EP3210231B1

EP3210231B1 - Electric fuse

Info

Publication number: EP3210231B1
Application number: EP14835723.9A
Authority: EP
Inventors: Brane Lebar; Darko Kos
Original assignee: Razvojni Center Enem Novi Materiali doo
Current assignee: Razvojni Center Enem Novi Materiali doo
Priority date: 2014-10-24
Filing date: 2014-12-05
Publication date: 2020-07-01
Anticipated expiration: 2034-12-05
Also published as: PL3210231T3; SI24871A; EP3210231A1; PT3210231T; WO2016064352A1; ES2819289T3; SI24871B

Description

The invention concerns an electric fuse with knife-blade contacts. Such inventions belong to electricity, namely to basic electric elements, namely to fuses in which the electric current flows through a part of fusible material and this current is interrupted by means of displacement or interruption thereof in the case of excessive current, namely to fuses with knife-blade-end contacts, and at the same time such invention may also concern the construction concept of the melting member as such.
The purpose of the invention is to prevent a fuse with knife-blade contacts from formation of electric arc in the area between said knife-blade contacts instead of increasing the length of the melting member and the casing of the fuse.
A fuse is disclosed in US 2008/0122574 A1 , which comprises a tubular casing, consisting of electric insulating material, which is on its both terminal portions closed by means of rigid covers. Each of said covers is furnished with a knife-blade contact, which consists of electric conductive material and is firmly connected therewith. A melting member is mounted inside of said casing and is conceived as a flat band consisting of electric conductive material having a pre-determined electric resistance as well as a pre-determined length and thickness. Said band is on the one hand in the area of its terminal portions electrically interconnected with said blade-knife contacts and is on the other hand furnished with a plurality of weak zones, which are formed as perforations in said band between both dominant surfaces thereof and arranged equidistantly along the band and each per se extend in the transversal direction of the band. Each of said weak zones is formed as a plurality of throughout passages, which are equidistantly arranged in the transversal direction of the band, so that the cross-section of the melting member in each weak zone is pre-defined and is smaller than the cross-section of any other area of said melting member. The interior of said casing is filled with a granulated non-flammable means i.e. a filler, in particular with a sand on the basis of silica, by which said melting member is surrounded. In addition to that, said melting member is surrounded by an elastomeric sheath, which is situated toward the middle if the melting member, since most fuses "open" in the middle of the melting member. Said sheath generally consists of silicone and can also extend along the entire length of the melting member.
Moreover, a circuit-protecting fuse is disclosed in US 4,032,879 , which also comprises a tubular casing, which consists of electric insulating material and is on its both terminal portions closed by means of rigid covers. Each of said covers is furnished with a knife-blade contact, which consists of electric conductive material and is firmly connected therewith. A melting member is mounted inside of said casing and is conceived as a flat band consisting of electric conductive material having a pre-determined electric resistance as well as a pre-determined length and thickness, wherein said band is on the one hand in the area of its terminal portions electrically interconnected with said blade-knife contacts and is on the other hand furnished with a plurality of weak zones. In said weak zones arc quenching means are attached to the melting member, namely disc-formed members consisting of a very special acetal resin, which by high temperature releases a deionizing gas. Such discs, which are just mechanically attached to the melting member are located apart from each other and each per se surround the melting member. Consequently, gasses are released from said very special material, which also means that physical properties of such material are quickly and essentially changed, starting from the very beginning of withstanding to the effects of an electric arc. Such discs appear to be able to act as thermal insulators, but cannot prevent the other arc products like flame and hot gasses from progressing along the fuse.
Still further, an electric fuse with knife-blade contacts is disclosed in EP 1 403 894 A1 as well as in DE 197 23 540 A1 . In both cases, the fuse comprises a tubular casing, which consists of an electric insulating material and is on its both terminal portions closed with rigid covers. Each of said covers is furnished with a so-called knife-blade contact, which is made of an electric conductive material and is insertable into appropriate fork-shaped seat, which consists of an electric conductive material and is integrated into each electric circuit, which is protected against the electric overloading by means of said fuse. A melting member is mounted within said casing between said apart from each other protruding knife-blade contacts, and is electrically interconnected with each of said contacts and surrounded with a granulated non-flammable means, in the practice usually with a sand on the basis of silica. Said melting member is conceived as a relatively thin band and consists of a metallic material having a pre-determined electric resistance, and is moreover furnished with throughout passages, which are equidistantly arranged along said band and by means of which weak zones are formed due to obtaining a pre-determined cross-section of said melting member, which together with said material with a pre-defined electric resistance defines the nominal capacity of the fuse i.e. conditions in which the material of said melting member is overheated and molten in the case of overloading of the electric circuit, by which the melting member and consequently also the electric circuit is then interrupted. The state of the art fuse is usually furnished with an indicator, by means of which interruption of the melting member can be visually detected from the outside.
Still further, a form fitting arc barrier for fuse links is disclosed in WO 96/41360 .
In the practice, the previously described fuse is functioning properly in the sense of protecting alternating electric circuits. When used in direct electric circuit, a huge problem occurs due to formation of the electric arc within the casing despite to interruption of the melting member. Such circuits are generally established in the field of photovoltaic appliances and are in modern electricity commonly known. Namely, when such formed electric arc progresses outside of the casing, in particular between the casing and anyone of the covers with knife-blade contacts, there is always the danger of generating fire. Consequently, in the case of higher values of direct voltage, a fuse with an essentially longer casing and melting member must be used, which leads not only to increasing of expenses but also to problems in the sense of inserting the fuse into existing standardized seats, which are commonly used in the practice.
The present invention refers to an electric fuse, which generally comprises a tubular casing, which consists of electric insulating material and is on its both terminal portions closed by means of rigid covers, wherein each of said covers is furnished with a knife-blade contact, which consists of electric conductive material and is firmly connected therewith, while a melting member is mounted inside of said casing and is conceived as a flat band consisting of electric conductive material having a pre-determined electric resistance as well as a pre-determined length and thickness, wherein said band is on the one hand in the area of its terminal portions electrically interconnected with said blade-knife contacts and is on the other hand furnished with a plurality of weak zones, which are formed as perforations in said band between both dominant surfaces thereof and arranged equidistantly along the band and each per se extend in the transversal direction of the band. Each of said weak zones is formed as a plurality of throughout passages, which are equidistantly arranged in the transversal direction of the band, so that the cross-section of the melting member in each weak zone is pre-defined and is smaller than the cross-section of any other area of said melting member, and at the same time the interior of said casing is filled with a granulated non-flammable means, in particular with a sand on the basis of silica, by which said melting member is surrounded.
Said technical problem is solved by means of features, which are included in the independent claim. Namely at least on each terminal portion of said melting member, namely between each belonging blade-knife contact and each neighboring weak zone, on both apart from each other facing dominant surfaces of said melting member, at least one barrier is arranged, which consists of a flexible and at least short-term thermally resistant material and which is adapted to prevent progression of the electric arc and extends along each of said dominant surfaces in the transversal direction of said melting member along the complete width thereof.
At least one further barrier consisting of flexible and at least short-term thermally resistant material is arranged on both apart from each other facing dominant surfaces of the melting member between at least two further weak zones thereof. A pre-determined distance between each of the terminal barriers, which are arranged closest to the belonging knife-blade contacts, and each knife-blade contact, is at least approximately 15% of the length of the melting member. It is particularly preferred, if in addition to said terminal barriers at least one barrier is available between each pair of each neighboring weak zones of the melting member. Moreover, the preferred embodiment of the invention provides that each barrier has approximately semi-circular profile with a diameter of 2 - 6 mm, preferably 3 - 4 mm, and consists of silicone, which is shortly thermally resistant up to 2000°C.
The invention will be described on the basis of an embodiment, which is presented in the enclosed drawings, wherein

Fig. 1: is a schematic cross-section of the fuse according to the invention along the first diametrical plane thereof; and
Fig. 2: is also a schematic cross-section of the fuse according to Fig. 1 along the second diametrical plane thereof, which is perpendicular with respect to previously mentioned plane.

The electric fuse as shown in Fig. 1 and 2 comprises a tubular casing 1, which consists of electric insulating material, in this particular case of ceramics. Said casing 1 is on its both terminal portions 11, 12 closed by means of rigid covers 21, 22, which are in the shown embodiment made of relatively thick metallic plates. Each of said covers 21, 22 is furnished with a knife- blade contact 210, 220, which consists of electric conductive material and is firmly connected with it, wherein said knife- blade contacts 210, 220 are arranged to extend along the central geometric axis of said casing 1 of the fuse and protrude apart from each other.
A melting member 3 is mounted inside of said casing 1 and is conceived as a flat band consisting of electric conductive material having a pre-determined electric resistance as well as a pre-determined length L (Fig. 1) and thickness, wherein said band is on the one hand in the area of its terminal portions 31, 32 electrically interconnected with said blade- knife contacts 210, 220 and on the other hand furnished with a plurality of weak zones 30, 30', 30", which are arranged equidistantly along the band and each per se extend in the transversal direction of the band. Thickness of said band is usually between 0,04 and 0,24 mm. Said weak zones 30, 30', 30" are similarly like in the state of the art fuses available as perforations on said band extending between both dominant surfaces 33, 34 thereof, and each of said weak zones 30, 30', 30" is formed as a plurality of throughout passages 300, which are equidistantly arranged in the transversal direction of the band. Consequently, the cross-section of the melting member 3 in each weak zone 30, 30', 30" is pre-defined and is smaller than the cross-section of any other area of said melting member 3.
Moreover, the interior of said casing 1 is filled with a granulated non-flammable means 4, in particular with sand on the basis of silica, by which said melting member 3 is surrounded.
As evident in Figs. 1 and 2, at least on each terminal portion 31, 32 of said melting member 3, namely between each belonging blade- knife contact 210, 220 and each neighboring weak zone 30, 30', 30", on both apart from each other facing dominant surfaces 33, 34 of said melting member 3, at least one barrier 51, 51', 51"; 52, 52', 52" is arranged, which is adapted to prevent progression of the electric arc and extends along each of said dominant surfaces 33, 34 in the transversal direction of said melting member 3 along the complete width thereof, and which consists of flexible and shortly thermally resistant material.
In accordance with the invention it is furthermore preferred, if at least one further barrier 51, 51', 51"; 52, 52', 52" consisting of flexible and shortly thermally resistant material is arranged on both apart from each other facing dominant surfaces 33, 34 of the melting member 3 between at least two further weak zones 30, 30', 30" thereof.
A pre-determined distance T between each of the terminal barriers 51, 51', 51"; 52, 52', 52", which are arranged closest to the belonging knife- blade contacts 210, 220, and each knife- blade contact 210, 220, should be approximately 15% of the length L of the melting member 3.
A further embodiment of the fuse provides that in addition to said terminal barriers 51, 51', 51"; 52, 52', 52" at least one barrier 51, 51', 51"; 52, 52', 52" is available between each pair of each neighboring weak zones 30, 30', 30" of the melting member 3.
The invention further provides that each barrier 51, 51', 51"; 52, 52', 52" has approximately semi-circular profile, wherein the diameter D of each barrier 51, 51', 51"; 52, 52', 52" should be 2 - 6 mm, preferably 3 - 4 mm. Each barrier 51, 51', 51"; 52, 52', 52" consists of silicone, which is at shortly thermally resistant up to 2000°C. A material, which is suitable for producing said barriers 51', 51"; 52, 52', 52", is at present commercially available under the commercial name »3M Fire Barrier 2000+« or »FIRESTOP«, and is actually a silicone with added aluminium trihydrate Al(OH)₃ and/or boron nitride BN.

Claims

Electric fuse, comprising a tubular casing (1), which consists of electric insulating material and is on its both terminal portions (11, 12) closed by means of rigid covers (21, 22), wherein each of said covers (21, 22) is furnished with a knife-blade contact (210, 220), which consists of electric conductive material and is firmly connected therewith, while a melting member (3) is mounted inside of said casing (1) and is conceived as a flat band consisting of electric conductive material having a pre-determined electric resistance as well as a pre-determined length (L) and thickness, wherein said band is on the one hand in the area of its terminal portions (31, 32) electrically interconnected with said blade-knife contacts (210, 220) and on the other hand furnished with a plurality of weak zones (30, 30', 30"), which are formed as perforations in said band between both dominant surfaces (33, 34) thereof and arranged equidistantly along the band and each per se extend in the transversal direction of the band, wherein each of said weak zones (30, 30', 30") is formed as a plurality of throughout passages (300), which are equidistantly arranged in the transversal direction of the band, so that the cross-section of the melting member (3) in each weak zone (30, 30', 30") is pre-defined and is smaller than the cross-section of any other area of said melting member (3), and wherein the interior of said casing (1) is filled with a granulated non-flammable means (4), in particular with a sand on the basis of silica, by which said melting member (3) is surrounded, characterized in that on each terminal portion (31, 32) of said melting member (3), namely between each belonging blade-knife contact (210, 220) and each neighboring weak zone (30, 30', 30"), on both apart from each other facing dominant surfaces (33, 34) of said melting member (3), at least one barrier (51, 51', 51"; 52, 52', 52") is arranged, and in that at least one barrier (51, 51', 51"; 52, 52', 52") is available between each pair of each neighboring weak zones (30, 30', 30") of the melting member (3), wherein each of said barriers (51, 51', 51"; 52, 52', 52") has approximately semi-circular profile and consists of a flexible and shortly thermally resistant material and is adapted to prevent progression of the electric arc and extends along each of said dominant surfaces (33, 34) in the transversal direction of said melting member (3) along the complete width thereof, and wherein a pre-determined distance (T) between each of the terminal barriers (51, 51', 51"; 52, 52', 52"), which are arranged closest to the belonging knife-blade contacts (210, 220), and each knife-blade contact (210, 220), is approximately 15% of the length (L) of the melting member (3).
Electric fuse according to Claim 1, characterized in that the diameter (D) of each barrier (51, 51', 51"; 52, 52', 52") is 2 - 6 mm.
Electric fuse according to Claim 2, characterized in that the diameter (D) of each barrier (51, 51', 51"; 52, 52', 52") is 3 - 4 mm.
Electric fuse according to anyone of the preceding Claims, characterized in that each barrier (51, 51', 51"; 52, 52', 52") consists of silicone, which is at least shortly thermally resistant up to 2000°C.