A Case Study of A Shunt and Preexisting Series Simultaneous Fault

On August 11th, 2023, a shunt fault occurred on a Dominion Energy networked line in South Carolina that had a previously existing series fault. The series fault was a missing jumper associated with Phase A, which created an open phase. Because the series fault was preexisting when the shunt fault occurred, both faults existed at the same time. This occurrence is defined as a simultaneous fault. Simultaneous faults are rare, and it can be difficult to discern that they occurred. They produce fault currents and voltages that are uncommon on the power system and uncommon to protective relay elements. This paper analyzes a real-world case study of a simultaneous fault on a transmission system to empower the industry with knowledge of how to discern future shunt and series simultaneous faults. The paper describes the fault, the voltages and currents observed during the fault, and the analysis that took place to discover that both a series and shunt fault existed at the same time. The paper also provides a brief description of how a series fault and shunt fault would have appeared on this system if they had occurred separately, to contrast with how the simultaneous fault appeared. This provides a way to distinguish between nonsimultaneous faults and this type of simultaneous fault. The paper discusses a corrective action that can be implemented to possibly prevent some shunt and series simultaneous faults in the future. The paper analyzes the fault using traditional methods and simulation and provides the opportunity to compare the power system response to analysis and simulation.