Fast-drive device for a high-speed earthing switch

A high-speed earthing switch for a gas-insulated, encapsulated switching installation, especially for an SF6 high-voltage switching installation, has moving contact pins (12, 14) which, in the event of a defect, must be moved very quickly onto phase conductors (32) which are located inside the encapsulation (30) of the switching installation and are at high-voltage potential, in order to earth them. In order that the switching-on process can be carried out more quickly, the drive device has a piston/cylinder arrangement (50, 36) whose piston (50) divides the cylindrical space into two mutually connected sub-spaces, of which one sub-space is connected to the encapsulation (30) while, on the other hand, the other sub-space can be suddenly evacuated in order to switch the high-speed earthing switch on. When this other sub-space is rapidly evacuated, then the piston is set in motion into the switched-on position of the high-speed earthing switch.