Study On Lightning Impulse Transient Characteristic Of Grounding Grid In Substation

Grounding grid plays an important role in the safe operation of the transformer substation, the grounding performance has always been one of the important performance focused by the design and production operation departments. Along with the continual improvement of electric power system capacity and voltage level, the impulse current into the grounding grid increases when substation occurs fault, which may lead the potential of grounding grid being abnormal higher. It will threat the safety of the operators, may also make the insulation of the secondary equipment be destroyed with counter, and even leads to the secondary equipment action or no action by mistake. So higher requests are put forward on substation grounding grid in the current divergence and voltage-sharing function, it is of great significance to carry out the research on ground grid impact characteristics.Firstly, the transient response calculation model of grounding grid through lightning shock is established by using the grounding analysis software CDEGS in this paper. The influence rule of grounding grid transient potential is analyzed under the different factors of injection point location of lightning current, grounding grid parameters and soil layered structures. It finds that the change of grounding potential gradient near injection point is larger, the potential when the lightning current is injected at center is smaller than the lightning current is injected at corner. The influence of grounding parameters on grounding transient potential is small, but the influence of soil resistivity and hierarchical structure is large.Secondly, based on the simulation model of grounding grid, the attenuation and diffusion laws of transient potential in grounding grid are studied. Through the analysis of the wave front difference of transient voltage, it finds that the real potential difference is greater than the difference of voltage amplitude. The characteristics of transient potential difference under different injection point location of lightning current have been studied, it is obtained that with the increase of soil resistivity, the wave front time of potential difference is more less than the and the wave front time of the transient potential at lightning injection point, the influence of voltage difference amplitude is more lager. The transient amplitude frequency characteristics of grounding grid are ascertained, it finds that the high frequency current flows more fast into the soil, the current under high soil resistivity flows more slowlv into the soil.Finally, the method of adding vertical grounding body is adopted to optimize and improve the transient characteristics of grounding grid, the influence rule of the vertical grounding body length, numbers and adding position on improvement effect is studied, it finds that the improvement effect is best when the vertical grounding body is injected at or near the lightning current injection point. The application of vertical grounding body in the heterogeneous soil is studied under different resistivity and thickness of soil. It is found that the transient potential of grounding grid decreases continuously with the increase of thickness of the upper soil layer under the reflection coefficient is positive, but the influence of soil thickness on the transient potential is small under the reflection coefficient is negative.