Analysis of Varying Soil Resistivity on Substation Earthing Design and Performance Using ETAP

Abstract

An earthing grid is a critical part of a substation that ensures people's safety and reliable operation of equipment. It achieves this by providing a low resistive path to earth for high currents during transient conditions, and in doing so, it limits the ground potential rise (GPR), step voltage, and touch voltage present in the vicinity of the substation within their tolerable thresholds. In this paper, a substation earthing grid was modeled, and simulations were conducted to evaluate the impact of varying soil resistivity on the design and performance of a substation earthing grid using the Electrical Transient Analyzer Program (ETAP) following the IEEE Std 80–2013 guidelines. It was observed that the touch voltage and step voltage safety limits are affected by the varying soil resistivity, with the touch voltage being the most sensitive safety limit to the soil resistivity variation. When the soil resistivity is low, the safety limits thresholds are relatively high, and when the soil resistivity is high, the thresholds are low, affecting the quantities of the other design parameters required to satisfy the design criteria for the same available earthing grid area.