关键词: 季节性冻土, 变电站, 接地电阻, 跨步电压, 接触电压, 垂直接地极, 电网安全

Abstract: After soil freezing in winter, the soil resistivity increases sharply, and the soil resistivity and depth of frozen soil layer vary with soil temperature, which not only affects the values of the contact voltage and step voltage, but also the allowable values of the step voltage and contact voltage. In order to explore the effect of seasonal frozen soil on the grounding safety of substation, the seasonal frozen soil model is established in this paper. The influence characteristics of seasonal frozen soil on the resistance, contact voltage and step voltage of substation grounding system are archived by simulations; the maximum allowable safety values with different grounding resistances, contact voltages, and step voltage are analysed. Finally, the methods to improve the grounding safety performance in the frozen soil region are studied. When the depth of frozen soil is less than the buried depth of grounding grid, the step voltage and touch voltage are effeted by the soil resistivity of the lower layer, and the grounding system is relatively safe. If the frozen soil depth is larger than the one of the grounding grid, there are sharp rises in the touch voltage and step voltage, which exceeded the safety value. At this time, the vertical grounding electrodes can effectively reduce the grounding resistance and limit the contact voltage and step voltage.

Key words: seasonal frozen soil, substation, grounding resistance, step voltage, touch voltage, vertical grounding electrode, power grid safty