Investigations On Algorithms And Testability Of Grounding Grids Corrosion Diagnosis And Their Applications

In order to diagnose the corrosion of the grounding grids and ensure the safty of power apparatus, electric power system and the human beings, the following contributions have been made:An augmented diagnosis equation to describe the nonlinear relationship between incremental branch resistances and incremental voltages between touchable nodes is established. An iteration least square approach is proposed, in which, an iterative algorithm is constructed to solve the nonlinear equation progressively by a series of linear least square approaches. A Tabu search based approach to diagnose the corrosion of grounding grids is investigated. The index is to minimize the summation of the squared errors between testing voltages and the evaluated values. The branch resistances form the solution vector. In each iteration step, a set of neighborhood is formed by increasing or decreasing the resistance of each branch with a certain level, respectively, while the other branches not changed.A Monte-Carlo based approach is proposed to evaluate and compare the performance of various grounding grid corrosion diagnosis algorithms. Under a complete test scheme, the testing samples are formed by randomly changing the resistances of branches and the initial values of iteration. The averaged value of relative accumulated error of branch resistances and its standard deviations are used as the indexes for evaluation. Comparsions are made on several grounding grid corrosion diagnosis algorithms, such as, the iteration least square based algorithm, the Tabu based algorithm, the simplex and Tabu search hybrid algorithm, the linear least square based algorithm and the nonlinear least square based algorithm.A Monte-Carlo based approach is proposed to evaluate the testability of grounding grid corrosion diagnosis. The resistances of the branches of a grounding grid are set randomly to form many samples. According to a certain test scheme, the diagnosis results of branches of each sample are worked out. A stastical approach is carried out on the diagnosis results of all the samples, based on which, the branches with their relative errors and standard deviations less than the given threshold are determined as clear branches, the other branches are uncertain branches. A novel improved approach is suggested, which identifies the clear-branches and uncertain-branches automatically by a minimum spanning tree based algorithm and takes the measures of adding a clear vertex and an uncertain vertex, second classification of branches, similar sample adjustment and the ideal sample automatic generation. With the improved approaches, not only are the correctness consideablely increased, but also the amount of calculation needed in the testability evaluation is remarkably reduced. Besides, a Monte-Carlo based approach to evaluate the testability in case of the test data being with the measurent errors is also putforward. Three kinds of testability of grounding grids corrosion diagnosis are defined with their indexes, such as the structural testability, the measurement testability and the disturbance testability.As for the new grounding grids to be built, a genetic algorithm based method of layout optimization of monitoring lines is put forward. The optimum layouts of making all of the branches clear with the minimum number of monitoring lines can be worked out. The suggested ways of the initial population forming, crossover and mutation operation can avoid of the unfeasible solutions in the process, which ensures the efficiency. The best layout of monitoring lines is selected according to the proposed principle of the highest ability of anti-disturbace or the proposed robust principle of M+Y-X. The layout optimization of monitoring lines in case of splitting the grounding grid into small scaled sub-grids to test is also investigated. Applying above achievements into the diagnose of existing grounding grids, a new approach of adding touchable nodes and tests for grounding grid corrosion diagnosis is put forward, with the help of which, the positions of digging and adding touchable nodes with the least manpower to make certain uncertain branches clear can be obtained.The analyses of examples show that the proposed approaches are feasible and efficient.