EP2503583A1 - Melt resistant insert and overload protection device - Google Patents

Abstract

The fuse insert (10) according to the invention, in particular for semiconductor protection fuses, has a ceramic body (11) filled with solidified sand, an additional body (14) being introduced into the solidified sand. This is designed such that when the internal pressure in the ceramic body (11) increases due to temperature expansion of the solidified sand through the additional body (14), an additional volume is released in the ceramic body (11) for expansion of the solidified sand. Damage to the ceramic body (11) due to stress cracks caused by the different degrees of thermal expansion of the solidified sand and the ceramic body (11) as a result of an increase in temperature and the associated increase in the internal pressure in the ceramic body (11) can be avoided or limited. The robustness of the fuse insert (10) is thereby significantly improved.

Description

The invention relates to a fuse insert - especially for semiconductor protection fuses - which has a filled with solidified sand ceramic body. Furthermore, the invention relates to an overcurrent protection device with such a fuse link.

A fuse is an overcurrent protection device that interrupts the circuit by melting one or more fusible links when the current exceeds a certain level over a certain period of time. It consists of an insulating body, which has two electrical connections, which are interconnected in the interior of the insulating body by a fusible link. The fusible conductor is heated by the current flowing through it and melts when the relevant nominal current of the fuse is clearly exceeded for a certain period of time. Due to its good insulating effect is used as the material for the insulating body mostly ceramic.

In a sand-solidified fuselage insert, the fusible link is surrounded by quartz sand. A ceramic body forms the housing of the fuse link, in which the solidified sand, the electrical connections and the fusible conductor are accommodated or held. The quartz sand acts as an arc extinguishing agent: the rated current of the fuse is clearly exceeded - for example, due to a short circuit - so this leads to a response of the fuse, in the course of which the fusible element melts first and then evaporated due to the high temperature development. This creates an electrically conductive plasma, via which the current flow between the electrical connections is initially maintained - it arises an arc. As the metal vapor of the vaporized fusible conductor precipitates on the surface of the silica sand grains, the arc is again cooled. As a result, the resistance in the interior of the fuse link increases in such a way that the arc finally disappears. The line to be protected by the fuse is thus interrupted.

For sand-solidified fusible link inserts with large volumes of sand, due to the different thermal expansion coefficients of the quartz sand on the one hand and the ceramic body on the other hand to tensions in the ceramic body, which can ultimately lead to breakage of the ceramic body. Available on the market fuse inserts meet this problem with the use of special, high-quality ceramics, which are characterized for example by a higher alumina content. Such ceramics have not only a higher strength but also a larger coefficient of thermal expansion than comparable ceramics with a lower alumina content. Both properties - the higher strength and the higher coefficient of thermal expansion - counteract the problem of damage to the ceramic body. However, the ceramic materials in question are relatively expensive due to their special quality properties.

To reduce the stresses in the ceramic body due to the temperature expansion of the solidified sand fusible inserts are further provided in which along the inner circumference of the ceramic body, a damping element between the ceramic body and the solidified sand is arranged. However, this arrangement has the disadvantage that the heat dissipation of the fuse link and thus the tripping and shutdown of the fuse link are significantly deteriorated.

It is therefore an object of the present invention to provide a fuse link as well as an overcurrent protection device with such a fuse link insert, which are characterized by improved robustness and at the same time simple and cost-effective manufacturability.

This object is achieved by the fuse link as well as the overcurrent protection device according to the independent claims. Advantageous embodiments are the subject of the dependent claims.

The fuse protection insert according to the invention, in particular for semiconductor protection fuses, has a ceramic body filled with solidified sand, wherein an additional body is introduced into the solidified sand. This is designed such that upon an increase in an internal pressure in the ceramic body due to a temperature expansion of the solidified sand by the additional body, an additional volume in the ceramic body for expansion of the solidified sand is released.

The ceramic body and the solidified sand generally have different coefficients of thermal expansion, ie, the solidified sand expands at a temperature increase more than the ceramic body surrounding the solidified sand, which at a temperature increase to an increase of the internal pressure in the ceramic body and thus to stresses in the ceramic body leads. By using an additional body, with the help of an increase in the internal pressure is provided an additional volume in the ceramic body, which is available for further expansion of the solidified sand, the internal pressure arising in the ceramic body can be limited to a tolerable value. In this way, damage to the ceramic body by stress cracks, caused by the different degrees of thermal expansion of the solidified sand and the ceramic body, avoided. The robustness of the fuse insert is thereby significantly improved.

Furthermore, can be used for the production of the ceramic body to a ceramic with a lower alumina content. On the one hand, such a ceramic is cheaper to produce and, on the other hand, simpler to process, so that the manufacturing costs of the fuse-linkage insert can be significantly reduced as a result. With designs for standard use, a simpler ceramic can thus be used for the same power; special designs for problematic operating conditions, which even high-quality ceramics are not sufficient for, can be realized by introducing an additional body into the solidified sand.

In an advantageous development of the fuse insert of the additional body is designed as a burst body, which breaks when a predefined internal pressure in the ceramic body, whereby the additional volume is released. The bursting body introduced into the sand generally has a thin-walled housing which irreversibly yields and breaks at a predefined internal pressure prevailing in the interior of the ceramic body, whereby the volume surrounded by the thin-walled housing is at least partially released and solidified for further expansion Sandes is available. In this case, a plurality of bursting bodies may be introduced into the solidified sand, which are designed, for example, for different internal pressures and, when the internal pressure swells, break one after the other, so that the additional volume for further expansion of the solidified sand is cascaded, ie. in several portions, is released.

In a further advantageous development of the fuse insert the bursting body is filled with an air or gas mixture. The filling of the bursting body with air represents a simple and cost-effective way to realize the improvement of the fuse link. Instead of air, a gas mixture - for example, inert, that is, inert gases such as nitrogen or noble gases - can be used.

In a further advantageous development of the fuse insert the bursting body is filled with unconsolidated sand. In this way, the additional volume to be provided by breaking the burst body can be limited to a low value without impairing the accuracy of the triggering of the fuse link insert. To maintain this accuracy, i. In order to determine the threshold value of the internal pressure, from which the bursting body should break, as accurately as possible, a certain manufacturing accuracy of the bursting body with respect to its geometry and its wall thickness is required; this in turn requires a minimum size of the burst body, which is difficult to implement with only a small additional volume. The filling of the bursting body with unconsolidated sand, however, makes it possible to provide only a small additional volume for further expansion of the solidified sand, even with the geometrically determined minimum size of the bursting body described above, wherein the breaking of the bursting body in dependence of the internal pressure with relative good accuracy can be predetermined.

In a further advantageous development of the fuse insert the bursting body is filled with an elastic material. Like filling with unconsolidated sand, filling with an elastic material is a suitable way to provide only a small additional volume for further expansion of the consolidated sand. The filling with elastic material has the further advantage that even after the bursting of the bursting body no voids are formed in the solidified sand. Instead, the further expansion of the solidified Sand at almost constant internal pressure realized by squeezing the elastic body.

In a further advantageous development of the fuse insert of the additional body is designed as a compressible solid body. Also in this case, the further expansion of the solidified sand is realized at almost constant or only slightly increasing internal pressure by compressing the elastic body. However, this principle does not act only from the threshold value of the internal pressure at which the auxiliary body breaks, but already from the beginning.

In a further advantageous development of the fuse insert of the ceramic body can be produced by extrusion. An extrusion process is a simple and extremely cost-effective way of producing the ceramic body, which is particularly suitable for the processing of simple ceramic materials. High quality ceramics, especially those with a high alumina content, are only partially suitable or even completely unsuitable for processing by means of an extrusion process.

The overcurrent protection device according to the invention has at least one fuse link according to the above explanations. With regard to the advantages of such an overcurrent protection device, reference is made to the preceding statements on the advantages of the fuse protection insert according to the invention.

Figur 1

eine schematische Darstellung des Schmelzsicherungseinsatzes in perspektivischer Ansicht,

Figur 2

eine schematische Schnittdarstellung des Schmelzsicherungseinsatzes in einer Seitenansicht.

In the following, an embodiment of the fuse link according to the invention will be explained in more detail with reference to the accompanying figures. In the figures are:

FIG. 1

a schematic representation of the fuse insert in a perspective view,

FIG. 2

a schematic sectional view of the fuse insert in a side view.

In the figures of the drawing, like parts are always provided with the same reference numerals. The description applies to all drawing figures in which the corresponding part can also be recognized.

In FIG. 1 the fuse protection insert 10 according to the invention is shown in a perspective view. FIG. 2 shows a corresponding thereto side view of the fuse link in a sectional view. The fuse link 10 has a ceramic body 11, which is formed in the present case as a hollow cylinder, wherein the interior of the ceramic body 11 substantially as a receiving space 12 for receiving solidified sand (not shown) is used. At each of the two openings of the hollow cylindrical ceramic body 11, a contact element 16 is arranged in each case, via which the fuse link 10 is electrically contacted. For this purpose, the contact element 16 has a receptacle 17 in the form of a blind hole, via which an electrical connection element can be securely connected, for example via a screw connection, to the fuse-link insert 10. With the aid of a respective cover plate 18, which can be fastened to the ceramic body via a plurality of bores 19 formed in the ceramic body 11, the respective contact element 16 is centered relative to the ceramic body 11. Furthermore, the openings of the hollow cylindrical ceramic body 11 are sealed pressure-tight by the two cover plates 18. Instead of a hollow cylinder and other hollow shapes for the design of the ceramic body 11, for example, hollow cuboid or hollow prisms are used.

In the receiving space 12, a plurality of fuse elements 13, which connect the two contact elements 16 in an electrically conductive manner, as well as a so-called identification wire, are furthermore provided 15, which also electrically conductively connects the two contact elements 16, arranged. The Kennmeldedraht 15 is guided at one end of the fuse link 10 to the outside and holds there held with a spring under mechanical tension indicator 21 - also called indicator - fixed. Each of the fusible conductor 13 has over its length a plurality of bottlenecks 20, on the design of the tripping characteristic of the fuse link 10 is selectively influenced. Furthermore, an additional body in the form of a bursting body 14 is arranged in the receiving space 12. The remaining receiving space 12 is filled with solidified sand, such as quartz sand, whereby the bursting body 14 is held in position. For reasons of clarity, the solidified sand is not shown in the figures. The bursting body 16 occupies a defined volume in the solidified sand and breaks up when the internal pressure in the interior of the ceramic body 11 exceeds a predefined threshold value, for example due to a temperature expansion of the solidified sand during activation of the fuse link insert 10.

At currents which are smaller than the rated current of the fuse link 10, only so much power dissipation is converted in the fusible elements 13 that they can be discharged in the form of heat quickly through the sand, the ceramic body 11 and the contact elements 16 to the outside. The temperature of the fuse element 13 does not increase beyond its melting point. However, flows a current that is in the overload range of the fuse link 10, the temperature rises steadily in the interior of the fuse element 10 until the melting point of the fuse element 13 is exceeded and they melt through at their bottlenecks 20. At high fault currents, for example due to a short circuit, so much energy is converted into the fusible links 13, that they are heated practically over their entire length and melt as a result at all bottlenecks 8 at the same time. Because liquid metal is still good electrical has conductive properties, the current continues to flow through the melt until it vaporizes and forms an arc. As a result of the extremely high temperatures occurring, the surrounding quartz sand is melted, resulting in a chemical reaction of the molten metal with the quartz sand. The resulting reaction product is a good insulator, which finally stops the current flow. Almost simultaneously with the melting of the fusible conductor 13 and the Kennmeldedraht 15 burns through. As a result, the indicator 21 is no longer held and moved due to the applied spring force in a new position. In this way, the triggering of the fuse link 10 is displayed.

By the formation of multiple arcs during the release of the fuse insert 10 much heat is generated, resulting in a temperature increase of the solidified sand and consequently - due to the thermal expansion - to an expansion of the solidified sand. Since the coefficient of thermal expansion of the solidified sand is greater than the coefficient of thermal expansion of the ceramic body 11 surrounding the solidified sand, this increases the internal pressure in the ceramic body 11. In order to avoid damage to the ceramic body 11 - for example, stress cracks - bursts from a defined threshold value of the internal pressure of the burst body 14. This is the trapped by the burst body volume - which, for example, with an air or gas mixture, with unconsolidated sand or with an elastic material can be filled - released. Since the solidified sand can now expand into this volume, the internal pressure drops back to a value below the threshold value. With a correct choice of the threshold value, damage to the ceramic body can thus be avoided.

LIST OF REFERENCE NUMBERS

10

Fusible link

11

ceramic body

12

accommodation space

13

fuse element

14

Additional body / bursting body

15

Characteristic signaling wire

16

contact element

17

admission

18

cover

19

drilling

20

bottlenecks

21

Fuses, indicator

Claims (8)

Fusible link insert (10), in particular for semiconductor protective fuses, having a solidified ceramic body (11),
characterized,
in that an additional body (14) is introduced into the solidified sand, which is designed such that an increase in an internal pressure in the ceramic body (11) due to a temperature expansion of the solidified sand by the additional body (14), an additional volume in the ceramic body (11 ) is released to expand the consolidated sand. Fuse-fuse insert (10) according to claim 1
characterized,
that the additional body is designed as a bursting body (14) which breaks when a predefined internal pressure in the ceramic body (11) is reached, whereby the additional volume is released. A fusible link insert (10) according to claim 2,
characterized,
that the bursting body (14) is filled with an air or gas mixture. A fusible link insert (10) according to claim 2,
characterized,
that the bursting body (14) is filled with unconsolidated sand. A fusible link insert (10) according to claim 2,
characterized,
that the bursting body (14) is filled with an elastic material. Fuse-fuse insert (10) according to claim 1
characterized,
that the additional body (14) is designed as a compressible solid body. Fuse-fuse insert (10) according to one of the preceding claims,
characterized,
that the ceramic body (11) is produced by extrusion. Overcurrent protection device having at least one fuse element (10) according to one of claims 1 to 7.

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