Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker (SE-DCCB) has been widely used in urban rail transit due to its excellent stability. It can realize forward and reverse interruption, but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process, which is known as arc root stagnation. A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure. The magnetic field, temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A. The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation. The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement, which significantly increases the arc duration time of small current interruption. Based on the research, the structure of the magnetic conductance plate of the actual product is improved, which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted. The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.