Characteristics of Surface High-resistance Coverings in Grounding System

In order to obtain the influence of the resistivity and thickness of high-resistance covering on the parameters of grounding grid, we set up a model of the high-resistance layer by using the electromagnetic numerical method, simulated the performance of a 50 m×50 m grounding grid with high-resistance covering, and summarized the problems that need to be considered when using the surface high-resistance coverings. Then we put forward the proposals on how to use the surface high-resistance coverings in order to guide the engineering practice. The investigation results based on numerical simulation show that the influences of the surface high-resistance coverings on the grounding resistance, ground potential rise, touch potential difference, and step potential difference are very small, while the surface high-resistance coverings can improve the tolerance limits of the touch potential difference and the step potential difference greatly. Thus, covering the earth surface with high-resistance layer is a very effective measure to improve the safety performance of the grounding grid. Due to the saturation trend of the tolerance limits with the increasing of the high-resistance coverings' thickness, it is suggested that the enough thickness of high resistivity layer should be 0.1~0.2 m. In order to guarantee the effect of the high-resistance coverings, the grounding grid should be buried in soil with a depth of 0.8 m, and then the high-resistance covering should be added directly on the soil's surface in actual project.