The effects of asynchronous interruption on arc motion characteristics of a triple‑break medium-voltage DC air circuit breaker

Multi‑break DC air circuit breakers are subject to asynchronous interruption due to dispersion of operating mechanisms, resulting in nonuniform transient voltage distribution among the breaks and thereby compromising interruption reliability. A controllable two-dimensional magnetohydrodynamic-external circuit coupled model is established for a 9 kV/100 kA triple-break DC air circuit breaker composed of three series-connected independent arc chambers. The asynchronous interruption process is simulated by assigning different arc initiation instants to each break. Four representative cases are investigated under two typical asynchronous interruption modes, namely sequential and grouped interruption, with different interruption time intervals. The simulation reveals the entire dynamic motion process of the arc in each break inside the arc chamber, from initiation to being split and stretched by the splitter plates, and finally to extinction. The results show that asynchronous arc development causes abrupt voltage rises, transfers, and significant dynamic fluctuations among the breaks. Moreover, the formation and coupled evolution of secondary arcs are observed, including cascading secondary arcs under the sequential interruption mode and a distinct voltage plateau under the grouped interruption mode. Increasing the asynchronous interruption interval intensifies the dynamic voltage fluctuation and prolongs the arc duration, leading to a higher temperature inside the arc chamber and degraded interruption performance. The grouped interruption mode exhibits poorer interruption performance than the sequential mode. These findings provide a theoretical basis for the synchronization design and structural optimization of multi‑break DC air circuit breakers.