Optimization Research on DC Air Circuit Breaker at High Altitudes Based on Arc Root Stagnation and Arc Reverse Movement Phenomena

Urban rail transit in high-altitude areas is developing gradually, but the failure of short circuit breaking of on-board large-capacity DC air circuit breaker (LC-DCCB) at 2–4 km altitudes has become severe and common. To interrupt short circuit current at 2–4 km altitudes of on-board LC-DCCB successfully, multi-physical coupling simulation of short circuit breaking of LC-DCCB at 2–4 km altitudes was conducted in this research based on the magneto-hydro-dynamics (MHD) model, and the simulation results were compared with those at 0 km altitude. The two-dimensional (2-D) transient distribution of physical parameters such as temperature, airflow, and electromagnetic fields in the arc chamber were obtained. The results indicate that the fundamental reasons for the failure of LC-DCCB to interrupt short circuit current arc at high altitudes are the arc root stagnation and arc reverse movement between splitter plates. Based on the simulation results, the arc chamber structure was optimized by setting U-shaped splitter plates to improve the interruption performance of LC-DCCB at high altitudes. Compared with the previous structure, the improved structure with three intercalary U-shaped splitter plates on both sides of the center line of the arc chamber has the best arc extinguishing performance at high altitudes, which can interrupt 18 kA short circuit current successfully at 3 km altitude, with an arc duration of 19.5 ms. This research reveals the fundamental cause for the difficulty in interrupting short circuit current arc in LC-DCCB at high altitudes, which can provide theoretical and technical guidance for the research and design of such a product.