The paper describes a concept for fast-acting circuit-breaker using vacuum interrupter (VI) assisted by a power-electronic converter with low output voltage. The converter excites a passive resonant circuit to create current zero-crossing in the arc in the VI to make it extinguish the current. A fast-acting actuator using a Thomson coil separates the contacts in a few milliseconds. The principle is outlined, and a laboratory prototype is described. In experiments 10 kA was successfully interrupted against 9 kV in 3 ms.