International Surveys on Circuit-Breaker Reliability Data for Substation and System Studies

Since the 1970s, CIGRE has conducted three worldwide surveys on high-voltage circuit-breaker (CB) reliability. The results of the last inquiry, published last year, are presented and compared with those of the former inquiries. With a focus on the CB's fundamental functions for the system, figures show the growth in reliability during the past decades. The reliability is expressed in failure per 100 CB years (CBY) or per 10 000 operating cycles for the relevant failure modes. The overall major failure rate improved largely from the first (1.58 per 100 CBY) to the second (0.67 per 100 CBY) to the third enquiry (0.30 per 100 CBY). The failure rate increases with higher voltage classes; GIS CBs have been shown to be twice as reliable and live tank CBs twice as bad as the average failure rate. Although improved, the mechanical operating mechanism is still the subassembly responsible for most failures; besides, CBs applied for frequent switching purposes show a higher failure rate than average.