Abstract—The paper presents the case study of SF6 circuit
breaker failure during switching-off an unloaded and relative
long 400 kV transmission line. Both breaking chambers of the
circuit breaker were destroyed. Due to the specific place and type
of fault the relay protection system did not operate during circuit
breaker failure and transients have been recorded only by a
power quality monitoring system installed in the nearby line bay.
Recorded events were used for circuit breaker post-mortem
analysis. Simulations and fault analysis were carried out using
EMTP-RV software.
Keywords: 400 kV circuit breaker failure, restrike, transient
recovery voltage, switching