US3453579A - Fuse cartridge - Google Patents

Description

United States Patent 01 fee Int. Cl. H01h 85/40 US. Cl. 337-203 3 Claims ABSTRACT OF THE DISCLOSURE The insulating body of the fuse has an axial conduit for passage of a cooling fluid such as air or de-mineralized water, the fusible elements being disposed in passages parallel to the aforesaid conduit and disposed around the latter. The end heads of the cartridge are annular in the case of air cooling and they form end covers in the case of a cooling liquid.

This invention relates to fuse cartridges which are used for the protection of electric lines against overloads or short circuits.

In such fuse cartridges the current which fiows through the fusible elements under normal operating conditions generates heat and thus causes an increase of the inner temperature of the cartridge. In fuse cartridges of relatively small dimensions this heat is easily transferred by conduction to the metallic end contacts where it is dissipated into the ambient atmosphere, but with big cartridges this cooling effect is no more sufiicient and the temperature of the cartridge rises in a substantial manner when it is operated at its full nominal rating. This is of course an important disadvantage since a hot cartridge will blow more easily (i.e. under a smaller current) than a cool one. In actual practice the nominal rating of a cartridge is limited by the fact that under prolonged operation the fusible elements may reach their melting point under a load which they would easily withstand in the cold state.

It has been proposed to enhance the cooling of fuse cartridges by providing fins on the metallic end members of the cartridge. But of course the cooling effect of such fins is limited by the rate of the heat trasfer between the fusible elements and the end members themselves. It has also been suggested to provide fins on the insulating body of the cartridge, but in big cartridges these fins are almost ineffective owing to the heat-insulating character of the mass of arc-quenching material in which the fusible elements are embedded and of the insulating body itself.

It is therefore an important object of the present invention to provide a fuse cartridge in which the heat generated in the fusible elements will be easily dissipated.

In accordance with the present invention a fuse cartridge comprises an insulating body having a number of passages, each containing a fusible element embedded in a mass of arc-quenching substance, and a conduit through which a cooling fluid is circulated during operation of the cartridge.

Each fusible element together with the corresponding mass of arc-quenching substance, may be considered as an elementary fuse cartridge of reduced dimensions in which heat is relatively easily transferred from the fusible element to the wall of the insulating body owing to the reduced thickness of the said mass. Since the insulating body itself is effectively cooled by the cooling fluid, this heat is easily dissipated and therefore the general temperature of the cartridge remains relatively low.

In a preferred embodiment the conduit for the cooling fluid is substantially co-axial with respect to the insulat- 3,453,579 Patented July 1, 1969 ing body and the passages containing the fusible elements are disposed in a circular row around the said conduit. The cooling fluid may be a gas, such as air, or a liquid, as for instance de-mineralized water.

In the accompanying drawings:

FIG. 1 is a longitudinal section of an air-cooled fuse cartridge according to the invention.

FIG. 2 is the corresponding end view with parts in section.

FIG. 3 is a longitudinal section of another embodiment wherein a liquid forms the cooling fluid.

In the embodiment of FIGS. 1 and 2, the fuse cartridge comprises a body 1, made of a fire-proof insulating material of square cross-section in the example illustrated, the said body being formed with an axial square conduit 1a and with a number of passages 1b (four in the example illustrated) regularly disposed around the said con duit. Each passage 1b, of elongated cross-section, contains a fusible ribbon 2 (as for instance of silver) surrounded by a mass 3 of an appropriate arc-quenching material such as pulverulent silica, sand, etc. The ends of ribbons 2 are soldered to annular heads 4 secured to the ends of insulating body 1 by screws 5, these heads 4 having lateral extensions 4a adapted to receive the electric conductors. A seal 6 is preferably inserted between body 1 and each one of the annular heads 4 in order to protect passages 1b. As illustrated the central hole of each head 4 corresponds substantially to the cross-section of the axial conduit 1a.

Each passage 1b containing a single fusible ribbon 2, the mass 3 of arc-quenching material required is of reduced importance and therefore heat may be easily transferred from the fusible ribbon, where it is generated, to the insulating body 1 through the said mass. Owing to the reduced thickness of the insulating body between each passage 1b and the axial conduit 1a, fliis heat is in turn easily transferred to the air which fills the conduit. The heated air flows upwardly from conduit 1a and is replaced by cold air from the surrounding atmosphere. This circulation of cooling air may be greatly improved by disposing the cartridge vertically, the axial conduit thus forming a kind of chimney through which air flows regularly from the lower end to the upper end.

When the cartridge of FIGS. 1 and 2 is mounted on a rotating support, as this sometimes occurs in electric machines such as alternators, the axial conduit 1a is preferably disposed radially in order to operate as the radial air passages of a centrifugal blower.

As illustrated in FIG. 2 the elongated passages 1b have a more or less elliptical cross-section with the major axis thereof substantially parallel to the adjacent side of the square cross-section of the central conduit. This arrangement reduces the thickness of the insulating wall between each passage lb and the axial conduit 1a, as also between each passage 1b and the outer surface of the insulating body 1.

Each fusible ribbon 2 is preferably pleated as indicated in FIG. 1, the fold lines or ridges 2a contacting alternately one and the other side of the corresponding passage 1b. This also increases the heat transfer rate between the strip and the insulating body. Owing to the elliptical profile of passages 1b, ample space is left for the fiow of pulverulent arc-quenching material during the filling operation of the cartridge.

It would obviously be possible to provide more than four pasages 1b, the axial conduit being shaped accordingly. For instance the cartridge could comprise six passages suchas 1b disposed around a hexagonal axial conduit. The axial conduit could be of circular cross-section, more particularly in the case of a relatively high number of passages 1h, as for instance six or more.

In the embodiment of FIG. 3 the end heads, here referenced 7, are in the form of covers which close the ends of the axial conduit 1a. Each head has a nozzle 7b adapted to be connected with an appropriate cooling fluid line by means of which a suitable cooling fluid, such as demineralized water, may be circulated through the cartridges. Annular seals 8, as for instance conventional 0- rings, are disposed in corresponding recesses of the inner side of heads 7 to prevent access of the cooling fluid to passages 1!). Owing to the high cooling power of liquids, and more particularly of water, the cartridge of FIG. 3 may be operated under a high load during long periods without any risk of a progressive overheating of the fusible elements.

I claim: t

1. A cartridge fuse comprising a tubular insulating body having a first end and a second end and having: an axial conduit extending between said first and second ends, said tubular body being formed with a plurality of openended substantially elliptical passages disposed therein around said conduit and extending between said first and second ends in substantially parallel relation thereto; each of said passages having an elongated cross-section with a major axis and a minor axis, the minor axis being disposed substantially radially with respect to said conduit; a pair of metallic contact heads adapted to receive electric conductors secured respectively to said first and second ends, each of said heads having an opening for passage of a cooling fluid through said conduit; a plurality of ribbon-like fusible elements each disposed in one of said passages and electrically connecting said metallic contact heads with each other; said fusible elements being folded in ziz-zag formation with the edges of the folds of the ribbon elements disposed parallel with the major axes of the elliptical passages so that the corners of the folds contact the tubular body within said passages; and a mass of arc quenching material filling each of said passages around each of said fusible elements.

2. In a cartridge fuse as set forth in claim 1, the opening of each of said heads registering substantially fully with said conduit of said body to permit free air circulation therethrough.

3. In a cartridge fuse as set forth in claim 1, the opening of each of said heads being formed to permit circulation of a cooling liquid through said conduit.

References Cited UNITED STATES PATENTS 961,139 6/1910 Keller 13-18 2,713,098 7/1955 Swain 200'120 3,251,968 5/1966 Cameron 20O120 BERNARD A. GELHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

U.S. Cl. X.R. 337-161, 186, 227

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