The Optimal Design Approach And Realization For Grounding System Of Substation

A good grounding system is the fundamental guarantee for the power systemrunning reliably and safety of operators. So the research of grounding system is veryimportant for the design of power system, and in which the optimal design ofgrounding grids is significant. In some substations with equidistant grounding grid,the gradient of earth surface potential is big and the leakage current of conductors arenot uniform．Therefore it is very vital to study the optimal design of non-equidistantgrounding grid based on inequipotential model．Firstly, this paper introduces the Green’s functions and its fast algorithm inhierarchical soil, then the complex image method is used to calculate theundetermined coefficient of Green’s function. Based on the field-circuit couplingtheory, an inequipotential model of grounding grid is built. The inner self-reactance,self-inductance of conductors and mutual inductance between conductors, mutualimpedance matrix of conductors are detailedly introduced. After that, a new optimaldesign method based on the two-layer soil model and inequipotential model isproposed, in which, a objective function is developed to make the maximum touchvoltage reach a minimum and the improved adaptive genetic algorithm is applied tocalculate the optimum compression ratio that can be used to confirm the optimumconduction distribution. On this basis, the effects of intertied grids and verticalgrounding rods to reduce the grounding resistance, step voltage and touch voltage isstudied by theoretical analysis and numerical calculation. This optimal design methodcan be used in some area with high soil resistivity.A grounding system in110kV substation is designed using the method proposedabove, and several optimization schemes are presented for different situation. Thesimulation results show this new method can make the surface potentialwell-distributed and decrease the maximum touch voltage remarkably compared withtraditional method. Connecting the intertied grids or vertical grounding rods to thegrounding system also can decrease the grounding resistance and the maximum touchvoltage signally. So, the safety level of grounding grid can be improved.