| In our country, electric power consumption increases rapidly with the development of economy. Our load centers concentrated in eastern coastal areas, but our coal power and hydropower resources mostly distribute in the west and southwest, therefore long-distance and high-capacity electricity transmission is needed. Multi-terminal high voltage direct current (MTDC) technology is suitable for long-distance transmission and power network interconnection, so it will have broad application prospects in our country. However, high-voltage DC switch technology development is slow. So far there is no suitable high voltage DC switch for engineering use, this seriously hindered the extensive application of MTDC technology.This paper mainly studies the high voltage direct current circuit breaker (DCCB) and its application in MTDC system. First, based on CIGRE_Benchmark HVDC transmission model, meshed three_terminal HVDC transmission model is established using PSCAD/EMPDC simulation software, control strategy is introduced, the start-up and steady state of the three terminal HVDC transmission model is studied.Then, several DC circuit breaking method are analyzed, ultimately the self-excited oscillation method is chosen, the high voltage DCCB model is established using the Cassie-Mayr arc model. According to the simulation waveform the process of DC breaking process is discussed detailed. Based on a lot of simulation data, the influence of the transfer loop parameters inductance, capacitance and resistance on the switch time is analyzed, and the double-break DCCB is studied in contrast with single-break DCCB.Finally, a meshed MTDC transmission model that includes DCCBs is established on the basis of the above work. The process of switching off DC transmission line and switching off faulted converter with DCCBs are analyzed.
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