1. Field of the Invention
This invention relates generally to current limiting fuses and more particularly to current limiting fuses having fuse elements in contact with a ceramic core evolving an electro-negative gas that provides superior fault interruption characteristics.
2. Description of the Prior Art
The use of arc induced gas evolution as an aid to fault current interruption is well known in current limiting fuse design. In U.S. Pat. No. 3,437,971, entitled "Current Limiting Fuse", issued by H. W. Mikulecky on Apr. 8, 1969, a fuse element is helically wound about an organic gas evolving support. The fuse element and support are embedded in an inert granular material encased in an insulating housing. The fuse element is in contact with the gas evolving support so that when an arc is drawn, upon fusion of the element, gas is evolved directly into the arc, cooling it and improving current interruption.
Organic cores used in existing fuses have an upper limit determined by how much energy they can absorb before they are damaged to the point where electrical breakdown and hence fuse failure occurs. This deficiency serves to restrict the current and voltage ratings possible with a given design. Typical stratagems employed over the years to minimize the problem are described in U.S. Pat. Nos. 3,849,754; 3,868,619; and 3,925,745, issued to D. D. Blewitt et al. The use of localized gas evolving suppressors on a core is disclosed in U.S. Pat. No. 3,925,745.