient and has a great impact on the operation of the power grid.Research on appropriate grounding grid corrosion diagnosis methods,develop corresponding corrosion diagnosis devices,and realize trenchless detection of substation grounding grid have important engineering significance for accurately grasping the status of substation grounding grid and accurately guiding the maintenance of substation grounding grid.Firstly,the structure of the grounding grid is analyzed,and the voltage and current relationship between nodes and branches in the substation grounding grid is analyzed according to the electrical network theory.The topological structure of the grounding grid before and after corrosion is the same,but the circuit resistance is different.The algebraic sum of the cross product of the voltage and current of the corresponding branch of the two grounding grids before and after corrosion is zero by using the Tellegen’s quasi-power conservation theorem.Based on this,a corrosion diagnosis equation group that inversely deduces the branch resistance increment from the resistance increment of the grounding grid port is established.Secondly,in view of the problem that the number of grounding grid corrosion diagnosis equations is far less than the number of unknown quantities,which leads to the high degree of uncertainty of the equation set and the difficulty in solving the problem,a method for solving the grounding grid corrosion diagnosis equation based on Lasso principle is proposed,and the L1 regularization penalty term is introduced on the basis of the least square method,which not only solves the problem that the least square method is easy to produce over-fitting and false fault,Moreover,by adjusting the penalty coefficient,the influence of slight corrosion branch of the grounding grid on the solution result can be restrained,and the branch with greater corrosion degree can be retained,thus reducing the dimension of the equation group,reducing the complexity and uncertainty of the equation group,and improving the accuracy and speed of the solution.Use MATLAB to build a grounding grid simulation model with 49 nodes and 84 branches.On the basis of the model,simulate the corrosion and resistance increase of the grounding grid branches.Conduct simulation tests on the resistance of the grounding grid ports.Diagnose the corrosion according to the simulation data and compare it with the settings.It is found that the corrosion of single branch,double branch and multiple branches can be accurately diagnosed.In the laboratory,a simulated grounding grid with the same structure as the simulation model was built with galvanized flat steel,and the accelerated corrosion test was carried out on some branches of the simulated grounding grid with hydrochloric acid solution.The proposed solution algorithm was verified with the measured port resistance value.The solution result was consistent with the actual control sample,which verified the feasibility and effectiveness of the proposed algorithm.A visual diagnosis system for substation grounding grid corrosion has been developed.The diagnosis system consists of grounding grid port resistance tester and grounding grid corrosion diagnosis program.Using Python and CAD interactive programming to achieve the basic parameters acquisition of substation grounding grid,test data reading,diagnosis results visual display and other functions.By reading the CAD design drawing of the substation grounding grid,the program automatically generates an association matrix according to the topology of the grounding grid,numbers the nodes and branches of the grounding grid,and obtains the basic parameters of the grounding grid.Input the actual measured port resistance data into it,and the program automatically calls the internal Lasso algorithm to solve.The corrosion degree of each branch of the grounding grid is divided according to the diagnosis results,and the visual display is realized by giving different colors to the branch on the grounding grid.The grounding grid corrosion diagnosis method in this paper is based on the electrical network theory,which has the advantages of no need for large area excavation,less interference from electromagnetic environment,convenient measurement,and small workload.The Lasso principle is used to solve the difficult problem of solving the corrosion diagnosis equations set up when using the electrical network theory.Build the simulation model of grounding grid and laboratory simulation grounding grid test to verify the effectiveness of the algorithm.A visual diagnosis system for corrosion of substation grounding grid is developed.Finally,the actual diagnosis test of the system was carried out in a substation.In order to verify the accuracy of the diagnosis results,the grounding grid was excavated and rechecked.The diagnosis results were basically consistent with the site excavation.The practical application value of this method is verified.