Electrical fuse

Abstract

The object of the invention is an electrical fuse comprising a housing (1) having a first end and a second end, wherein the electrical fuse further comprises two end caps (2) arranged respectively at the first end and the second end of the housing (1), two contacts (3), and at least one fusible element (4) of an electrically conductive material arranged inside the housing (1). The contacts (3) are electrically conductively connected by the fusible element (4) and pass axially through the end caps (2) away from the housing (1). The end caps (2) are of an electrically non-conductive material.

Description

[0001] Electrical fuse

[0002] Technical field

[0003] The invention relates to an electrical fuse designed to protect devices, including apparatuses and parts thereof using the power grid for their function, against overcurrent.

[0004] Background of the invention

[0005] Due to their compactness and small dimensions, electrical fuses are often used in various fields to protect devices, including apparatuses and parts thereof using the power grid for their function, against overcurrent. In addition to their small dimensions, modern electrical fuses provide users with high utility characteristics thanks to their high breaking capability, low electric losses, and a wide range of rated currents and ampere-second characteristics. Their design typically uses a tubular housing with a fusible element inside a cavity, wherein this cavity may be filled with an arc extinguisher, most commonly silica sand. At each end of the tubular housing there are metal caps and associated contacts (also called leads). The metal caps, however, generally represent unprotected metal surfaces that present an electric safety risk of accidental human contact or may allow an accidental short circuit to form if a metal piece touches adjacent surfaces.

[0006] Electrical fuses are also described in the patent literature, e.g. in the document WO99 / 40599 A1 . A fuse insert according to this document contains a fuse housing that is filled with an arc extinguishing medium, cover plates laterally attached to the fuse housing, and a main fusible conductor electrically connected to contact pins that protrude through said cover plates. The contact pins are adapted for installation in a fuse holder by means of which they are connected via conductors to the protected device and to the low-voltage power grid. An improved fuse according to the document WO2013 / 063037 A1 has a fuse body made of an electrically insulating material with a cavity extending from a first end of the fuse body to a second end of the fuse body. The fusible element is placed within the cavity. Insulated plugs are placed in the cavity at the first and second ends of the fuse body, wherein the plugs adhere to the inner surface of the fuse body and form seals that seal the inner cavity. The fuse may further contain terminals that are applied to the ends of the fuse body in electric contact with the fusible element. These terminals are made of an electrically conductive material.

[0007] The document US6653925 B1 describes a fuse with insulation of the thermal fuse leads with an insulating tube and also describes the method of its manufacture.

[0008] The fuse according to the document US5905426 A contains an elongated electrically insulating tube, a pair of knife contacts protruding axially outward from the opposite ends of the tube, at least one fuse element placed in the tube and electrically connected between the clamps, and further a pair of metal end caps placed at opposite ends of the tube. Electrically insulating elements are placed between the end caps and the knife contacts.

[0009] The document WO2018 / 089156 A1 describes a fuse comprising a fuse body, a fuse element containing a first terminal protruding from a first end of the fuse body and a second terminal protruding from a second end of the fuse body, as well as end caps. The material of the end caps is not specified in this document.

[0010] The technical solution according to the Czech utility model No. 19694 concerns an electrical fuse consisting of an insulating body, provided with cylindrical caps at opposite ends and equipped with a continuous cavity with at least one strip fusible conductor, wherein the continuous cavity is filled with an arc extinguisher and is provided with plugs in the end parts.

[0011] The document US201 1298577 A1 describes an electrical fuse having one or more counter openings in the inner wall of a hollow tube that serves as a fuse housing. The fuse has a first and second end lids connected to the respective ends of the tube, wherein these lids are made of an electrically conductive material.

[0012] In the above documents, metal lids, or generally lids made of an electrically conductive material, are typically used. For this reason, there may be a risk of electric shock if a person accidentally touches the metal lids. This problem is either not addressed in the above documents or is addressed by an disadvantageous modification of the fuse. For example, according to the document US5905426 A, electrically insulating elements must be arranged between the end caps and the corresponding contacts. This complicates manufacture and increases manufacturing costs.

[0013] It would therefore be desirable to come up with a solution that would eliminate the risk of electric shock to a person or the risk of short circuit due to contact with conductive surfaces. At the same time, the proposed solution should be characterized by a simple design, one that is easy to manufacture in terms of cost and the technology used.

[0014] Summary of the Invention

[0015] The above shortcomings are to a certain extent eliminated by an electrical fuse comprising a housing having a first end and a second end, wherein the electrical fuse further comprises two end caps placed respectively at the first end and the second end of the housing, two contacts, and at least one fusible element of an electrically conductive material placed inside the housing. The contacts are electrically conductively connected by the fusible element and pass axially through the end caps away from the housing. The electrical fuse of the present invention is based on the fact that the end caps are of an electrically non-conductive material.

[0016] Because the end caps are made of an electrically non-conductive material, the risk of electric shock if a person touches the end caps is eliminated. The risk of accidentally creating a short circuit if the end cap were to come into contact with any of the adjacent metal surfaces is also minimized. In addition, the manufacture of end caps from electrically non-conductive material is simple and less costly than manufacturing end caps from metal. There is also no need to provide the fuse with any additional insulating elements between the end caps and the contacts, which keeps its design simple and reduces manufacturing costs. Thus, the end caps close the housing at both of its ends and comprise openings for the contacts to pass through. The contacts pass through these openings axially, which means that they extend from the end caps away from the housing in the axial direction, i.e. in the direction of the axis of the housing. Thus, the contact may pass through the end cap in a direction coincident with this axis, i.e. typically through the center of the end cap, however, it may also pass through the end cap in a direction that is offset relative to the axis of the housing, i.e. it may pass through the end cap at a different place thereof, e.g. at a place closer to the edge of the end cap.

[0017] When we say that the contacts are electrically conductively connected to the fusible element, this conductive connection may be implemented e.g. by the contact and the fusible element forming two different pieces that are electrically conductively connected to each other during the manufacture. However, the contacts may also be connected by the fusible element so that they are an extension of the fusible element at both ends thereof. In other words, this means that the contacts can be formed from the same piece as the fusible element and together with the fusible element form one solid piece. The partition between the fusible element and the contacts is then formed by weakening of the part of the fusible element that is placed inside the housing, relative to the contacts, or by the strengthening of the contacts relative to the fusible element.

[0018] Both end caps may be made of the same electrically non-conductive material. Alternatively, the respective contacts may be made of different electrically non-conductive materials.

[0019] The electrically non-conductive material of the end cap is preferably a plastic material. The plastic material may be any electrically non-conductive plastic material, or it may also be an electrically non-conductive composite material of which at least one component is plastic. A plastic material may also be a so-called blend, i.e. a mixture of two or more compatible polymers. More specifically, the plastic material may be e.g. one of the thermoplastics (polyamide, polycarbonate) or thermosets, which generally have a higher resistance to thermal stress than thermoplastics.

[0020] The electrically non-conductive material of the end cap is preferably polyamide modified with glass fibers. This material is tough, flexible, and resists thermal loads well. The ratio of the glass fiber additive may be 15 to 30 %, or another suitable ratio of this additive may be chosen. The end caps are preferably made by injection molding of plastic material, however, alternatively the end caps may be made using additive manufacturing technology (3D printing), i.e. the end cap may be a 3D printed piece. Additive manufacturing technology can be preferably used for small batches.

[0021] The end caps are preferably molded on the outer surface of the housing. This allows the end caps to withstand the overpressure generated inside the housing when the electric arc is interrupted. The adhesion resistance of the end caps, i.e. the force required for the molding thereof, is preferably greater than 100 N. Alternatively, the end caps may be glued to the outer surface of the housing.

[0022] Each contact preferably comprises a first part of the contact electrically conductively connected to the fusible element and a second part of the contact extending perpendicularly from the first part of the contact, wherein the second part of the contact passes axially through the end cap. Thus, the contact may, for example, have a shape resembling the letter L. Such a contact arrangement is preferable in that it is also suitable for miniature fuses designed for surface-mount devices (SMDs) on printed circuit boards. The first part of the contact matches in shape the cross-section of the housing, i.e. it has a circular cross-section if the housing has a circular cross-section, or has a square or other cross-section if the housing has such a square or other cross-section. It is to this first part of the contact that the respective end of the fusible element is electrically conductively connected.

[0023] Description of the Drawings

[0024] A summary of the invention is further clarified using exemplary embodiments thereof, which are described with reference to the accompanying drawings, in which: fig. 1 shows an electrical fuse in the first exemplary embodiment of the present invention, fig. 2 shows the electrical fuse in the first exemplary embodiment of the present invention in a longitudinal section, and fig. 3 shows the electrical fuse in the second exemplary embodiment of the present invention in a longitudinal section.

[0025] Exemplary Embodiments of the Invention

[0026] The invention will be further clarified using exemplary embodiments with reference to the respective drawings.

[0027] In the first exemplary embodiment, as shown in fig. 1 and fig. 2, the electrical fuse comprises a housing 1_, two end caps 2, two contacts 3, a fusible element 4 of an electrically conductive material, and an arc extinguisher 5. In the following text, this first exemplary embodiment will be described in detail.

[0028] In the described and shown first exemplary embodiment, the housing 1 has a tubular shape, i.e. it comprises a first and a second end of the housing 1. and a further continuous cavity that terminates at these two ends of the housing T In the exemplary embodiment, the housing 1 has a circular cross-section, or alternatively a square crosssection or a cross-section of another shape, if such a cross-section allows the fusible element 4 to be arranged inside the housing 1_. The housing 1 is made of an electrically non-conductive material, for example ceramic (e.g. steatite), non-conductive composite materials, or glass.

[0029] To close the housing 1 at its first and second ends, the electrical fuse comprises two end caps 2. Thus, these end caps 2 are respectively arranged at the first or second end of the housing 1_, wherein more particularly they are molded onto the outer surface of the housing 1. to resist the overpressure generated inside the housing 1. when the electric arc is interrupted. The adhesion resistance of the end caps 2, i.e. the force required to mold them, is, for example, greater than 100 N.

[0030] In order to eliminate the risk of electric shock to a person, the end caps 2 are made of an electrically non-conductive material, more specifically a plastic material. This electrically non-conductive material can be either a simple material or a composite material (e.g. so-called blends, i.e. mixtures of two or more compatible polymers). In the most preferred embodiment of the end caps 2, the end caps 2 are made by injection molding of plastic from a polyamide material modified with glass fibers, for example with an addition of 15 to 30 % glass fibers. Alternatively, the ratio of the glass fibers may be different. In other alternative embodiments of the end caps 2, the end caps 2 are made of, for example, one of the thermoplastics (polyamide, polycarbonate, etc.) or thermosets that generally exhibit a higher resistance to thermal stress than thermoplastics. The above specific examples of materials are intended to be illustrative and not an exhaustive list of applicable materials. A person skilled in the art would have no problem using any other known electrically non-conductive material.

[0031] In the first exemplary embodiment of the fuse of the present invention shown, the fusible element 4 of an electrically conductive material, e.g. copper, silver, or various alloys, is arranged in the housing T Such a fusible element 4 is generally known in the state of the art and is also referred to as a fusible conductor. The fusible element 4 has, for example, the shape of a wire or a strip. As can be seen in fig. 2 in longitudinal section, the fusible element 4 is arranged inside the housing 1 and extends in the axial direction between the both ends of the housing T It is the fusible element 4 that provides protection against overcurrent, since it will melt if too much current passes through it. This principle and the particular materials of the fusible conductor are well known in the state of the art. As can also be seen in fig. 2, the housing 1 is filled with an arc extinguisher 5, such as silica sand, to better extinguish the electric arc and interrupt the subsequent current.

[0032] The fusible element 4 electrically conductively connects the contacts 3, wherein in the first exemplary embodiment shown, both contacts 3 are implemented in a shape resembling the letter L, and these contacts 3 are electrically conductively connected to both ends of the fusible element 4. As can be seen in fig. 2, the contacts 3 comprise a first part that is arranged at the respective end of the housing 1_, i.e. at the place where the continuous cavity thereof terminates. This first part of the contact 3 matches in shape the cross-section of the housing 1_, i.e. it has a circular cross-section if the housing 1 has a circular cross-section, or has a square or other cross-section if the housing has such a square or other cross-section. It is to this first part of the contact 3 that the respective end of the fusible element 4 is electrically conductively connected. In this context, it can be mentioned that the end cap 2 is adapted in shape to cover the respective end of the housing 1. together with the first part of the contact 3. Specifically, this means that the end cap 2 comprises a cavity with inner diameter that corresponds to the outer diameter of the housing 1. and the first part of the contact 3 or is slightly larger than the outer diameter of the housing 1 and the first part of the contact 3. This allows the end cap 2 to be fitted over the first part of the contact 3 and the outer surface of the housing 1, as can be seen in fig. 2.

[0033] Each contact 3 then, in the first exemplary embodiment of fig. 1 and fig. 2, further comprises a second part of the contact 3 that is perpendicular to the first part of the contact 3 and that passes axially through the respective end cap 2 out of the housing 1. For this reason, an opening is made in each end cap 2 for the second part of the contact 3 to pass through. The contacts 3 are made of an electrically conductive material, typically metal, and are adapted in shape for connection to the protected device, e.g. the second part thereof is adapted in shape to be secured in a fuse holder, through which and by means of conductors the contact 3 is subsequently connected to the protected device. In the first exemplary embodiment shown, the second part of the contact 3 is longer than the first part of the contact 3, however, in one of the alternative embodiments, the second part of the contact 3 may be as long as the first part of the contact 3 or even shorter.

[0034] The first exemplary embodiment described above may be further modified in various ways to create various other alternative embodiments of the fuse. Alternatively, for example, the housing 1. is not filled with the arc extinguisher 5. In another alternative embodiment, the fuse comprises multiple fusible elements 4, i.e. multiple fusible conductors. In a further alternative embodiment, the end caps 2 are not molded onto the outer surface of the housing 1 but are glued thereto.

[0035] In a further alternative embodiment of the fuse, which we will call the second exemplary embodiment and which is shown in fig. 3, the contacts 3 are connected by the fusible element 4 in such a way that they are an extension of the fusible element 4 at both ends thereof. In other words, the contacts 3 are formed from the same piece as the fusible element 4 and together with the fusible element 4 form one solid piece. The partition between the fusible element 4 and the contacts 3 is then formed by weakening of the part of the fusible element 4 that is placed inside the housing 1, relative to the contacts 3, or by the strengthening of the contacts 3 relative to the fusible element 4. This weakening of the fusible element 4, or the strengthening of the contacts 3, can be seen in fig. 3. In practical use, only this weakened part (corresponding to the fusible element 4) melts in the case of an overcurrent, while the stronger parts (corresponding to the contacts 3) remain intact. The melting of the fusible element 4 thus breaks the mutual conductive connection of the contacts 3.

[0036] The other parts of the fuse, i.e. the housing 1 and the end caps 2, are in the second exemplary embodiment implemented in the same way as in the case of the first exemplary embodiment described above, but the fuse in the second exemplary embodiment further comprises two faces 6. As can be seen in fig. 3, these faces 6 are arranged at the respective ends of the housing 1_, i.e. at the place where the continuous cavity thereof terminates. The faces 6 are thus arranged analogously in the same space as the first parts of the contacts 3 of the first exemplary embodiment of fig. 1 and fig. 2. Like these first parts of the contacts 3 in the first exemplary embodiment of the fuse, the faces 6 in the second exemplary embodiment of the fuse match in shape the cross-section of the housing 1 and the shape of the cavity of the end cap 2. Specifically, this means that the end cap 2 comprises a cavity with inner diameter that corresponds to the outer diameter of the housing 1. and the face 6 or is slightly larger than the outer diameter of the housing 1. and the face 6. This allows the end cap 2 to be fitted over the face 6 and the outer surface of the housing 1_.

[0037] In contrast to the first part of contacts 3 of the first exemplary embodiment, the faces 6 of the second exemplary embodiment do not serve for electrically conductive connection of the fusible element 4. Instead, each face 6 comprises an opening for the fusible element 4 terminated by the contacts 3 to pass through. Further openings are then made in both end caps 2, wherein these openings are placed coaxially with the openings in both faces 6. This allows the contacts 3, which terminate the fusible element 4, to pass through the faces 6 and then through the end caps 2 axially out of the housing 1_. In the second exemplary embodiment, the face 6 is in contact with the respective contact 3 but it is not electrically conductively connected to the contact 3. Alternatively, the second exemplary embodiment may be modified such that the face 6 is conductively connected to the respective contact 3. Industrial Applicability

[0038] The above-described electrical fuse can be used to protect various devices against overcurrent, including devices and parts thereof using the power grid for their function.

[0039] List of Reference Signs

[0040] 1 - housing

[0041] 2 - end cap

[0042] 3 - contact

[0043] 4 - fusible element

[0044] 5 - arc extinguisher

[0045] 6 - face

Claims

CLAIMS1. An electrical fuse comprising a housing (1 ) having a first end and a second end, wherein the electrical fuse further comprises two end caps (2) placed respectively at the first end and the second end of the housing (1 ), two contacts (3), and at least one fusible element (4) of an electrically conductive material placed inside the housing (1 ), wherein the contacts (3) are electrically conductively connected by the fusible element (4) and pass axially through the end caps (2) in a direction away from the housing (1 ), characterized in that the end caps (2) are of an electrically non-conductive material.

2. The electrical fuse according to claim 1 , characterized in that the electrically non- conductive material of the end cap (2) is a plastic material.

3. The electrical fuse according to claim 2, characterized in that the electrically non- conductive material of the end cap (2) is a polyamide modified with glass fibers.

4. The electrical fuse according to any one of the preceding claims, characterized in that the end caps (2) are molded on the outer surface of the housing (1 ).

5. The electrical fuse according to any of the preceding claims, characterized in that each contact (3) comprises a first part of the contact (3) electrically conductively connected to the fusible element (4) and a second part of the contact (3) extending perpendicularly from the first part of the contact (3), wherein the second part of the contact (3) passes axially through the end cap (2).

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