Analysis and Test of the High Current Forced Commutation Interruption Characteristics for a DC Vacuum Circuit Breaker

With the well flexibility to expand for medium & high voltage large power application, the DC vacuum circuit breaker (VCB) based on active forced current commutation is becoming a very important development direction for DC interruption technology. For a 10 kV DC VCB, lots of experimental studies for the high current commutation interruption (CCI) process were conducted after a further analysis of the CCI characteristics in this paper. The experimental results indicated that the VCB could not interrupt reliably at the current zeros for the peak arc current about 23 kA and the fall rate about 300 A/μs. In addition, some dispersion and randomness took place in the vacuum gap (VG) post-arc dielectric recovery (PADR) process. In order to improve the high current PADR characteristics, a DC VCB CCI scheme was proposed with a diode connected in series, which could provide a current zero interval for the high current vacuum arc through the diode reverse blocking. According to the comparative interruption test results under the same parameters, although the process of dielectric recovery, dielectric breakdown, dielectric recovery' might be repeated continuously during the diode reverse blocking, the arc reigniting would not happen in the VG. Finally, the VG was able to built enough dielectric strength before the commutation capacitor voltage polarity becoming positive, so that reliable interruption of the high DC current could be realized. Meanwhile, under the test conditions, it would take at least 85 μs to completely recover the dielectric strength in the post-arc stage. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.