A fluid-blast piston-type circuit interrupter utilizes two stationary accelerating coils and one moving accelerating coil carried by a fluid-driving piston assembly. During the opening operation, the series fault current is inserted serially into the three accelerating coils, and their magnetic attraction and repulsion forces assist the operating mechanism to move the fluid-driving piston assembly, and thereby to drive fluid, such as sulfur-hexafluoride (SF6) gas, through the established arc drawn within an orifice member to effect its extinction.