The Impact of System Fault Level on the Design of a Substation Earthing Grid Simulation Using ETAP

Abstract

As part of a substation design, the earthing grid design is an important scope that must be carefully considered during the design phase as it plays a major role in ensuring people's safety and maintaining the integrity of equipment and power supply. The earthing grid limits the touch voltage, step voltage, and ground potential rise (GPR) safety limits with tolerable limits by providing a low resistive path to earth for fault currents. In this paper, a substation earthing grid was modeled, and simulations were conducted to evaluate the impact of varying the system fault level on the design and performance of a substation earthing grid using the Electrical Transient Analyzer Program (ETAP) following the IEEE Std 80-2000 guidelines. It was observed that the ground potential rise and the thermal current carrying capacity of the earth conductors and electrodes are greatly affected by the variation of the system fault level. As the fault level increases, the ground potential rise increases by large margins compared to the touch voltage and step voltage, and the thermal current carrying capacity of the earth conductors and electrodes reduces. The higher the system fault level, the bigger the earth conductors and electrodes will be required to satisfy the design criteria.