Seasonal influences on safety of substation grounding system

Abstract

The low or high resistivity soil layer formed in raining or freezing season affects the safety of the grounding system, and leads to changes of grounding resistance of the grounding system, step and touch voltages on the ground surface. This paper systematically discusses the seasonal influence on the safety of grounding system by numerical analysis method. If the thickness of the low-resistivity soil layer formed in raining season is smaller than the burial depth of the grounding system, the touch voltage would increase. On the other hand, the raining season leads the limit of touch voltage is smaller than the actual touch voltage, even if a surface granite layer is used. The influences of raining on the safety of grounding system must be comprehensively considered. When the high resistivity soil layer is formed in freezing season, the grounding resistance, step and touch voltages would increase with the thickness or resistivity of the freezing soil layer. When the thickness of high resistivity soil layer exceeds the burial depth of the grounding system, the grounding resistance, step and touch voltages would increase sharply, and the touch voltage would exceed the limit of touch voltage decided by a surface granite layer. In order to ensure the safety of the grounding system in freezing season, the grounding system must be designed carefully, and special measures should be used, long vertical grounding electrodes added to the grounding system can effectively attenuate the seasonal influence, and improve the safety of the grounding system.