Comparison of artificial current zero impulses for a vacuum interrupter based direct current circuit breaker

Investigations on direct current (DC) circuit breakers (CB) become more and more important. The major challenges of DC CBs compared to alternating current (AC) CBs are the lack of a natural current zero and the required absorption of the energy in the system. With an artificial current zero created by a parallel commutation path a vacuum interrupter (VI) can handle this duty. The commutation path has an important influence on the current interruption. Typically, a current zero impulse (CZI) is generated by an RLC circuit and is superimposed in opposite direction of the DC in the VI. Therefore, the capacitor in the RLC circuit is charged inversely to the VI voltage. By charging the capacitor in the same direction, the first half wave of the current impulse flows in the same direction and is added to the DC in the VI. As a result, the capacitor voltage changes polarity and now superimposes a CZI in the opposite direction. In this paper the influence of the CZI direction on the interruption performance of a VI is investigated. Furthermore, an alternative arrangement of the commutation circuit that generates a saw tooth-shaped CZI is presented and compared with the sinusoidal one.