Novel solid-state circuit breaker based on active thyristor topologies

Solid-state circuit breakers (SCB), based on modern high-power semiconductors, offer enormous advantages when compared to mechanical circuit breakers with respect to speed and life. For instance, the voltage quality during a short circuit is increased and therefore the fault current is reduced. Distortions caused by a three phase short can be reduced to a few 100 mus, in contrast to some 100 ms achieved with present technology. Major drawbacks of all solutions for SCBs presented so far are material costs and on-state losses. Primarily because of these disadvantages SCB systems have not undergone industrial realization. Consequently, new solutions should be developed which are much more cost effective and offer reduced on-state losses. This paper presents a different conceptual approach based on active thyristor circuits and on auxiliary circuits, which are of utmost importance for the design of such kind of systems. It has been shown that forced commutation circuits are able to turn-off short circuits in medium-voltage grids actively and thus rapidly. Therefore, the overall life-cycle costs are reduced significantly. After a presentation of the SCB system, the critical design of the auxiliary circuits will be discussed. There will be a comparison of one conventional and two new innovative circuits for charging the commutation capacitor.