Electrical fuse

Abstract

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 individually at the first end and the second end of the housing (1), two contacts (3) and at least one fusible element (4) made of electrically conductive material arranged inside the housing (1), wherein the contacts (3) are electrically connected to each other by the fusible element (4) and extend axially through the end caps (2) in a direction away from the housing (1), characterized in that the end caps (2) are made of electrically non-conductive material.

Description

Technical subject area

[0001] The invention relates to an electrical fuse for protecting installations, including devices and parts thereof, which use the power grid for their function, against overcurrents. State of the art

[0002] Electrical fuses are widely used in a variety of applications to protect equipment, including devices and components that rely on the power grid, from overcurrents due to their compact size and small dimensions. In addition to their small size, modern electrical fuses offer users excellent performance characteristics thanks to their high breaking capacity, low electrical losses, and wide range of rated currents and ampere-second characteristics. Their design typically uses a tubular housing with a fusible element inside a cavity, which may be filled with a quenching medium, usually quartz sand. Metal closures and corresponding contacts (also called leads) are located at both ends of the tubular housing.However, metal fasteners generally represent unprotected metal surfaces which, if accidentally touched by humans, pose an electrical safety risk or can cause an accidental short circuit if a metal part touches adjacent surfaces.

[0003] Electrical fuse links are also described in patent literature, e.g., in document WO99 / 40599 A1. A fuse link according to this document comprises a fuse housing filled with a quenching agent, cover plates attached to the sides of the fuse housing, and a main fuse element electrically connected to contact pins that extend beyond the cover plates. The contact pins are adapted for installation in a fuse holder, through which they are connected to the protected equipment and the low-voltage network by means of conductors.

[0004] The improved fuse according to WO2013 / 063037 A1 has a fuse body made of an electrically insulating material with a cavity extending from one end of the fuse body to the other. The fusible element is located inside the cavity. Insulated plugs are fitted into the cavity at the first and second ends of the fuse body, adhering to the inner surface of the fuse body and forming seals that close the inner cavity. The fuse may also include end pieces that are inserted at the ends of the fuse body in electrical contact with the fusible element. These end pieces are made of an electrically conductive material.

[0005] Document US6653925 B1 describes a fuse with insulation of the fuse leads by an insulating tube and also describes the method for its manufacture.

[0006] The fuse according to US5905426 A comprises an elongated, electrically insulating tube, a pair of blade contacts extending axially outward from opposite ends of the tube, at least one locking element arranged within the tube and electrically connected between the terminals, and further, a pair of metal end caps arranged at opposite ends of the tube. Electrically insulating elements are located between the end caps and the blade contacts.

[0007] Document WO2018 / 089156 A1 describes a locking device comprising a locking body, a locking element comprising a first end piece extending from a first end of the locking body, and a second end piece extending from a second end of the locking body, as well as end caps. The material of the end caps is not specified in this document.

[0008] The technical solution according to Czech utility model no. 19694 relates to an electrical fuse consisting of an insulating body which is provided with cylindrical covers at opposite ends and which has a continuous cavity with at least one ribbon-shaped fusible conductor, wherein the continuous cavity is filled with a quenching agent and is provided with stuffing boxes at the end parts.

[0009] Document US2011298577 A1 describes an electrical fuse with one or more counter-openings in the inner wall of a hollow tube that serves as the fuse housing. The fuse has a first and a second end cap that are connected to the respective ends of the tube, these caps being made of electrically conductive material.

[0010] The aforementioned documents typically use metal caps or, more generally, caps made of electrically conductive material. Therefore, there is a risk of electric shock if a person accidentally touches the metal caps. This problem is either not addressed in the aforementioned documents or solved by a disadvantageous modification of the fuse. For example, according to document US5905426 A, electrically insulating elements must be placed between the terminations and the corresponding contacts. This complicates production and increases manufacturing costs.

[0011] It would therefore be desirable to find a solution that eliminates the risk of bodily injury from electric shock or the risk of a short circuit due to contact with conductive surfaces. At the same time, the proposed solution should be characterized by a simple design that does not place high demands on production in terms of cost and technology. Description of the invention

[0012] The above-mentioned deficiencies are eliminated to a certain extent by the electrical fuse, comprising a housing with a first end and a second end, wherein the electrical fuse further comprises two end caps arranged individually at the first and second ends of the housing, as well as two contacts and at least one fusible element made of electrically conductive material, which is arranged in the housing. The contacts are electrically connected by a fusible element and extend axially from the housing through the end caps. The key feature of the electrical fuse according to the invention is that the end caps are made of electrically non-conductive material.

[0013] Since the terminals are made of a non-conductive material, there is no risk of electric shock if a person touches them. The risk of an accidental short circuit if the terminal comes into contact with an adjacent metal surface is also minimized. Furthermore, manufacturing terminals from non-conductive material is simpler and less expensive than manufacturing them from metal. Additionally, there is no need to include extra insulating elements between the terminals and the contacts, which simplifies the design and reduces manufacturing costs.

[0014] The end caps therefore close the housing at both ends and contain openings for the passage of contacts. The contacts are guided axially through these openings, meaning they protrude from the end caps in an axial direction from the housing, i.e., in the direction of the housing axis. Thus, the contact can pass through the end caps in a direction that coincides with this axis, i.e., typically through the center of the end cap. However, it can also pass through the end cap in a direction that is offset from the housing axis, i.e., it can pass through the end cap at a different location, for example, at a point closer to the edge of the end cap.

[0015] When we say that the contacts are electrically connected to the fusion element, this conductive connection can be achieved, for example, by the contact and the fusion element forming two separate parts that are electrically connected during manufacturing. However, the contacts can also be connected by a single fusion element, so that they represent an extension of the fusion element at both ends. In other words, this means that the contacts can consist of the same material as the fusion element and, together with the fusion element, form a single, unified whole. The dividing line between the fusion element and the contacts is then formed by a weakening of the portion of the fusion element located inside the housing relative to the contacts, or by a strengthening of the contacts relative to the fusion element.

[0016] Both end caps can be made from the same electrically non-conductive material. Alternatively, the individual contacts can also be made from different electrically non-conductive materials.

[0017] The electrically non-conductive material of the end closure is preferably a plastic material. This plastic material can be any electrically non-conductive plastic or an electrically non-conductive composite material in which at least one component is made of plastic. The plastic material can also be a so-called blend, i.e., a mixture of two or more compatible polymers. More specifically, the plastic material can be, for example, a thermoplastic (polyamide, polycarbonate) or a thermoset, which generally exhibit higher temperature resistance than thermoplastics.

[0018] The electrically non-conductive material of the end cap is preferably a glass fiber-modified polyamide. This material is tough, flexible, and highly resistant to temperature fluctuations. The proportion of glass fiber added can be 15 to 30%, or another suitable proportion can be selected. The end caps are preferably manufactured from plastic material using injection molding; however, they can alternatively be produced using additive manufacturing technology (3D printing), meaning the end cap can be a 3D-printed part. Additive manufacturing technology is particularly advantageous for small production runs.

[0019] Preferably, the end caps are pressed onto the outer surface of the housing. This allows the end caps to withstand the overpressure that builds up inside the housing when an arc is interrupted. The adhesive resistance of the end caps, i.e., the force required for pressing them on, is preferably greater than 100 N. Alternatively, the end caps can also be bonded to the outer surface of the housing.

[0020] Each contact preferably comprises a first part of the contact, which is electrically connected to the fuse element, and a second part of the contact extending perpendicularly from the first part, the second part of the contact passing axially through the end closure. This contact can, for example, have an L-shape. Such a contact arrangement is advantageous in that it is also suitable for miniature fuses intended for surface mounting (SMD, surface-mount device) on printed circuit boards. The shape of the first part of the contact is adapted to the cross-section of the housing; that is, it has a circular cross-section if the housing has a circular cross-section, or a square or other cross-section if the housing has such a square or other cross-section. The respective end of the fuse element is electrically connected to this first part of the contact. Explanation of drawings

[0021] The essence of the invention is further clarified by exemplary embodiments described with reference to the accompanying drawings, wherein: Fig. 1 represents an electrical fuse in the first embodiment according to the present invention, Fig. 2 shows an electrical fuse in the first embodiment according to the present invention in longitudinal section and Fig. Figure 3 shows an electrical fuse in the second embodiment according to the present invention in longitudinal section. Exemplary embodiments of the invention

[0022] The invention is further explained in more detail with reference to exemplary embodiments and the corresponding drawings.

[0023] In the first embodiment, as in the Fig. 1 and in the Fig. As shown in Figure 2, the electrical fuse comprises a housing 1, two end caps 2, two contacts 3, a fusible element 4 made of electrically conductive material, and a quenching agent 5. This first embodiment is described in detail below.

[0024] In the first described and illustrated embodiment, the housing 1 is tubular, i.e., it comprises a first and a second end and a continuous cavity opening into both ends. In one embodiment, the housing 1 has a circular cross-section, or a square cross-section, or a cross-section of another shape if such a cross-section allows the arrangement of the melting element 4 inside the housing 1. The housing 1 is made of an electrically non-conductive material, e.g., ceramic (e.g., steatite), non-conductive composite materials, or glass.

[0025] To seal the housing 1 at its first and second ends, the electrical fuse comprises two end caps 2. These end caps 2 are thus arranged individually at the first and second ends of the housing 1, respectively, and are specifically pressed onto the outer surface of the housing 1 to withstand the overpressure that arises when an electric arc inside the housing 1 is interrupted. The adhesive strength of the end caps 2, i.e., the force required for pressing them on, is, for example, greater than 100 N.

[0026] To eliminate the risk of bodily injury from electric shock, the end caps 2 are made of electrically non-conductive material, in particular plastic. 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, they are manufactured by injection molding from a glass fiber-modified polyamide material, for example, with an addition of 15 to 30% glass fibers. The glass fiber ratio can alternatively be different. In other alternative embodiments of the end caps 2, they consist, for example, of one of the thermoplastics (polyamide, polycarbonate, etc.).) or from one of the thermosets, which generally exhibit higher resistance to thermal stress than thermoplastics. The specific examples of materials mentioned above are for illustrative purposes only and do not constitute an exhaustive list of all usable materials. A person skilled in the art would also have no problem using any other known electrically non-conductive material.

[0027] In the illustrated first embodiment of the fuse according to the invention, a fusible element 4 made of an electrically conductive material, such as copper, silver, or various alloys, is arranged in the housing 1. Such a fusible element 4 is generally known in the prior art and is also referred to as a fusible link. The fusible element 4 has an exemplary wire or strip shape. As in the Fig. As shown in the longitudinal section in Figure 2, the fusible element 4 is located inside the housing 1 and extends axially between the two ends of the housing 1. The fusible element 4 provides overcurrent protection, as it melts when too much current flows through it. This principle, as well as the specific materials of the fusible element, are well known in the prior art. As also shown in the Fig. As can be seen in Figure 2, the housing 1 is filled with an extinguishing agent 5, e.g. quartz sand, to better extinguish the electric arc and interrupt the subsequent current flow.

[0028] The melting element 4 electrically connects the contacts 3, wherein in the illustrated first embodiment the two contacts 3 are L-shaped and the contacts 3 are electrically connected to both ends of the melting element 4. As in the Fig. As shown in Figure 2, the contacts 3 comprise a first part located at each end of the housing 1, i.e., at the point where the through cavity of the housing opens. The shape of this first part of the contact 3 is adapted to the cross-section of the housing 1; that is, it has a circular cross-section if the housing 1 has a circular cross-section, or a square or other cross-section if the housing has such a square or other cross-section. The respective end of the melting element 4 is electrically connected to this first part of the contact 3. In this context, it should be noted that the end cap 2 is shaped to cover each end of the housing 1, including the first part of the contact 3.Specifically, this means that the end cap 2 includes a cavity whose inner diameter 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 used as shown in the diagram. Fig. 2 can be seen, placed over the first part of the contact 3 and the outer surface of the housing 1.

[0029] In the first embodiment, each contact 3 then comprises according to the Fig. 1 and Fig. 2 a second part of the contact 3, which is perpendicular to the first part of the contact 3 and extends axially outwards through the respective end cap 2 from the housing 1. For this reason, an opening for the passage of the second part of the contact 3 is provided in each end cap 2. The contacts 3 are made of electrically conductive material, typically metal, and are shaped so that they can be connected to the protected device; for example, their second part is shaped so that it can 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 illustrated first embodiment, the second part of the contact 3 is longer than the first part of the contact 3; however, in an alternative embodiment, the second part of the contact 3 can be the same length as the first part of the contact 3 or even shorter.

[0030] The first embodiment described above can be further modified in various ways to create several alternative embodiments of the fuse. For example, the housing 1 is not filled with extinguishing agent 5. In another alternative embodiment, the fuse comprises a plurality of fusible elements 4, i.e., a plurality of fusible conductors. In yet another alternative embodiment, the end caps 2 are not pressed onto the outer surface of the housing 1, but rather glued onto it.

[0031] In another alternative embodiment of the safety device, which we refer to as the second embodiment and which is described in the Fig. As shown in Figure 3, the contacts 3 are connected by a fusion element 4, so that they represent an extension of the fusion element 4 at its two ends. In other words, this means that the contacts 3 consist of the same part as the fusion element 4 and together with the fusion element 4 form a single unit. The dividing line between the fusion element 4 and the contacts 3 is then formed by a weakening of the part of the fusion element 4 located inside the housing 1 relative to the contacts 3, or by a strengthening of the contacts 3 relative to the fusion element 4. This weakening of the fusion element 4 or the strengthening of the contacts 3 is shown in the Fig. 3. In practice, in the event of an overcurrent, only the weakened part (corresponding to the melting element 4) melts, while the stronger parts (corresponding to the contacts 3) remain undamaged. The melting of the melting element 4 interrupts the conductive connection between the contacts 3.

[0032] The other parts of the fuse, i.e., the housing 1 and the end caps 2, are designed in the second embodiment in the same way as in the first embodiment described above, but the fuse in the second embodiment additionally includes two front plates 6. As in the Fig. As can be seen in Figure 3, these front plates 6 are arranged at the respective ends of the housing 1, i.e., at the point where the continuous cavity of the housing opens. The front plates 6 are thus located in the same space as the first parts of the contacts 3 according to the first embodiment. Fig. 1 and Fig.2. Just as these first parts of the contacts 3 in the first embodiment of the fuse are, the front plates 6 in the second embodiment of the fuse are also adapted in shape to 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 includes a cavity whose inner diameter corresponds to the outer diameter of the housing 1 and the front plate 6, or is slightly larger than the outer diameter of the housing 1 and the front plate 6. This allows the end cap 2 to be fitted over the front plate 6 and the outer surface of the housing 1.

[0033] In contrast to the first part of the contacts 3 of the first embodiment, the front plates 6 of the second embodiment do not serve for the electrically conductive connection of the melting element 4. Instead, each front plate 6 includes an opening for the passage of a melting element 4, which is closed off by contacts 3. Further openings are subsequently formed in both end caps 2, with these openings being arranged coaxially with the openings in the two front plates 6. This allows the contacts 3, which close off the melting element 4, to pass through the front plates 6 and then axially out of the housing 1 through the end caps 2. In the second embodiment, the front plate 6 is in contact with the respective contact 3, but is not electrically connected to the contact 3.Alternatively, the second embodiment can be modified so that the front panel 6 is conductively connected to the corresponding contact 3. Industrial applicability

[0034] The electrical fuse described above can be used to protect various installations, including devices and parts thereof that use the power grid for their function, against overcurrents. Reference symbol list 1 case 2 End closure 3 Contact 4 Melting element 5 extinguishing agents 6 Front panel QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 99 / 40599 A1

[0003] WO 2013 / 063037 A1

[0004] US 6653925 B1

[0005] US 5905426 A [0006, 0010] WO 2018 / 089156 A1

[0007] US 2011298577 A1

[0009]

Claims

[1] An electrical fuse comprising a housing (1) having a first end and a second end, the electrical fuse further comprising two end caps (2) arranged individually at the first end and the second end of the housing (1), two contacts (3) and at least one fusible element (4) made of electrically conductive material arranged inside the housing (1), wherein the contacts (3) are electrically connected to each other by the fusible element (4) and extend axially through the end caps (2) in a direction away from the housing (1), characterized by , that the end closures (2) are made of electrically non-conductive material. [2] Electrical fuse according to claim 1, characterized by , that the electrically non-conductive material of the end closure (2) is a plastic material. [3] Electrical fuse according to claim 2, characterized by, that the electrically non-conductive material of the end closure (2) is a glass fiber modified polyamide. [4] Electrical fuse according to any one of the preceding claims, characterized by , that the end closures (2) are pressed onto the outer surface of the housing (1). [5] Electrical fuse according to any one of the preceding claims, characterized by , that each contact (3) comprises a first part of the contact (3) which is electrically conductively connected to the melting element (4) and a second part of the contact (3) which extends perpendicularly from the first part of the contact (3), wherein the second part of the contact (3) passes axially through the end closure (2).

Images