Current-limiting surge arrester disconnector

A protective device for use in association with a surge arrester having a ground lead terminal, the device being capable of limiting and interrupting fault current, comprising

• an insulative housing,
• first terminal means mounted at one end of the housing, said first terminal means providing external means for connection to the ground lead terminal of a surge arrester,
• second terminal means mounted at the other end of the housing, said second terminal means having a separable external portion providing means for connection to a ground lead,
• a current-limiting fuse connected in circuit between said first and second terminal means,
• a bypass switch shunting the fuse, said bypass switch having a fixed contact formed by a metal cap providing an internal chamber for housing a chemical propellant charge, and a movable contact operable by ignition of the chemical propellant charge to open the switch,
• fault sensing means connected in circuit between the first terminal means and said fixed contact, triggering means responsive to said fault sensing means for igniting the charge in response to a fault condition, thereby to open the bypass switch and so direct switch current to the fuse, and
• means constraining the movable switch element, when operated to open the switch, to strike said separable portion of the second terminal means thereby separating said portion and so isolating the surge arrest from ground.

A surge arrester disconnector for use in association with a surge arrester having a ground lead terminal, the device being capable of limiting and interrupting fault current, comprising

• an insulative cylindrical housing,
• first terminal means mounted at one end of the housing,
• said first terminal means having a cap portion closing said one end and an external portion providing means for connection to the ground lead terminal of a surge arrester,
• second terminal means mounted at the other end of the housing, said second terminal means having an annular terminal portion fixedly mounted at said other end and an external separable portion connected thereto by frangible fastenings, said external separable portion providing means for connection to a ground lead,
• an insulative cylinder mounted in the housing coaxially therewith and defining a longitudinally extending channel, one end of the insulative cylinder extending through the annular terminal portion of the second terminal means to said external separable portion,
• switching means comprising a switch head mounted at the other end of the insulative cylinder and a movable element constituted by a piston which is slidable along the cylinder, the piston frictionally engaging the switch head in the closed switch position,
• said switch head providing a chamber for housing a chemical propellant charge positioned to actuate the piston when the charge is ignited,
• a flexible conductor lead interconnecting the piston with the separable portion of the second terminal means, the lead extending along said channel,
• a current-limiting fuse connected in circuit between the switch head and the second terminal means,
• fault sensing means connected in circuit between the first terminal means and the switch head and triggering means responsive to said fault sensing means for igniting the chemical charge whereby, in the event of a fault;
• the piston is driven from the closed switch position thereby diverting fault current to the fuse, and is guided into striking contact with said separable portion and so separating said portion to isolate the surge arrester from ground.