Current-limiting fuse with improved means for interrupting low overcurrents

A high-voltage current limiting fuse comprising:

• (a) a generally tubular electrically insulating casing, terminal means disposed adjacent each of the opposite ends of the casing, and a pulverulent arc-quenching filler within said casing,
• (b) a ribbon-type fusible element disposed within said filler and electrically interconnecting said terminal means,
• (c) means at a predetermined location on said fusible element for causing said fusible element to melt at said predetermined location in response to prolonged overcurrents of relatively low value, thereby initiating an arc at said location when said prolonged overcurrents have persisted for a predetermined duration,
• (d) gas-evolving means for increasing the arc voltage developed by said arc comprising an electrical insulating member disposed about said fusible element in the region of said predetermined location and at a point sufficiently close to said predetermined location that at least a portion of said arc burns within said insulating member and causes vapors to be evolved from the material of said insulating member,
• (e) said insulating member being primarily of a baked material, a major portion of which is hydrated aluminum silicate including water of hydration that is released only at temperatures in excess of those attained by said insulating member during prolonged overcurrents as long as one hour,
• (f) said material being baked for several hours at temperatures up to at least the value reached by said insulating member during prolonged overcurrents as long as one hour.