Open-Circuit Fault in EHV/UHV Transmission System and New Zero Sequence Over-current Protection Scheme

摘要

In electric grid operation, open-circuit fault may cause mal-trip of zero sequence over-current protection of adjacent transmission lines. Especially for multi-circuit transmission lines with heavy load, mal-trip of zero sequence over-current protection at the same cross section may expand the accident. In this paper, fault characteristics of open-circuit fault of transmission line and reason of mal-trip of zero sequence over-current protection are analyzed, result shows that zero sequence current generated by open-circuit fault is proportional to load current before open-circuit, and will lead to mal-trip of zero sequence over-current protection under heavy load. An improved zero sequence over-current protection scheme is proposed to detect open circuit fault and avoid mal-trip.