High voltage current limiting fuse with improved low overcurrent

Abstract

A high voltage current limiting fuse has improved low fault current interruption due to an end-sealed sleeve separating a fusible length from pulverulent sand in a casing of the fuse while permitting venting of gas and vaporized metal plasma due to melting and arcing at the fusible length. The fuse can have one or more fusible elements, of which at least one, preferably each one, is surrounded along at least a selected portion along its length by a polytetrafluoroethylene polymer, fluoroethylene polymer, or derivatives thereof, which can be heat shrinkable or not. The sleeve is sealed so as to allow escape of gases upon arcing from the sleeve but to prevent pulverulent materials from penetrating within the sleeve. The sleeve seals are either melted and crimped together with the fusible element, heat shrunk down onto the fusible element, or taped over the fusible element so as to leave a gap small enough to exclude the pulverulent material while venting gas and plasma. A high voltage current limiting fuse has improved low fault current interruption also due to inclusion of a separate low fault current compartment with at least one gas-venting end-sealed sleeve separating a fusible length from either pulverulent sand or air in a casing of the fuse. The sleeve in the low fault current compartment can include a plurality of spaced passageways for inclusion of multiple fusible elements. The sleeve portions of the fusible elements in the low fault current compartment can also be positioned in channels in a block of insulative material placed in this compartment.