STUDY ON CONTACT DEGRADATION OF ARC CONTACT OF SF₆ CIRCUIT BREAKER FOR REACTIVE SWITCHING

Frequent operation of SF6 circuit breaker for switching capacitor banks leads to radial loss and stress relaxation of arc contact, and contact degradation occurs, which seriously affects its performance and operating life. In order to study the influence of radial loss and stress relaxation on contact degradation of SF6 circuit breaker arc contact, this paper established a contact resistance model based on Holm theory, and obtained the relationship between radial loss and increase of contact resistance, then influence of arc contact stress relaxation on contact resistance was studied through theoretical calculations. Results show that contact resistance increases with the increase of radial loss of arc contact. When inrush current peak is 15kA, radial loss reaches 0.2366mm, and contact resistance increases by 54μΩ. At the same time, it is found that stress relaxation during long-term deformation will lead to a decrease in contact force. It is predicted that stress loss will be close to 40% of initial stress after 20 years, and stress relaxation will increase contact resistance by 50μΩ.