EP0046392A2

EP0046392A2 - Full range current limiting fuse

Info

Publication number: EP0046392A2
Application number: EP81303727A
Authority: EP
Inventors: William J. Huber; Gordon T. Borck
Original assignee: RTE Corp
Current assignee: Cooper Power Acquisition Corp
Priority date: 1980-08-18
Filing date: 1981-08-14
Publication date: 1982-02-24
Also published as: KR830006794A; JPS5772231A; AR225236A1; EP0046392A3; BR8104965A; AU7358481A

Abstract

A fuse assembly comprising a silver wire, a tube formed from a material which produces a deionizing atmosphere at the temperature of an arc and a eutectic member soldered to the wire intermediate the ends thereof. The fuse assembly being capable of being connected in series with high time-current clearing fuse members to provide a multiple range of fuse clearing characteristics.

Description

In U.S. Patent No. 3,840,836 entitled "Current Limiting Sand Fuse", issued October 8, 1974, to Edwin A. Link, a full range fuse was disclosed in which the fuse assembly included both a high and a low current clearing fuse assembly. The low current clearing fuse assembly included a tin wire having a low melt characteristic enclosed within a silicone tube. This assembly is used to clear long time low current faults. However, at high currents, the silicone tubing bursts under the high internal pressures produced within the tubes on vaporization of the tin wire and fails to clear the arc. At these high current levels, the silver ribbons which are connected in series with the tin wire are called upon to clear the arc. However, the silver ribbons do not melt open in a manner to permit efficient clearing of the arc. One of the causes of the pressure build-up within the silicone tube using a tin wire is that the tin has a homogenous resistance per unit length thus heating of the wire will occur across the full length of the wire. Once the wire reaches the melting temperature, under relatively high current, the entire wire vaporizes and turns into an arc path. This sudden change of state of the complete wire causes high enough pressure levels to burst the tube because there is no time for the gases to travel the length of the tube and escape at the ends. The molten tin is also forced to the ends of the tube obstructing the free flow of gases out of the ends of the tube.
The low current fuse assembly, according to the present invention, uses a silver wire inside of a constricting silicone tube with an M-spot provided on the wire intermediate the ends of the tube. The M-spot comprising an eutectic solder member soldered to the center of the wire. The M-spot provides two functions: it causes the silver wire to melt open at a temperature not much higher than tin, thus protecting the tube from thermal damage, and consistently opens the silver wire at the midpoint, thereby initiating arcing at the midpoint of the wire. The broken wire thus burns back in both directions and because of the higher vaporization temperature of silver, it requires more time to burn back under the same arc energy conditions as encountered by the tin wire. This slower vaporization permits the gases to escape through the ends of the tube before pressures are built up in the tube sufficient to burst it. The internal pressure within the tube is still effective to deionize and terminate the arc.
The slower vaporization of the silver wire also allows a more efficient escape of the molten metal and gases from the tube. As the silver wire is slowly consumed by the arc, the molten by-products of the wire are expelled from the tube with the high pressure gases and clogging is prevented since the exit openings at the ends of the tube are large enough to handle the molten metal and gases generated by the heat of the arc.

Figure 1 is a side elevational view in section showing the low current fuse assembly according to the invention.
Figure 2 is a side elevational view in section of an alternate embodiment of the low current fuse assembly according to the invention.
Figure 3 is a side elevational view partly in section of a low duty non-current limiting fuse utilizing the fuse assembly of Figure 1 or Figure 2.
Figure 4 is a view of a full range fuse assembly showing the low current fuse assembly according to the invention connected in series with the high current fuse assembly.
Figure 5 is a side elevation view partly in section showing a three element fuse utilizing the fuse assembly of Figure 1 or 2 in combination with two other fuse assemblies, each of which has time-current melt characteristics different from the others.

Referring to Figure 1 of the drawings, the fuse assembly 10 according to the present invention, generally includes an insulating tube 12 formed of a material such as silver which deionizes at the arcing temperature of the wire. A silver wire 14 is placed in the tube and extends outwardly from each end of the tube. An M-spot 16 is provided on the wire 14 intermediate the ends and consists of a low melting eutectic alloy such as solder. Means can be provided on the tube 12 to strengthen the tube. Such means can be in the form of a glass roving sleeve 18 provided on the outside surface of the tube 12.
The operation of the fuse assembly basically involves the introduction of a high current through the silver wire 14 which causes the silver wire 14 to generate heat sufficient to melt the eutectic solder 16. The eutectic solder amalgamates with the silver wire 14 causing it to break at the center, producing a gap. The gap increases in width as the arc across the gap vaporizes the exposed ends of the silver wire. The gap progressively increasing until sufficient heat has been created to cause the tube to produce a deionized atmosphere within the tube which extinguishes the arc.
Referring to Figure 2, an alternate embodiment of the invention is shown in which the fuse assembly 110 includes a tube 112 and a pair of silver wires 114 which abut each other centrally within the tube 112. Means are provided at the point of abutment of the two wires 114 to produce a low current characteristic for the silver wires. Such means is in the form of a eutectic solder 116 which connects the two wires 114. Means in the form of a glass roving 118 can be provided on the outside surface of the tube 112 to reinforce the tube if required.
Either of the fuse assemblies 10 or 110 can be used in a low duty non-current limiting fuse 20 as shown in Figure 3. The fuse 20 includes an insulating housing 22 having conductive caps 24 mounted on each end. The fuse assembly 10 is positioned within the housing with the ends of the silver wire 14 soldered to the end caps 24. The housing is filled with an arc quenching material 26 such as silica sand.
Either of the fuse assemblies 10 and 110 can also be used in conjunction with a full range current limiting fuse assembly 30 as seen in Figure 4. The full range fuse assembly 30 includes a spider 32 having a first fuse assembly 34 having a high current clearing characteristic and a second fuse assembly 36 having low current clearing characteristics. The second fuse assembly consisting of four of the fuse assemblies 10 or 110 connected electrically in parallel which are in series to the first fuse assembly. Conventionally the fuse assembly 30 is placed in a casing and filled with arc quenching material such as silica sand. The elements 36 interrupt currents of low (1.5 x-rating) to intermediate (6-7 x-rating) levels while the first fuse assembly 34 interrupt currents from intermediate levels to the maximum rating of the fuse.
Referring to Figure 5, a multiple time current fuse 40 is shown which generally includes a housing 42 having electrically conddctive end caps 44 secured to each end. The end caps 44 are electrically interconnected by means of a number of series connected fuse members. Such means includes either of the fuse assemblies 10 or 110 connected in series with a first fuse member 46 and a second fuse member 48. The first fuse member 46 includes a tin wire 52 confined within a tube 50. The tin wire 52 having a low time current clearing characteristic. The second fuse member 48 includes a copper or silver wire 56 confined within a tube 54. The silver wire providing a high time current clearing characteristic. The fuse assemblies 10 and 110 provide an intermediate time current clearing characteristic. The housing is filled with an arc quenching material 58 such as silica sand. Each basic assembly thus providing a time-current melt characteristic different from the others. A composite-melt curve is thus achieved with each assembly having a unique time-current characteristic to control a specific range of melt characteristic for the fuse assembly.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed, are defined as follows:
J. A low current fuse assembly comprising an insulating tube formed of a material which deionzes at the temperature of an electric arc,

an electrically conductive wire having a high current carrying characteristic positioned in said tube,

and metallic means on said wire intermediate the ends thereof having a low temperature melting characteristic whereby said metallic means on reaching melting temperature will amalgamate with said wire to reduce the temperature characteristic of the amalgamated portion of said wire to a low current carrying characteristic whereby the wire fuses at the melting temperature of said metallic means.
2. The assembly according to claim 1 wherein said wire is silver and said metallic means is utectic solder.
3. The assembly according to claim 1 wherein said wire is formed of two wires having their ends in abutting relation at the center of said tube and said metallic means is affixed to the abutting ends of said wire to hold the wire in the abutting relation.
4. A low current limiting fuse comprising an insulating housing,
a conductive cap at each end of said housing,

an electrically conductive wire within said housing connected to each of said caps,

an insulating tube surrounding said wire and extending the full length thereof,

said tube being responsive to the heat of an arc to produce a deionizing atmosphere within said tube,

granular dielectric material within said housing and surrounding said tube and a metallic material having a low temperature characteristic affixed to said wire at the center of the tube thereof, whereby said wire will break at the melting temperature of said metallic material.
5. The fuse according to claim 4 wherein said conductive wire is formed of silver and said metallic material is formed of eutectic solder.
6. The fuse according to claim 4 wherein said wire is formed of two wires which abut at the center of said tube and said metallic material holds said ends in abutting relation within said tube.
7. A current-limiting fuse comprising a housing,
an electric terminal cap at each end of the housing,

a first fusible assembly having a high-current clearing characteristic, and being connected to one of said caps

said second fusible assembly including a silver wire and a eutectic member soldered to said wire intermediate the ends thereof,

an arc extinguishing member enclosing the full length of said wire assembly,

said arc extinguishing member being formed of material which is deionizing under the influence of an electric arc and

a granular dielectric material completely filling said housing and surrounding said assembly.
8. The current limiting fuse according to claim 7, said second fusible assembly includes a number of silver wires connected in parallel, each wire being enclosed in a deionizing tube and a eutectic member soldered to each of the wires intermediate the ends thereof.
9.. A low-current clearing fuse assembly comprising a silver wire, means having a melting temperature characteristic lower than said silver wire connected to the wire intermediate the ends of said wire to produce an amalgamation of the silver wire under low-current conditions and
a tube of deionizing material enclosing the full length of the wire, whereby on breaking of the wire the gas generated by the heat of the arc across the break in the wire is retained in the tube to deionize the arc.
10. A multiple time current fuse comprising a housing having an electrically conductive end cap at each end, and a multiple time-current clearing fuse assembly interconnecting said end caps,
said assembly including a first fuse member having a low time-current clearing characteristic,

a second fuse member having a high time current clearing characteristic,

and a fuse assembly having a predetermined time current clearing characteristic intermediate said high and low fuse members, said fuse assembly including a silver wire having a eutectic member soldered to the wire intermediate the ends thereof and enclosed within a deionizing tube.