Novel Reclosing Strategy Based on Transient Operating Voltage in Pseudobipolar DC System With Mechanical DCCB

To ensure the reliability and flexibility of direct current (dc) system, direct current circuit breakers (DCCBs) are in urgent demand. Compared with solid-state and hybrid DCCBs, mechanical DCCBs have features of low operating losses and investment, showing bright application prospects. Until now, without concern about transient operating voltages (TOV) in the whole dc system, the reclosing of DCCB is still an open problem, and it is the emphasis of this article. First, overview of TOV in typical pseudobipolar dc system is introduced. Then, focused on hardware, electrical characteristic of a novel mechanical DCCB is analyzed, and verification tests are carried out in our laboratory. By taking interaction between the dc system, DCCB, and lines into consideration, distribution patterns of TOV under different faults and its mechanism are revealed. Based on TOV, novel reclosing strategy is proposed for mechanical DCCBs, and case studies are conducted in PSCAD/EMTDC for verification. Remarkable advantages of novel reclosing strategy are: fault type could be identified without operating any component of DCCB after fault current interruption; no risk of reclosing a permanent fault point; an explicit time could be reserved for the dielectric recovery of temporary fault point.