Dynamic dielectric recovery performance of serial vacuum and SF₆ gaps in HVDC interruption and its regulation method

Vacuum gaps have rapid dynamic dielectric recovery speed while SF₆ gaps have high insulation strength. The series-connected vacuum and SF₆ gaps are used as the main switch (MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF₆ gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance (DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker (VCB) and SF₆ gas circuit breaker (GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker (CB) based on series-connected vacuum and SF₆ gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage (TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.