DC circuit breakers serve as a key device for multi-terminal DC transmission and DC distribution networks. The difficulties of mechanical and hybrid DC circuit breakers are arcs between the contacts of mechanical switches during the breaking process. This paper discusses the electric field intensity and voltage conditions for arcs. By statistical analysis of a large number of experiments

the electric field intensity and voltage conditions to be met for arc suppression are summarized. An auxiliary buffer circuit for arc suppression is designed to limit the voltage rise between the contacts during breaking. This makes the voltage lower than the medium isolation voltage between the contacts determined by the speed of mechanical switches

so that DC circuit breakers can break without arcs. The correctness and effectiveness of the arc suppression principle and buffer circuit design are verified by simulations and low-voltage simulation experiments

and the feasibility of a medium-voltage arcless DC circuit breaker is analyzed.