The Grounding System Optimization Of Hydropower Station Based On The Three-layer Soil Model

The Hydro-power Station grounding system is an important measure to maintainreliable operation of power systems and ensure the safe of equipment and human body.Therefore, research on the grounding system has played a decisive role in the design ofgrounding system in substation. In our country’s grounding procedures and IEEE Std80-1986only considered uniform soil model to calculate grounding resistance. But inengineering practice, the soil structure is complex, block and hierarchy, and soilresistivity is very high. Therefore, we need to find a equivalent simplification analysismethod of multi-layer soil. Using the uniform soil model for design and calculation, willproduce large error. And, the existing calculation of grounding parameter for multi-layersoil model is very complicated. We need to find the simplified equivalent model, toprovide theoretical guidance for the design of the grounding grid.Existing hydropower stations are based on the classic three layer soil model, so thispaper simulatively analyzes the influence of upper soil resistivity, upper soil layerthickness, middle soil resistivity, middle soil thickness and lower soil resistivity on thelevel three-layer soil grounding resistance and the equivalent uniform soil resistivity.Also, simulatively analyzes the influence of the left bank, right bank and middle layersoil resistivity, and the thickness of middle layer on the vertical three-layer soilgrounding resistance and the equivalent uniform soil resistivity. To identify theimportant parameters of the equivalent uniform soil resistivity, establish the level andvertical three-layer soil structure equivalent to a single-layer model. Then, based on theprinciple of BP neural network, using MATLAB program, complete the calculation ofthe high resistivity region Hydropower equivalent soil resistivity, and using the uniformsoil resistivity formula launched against the value of the grounding resistance.Grounding resistance calculated by this way, CDEGS, ANSYS and complex imagemethod are approximate, that the method is effective, can be applied in engineeringpractice.This paper takes Ahai Hydropower station as an example,for the study ofgrounding system. According to the characteristics of Ahai Hydropower station, usingthree-layer soil model and established procedure to calculate the equivalent uniform soilresistivity, and finally got the grounding resistance. Combining the biggest short-circuitcurrent, check the maximum step potential and the maximum contact potential, analysis of the maximum ground potential rise, come to the grounding resistance of Ahai doesnot meet the requirements. In this paper, we have a brief introduction about resistancereducing measures of the hydropower station grounding grip in high resistivity areas.Finally, choose to use an additional110,600m2underwater grounding grid to reducethe grounding resistance, arrange8*50m the ground angle is45°inclined groundingelectrodes around500kV outlet to improve the ground potential distribution, combingwith the actual conditions about Ahai Hydropower station.