US 3140371 A
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July 7, 964 H.IJOHANN ETAL FUSE CONSTRUCTIONS Filed Dec. 2, 1959 5 *3? Fig.|.
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ATTORNEY United States Patent i 3,140,371 FUSE CONSTRUCTIONS Hans Johann and Josef Graf, Amberg, Germany, assignors to Siemens-Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Dec. 2, 1959, Ser. No. 856,768 5 Claims. (Cl. 200-135) The present invention relates to fuse constructions in general, and, more particularly, to fuse-link constructions for fuses or fusible cutouts.
A general object of the present invention is to provide a fuse link having improved fusing characteristics.
More particularly, the present invention relates to a fuse having a fusible conductor which is destroyed, upon heating, by forming an alloy, or through a chemical reaction upon attainment of the reaction temperature. Generally, fuses, particularly low-voltage heavy-duty fuses consist essentially of an insulating member with end ferrule contacts, the insulating member containing a filling of a' granular extinguishing medium, preferably sand, in which the fusible conductors are imbedded.
In most instances, the fusible conductors are bandshaped and are made of an electrically good conductive metal, for example, silver, copper or an alloy of these two metals. Alloy-forming substances, for example, tin, which will melt upon heating, are applied upon the fusible conductors, or upon bridging members between portions of the fusible conductors and, reacting with the fusible conductors will form an alloy having a higher electrical resistance. This increase of the resistance results in the destruction of the fusible conductor due to excessive heating and the vaporization thereof, the fusing temperature at the same time being reduced.
There are also known fusible cutouts utilizing chemical reagents, instead of a coating of solder, said chemical reagents being adapted to form compounds with the fusible conductor at a certain temperature. In most cases, these compounds are either poor conductors or nonconductors, thereby increasing the resistance of the fusible conductor within the region in which such chemical reaction takes place. This increase of the resistance results in a quick destruction of the fusible conductor.
Other known fusible conductors are provided with sections having a reduced cross-sectional area obtained, for example, by means of perforations, such sections functioning as interruption points upon the occurrence of high fault currents.
It has been discovered that the formation of alloys, or the chemical reaction, occurs before the temperature required for a fusion has been reached. This results in an increase of the resistance of the alloyed sections, or the sections where a chemical reaction takes place, so that the temperature will continue to rise gradually until the melting point of the alloy, or the temperature region for the chemical reaction is reached. Only then will the fusible conductor be interrupted.
The duration of this alloying action and the degree of the final fusing temperature depends upon the local proportions of the alloying components and the temperature of the chemical coating materials, respectively. Particularly in connection with fusesrated for the higher currents, it is generally difficult and sometimes even impossible to apply the solder or the chemical reaction agents upon the fusible conductor and in. intimate contact therewith in quantities as would be required to obtain a sufiiciently low fusing temperature. L
It is, therefore, aprimary object of the present invention to obtain a maximum ratio of applied solder to the basic material, that is the fusible conductor, in order to reduce the fusing temperature, and on the other hand, to increase the reaction velocity.
3,140,371 Patented July 7, 1964 One solution to the problem would be an increase in quantity of the effective material, that is, either the solder or the chemical reaction agent,'in excess of the usual quantity used. This has, however, considerable disadvantages, and, in particular, would impair the shortcircuit interrupting ability of the fuse. An increase in quantity of the applied solder results in an increased vapor pressure, and this is true, on a smaller scale, also with respect to chemical reaction agents. As a result, the interruption during short-circuit conditions is renderedextremely difficult especially if the vapor has a high metallic content.
These disadvantages are overcome by the present invention, according to which the mass of the total materialin the reaction zone is decreased without decreasing the mass of the solder material, and the electrical resistance is simultaneously increased. This is achieved, for example, by weakening thefusible conductor in the immediate proximity of the coating of the reaction medium or the solder by means of small recesses. Instead of providing such recesses, or in addition thereto, there may also be used fusible conductor sections of reduced thickness: and/ or width.
These fusible conductor sections are preferably interposed between two solder strips so as to form bridging members therebetween. It is also possible to make the: inserted bridging members of reduced thickness of a.- material which promotes alloying. If this is done, it is. important, however, that those sections of the fusible conductor, which have a reduced cross-sectional area, will remain strong enough within said reduced cross-sectional. area to' prevent an interruption at said sections prior to an interruption at the normal interrupting points predetermined to respond to an occurrence of heavy fault currents.
The present invention offers the additional advantage of increasing, within the area designed for alloying, the ratio of the solder, or reaction agent, to the material of the fusible conductor. This consequently reduces the melting point, without introducing any difiiculties in the accommodation of the solder or the reaction agent. At the same time, the alloying velocity is increased since these weakened sections have a moderate over-temperature with respect to the applied solder or the available chemical reagent.
Accordingly, it is a further object of the present invention to improve upon the configuration and shape of fuse-link sections so as to obtain an improved fuse-link construction.
Other objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawing, in which:
, FIGURE 1 is a plan view of a fuse-link construction embodying the principles of the present invention, the fuse link being shown in its intact condition;
FIG. 2 is a side elevational view of the fuse-link con struction of FIG. 1;
FIG. 3 is a plan view of a modified form of fuse-link construction;
FIG. 4 is a side elevational view of the modified form of fuse-link construction illustrated in FIG. 3;
FIG. 5 is a plan view of a further modified form of fuse-link construction;
FIG. 6 is a side elevational view of the fuse construction illustrated in FIG. 5;
. FIG. 7 is a plan view of a further modified form of fuse-link construction; and,
place during the occurrence of heavy fault currents. As shown, the fusible conductor includes generally two half L-shaped sections, which are connected together by means of a bridging mass 3 of soldering material, such as tin, or other metals capable of alloying with the fusible conductor sections 1.
Immediately adjacent to the solder bridge 3, the fusible conductor sections 1 are provided with small perforations 4, whereby the ratio of the solder 3 to the material of the fusible conductor 1 is increased within the region of the bridging portion 3. If the soldering bridge 3 is heated up to a temperature above the melting temperature of the solder, there will result a limited flow of solder toward the fusible conductor sections 1 due to wetting of the material. This slight flow of solder is sufficient to fill, in addition, the recesses 4 with soldering material, thereby forming an alloy having an increased electrical resistance. This increase in resistance effects the vaporization of the fusible conductor.
FIGS. 3 and 4 illustrate a modified form of the invention, wherein the fusible conductor sections 6 are provided with generally U-shaped portions 7 filled with the soldering material, or with the chemical reagents. Intermediate the generally U-shaped portions 7, as shown in FIG. 4, the fusible conductor 6 is provided with holes 4, Whose function is the same as the holes 4 illustrated in FIGS. 1 and 2 of the drawings. In the modification of the invention illustrated in FIGS. 3 and 4, a particularly favorable alloying ratio will be obtained due to the fact that the solder 3 will flow toward the holes 4 from two directions.
FIGS. 5 and 6, together with FIGS. 7 and 8, illustrate embodiments of the invention utilizing bridging members 8, 9 having reduced cross-sectional areas, the bridging members 8, 9 being respectively inserted between fusible conductor sections 11, 12. For the sake of simplicity, the bridging members 8, 9 in these two embodiments of the invention are connected to the fusible conductor sections 11, 12 through the intermediary of the layers of solder 3. It is to be understood, of course, that the bridging members 8, 9 could be connected to the fusible conductor section 11, 12, for example, by welding when chemical reaction agents are employed. Preferably, the bridging members 8, 9 are made, wholly or partially of a more precious material than the fusible conductors 11, 12 to facilitate alloying. For example, the fusible conductor sections 11, 12 may be made of copper, and the interposed bridging members 8, 9 may consist of silver.
In some instances it may be advantageous to provide the fusible conductor sections 1, 6 with capillary grooves between the holes 4 and the regions where the solder, or the chemical reagents are applied, in order to increase the creep properties of the solder, or the chemical reagents applied.
From the foregoing description it will be apparent that there is provided a novel fuse-link construction in which the reaction time is reduced with the fuse-link adapted for effective and consistent operation. It will be observed that a number of alternate arrangements are possible utilizing the principles set forth above.
Although several fuse-link constructions have been illustrated and described, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the invention.
1. A fuse-link construction including means defining at least one terminal portion, an adjoining conducting portion comprised of silver and dilferent from the material of said terminal portion, a mass of solder disposed between said terminal portion and said silver portion for 4. initiating alloying action upon a predetermined rise of fuse-link temperature to assist in low overload current interruption, said silver portion being deformed to increase the ratio of the mass of solder t0 the mass of contiguous deformed silver in the reaction zone to increase the velocity of alloying reaction without decreasing the mass of the solder material.
2. A fuse-link construction including means defining terminal portions, an intermediately-disposed conducting portion connected between said terminal portions and composed of relatively high-melting-point material different from the material of the terminal portions, a portion of said conducting portion being fusible at least on relatively low overload currents and comprising a mass of solder for initiating alloying action upon a predetermined rise of fuse-link temperature, said intermediately-disposed con ducting portion being of a U-shape with each leg of the U being connected to only one of the terminal portions, said last-mentioned fusible portion being deformed to increase the ratio of the mass of solder to the mass of contiguous deformed high-melting-point fusible material in the reaction zone to increase the velocity of alloying reaction Without decreasing the mass of the solder material.
3. A fuse-link construction including a sectionalized fusible conductor having end sections comprised of one metal of a predetermined cross-sectional area, a mass of solder disposed adjacent the opposed inner ends of the fusible conductor end sections, a bridging fusible conductor section comprised of silver and different from the material of the end sections, said bridging fusible conductor section being of smaller cross-sectional area than the end sections and disposed between adjacent masses of solder and spaced from the end sections by the solder, said bridging fusible conductor section conducting the current serially through the fuse link, and the metal in the bridging conductor alloying more readily with the solder than does the metal in the end sections.
4. A fuse-link construction including a sectionalized fusible conductor having end sections comprised of one metal of a predetermined cross-sectional area, a mass of solder disposed adjacent the opposed inner ends of the fusible conductor end sections, a bridging fusible conductor section comprised of a different metal of smaller crosssectional area disposed between adjacent masses of solder for conducting the current serially through the fuse link, the bridging fusible conductor being U-shaped with each leg of the U being joined to only one of the end sections by the solder, and the metal in the bridging conductor alloying more readily with the solder than does the metal in the end sections.
5. The fuse-link construction of claim 3, wherein the end sections are comprised of copper.
References Cited in the file of this patent UNITED STATES PATENTS 569,803 Scott Oct. 20, 1896 713,831 Badeau Nov. 18, 1902 1,231,036 McDonald June 26, 1917 1,473,284 Feldkamp Nov. 6, 1923 1,660,828 Bird Feb. 28, 1928 1,770,196 Bussman July 8, 1930 2,111,628 Hoban Mar. 22, 1938 2,816,989 Sugden Dec. 17, 1957 2,827,532 Kozacka Mar. 18, 1958 2,858,396 Sugden Oct. 28, 1958 2,876,312 Frederick Mar. 3, 1959 2,988,620 Kozacka June 13, 1961 FOREIGN PATENTS 439,517 Great Britain Dec. 9, 1935 635,089 Germany Sept. 9, 1936 571,298 Great Britain Aug. 17, 1945