Circuit breaker

A circuit breaker, in particular a high-voltage circuit breaker, insulated by SF.sub.6 gas, comprising, a fixed contact part, a movable switching piece, the movable switching piece being provided with a blast nozzle and adapted to be actuated by a drive, a SF.sub.6 gas containing compression space being decreased in volume during the process of tripping out such that a flow of the SF.sub.6 gas is directed by the blast nozzle toward the arc being produced during the tripping out, the compression space being bounded by a piston-cylinder arrangement for generating the gas flow during the process of tripping out, the piston-cylinder arrangement being such that at least one of a movable piston and a movable cylinder is pulled toward at least one of a stationary cylinder bottom and a stationary piston head, respectively, the compression space being concentrically surrounded by a coil for generating a magnetic field, said coil being adapted to be switched into the current path such that during the process of tripping out a short-circuit current does not flow through the coil until disconnection has been effected at a main contact point of the breaker, a cylindrical inner shell is provided inside a cylindrical outer shell which bounds the compression space externally, the inner shell being arranged with a clearance relative to the outer shell and being insulated therefrom, the coil being located between the outer and inner cylindrical shells, an auxiliary piston being movably arranged in the compression space, the auxiliary piston being adapted to be driven by the magnetic field toward the contact point to render the compression space still smaller.