DC current interruption in HVDC SF6 gas MRTB by means of self-excited oscillation superimposition

The Kii-Channel HVDC Link under construction in Japan is equipped with meta llic return transfer breakers (MRTBs) in one converter station. A new MRTB for an interrupting current of 3500 A d.c. was developed. To interrupt a d. c. current, a method that produces a current zero point by superimposing a self-excited oscillatory current on a d.c. arc current was employed. For th is purpose, a LC circuit was coupled in parallel to a SF6 gas circuit break er. Developing a SF6 gas circuit breaker that has a large arc voltage drop gradient against currents permitted a large oscillatory current to be gener ated. A modified Mayr-type dynamic arc equation was newly presented. The d. c. interruption limits calculated using this equation agreed with the measu red values.