Event Investigation of 69 kV Double-Circuit Faults
[Presented at Texas A&M 2020]
Two rare yet similar faults occurred within hours on SDG&E's 69 kV parallel circuits. Because the faults involved two parallel lines, they caused unconventional fault waveforms seen by multiple relays. This, in turn, challenged the directional elements and overcurrent coordination, producing unexpected relay operations.
This paper presents the performed investigation that helped correlate the captured fault oscillography with the type of fault. The paper explains the relay operation, focusing on the directional element, and concludes with lessons learned and suggestions for relay security improvements. The paper also emphasizes system-wide, time-coordinated event report analysis, which was indispensable to the root cause analysis.