Impact of seasonal variation of soil resistivity on safety of substation grounding system

摘要

This paper presents impact of seasonal variation of soil resistivity on performance indices of grounding system. The grounding system initially designed for uniform soil, may become two layer or multilayer soil structure due to seasonal variation such as rainy, early spring and winter season. The formation of low or high resistivity soil layers leads to change grounding grid resistance and affects the most stringent safety criterion like step and touch voltages on the ground surface. The grounding system is extensively analysed for various seasons like raining and freezing in winter considering two layer soil model due to formation of low or high resistivity soil layers. Moreover, safety is analysed using multilayer soil model for some cases. The study reveals that the grounding grid designed for uniform soil may becomes unsafe during freezing and early spring. Therefore, grounding system must be designed very carefully. Use of long vertical ground rods can effectively attenuates the seasonal influence and improves the safety of grounding system. The simulation has been carried out by using Autogrid-Pro grounding software of SES & technology, Canada.