The Numerical Calculation Method And Optimal Design Of Grounding Grids And Its Application

The good grounding system is the fundamental guarantee for the power system's safety, so the research of grounding technology is very important for the design of power system, and the parameters calculation and optimal design of grounding grids constitute an important component in this research. Grounding parameters are calculated by empirical formulass in traditional method, which brings about major errors and can't show the distribution of surface potential, step voltage and touch voltage, and can't meet the greater demand of an exact parameter calculation. In some substations with equidistant grounding grid, the gradient of earth surface potential is big and the leakage current of conductors are not uniform. Thus it is vital to study the optimal design of non-equidistant grounding grid.This paper firstly introduces the Green's function and its fast algorithm in hierarchical soil with the constant current filed, the classical image method and the complex image method are used to calculate the coefficient of Green's function, and the results show the complex image method is better. Then the various methods and the corresponding characteristics of optimal design of grounding grids are analyzed. based on improved genetic algorithm, a new optimal design method for two-layer soil model is developed, the proposed function is used to make the maximum touch voltage minimal and then the optimal compression ratio is calculated so that the optimal conduction distribution can be obtained.The software to calculate grounding parameters and design the grounding grids is developed based on the proposed method. Modulization design and hybrid programming of Matlab and VB is adopted, which makes the program easy to extend and transplante. This software can not only calculate the parameters of complex grounding grids including grounding resistance, step voltage, touch voltage and surface potentiassl, but also provide optimal design for the grounding grid whose topological structure is regular. What's more, it can display 3D figures for these grounding parameters.Finally, actual grounding grids——GaoXin and XiJiao substations are calculated. The results show this software has high efficiency and precision in the simulation calculation, and the proposed optimal design method can make the surface potential well-distributed and decrease the maximal touch voltage greatly. As a result, the safety level of grounding grid can be improved.