Multi-terminal DC transmission technology is suitable for multi-power supply and multi-drop receiving, and has the advantages of large transmission capacity and flexible control. The DC high-speed switch (HSS) is a key device in the multi-terminal DC transmission system. It can close, load and break DC current under specified conditions, as well as quickly isolate grid faults. Although HSS only needs to break small DC currents, the phenomenon of after-arc breakdown cannot be ignored, which is extremely important for evaluating switching performance. In this paper, the ±800kV DC HSS filled with SF₆ at 0.52MPa is investigated by the magneto-hydro-dynamic (MHD) model. According to the switch structure and the SF₆ real gas model, the MHD model of the DC small current arc combustion process is established, and the distribution law of temperature, pressure and velocity in the arc extinguishing chamber is analyzed. In addition, an evaluation method for post-arc breakdown is established, which predicts the most likely area of post-arc electrical breakdown based on the temperature and pressure distributions when the current crosses zero. Based on the consistency of experimental results and simulation results, the established model in this paper is valid and can be widely used in arc simulation and the evaluation of dielectric recovery, which provides a sufficient theoretical basis for studying the influence of different factors on interruption performance and optimizing the design of HSS arc extinguishing chamber.
 

dielectric recovery,thermal interruption performance,DC high speed switch,magneto-hydro-dynamics (MHD)