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DC circuit breaker is the key equipment for control and protection in the medium and high voltage DC system. Mechanical DC circuit breakers have transient overvoltage in breaking, which may lead to re-breakdown of the breaker or even breaking failure in severe cases. In this paper, the transient overvoltage in the breaking process of typical mechanical DC circuit breakers is studied. An improved topology which can supress the transient voltage is propose. The effect of different capacitance and resistance parameters on weakening the transient voltage is investigated, and the adaptability of the proposed method to different breaking currents is studied.

With the rapid development of DC power systems in recent years, more stringent requirements have been put forward for the fast reliability of DC circuit breakers. At present, in the medium voltage DC circuit breaker, the mechanical switch commonly uses an external secondary power supply to charge the mechanism drive capacitor, which has the problems of large breaker size and high cost. In this paper, we propose a DC circuit breaker topology that uses short-circuit current to charge the mechanism drive capacitor of the mechanical switch. When the short-circuit current rises, a voltage drop is formed across the series inductor, and this voltage charges the drive capacitor in parallel through a diode, avoiding the use of a secondary power supply to charge the drive capacitor and reducing the complexity of the DC circuit breaker system. The operating principle of the circuit breaker is analysed and the rationality of the proposed scheme is verified by simulation calculations.

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