Ribbon-type fusible element for high-voltage fuses and fuse including the element

Claim 2

A fusible element for electric fuses having a voltage rating in excess of 5 kV formed by a narrow strip of sheet silver including a relatively long center portion and end portions each having a length substantially less than the length of said center portion, said center portion having a straight edge on one side thereof and an undulating edge on the opposite side thereof and varying periodically in width from a minimum width to a maximum width, and each of said end portions having straight parallel edges having a spacing substantially equal to said maximum width of said center portion.

Claim 3

A fusible element as specified in claim 1 wherein the ratio of said minimum width of said center portion to said maximum width of said center portion is in the order of 1:2.

Claim 4

A fusible element as specified in claim 1 wherein said undulating edge is formed by a series of circular elements each having a radius of curvature being a large multiple of said maximum width of said center portion.

Claim 5

An electric fuse for circuits having an elevated circuit voltage including a. a tubular casing of electric insulating material; b. a pair of terminal elements arranged adjacent the ends of and closing said casing; c. an arc-quenching filler of quartz sand inside said casing; and d. fusible element means inside said casing submersed in said arc-quenching filler and conductively interconnecting said pair of terminal elements, said fusible element means being formed by a narrow strip of sheet silver having a relatively long center portion and end portions each having a length substantially less than the length of said center portion, said center portion having a straight edge on one side thereof and an undulating edge at the opposite side thereof and varying periodically in width from a predetermined minimum width to a predetermined maximum width, and each of said end portions having straight parallel edges spaced substantially equal to said predetermined maximum width of said center portion.

Claim 6

An electric fuse for circuits having an elevated circuit voltage including a. a tubular casing of electric insulating material; b. a pair of terminal elements arranged adjacent the ends of and closing said casing; c. an arc-quenching filler of quartz sand inside said casing; and d. fusible element means inside said casing submersed in said arc-quenching filler and conductively interconnecting said pair of terminal elements, said fusible element means being formed by a narrow strip of sheet silver having a relatively long center portion and end portions each having a length substantially less than the length of said center portion, said center portion having a straight edge on one side thereof and an undulating edge at the opposite side thereof and varying periodically in width from a predetermined minimum width to a predetermined maximum width, and each of said end portions having straight parallel edges spaced substantially equal to said predetermined maximum width of said center portion.

Claim 7

An electric fuse as specified in claim 4 wherein said pair of terminal elements is conductively interconnected by a plurality of substantially helically wound fusible element means, the ratio of said predetermined minimum width of said center portion to said predetermined maximum width of said center portion of said plurality of fusible element means being in the order of 1:2, and a plurality of beads of an electric insulating material each having a plurality of substantially parallel bores, each of said plurality of fusible elements being threaded through one of said plurality of bores in each of said plurality of beads to maintain a substantially fixed axial spacing between said plurality of fusible element means in the absence of a mandrel structure for supporting said plurality of fusible elements.

Claim 8

An electric fuse as specified in claim 6 wherein said plurality of beads consist of an epoxy resin having an inorganic non-tracking filler material.

Claim 9

An electric fuse as specified in claim 4 wherein the ratio of said predetermined minimum width of said center portion to said predetermined maximum width of said center portion is in the order of 1:2.

Claim 10

An electric fuse as specified in claim 4 wherein the length of each of said end portions is in the order of L cm as determined by the equation L 1/2 (2.30 X 10 3 X one-sixthj), wherein j is the current density in amp/cm2 prevailing in said end portions of said fusible element means at about 12 times the E rating of the fuse.

Claim 11

An electric fuse as specified in claim 4 wherein the length of each of said end portions is about 7 to 10 percent of the length of said center portion.

Claim 12

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal elements arranged adjacent the ends of and closing said casing; c. a pulverulent arc-quenching filler inside said casing; d. a plurality of substantially wire-like substantially helically wound fusible element means inside said casing submersed in said arc-quenching filler and conductively interconnecting said pair of terminal elements; and e. a plurality of beads of an electric insulating material each having a plurality of substantially parallel bores, each of said plurality of fusible elements means being threaded through one of said plurality of bores in one of said plurality of beads to maintain a substantially fixed spacing between contiguous turns of said plurality of fusible element means in the absence of a mandrel structure for supporting said plurality of fusible element means.

Claim 13

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal elements arranged adjacent the ends of and closing said casing; c. a pulverulent arc-quenching filler inside said casing; d. a plurality of substantially wire-like substantially helically wound fusible element means inside said casing submersed in said arc-quenching filler and conductively interconnecting said pair of terminal elements; and e. a plurality of beads of an electric insulating material each having a plurality of substantially parallel bores, each of said plurality of fusible elements means being threaded through one of said plurality of bores in one of said plurality of beads to maintain a substantially fixed spacing between contiguous turns of said plurality of fusible element means in the absence of a mandrel structure for supporting said plurality of fusible element means.

Claim 14

An electric fuse as specified in claim 10 wherein said plurality of beads consist of a gas-evolving insulating material having a thermal conductivity of less than 0.50 Btu/hr/sq ft/*F/ft.

Claim 15

An electric fuse as specified in claim 10 wherein said plurality of wire-like fusible element means consist of silver wires of circular cross-section.

Claim 16

An electric fuse as specified in claim 10 wherein said plurality of wire-like fusible element means consist of narrow strips of sheet silver having a straight edge on one side thereof and a substantially undulating edge on the opposite side thereof.

Claim 17

An electric fuse as specified in claim 11 wherein said plurality of wire-like fusible element means consist of conductors of silver having a length and a cross-section adapted to result in a time-current curve whose low current tangent and whose high current tangent intersect in the range of 1 second to 10 seconds.

Claim 18

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal plugs arranged adjacent the ends of and closing said casing, one of said pair of terminal plugs having a plurality of eccentric recesses in the axially inner end surface thereof and the other of said pair of terminal plugs having eccentric bores in registry with said eccentric recesses and plugged by bore-plugging means; c. a pulverulent arc-quenching filler inside said casing; d. a helically wound fusible element means of silver inside said casing submersed in said arc-quenching filler conductively interconnecting said pair of terminal plugs, said fusible element means being supported by said arc-quenching filler in the absence of a supporting mandrel therefor, the length and the cross-section of said fusible element means being adapted to establish in a time-current curve whose low current tangent and whose high current tangent intersect in the range of 1 second to 10 seconds, said fusible element means having a center portion provided with a plurality of spaced points of reduced cross-sectional area forming series arclets at the occurrence of major faUlt currents, and said fusible element means having axially outer end portions adapted to result in a smaller backburn velocity in axially outward direction than the backburn velocity in axially inward direction incident to formation of a break adjacent a point of transition from said center portion to said axially outer end portions of said fusible element means; and e. an overlay of a silver-severing low fusing point metal supported by said center portion of said fusible element means.

Claim 19

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal plugs arranged adjacent the ends of and closing said casing, one of said pair of terminal plugs having a plurality of eccentric recesses in the axially inner end surface thereof and the other of said pair of terminal plugs having eccentric bores in registry with said eccentric recesses and plugged by bore-plugging means; c. a pulverulent arc-quenching filler inside said casing; d. a helically wound fusible element means of silver inside said casing submersed in said arc-quenching filler conductively interconnecting said pair of terminal plugs, said fusible element means being supported by said arc-quenching filler in the absence of a supporting mandrel therefor, the length and the cross-section of said fusible element means being adapted to establish in a time-current curve whose low current tangent and whose high current tangent intersect in the range of 1 second to 10 seconds, said fusible element means having a center portion provided with a plurality of spaced points of reduced cross-sectional area forming series arclets at the occurrence of major faUlt currents, and said fusible element means having axially outer end portions adapted to result in a smaller backburn velocity in axially outward direction than the backburn velocity in axially inward direction incident to formation of a break adjacent a point of transition from said center portion to said axially outer end portions of said fusible element means; and e. an overlay of a silver-severing low fusing point metal supported by said center portion of said fusible element means.

Claim 20

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal plugs arranged inside said casing adjacent the ends thereof closing said casing; c. a filler of quartz sand inside said casing; d. a helically wound fusible element of silver inside said casing submersed in said filler and conductively interconnecting said pair of terminal plugs, said fusible element being formed by a narrow strip of sheet silver having a relatively long center portion and end portions each having a length substantially less than the length of said center portion, said center portion having a straight edge on one side thereof and an undulating edge at the opposite side thereof and varying periodically in width from a predetermined minimum width to a predetermined maximum width, and each of said end portions having straight parallel edges having a spacing substantially equal to said predetermined maximum width of said center portion; e. a plurality of overlays of a low fusing point silver-severing metal arranged in spaced relation along said fusible element; and f. a plurality of beads of a material having a lower thermal conductivity than said filler of quartz sand mounted on said fusible element, each of said plurality of beads covering one of said plurality of silver-severing overlays, and the length of each of said plurality of beads exceeding the spacing between a contiguous pair of points of said predetermined maximum width of said fusible element.

Claim 21

An electric fuse including a. a tubular casing of electric insulating material; b. a pair of terminal plugs arranged inside said casing adjacent the ends thereof closing said casing; c. a filler of quartz sand inside said casing; d. a helically wound fusible element of silver inside said casing submersed in said filler and conductively interconnecting said pair of terminal plugs, said fusible element being formed by a narrow strip of sheet silver having a relatively long center portion and end portions each having a length substantially less than the length of said center portion, said center portion having a straight edge on one side thereof and an undulating edge at the opposite side thereof and varying periodically in width from a predetermined minimum width to a predetermined maximum width, and each of said end portions having straight parallel edges having a spacing substantially equal to said predetermined maximum width of said center portion; e. a plurality of overlays of a low fusing point silver-severing metal arranged in spaced relation along said fusible element; and f. a plurality of beads of a material having a lower thermal conductivity than said filler of quartz sand mounted on said fusible element, each of said plurality of beads covering one of said plurality of silver-severing overlays, and the length of each of said plurality of beads exceeding the spacing between a contiguous pair of points of said predetermined maximum width of said fusible element.