DE8703456U1 - Electrical fuse - Google Patents

Description

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Patent attorneys 1 1768.5

Wenzel & Kalkoff
PO Box 2448
Flaskuhle 6
5810 Witteri/Ruhr

Applicantini Wickmann-Werke GmbH

Annenstr.113 5810 Witten 6

Description: Electrical fuse

The invention relates to an electrical fuse with a fuse element that melts or evaporates in the event of an overload in a space that is essentially pressure-tight and sealed with a shell/filled with gas or liquid or is empty of air.

Electrical fuses of this type are used to irreversibly disconnect electrical consumers from the power source if overcurrents, up to short-circuit currents, or excessive temperatures trigger the fuse, i.e. cause the fuse element to melt or evaporate. The invention relates exclusively to fuses in which the fuse element is located in a space that is enclosed by a pressure-resistant shell. The space is filled with a flowable medium or is evacuated of air so that the fuse element is exposed in the space and

is not tightly enclosed, as is the case with sand or glass fillings, for example. The free position of the fusible element in the space enables the specification and compliance with certain current-time characteristics of the fuse.

When the fuse is in use, after a certain time a steady state occurs at a certain temperature level, at which the energy supplied to the fuse is equal to the energy dissipated. The fuse is designed to switch off when a higher overcurrent or even a short-circuit current flows through the fuse. Then the energy supplied exceeds the energy that can be dissipated, with the result that the fuse element reaches such a high temperature that it melts or suddenly evaporates. The flow of current is generally not interrupted by this, since the charge carrier transport now takes place via an arc that forms. For this reason, so much energy must be removed from the arc for it to be extinguished for it to be finally separated. The arc extinguishing is promoted by high pressure in the space, because then the free path for the generation of new charge carriers is too small at a given voltage. The casing of the fuse should therefore be as pressure-resistant as possible.

However, in fuses of known design, the high internal pressure that develops when the fusible element evaporates often leads to an explosive destruction of the casing surrounding the fuse compartment, for example a plastic cap, and in other cases the arc is not extinguished or at least not within the time specified by the fuse characteristics.

DE-OS 31 18 943 of the applicant already discloses a fuse of the type mentioned above, which has a plastic cap on a plastic base, whereby the cap is completely or partially covered with an insulating material

is lined with ceramics. The lining consists in particular of glued or inserted ceramic paper or of an inner coating of the cap with a suspension of aluminum oxide or silicon oxide. These measures can already reduce the risk of the fuse being destroyed, apparently because the ceramic lining contributes to the absorption of heat and thus promotes a reduction in pressure. However, a significant improvement in the switching capacity and switching accuracy, in particular rapid and definitive arc extinguishing, cannot be achieved in this way.

US-PS 4,283,700 discloses a device fuse in the form of a tube with end caps, whereby the tube has a two-layer structure and forms a cylindrical chamber in which the fuse element runs centrally and coaxially between the caps. The outer layer of the tube should be made of a material with low thermal conductivity and high resistance to the heat shock when the fuse element melts through. Conversely, the inner layer should be made of a material with high thermal conductivity but low resistance to the heat shock. The aim of this is that the inner layer absorbs as much heat as possible when the fuse is triggered and is simultaneously destroyed by the heat shock, i.e. breaks down into small particles. The arc and the metal particles of the destroyed or vaporized fuse element should penetrate into the gaps and spaces between the layer particles in order to absorb the arc energy and cool the gases. The outer layer is designed to withstand the heat shock and form a safe enclosure. However, the deliberate destruction of the inner layer leads to an uncontrollable distribution of the burst layer in the interior of the fuse, which does not exclude undesirable bridging by larger layer particles that lead to melting conductor deposits. This fuse can also be found in DE-OS 30 35 666.

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In a miniature or fine tube-shaped fuse known from Ud-PS 4,540,970, a ceramic tube is covered with an epoxy layer. The smooth inner wall of the ceramic tube serves to absorb heat and to absorb the metal particle deposit when the fusible element evaporates, while the epoxy layer is intended to form a pressure-resistant casing. However, it has been shown that even this known fuse cannot bring about the necessary electrical separation and the desired rapid energy absorption in all cases.

The task is therefore to create a fuse of the type mentioned above, with which a rapid arc extinguishing and a safe separation of the metal particle deposit that is formed by evaporation of the fusible conductor can be achieved.

To achieve this object, the invention provides that the inner wall of the space is covered at least to a significant extent with geometrically arbitrary, regular or irregular, shaped depressions and/or elevations in such a way that the surface of the inner wall increases.

It has been shown that a fuse designed in this way switches off reliably and is no longer exposed to the danger of explosive destruction. An inner wall of the fuse with recesses and/or elevations provides a much larger surface area for heat dissipation compared to a smooth wall, so that even a relatively high internal pressure in the first phase of the tripping process, which promotes effective arc extinguishing, can be quickly reduced.

However, the depressions or elevations not only increase the surface area that absorbs the heat from the gases and/or rays acting on the inner wall,

Not only can they absorb the metal particles, they also form a much larger surface area for them to collect. In addition, the surface area is not enlarged at the same level, but rather at different levels staggered in depth due to the depressions and elevations. This is why the metal particles are separated from one another by a corresponding distance when they deposit on such a rough surface, even if, viewed in surface projection, they are directly adjacent to one another or even partially overlap. This is because some of them reach the depressions, while others will deposit on or at the elevations of the inner wall. This ensures that the metal particles are safely separated from one another and from any fusible conductor residue, meaning that the fuse cannot become live again if the voltage is still present. For heat absorption and for reliable electrical separation of the metal particles deposited on the inner wall, it is irrelevant whether the depressions or elevations have a specific geometric shape or whether they are regular or irregular. However, because of the effects that can be achieved with a rough surface, as large a part of the inner wall of the space in which the fusible conductor is located as possible will generally be provided with corresponding depressions or elevations.

According to a very important development of the invention, it is provided that the inner wall, in particular the depressions and/or elevations, of the space consists at least to a significant extent of a material with high thermal conductivity and/or high heat storage capacity. A material with high conductivity and also high storage capacity is optimal.

Especially if the depressions or elevations on the inner wall itself are made of such a material, the heat absorption capacity of the wall increases accordingly, because the heat absorption

tion. The switching capacity of the fuse increases accordingly. Due to the high thermal conductivity, the heat transported by the gases and radiation and finally by the metal particles is quickly absorbed by the inner wall.

Due to the high heat storage capacity, an undesirable heat build-up on the surface of the inner wall is avoided, if the heat cannot be released to the outside at the same speed as it is absorbed by the inner wall. The increase in surface area through the depressions or elevations provides a sufficiently large absorption area for heat transfer.

According to the invention, the depressions and elevations ^5 can be formed either mechanically, chemically or by molding

the shell, which is preferably pressure-resistant and made of plastic, ceramic or glass, for example, and which encloses the space. In this case, the depressions or elevations of the rough surface are made of the same 2Q material as the shell of the fuse.

Alternatively, the depressions and elevations on the inner wall can be made according to the invention from an inner shell made of or with sand (SiO ₂ ; Al ₂ O ₃ ) on a preferred

2g pressure-resistant outer shell made of e.g. plastic, ceramic or glass. For the formation of such an inner shell and its connection with the pressure-resistant outer shell, as well as for the above-mentioned formation of the depressions and elevations, there are mechanical,

There are numerous possibilities, either chemically or by means of molding. The inner shell can be an independent body, for example in the form of a tube or cap, made of sand bound with plastic, preferably with a smooth outer surface, and can be pressed or glued with

g ₅ of the outer shell. However, the sand can also be glued to the inner wall of a bowl made of glass, ceramic or plastic, or welded to the surface or permanently bonded to it in some other way.

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bind. The sand is preferably applied as granules. Sand is ideally suited for the purpose at hand because it is thermally conductive and capable of storing heat to the desired degree and, in addition, by forming generally irregular depressions or elevations, it leads to a very significant increase in the surface area of the inner wall of the space surrounding the fusible element.

For tubular or tube fuses, the invention provides that the space for the fusible conductor is essentially tubular and that the inner wall, in particular the outer surface of the tube, is provided with depressions and/or elevations. In this way, the wall that makes a significant contribution to arc extinguishing and to the definitive shutdown of the fuse is directly opposite the fusible conductor.

For the same reason, it is provided for another safety ^device P that the space essentially consists of the interior of a particularly cylindrically shaped cap, which is closed, for example, with a base, wherein in particular the inner wall of the cap is provided entirely or partially with depressions and/or elevations.

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As a further measure to improve the switching capacity, the invention provides that an adjacent chamber with a cooling system, for example a cooling medium, is connected to the chamber, which is at least partially provided with depressions and/or elevations on its inner wall, and that the two chambers have a heat-conducting connection. This

Further development increases the heat dissipation and heat storage capacity, so that a corresponding increase in the switching capacity of the fuse is achieved.

35

The invention is in principle applicable to all electrical fuses in which a fusible element is surrounded by a flowing medium or

surrounded by vacuum. There is also no limitation on the applicability with regard to the switching capacity of the respective fuse. In this respect, the invention is just as effective for miniature or fine fuses as it is for high-voltage fuses.

Embodiments of the invention are explained below with reference to the drawings. In the drawings:

Fig. 1 is a cross-sectional view of a conventional sub-miniature fuse,

Fig. 2-8 cross-sectional views of caps designed in various ways according to the invention for a sub-miniature fuse according to Fig. 1;

Fig. 9 is a cross-sectional view of a cap for a sub-miniature fuse according to Fig. 1, provided with additional heat dissipation and designed according to the invention;

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11 to 12 show three views of the application of the invention to tube fuses in a schematic representation;

Fig. 13

up to 15 wall sections, each as a cross-sectional view to show different designs of a wall with depressions and elevations

inner wall of a security room,

The commercially available miniature fuse shown in Figure 1 consists essentially of a base 1 with a circular cross-section, on which a corresponding hollow-cylindrical cap 2 is arranged and fastened in the manner shown in the drawing. Both parts are made of plastic.

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There are two electrical conductors 3, to the ends of which protrude beyond the base 1, a fusible conductor 5 is attached using solder 4. The cap 2 forms with the base 1 a pressure-resistant and gas-filled space 6, on the inner wall 7 of which the metal particles settle when the fusible conductor 5 evaporates when the fuse is triggered.

In Fig. 2 to 9, embodiments of caps 2 are shown, which are designed in different ways, in particular on the inside, and which can be used for a miniature fuse according to Fig. 1 in order to implement the invention. However, the surface 8 of the base can also be designed in the manner according to the invention.

All embodiments of the caps 2 according to Figures 2 to 9 have in common that their inner wall 7 is entirely or partially provided with depressions 9 and elevations 10.

In the embodiments according to Figures 2 and 3, the depressions 9 and elevations 10 are each formed directly on the inner wall 7 of the plastic shell 11 of the cap 2, according to Figure 2 with an approximately zigzag-shaped cross-section in the depressions 9 and the elevations 10, while according to Figure 3 these are each formed as regular rectangles, namely as grooves running across the cap base or as individual depressions 9 and elevations 10, which form a corresponding pattern on the cap base. In addition to the cap base, the cylinder-shaped part of the inner wall 7 of the cap 2 can also be provided with a rough surface in the same way. The cap 2 can also be made of ceramic, glass or even metal, as long as the base 1 is made of insulating material.

In contrast to the single-shell design of the cap according to Figures 2 and 3, Figures 4 to 7 show double-shell designs. According to Figure 4, the cap 2 is only partially.

namely at the base of the cap, with an inner shell 12, which in this case consists of sand. The sand is glued to the inner wall 7, for example using epoxy glue, or welded into it or secured there in another way, in any case in such a way that the sand grains protrude freely inwards with most of their surface, so that the desired depressions 9 and elevations 10 are formed in this way. The advantages of a sand lining are primarily that not only, as already explained in detail at the beginning, the surface of the inner wall 7 is significantly increased, but that the sand forms a material with high thermal conductivity and high heat storage capacity, so that rapid heat absorption is achieved when the fuse is triggered. Figure 5 shows that the rough surface formed by a sand coating of the inner wall can also cover the entire inner surface of the cap 2. The more surface area in the chamber 6 is available for heat absorption and for the precipitation of metal particles, the quicker and more effectively the fuse is switched off. Therefore, covering as large an area as possible of the inner wall 7 of the chamber 6 of the fuse with a layer of depressions 9 and elevations 10 is generally preferable to partial covering.

In the embodiments according to Figures 6 and 7, the inner shells 12 are manufactured as independent parts and then inserted into the shell 11 and secured there. While in the embodiment according to Figure 6 an inner shell 12 with the largest possible surface area with a pattern of irregularly shaped depressions 9 and elevations 10 is illustrated, Figure 7 only shows a circular inner shell 12 with regularly shaped depressions 9 and elevations 10 on the cap base.

Figures 10-12 illustrate the application of the invention to tube fuses, with Figures 10 and 11 showing tube bodies 13 in a half-shell design. Figure 10 shows a single-shell design in which the shell 11 has an inner wall 7 with depressions 9 and elevations 10, which can be formed in a similar way to the embodiments according to Figures 2 and 3. In the double-shell design according to Figure 11, the inner shell 12 inserted into the shell 11 consists, for example, of a component formed from sand, for example sintered, with corresponding depressions 9 and elevations 10. The material of the shell 11 is practically arbitrary, as long as a minimum level of heat transfer and pressure resistance is ensured. Whether it is a conductive or non-conductive material depends on the respective application. In the embodiment according to Figure 12, the tube body is hollow-cylindrical and its inner wall 7 is covered, for example, with a layer of sand forming the desired depressions 9 and the elevations (10).

Figures 13-15 show schematically, using enlarged wall sections, how the rough surface consisting of depressions and elevations 10 affects the inner wall 7, which encloses the space 6 of the fuse. Figure 13 uses a section of a single-shell wall consisting of a shell 11 to illustrate how metal particles 14 are deposited in the depressions 9 and on the elevations 10 when the fuse is triggered and the associated evaporation of the fusible conductor, e.g. 5, so that a reliable electrical separation of the metal particles occurs. The illustration, like the views in Figure 14, also shows schematically the enlargement of the surface of the inner wall 7. Figure 14 shows corresponding sections of the double-shell design with a shell 11 and an inner shell 12, in the upper part with regularly shaped and arranged depressions 9 and 10 as well as

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with irregular depressions and elevations 9 and 10 in the lower part. Figure 15 also illustrates a two-shell design, whereby the inner shell 12, however, consists of sand grains 15 which are glued to the shell 11 with an adhesive layer 16B. If space allows, the sand layer can also be made thicker so that the sand grains lie on top of each other in the direction of the layer thickness. In any case, it is essential that the sand grains 15 are only embedded as far as is necessary for their attachment, so that as large a part of their surface as possible is available for heat absorption and for the deposition of metal particles.

In the embodiment according to Figure 9, in addition to a two-shell cap design with corresponding depressions and elevations 9 and 10, an adjacent chamber 17 is provided which adjoins the chamber 6 of the fuse but is preferably separated from it in a pressure-tight manner in order to provide additional cooling of the fuse.

For this purpose, a heat-conducting connection 18 is provided between the room 6 and the adjacent room 17. In the adjacent room 17 there is, for example, a cooling medium.

The required degree of roughness of the inner wall must be selected depending on the size of the fuse, the required breaking capacity, the material in question and its deformability. The conventional roughness of glass and ceramic surfaces, as is usually already used for the inner wall of fuses, especially device fuses, etc., is not sufficient. It is usually too fine to lead to a significant increase in surface area and to sufficient roughness for the desired separation of the metal particle deposit.

Claims (1)

Patent attorneys Wenzel & Kalkoff 1768.5 Flaskuhle 6 PO Box 2448 Witten/Ruhr Protection claims 1. Electrical fuse with a fusible conductor that melts or evaporates in the event of an overload in a gas- or liquid-filled or airless space that is essentially sealed with a shell in a pressure-tight manner, characterized in that the inner wall (7) of the space (6) is covered at least to a considerable extent with geometrically random, regular or irregular, shaped depressions (9) and/or elevations (10) in such a way that the surface of the inner wall (7) increases. 2. Electrical fuse according to claim 1, characterized in that the inner wall (7), in particular the depressions (9) and/or the elevations (10), of the space (6) consists at least to a significant extent of a material with high thermal conductivity and/or high heat storage capacity. 3. Electrical fuse according to claim 1 or 2, characterized in that the depressions (9) and elevations (10) are formed mechanically, chemically or by means of molding on the preferably pressure-resistant shell (11), for example made of plastic, ceramic or glass, which envelops the space (6). * · · &igr; t t 3. Electrical fuse according to claim 1 or 2, characterized in that the depressions (9) and elevations (10) on the inner wall (7) of an inner shell (12) made of or with sand (SiO ₂ ; Al ₂ O ₃ ) are formed on a preferably pressure-resistant outer shell (11) made of, for example, plastic, ceramic or glass. 5. Electrical fuse according to one or more of claims 1-4, characterized in that the space \5) for the fusible conductor (5) is essentially tubular and as an inner wall (7) in particular the outer surface of the tube is provided with depressions and/or elevations (10)-15 6. Electrical fuse according to one or more of claims 1-4, characterized in that the space (6) for the fusible conductor (5) consists essentially of the interior of a cap (2) which is in particular cylindrically shaped and which is closed, for example, with a base (1), whereby in particular the inner wall (7) of the cap (2) is completely or partially provided with depressions (9) and/or elevations (10). 7. Electrical fuse according to one or more of claims 1-6, characterized in that an adjacent space (17) with a Cooling, for example with a cooling medium, and the two spaces (6, 17) have a heat-conducting connection (18).