Grounding Grids Corrosion Diagnosis Based On Block Model And Influences Of Touchable Nodes Deviation

In order to diagnose the corrosion of the grounding grid and down lead lines conveniently, find out the defects in time and ensure the safety of power apparatus, electric power system and the personal safety, the following contributions have been made:To benefit for dividing a large grounding grid into several small grounding grids, based on hierarchical simplification model, a novel block model for grounding grids is proposed. The originalshape and projection concept of block are defined in the block. According to the block model, the grounding grid can be divided into different scale blocks, which are independent each other and can be classified into different kinds blocks such as clear block,uncertain block and mixed block, the different methods for different kinds of block is presented, which the diagnosing the corrosion of grounding grids can be achieved. Using the splitting method based on the block model, the testability of grounding grids can be kept identical all time.The block diagnosing method based on the block model for grounding grids is put forward. A linear new approach is presented, which the intrinsic branch resistances can be solved accurately. The cross-interferences of testing data between the blocks are reduced and the efficiency is improved rapidly, meanwhile it is helpful to reduce the sensitivity from intrinsic branch resistance measurement error. The branch resistances of actual grounding grids can be solved by the tracing method to calculate the current branch resistance according to the upper level branch resistances. So, the corrosion diagnoses of partition and part block can be acheived.To diagnose the corrosion of down lead lines, two novel methods are proposed. One method is to achieve the resistances of the horizon conductors firstly based on the sufficient test data avoiding the effect of the down lead lines. Then, the linear equation group of down lead line resistances are established based on the test data of resistances between each two touchable nodes. The other method is based on the proposed block model. The ratios of the intrinsic branch resistances are achieved firstly based on the sufficient test data. Then, the linear equation group of down lead line resistances and the resistance of a certain intrinsic branch can be established based on the test data including the influence of the down lead lines; the resistances of the down lead lines can be thus solved.The amount of test work is calculated for the cases of using normal measurement equipments and with automatic testing system, respectively. An optimization approach of test schemes based on dynamic programming is put forward to reduce the amount of test work in the process of grounding grid corrosion diagnosis.In the practice of grounding grid test, the down lead lines are used as touchable nodes and normalized into the nearby cross nodes of the network, respectively, resulting in touchable nodes deviation problems. The influences of touchable nodes deviation on the accuracy and the testability of the results of grounding grids corrosion diagnosis are analyzed. A Tabu search based on correction approach is put forward. The diagnosis results in case of deviation are used as the initial solution. The index is to minimize the summation of the squared differences between the observed voltages and the voltages after correction. A method to access the correction in quantity is suggested.Experiments are made on the test grounding grid with sixty branches and the thirty-eight grounding grid buried in Weinan 330kV Substation are tested and diagnosed, respectively, the diagnose results of which show that the proposed approaches and algorithms are correct and feasible.