Enhancing Fault Location Accuracy by Addressing Flashovers in Segmented Static Wires

Accurately locating faults on 500 kV lines using impedance-based methods has long been a challenge for Dominion Energy Virginia. Systems methods that were implemented to mitigate the fault location errors worked well; however, single-ended, impedance-based methods kept returning inaccurate fault locations. In early 2020, we experienced an “ah-ha” event that changed the way we determine fault location for 500 kV lines. While static wires are continuous on our 115 and 230 kV lines, for 500 kV lines they are segmented to reduce losses. When a fault in a substation caused the remote end of a 500 kV line to trip on Zone 1, the digital fault recorders (DFRs) incorrectly reported the fault location as being on the line. While using the known location to analyze the fault, we discovered that during certain faults segmented static wires would flash over at their segmentation points, causing the segments to appear continuous. The resulting zero-sequence impedance was vastly different than the system model. Based on this information, Dominion is developing a process to calculate the fault current levels required for flashover for each of its 500 kV lines. This paper describes the steps to our discovery, reviews our fault location methods, and discusses other methods of determining fault location based on a known location. We conducted a PSCAD study to analyze induced voltage under various conditions.