The Calculation Of Grounding Resistance In Complex Soil Structure And Its Application In Grounding Grid Reconstruction

The increase of power transmission and the appearance of EHV large capacity substations desire lower resistances, while the condition for grounding grid lying becomes worse, because of some reasons like the lack of land. To reach better results in reducing resistance, all types of grounding resistance reducing methods are commonly used, which work by expanding the area of current flow or changing the soil structure. And these methods are deserved a systematic overall theoretical calculation method which hasn't been studied at home and abroad. To improve the application in practice, after studying the working principle of these methods, base on the numerical methods for electromagnetic fields, models with common applicability are built and the calculating methods are offered.In this paper, firstly, potential functions in complex-layer soil structures are deduced by recursive method and equivalent complex image method, and the program for calculating the potential distribution is developed. The calculation results from the program are identical with those from reference at home and abroad. And then, by modeling the electric character of conductor in the soil medium, the equal potential and the unequal potential method for calculating the grounding resistance are provided.To the electrodes with different shapes commonly used in grounding resistance reducing methods, according to the current diffusion characteristic on the surface, micro-element division is done on the main diffused surface and then the calculating methods of self-resistance and mutual-resistance which is necessary in the calculation of resistance is provided. To the change of soil structure in grounding resistance reducing methods, firstly, attain the resistivity characteristic along vertical or horizontal or both directions according the measured data and then transform equivalently to the complex-layered structure mentioned above through right segment.The ionic grounding equipment works through reducing the soil resistivity gradually due to the ion diffusion in both of vertical and horizontal directions and expanding the area at the same time, so it's chosen to experiment. According of the measured data, with Fick first law, the relationship between the resistivity and distance is worked out. Segment according to the relationship and build the complex-layered soil structure, then calculate, we find that the measured result matches well with the calculated result, which verifies the modeling method. Finally, model several resistance reducing methods and calculate, do a comparative analysis between them and find that changing soil structure is the better way reducing resistance than expanding area of current diffusion on the electrode.