Abstract: A zinc oxide varistor disc is provided with one or more circumferential recesses in its rim to reduce the current density at the edges of the electrodes on the opposed disc faces, which electrodes are of a lesser diameter than the varistor disc. It has been discovered that optimum results are achieved when the diameter at the bottom of the recess is somewhat less than the diameter of the electrodes.

Abstract: Capacitance grading is provided within gas insulated lightning arresters containing stacked zinc oxide varistors by means of a grading ring electrically connected to the line terminal or, for arresters of the higher voltage ratings, by means of a plurality of telescoping external electrostatic shields. The shields are arranged so that the degree of overlap between sequential shields decreases from the line end to the ground end of the varistor stacks. The capacitance grading is provided by the degree of overlap between the sequential shields and the ratio of the radii of the overlapping shields.

Abstract: A heat transfer arrangement for zinc oxide varistors comprises a metal heat sink disk held in contact with one face of the varistor by means of a circumferential elastic sleeve. The heat generated within the varistor rapidly conducts into and is absorbed by the metal disk and transmits through the elastic sleeve to the environment. When the varistor heat sink assembly is mounted within a surge voltage arrester, a flexible positioning member holds the assembly tightly against the arrester housing for transferring the heat to the housing.

Abstract: Voltage surge arrester devices having predetermined shunt gap sparkover voltages are provided by the series combination of high- and low-exponent varistors. In one embodiment the high-exponent varistor comprises zinc oxide and the low-exponent varistor comprises silicon carbide.

Abstract: Metal oxide varistors having a uniform wattage gradient across the varistor surfaces are provided by removing a thin layer of metal oxide surface material from the periphery of the varistors prior to applying an insulating collar and a silicone rubber encapsulation for the purpose of heat dissipation.

Abstract: A voltage surge arrester disposed in a metal enclosure pipe containing an insulating gas is provided with a gas vent adjacent the line voltage terminal end of the arrester for venting gases which are generated inside the arrester. The vent is directed toward, and is in close proximity to, the inside surface of the metal housing. Upon failure of the arrester, the venting establishes a short circuit at the arrester line terminal, which both initiates the operation of a protective current interruption device elsewhere in the system and instantly diverts fault current from the arrester itself. As a result, fracturing of the porcelain, which would otherwise result from further pressure buildup in the arrester or from thermal shock, is avoided.