A New Type of Forced Commutation Vacuum DC Circuit Breaker

In medium and high voltage DC power systems, traditional forced commutation breaking technology has the problem of breaking failure due to heavy breakdown after arc current crosses zero when turning off short-circuit current. This article proposes a new type of forced commutation vacuum DC circuit breaker from two aspects: reducing the current drop rate during short-circuit breaking process and the voltage rise rate during transient recovery process. A mathematical model was constructed, and the short-circuit breaking principle of the circuit breaker was analyzed in detail. This aspect was optimized from several aspects such as branch stray inductance, auxiliary commutation input time, arc voltage, etc. Finally, a test circuit was constructed to verify the high current breaking test. The results show that through the conduction and diversion effect of the auxiliary switch, without significantly affecting the rapid current transfer process, the current drop rate near the arc extinguishing can be effectively reduced, and a sufficiently long low current change rate range can be maintained; Meanwhile, after the arc is extinguished, the transient recovery voltage at both ends of the vacuum circuit breaker can be clamped at a relatively low level for a relatively long time. The new commutation scheme simultaneously improves the arc current characteristics and post arc recovery voltage characteristics of vacuum circuit breakers. Compared with existing improvement schemes that only focus on pre arc current characteristics or post arc voltage characteristics, it has more obvious advantages in improving the reliability of DC vacuum circuit breakers in high current breaking.