Electric fuse with knife blade contacts and a complex melting assembly

Abstract

Invention refers to an electric fuse (1) with knife blade contacts (5, 5') and a complex melting assembly (4). The purpose of the invention is creation of an electric fuse (1) with knife blade contacts (5, 5') and a complex melting assembly (4), which should upon integration into a high-performance DC electric circuit assure a durable and reliable protection thereof despite to occasionally interrupting and re-establishing the electric circuit, and also despite to essential oscillations of the electric voltage within said electric circuit, in which the fuse (1) is integrated, wherein also all loadings, to which said melting assembly (4) is exposed, would have to be uniformly distributed among all disposable single melting members (4', 4", 4"', 4iv, 4v, 4vi) in said melting assembly (4). According to the invention, the throughout passage (200) within the casing (2) of the fuse is cylindrical, and the transversal cross-section thereof is a regular circle. A melting assembly (4) is inserted within said throughout passage (200) and consists of six equidistantly spaced melting members (4', 4", 4"', 4iv, 4v, 4vi), which are arranged on diagonals of a regular hexagon, inscribed in said regular circle of the cross-section.

Description

[0001] Electric fuse with knife blade contacts and a complex melting assembly

[0002] The present invention generally refers to an electric fuse with knife blade contacts as well as with a complex melting assembly, consisting of several melting members. Such inventions belong to electricity, namely to basic electric components, namely to fuses, in which the electric current flows through a part of a meltable material, which is by successive current interrupted or displaced, and in particular to fuses with knife blade contacts. Pursuant to International Patent Classification, such an invention should belong to the class H OI H 85 / 153.

[0003] The purpose of the invention is to conceive an electric fuse with knife blade contacts and a complex melting assembly, which should, upon integration thereof into an electric circuit, be capable of establishing a reliable and long-term protection of a heavy duty direct current (DC) electric circuit, in which the electric voltage values should be within the range of at least 1000 - 1500 V, even despite to occasional switching-off or switching-on said electric circuit, and also despite to essential variations of the electric voltage within said electric circuit, in which such fuse is integrated, wherein such fuse should also be capable of withstanding the forces which are generated by such electric current within each relevant electric conductor and also to any other other mechanical loads, which may occur in such heavy duty electric conductors, which are intended for transmission of e.g. 100 kA or even higher electric current, and wherein during operation of such fuse all electrical, mechanical and thermal loadings should be uniformly distributed to all disposable melting members within said complex melting assembly. A knife blade fuse is disclosed in EP 0 088 297 A2. Such fuse comprises a tubular casing, consisting of an electric insulating material, usually of ceramics. A similar fuse is also disclosed in DE 25 28 949 Al, while the fuse casing as such is disclosed in SI 26217 A. Regarding all previously mentioned solutions, the casing is a tubular body with a typical cross-section, which is open on its both terminal areas, and the external silhouette of which is approximately square or rectangular, while its internal silhouette is usual square or rectangular with slightly rounded corner areas, or may also be a circle, which is slightly flattened in one or two directions. Regarding said cross-section, there are throughout round bores provided in its comer areas, which extend along the complete length of the casing. Such casing is on each of its terminal area ended with a plane and smooth front surface. A covering plate is placed onto each one of said both front surfaces, which consists of an electric conductive material like brass or any other suitable alloy on the basis of copper. Thus, both covering plates are each per se tightly matching placed on corresponding front surfaces of the casing and are connected with each other by means of suitable connecting members like screws or rivets, which are inserted in said throughout bores in the comer areas of the casing. Within the interior of the fuse casing there is a melting member, which is soldered onto each one of said covering plates and is moreover, in most of modem commercially available fuses, surrounded with a granulated fireproof arc-extinguishing material, e.g. with silica sand. In fact, such concept of the fuse is already suitable for integration into an electric circuit and is capable for protection of said circuit against potential electric overload. Namely, as soon as such fuse is integrated within an electric circuit, electric current may flow between both electric conductive covering plates and throughout the melting member, which is heated and starts melting at a predetermined nominal value of the electric current, upon which the electric circuit becomes interrupted. However, within the context of the present invention, fuse with a knife blade contacts of NV -type is really relevant, which is as such also disclosed in standards (e.g. in group IEC EN 60269 or DIN 43620). As correspondingly also mentioned in said EP 0 088 297 A2, each one of said covering plates is furnished with a knife blade contact. Each one of said knife blade contacts is in fact a relatively rigid metallic band, consisting of an electric conductive material, and is firmly attached to the surface of said covering plate, protruding thereby apart from the melting member and in a direction rectangular to said covering plate, wherein the knife blade contacts on both covering plates are arranged co-axially with each other and within the same plane, namely within the central longitudinal plane of the fuse as such, along which regularly also the melting member should extend. Consequently, the fuse is by means of said knife blade contacts in a detachable manner insertable into an electric circuit, which is for such purpose furnished with standardized fork-like contacts, namely between two pairs of mutually spaced elastically deformable and electric conductive cantilevers, so that each blade knife contact of the fuse, when properly forced, may be jammed between each pair of them. In order to assure a precise and reliable inserting of each knife blade contact, at least one of its longitudinal edges, or both of them contact is properly inclined, which is connected with naming of such type of the fuse.

[0004] However, the present invention as such is not limited to the previously disclosed concept of knife blade contacts on the fuse. There is also another group of knife blade fuses, which are commercially available and are, similarly like the fuses according to EP 0 088 297 A2 ali DE 25 28 949 Al, furnished with knife blade contacts, which are however not foreseen for insertion into said fork-like contacts and jamming therein, but for interconnection with electric conductors by means of screws. In such case, each knife blade contacts is firmly, namely in a non- detachable manner, connected with a belonging covering plate and is protruding apart from the melting member, so that both knife blade contacts on the fuse are arranged coaxially and within the same plane, wherein each knife blade contact is furnished with a throughout bore, or a suitable recess, which is adjusted for receiving a screw, by which a reliable interconnection between an electric conductor and a suitable connecting eye on said electric conductor may be established. Thus, the expression “knife blade contact” should in this application include both previously described types of knife blade contacts.

[0005] In practically all known solutions of fuses with knife blade contacts, problems may arise during realization of said non-detachable interconnection between a covering plate and the belonging knife blade contact. As mentioned, the covering plate consists of an electric conductive material, like brass or another suitable alloy on the basis of copper, and the same applies also for the belonging knife blade contact. The manufacturing process however requires separately manufacturing of covering plates, on the one hand, and knife blade contacts, on the other hand. In order to enable assembling of such covering plate and the belonging knife blade contact, the covering plate is usually furnished with a throughout passage, the silhouette of which should correspond to the silhouette of the knife blade contact. Consequently, each knife blade contact is insertable into said passage within the covering plate in a position rectangular to said covering plate. In such position, said non-detachable interconnection between the covering plate and the knife blade contact is established by means of soldering, wherein the molten solder material is brought into a gap between said passage within the covering plate and the circumference of the knife blade contact within said passage of the covering plate. But in practice it may happen that even a visually controlled and perfectly manufactured fuse may in fact include serious deficiencies, which can however not be detected and evaluated in advance. By using such method of manufacturing, it is quite impossible to ensure that the said gap between the passage in the covering plate and the surface of the knife blade material is completely filled with the soldering material along the complete depth of the passage. Consequently, in practice during the use of such fuse all the areas within said passage, which are not covered by the soldering material, are exposed to corrosion. In addition to that, electric circuits, when protected by means of such a fuse, are in most cases exposed to dynamic conditions, which means that during operation of the electric circuit heating and cooling may occur, which leads to extensions and shrinking or similar thermal effects, which may during the time lead to mechanical weakening of such soldered interconnection. On the other hand, a huge problem may also result from purely mechanical stresses, which may occur in heavy-duty electric circuits, in which the electric or magnetic forces due to electric current, in particular by switching-on or switching-off, may be so high that an usual fuse with knife blade contacts would be pulled-out from the standardized fork-like contacts. This is also the reason why in such cases the fuse must be via the knife blade contacts by means of screws connected with the belonging electric conductors, although even in such state all generated loadings are still transmitted via the knife blade contacts, covering plates and the casing, under provision that the melting member within the interior of the fuse casing may all the time be maintained in its perfect condition and prepared for interruption of the electric circuit when needed, e.g. as soon as the electric current value would overcome a pre-determined nominal value, or when a short circuit would occur.

[0006] In widely used fuses, serving for protection of common electric circuits, a melting assembly is normally a single straight and properly weakened strip consisting of an electric conductive metallic material, which is on each one of its terminal areas soldered to an electric conductive covering plate as placed onto the fuse casing, and is therefore mechanically and electrically connected with said covering plates. In such case, said melting assembly comprises a single melting member, but in particular in fuses for protection of highly loaded electric circuits, said melting assembly may also be more complex, which means that the melting assembly may comprise two, three or even up to twelve metallic strips, which are in a suitable pattern arranged within the interior of the electric insulating tubular fuse casing, such that they are sufficiently spaced apart from each other and are also, each per se, surrounded with the previously mentioned arc extinguishing material and both mechanically and electrically connected with said covering plates. A predetermined electric resistance of each one of said strips, either in an uniform or a complex melting assembly, is determined on the one hand by selection of a suitable material of said strip of a pre-determined thickness and width, or on the other hand also by providing a sequence of weak areas for reduction of the cross-section of the strip, which are equally spaced apart from each other in a longitudinal direction of the strip, wherein each one of said weak areas is in fact a sequence of throughout bores of a pre-determined diameter, which are equidistantly arranged in a transversal direction of said strip, by which a sequence of bridges with a predetermined width is formed, by which the cross-section of the strip, which is available for conducting of the electric current through the fuse, is exactly determined in advance. Such concept of providing a melting member is disclosed in EP 3 210 231 Bl, although the solution disclosed therein is merely dealing with extinguishing of electric arc by means of silicone barriers, which are applied onto the melting member on the surface thereof between the neighboring weak areas.

[0007] Still further, a low voltage fuse is disclosed in EP 3 270 403 Bl, which is intended for protection of DC electric circuits, in which the electric voltage should not exceed 900 V, while the electric current should be at least 250 A. Such fuse comprises a tubular electric insulating body, as well as an electric conductive melting member extending there-through. Regarding its transversal cross-section in a plane perpendicularly with regard to the longitudinal geometric axis thereof, said body is rectangular or at least approximately rectangular, wherein said melting assembly, which extends through it, comprises several, namely up to four, or up to eight, melting members, which are each per se shaped as s perforated strip, wherein each one of said melting members is placed on a diagonal of the said approximately rectangular cross-section. In practice, external dimensions of the fuse are limited by standards, by which dimensions of connecting arrangements for mounting of fuses into electric panels i.e. into each electric circuit are determined.

[0008] Whenever such melting assembly, comprising four melting members arranged on diagonals of said rectangle, is applied, said melting members are uniformly exposed to all loadings, but in extremely loaded electric circuits applying just four melting members might sometimes be insufficient. Whenever eight melting members are used, four of them are located on diagonals, and four of them on each belonging axis of symmetry. In a rectangle, lengths of axis of symmetry differ from each other and are also shorter than the length of diagonals, which means that two melting members on the shorter line of symmetry are essentially more distanced apart from the melting members on diagonals that the melting member on a longer line of symmetry. Variations in operation of the electric circuit, e.g. in photovoltaics, may lead to heating and cooling of melting members, so that different thermal conditions may occur in certain zones within the fuse casing, when comparing e.g. zones where the melting members are more concentrated, i.e. on terminal portions of the longer line of symmetry, or the central zone. Such heat concentrations may lead to early melting of the most exposed single melting member, despite to the fact that the nominal capacity of the fuse has not been exceeded at all. Upon melting of just one melting member of eight, just seven melting members remain capable to operate, which are due to such reduction unable to take over a complete nominal capacity of the fuse, and moreover, distribution of thermal loadings among them becomes even much more inappropriate. When protecting such circuits by using such fuses with melting members, each melting member is furnished with said weak areas and is intended to interrupt the electric circuit as soon as the pre-determined value of the electric current is achieved. Due to said variations of the electric current flowing through the melting member, the melting member may be occasionally exposed to intensive heating, although the electric current is still below the pre-determined nominal value, which is required for interrupting of the electric circuit, upon which, due to decreasing of the electric current, it is cooled again. Consequently, due to such randomly repeating and usually quite intensive heating and extending, which is then followed by cooling and shrinking, such melting member is therefore exposed to intensive dynamic mechanical stresses, which may during the time lead to damages on the melting member, or even to interruption thereof, although from purely electric point of view the pre-determined nominal electric current value has never been reached or even exceeded at all. Namely, the melting member is mechanically connected with both covering members, which are spaced from each other at an unchangeable distance, and is by heating thereof correspondingly extended, by which the previously mentioned bridges between each two throughout bores in each weak area are exposed to plastic deformations. Namely, when the melting needs some freedom to extend, which is due to said unchangeable distance between the covering plates impossible, then in plasticized state of the material thereof in said weak area said bridges are exposed to compression, which leads to enlargement of cross-section of the weak area, which may lead to undesired change of the electric resistance of the fuse, which is a crucial characteristics thereof. But in addition to that, as soon as the electric current through the fuse is decreased, such plasticized material is solidified and is during subsequent cooling the melting member would need some freedom for shrinking, which is due to said unchangeable distance between the covering plates also impossible. Consequently, said bridges between bores in the weak area on the melting member may upon cooling thereof be exposed to essential tension stresses. Those skilled in the art will understand that such repeating exposure of the melting member to essential oscillations of the electric current as well as to related variations of temperature may even during a regular operation of the fuse gradually lead to essential mechanical damages on the melting member, which are expressed either as cracking or interruption of the material in the area of certain bridges, which however leads to reduction of the cross-section of the melting member, which may result in interruption of the electric circuit through the fuse, despite to the fact, that the maximally allowed electric current value has never been achieved, or even exceeded, at all.

[0009] The present invention concerns an electric fuse with knife blade contacts and a complex melting assembly, wherein such fuse generally comprises at least

[0010] - a tubular casing, which consists of electric insulating material and is in at least two of its corner areas furnished with a throughout bore, which extends in parallel with a central longitudinal geometric axis of the casing as such, wherein said casing is on each one of its terminal areas furnished with a flat and smooth front surface, and wherein said front surfaces are arranged in parallel with each other and perpendicularly with regard to said central longitudinal geometric axis of the casing as such;

[0011] - two covering plates, which are formed of a sufficiently rigid and electric conductive metallic material, and each one of them is tightly matching placed onto a belonging front surface of the casing, so that the throughout passage within said tubular casing, namely the cross-section of said internal throughout passage in said tubular casing, is completely covered by them, wherein said covering plates are interconnected with each other by means of attaching elements, which are inserted in said throughout bores in said comer areas of the casing and simultaneously extend through correspondingly arranged bores in said covering plates, and wherein each one of said covering plates is furnished with a central passage of a pre-determined shape as well as with at least two further throughout bores, which are arranged adjacent to the lastly mentioned passage and are adjusted for passing of said attaching means there-through;

[0012] - two knife blade contacts, consisting of a sufficiently rigid electric conductive metallic material, wherein each one of said knife blade contacts is arranged on the one of both opposite terminal portions of the casing of said fuse, and wherein each one of said knife blade contacts comprises, on the one hand, a blade, which is conceived as a straight and suitable rigid bearing member of a pre-determined thickness, width and length, and on the other hand an attaching member, which is conceived as a flange, adjusted for resting on a belonging covering plate and furnished with at least two throughout bores, which are arranged coaxially with said throughout bores on the belonging covering plate, so that said knife blade contacts are inserted through said central passages in said covering plates, the previously mentioned pre-determined shape of which is adjusted to the shape of the external silhouette of the transversal cross-section of the blade of each knife blade contact, while the attaching members thereof are arranged within the passage in the casing of the fuse and are each per se by means of suitable connecting means, which are inserted through said throughout bores and throughout the bores in said covering plates, connected with each belonging connecting plate, and wherein said blades of the knife blade contacts are arranged in coplanar and coaxially with each other and, and protrude out from the casing of the fuse apart from each other,

[0013] - a melting assembly, consisting of several single melting members, wherein each of them consists of electric conductive material and is properly weakened in order to allow transmission of the electric current below a pre-determined nominal value, and wherein said melting assembly is arranged within the interior of said throughout passage in the casing of the fuse, and wherein the first terminal portion of each melting member is mechanically connected with the attaching member of the first knife blade contact and is such also electrically connected there-with, while the residual terminal portion of each melting member is mechanically connected with the attaching member of the second knife blade contact and is such also electrically connected there-with; and moreover also

[0014] - a suitable amount of granulated solid filling particles, consisting of non-metallic fireproof electric insulating material, which is suitable for extinguishing of the electric arc, wherein said filling particles are inserted within said throughout passage in the casing of the fuse, so that each one of said melting members in the melting assembly is at least almost completely surrounded by said filling particles.

[0015] In accordance with the proposed electric fuse according to the invention it is however proposed that said throughout passage within said casing of the fuse is cylindrical, so that its transversal cross-section is a regular circle, wherein a melting assembly is inserted within said throughout passage in the casing of the fuse, which consists of six symmetrically arranged and equally with regard to each other spaced melting members, which are arranged on diagonals of an imaginary hexagon as inscribed in a circle of said circular transversal cross-section of the throughout passage in a casing of the fuse, and wherein each of said melting members is spaced apart from the circumferential wall of said throughout passage, as well as that each one of said knife blade contacts is uniformly conceived, namely that the blade and the attaching member of the knife blade contact are formed as perpendicularly with regard to each other extending arms of an uniform T-profile, namely as a web and a flange of a T-profile, wherein the circumferential silhouette of the attaching member of the knife blade contact is a regular hexagon, the diagonal of which is shorter than the diameter of said throughout passage in the casing of the fuse.

[0016] In one of the embodiments of the invention, an arc extinguishing barrier, consisting of a fireproof material, in particular of high-temperature resistant silicone, is formed on the surface of each one of said melting members in the area either between each neighboring weak areas or between the attaching member of the knife blade contact and the nearest weak area, wherein said barrier is shaped as a continuous convex rib, extending transversally with regard to said longitudinal geometric axis of the throughout passage within the casing of the fuse.

[0017] A further embodiment of the invention provides that each one of the melting members in said melting assembly is formed as a strip, which is its longitudinal direction easily deformable, namely extendable or shrinkable, and which consists of electric conductive metallic material having pre-determined melting temperature and electric resistance, and comprises straight terminal areas, extending in a longitudinal direction od said throughout passage within the casing of the fuse and being coplanar with regard to each other, between which there is a corrugated central area, consisting of a sequence of deflections and indentations, which are rectangular in profile and have the same dimensions with regard to each other, namely a pre-determined width C and height B, and which moreover extend equidistantly and in parallel with each other, so that between two neighboring deflections one indentation is available, or vice versa, wherein each weak area comprises a sequence of throughout openings of mutually equal shape and characteristic dimension D, which are equidistantly spaced apart from each other at a distance d, wherein said characteristic dimension D of said throughout openings is smaller than the width C of said deflections and indentations, and wherein said weak areas are formed on just some of all disposable deflections or on just some of all disposable indentations, and are consequently, with regard to said longitudinal geometric axis of the throughout passage within said casing of the fuse always formed only on the one side of each melting member of the complex melting assembly of the fuse.

[0018] In accordance with a preferred embodiment of the invention, the thickness A of the metallic plate or a strip, of which each melting member in the melting assembly is formed, is selected within the range

[0019] 0,04 mm A 0,5 mm, the width d of each one of said bridges between each neighboring throughout openings in each one of said weak areas is selected within the range

[0020] 0,1 mm d 0,5 mm, said height B of deflections as well as of indentations is determined in dependency on said thickness A of the metallic strip, of which each one of said melting members is formed, such that the following condition is fulfilled

[0021] 10 x A B S 40 x A, and said width C of deflections, as well as of indentations, is determined in dependency on said characteristic dimension D of each one of said throughout openings of the metallic strip in each one of said weak areas, such that the following condition is fulfilled

[0022] 1,0 2,0 x D.

[0023] A still further embodiment of the invention provides that at least one of both longitudinal edges on the blade of the knife blade contact is on its both sides inclined and slanted.

[0024] According to the first alternative aspect of the previously mentioned embodiment, said blade of each knife blade contact is furnished with a transversally extending U-shaped recess, which is directed from one longitudinal edge of the blade towards the other longitudinal edge of the blade, and is in such extent spaced apart from the attaching member of the knife blade contact, that a screw or a similar connecting means is insertable there-into due to establishing of a detachable mechanical interconnection between the knife blade contact and a corresponding electric conductor of an electric circuit, into which the fuse is to be integrated.

[0025] According to the second alternative aspect of the previously mentioned embodiment, said blade of each knife blade contact is furnished with a longitudinally extending U-shaped recess, which is directed from the free terminal portion of the blade towards the attaching member of the blade, and is in such extent spaced apart from the attaching member of the knife blade contact, that a screw or a similar connecting means is insertable there-into due to establishing of a detachable mechanical interconnection between the knife blade contact and a corresponding electric conductor of an electric circuit, into which the fuse is to be integrated. The invention will be explained in more detail on the basis of embodiments, which are presented in the attached drawings, where

[0026] Fig. 1 presents a commonly known electric fuse with knife blade contacts and a melting member, in isometric view;

[0027] Fig. 2 presents an electric fuse according to the invention, in a partial longitudinal cross-section;

[0028] Fig. 3 presents a casing of the fuse according to Fig. 2 together with a melting assembly as inserted therein, in a side view;

[0029] Fig. 4 presents a basic embodiment of a knife blade contact on the fuse according to the invention;

[0030] Fig. 5 presents the first alternative embodiment of a knife blade contact on the fuse according to the invention;

[0031] Fig. 6 presents the second alternative embodiment of a knife blade contact on the fuse according to the invention;

[0032] Fig. 7 symbolically presents an embodiment of a single melting member in the melting assembly of the fuse according to the invention; while

[0033] Fig. 8 presents a detail W, namely a concept of creation of said melting member in a melting assembly of the fuse according to the invention.

[0034] An usual and nowadays commercially still available electric fuse 1 with knife blade contacts 5, 5' and a complex melting assembly 4 is presented in Fig. 1. Such fuse comprises at least a casing 2 with a longitudinal central geometric axis 20, which is as such presented in Fig. 2, and is furnished with a melting assembly 4, which is mounted within a throughout passage 200 within said casing 2. Such fuse 1 is furnished with knife blade contacts 5, 5’, which are, regarding the context of this application, just symbolically presented in Fig. 1 and are created in accordance with relevant standards in order to be insertable into a standardized fork-shaped receiving assembly as a part of an electric circuit, which is intended to be by means of such fuse 1 protected against electric overloading.

[0035] Said tubular casing 2 consists of electric insulating material and is in at least two of its comer areas 21, 22, 23, 24 furnished with a throughout bore 210, 220, 230, 240, extending in parallel with said central longitudinal geometric axis 20 of said casing 2. Moreover, said casing 2 is on each one of its terminal areas furnished with a flat and smooth front surface 251, 252, so that both front surfaces 251, 252) are arranged in parallel with each other and perpendicularly with regard to said central longitudinal geometric axis 20 of the casing 2 as such.

[0036] Said fuse 1 moreover comprises two covering plates 3, 3', which are formed of a sufficiently rigid and electric conductive metallic material, and each one of them is tightly matching placed onto a belonging front surface 251, 252 of the casing 2, by which the throughout passage 200 within said tubular casing 2, namely the crosssection of said internal throughout passage 200 in said tubular casing 2, is completely covered. Moreover, said covering plates 3, 3' are interconnected with each other by means of attaching elements, which are inserted in said throughout bores 210, 220, 230, 240 in said comer areas 21, 22, 23, 24 of the casing 2 and simultaneously extend through correspondingly arranged bores in said covering plates 3, 3'. Each one of said covering plates 3, 3' is furnished with a central passage 31 of a pre-determined shape as well as with at least two further throughout bores 33, 33", which are arranged adjacent to the lastly mentioned passage and are adjusted for passing of attaching means 35', 35" there-through.

[0037] Said two knife blade contacts 5, 5' consist of a sufficiently rigid electric conductive metallic material, and each one of said knife blade contacts 5, 5' is arranged on the one of both opposite terminal portions 201, 202 of the casing 2 of said fuse 1. Each one of said knife blade contacts 5, 5' comprises, on the one hand, a blade 51, 51', which is conceived as a straight and suitable rigid bearing member of a predetermined thickness, width and length, and on the other hand an attaching member 52, 52', which is conceived as a flange, which is adjusted for resting on a belonging covering plate 3, 3' and is furnished with at least two throughout bores 53', 53", which are arranged coaxially with said throughout bores 33', 33" on the belonging covering plate 3, 3'. Consequently, each one of said knife blade contacts 5, 5' is inserted through said central passage 31 in the belonging covering plate 3, 3', the previously mentioned pre-determined shape of which is adjusted to the shape of the external silhouette of the transversal cross-section of the blade 51, 51' of the knife blade contact 5, 5'. Said attaching members 52, 52' of the knife blade contacts 5, 5' are arranged within the passage 200 in the casing 2 of the fuse 1 and are each per se by means of suitable connecting means 35', 35", which are inserted in said throughout bores 53', 53" as well as in said throughout bores 33', 33" on said covering plates 3, 3', connected with each belonging connecting plate 3, 3', wherein however said blades 51, 51' of the knife blade contacts 5, 5' are arranged coaxially with each other and in the same plane, and protrude out from the casing 2 of the fuse 1 apart from each other.

[0038] Said melting assembly 4 of the fuse 1 is complex and therefore consists of several single melting members 4', 4", 4'", 41V, 4V, 4V1, wherein each of them consists of electric conductive material and is properly weakened in order to allow transmission of the electric current below a pre-determined nominal value. As evident in Figs. 2 and 3, said melting assembly 4 is arranged within the interior of said throughout passage 200 in the casing 2 of the fuse 1, such that the first terminal portion 44' of each melting member 4', 4", 4'", 4IV, 4V, 4V1is mechanically connected with the attaching member 52 of the first knife blade contact 5 and is also electrically connected there-with, while the residual terminal portion 44" of each melting member 4', 4", 4"', 41V, 4V, 4V1is mechanically connected with the attaching member 52' of the second knife blade contact 5' and is such also electrically connected there-with.

[0039] In general, such fuse 1 also comprises a suitable amount of granulated solid filling particles 8, which consist of non-metallic fireproof electric insulating material, which is suitable for extinguishing of the electric arc, wherein said filling particles 8 are inserted within said throughout passage 200 within the casing 2 of the fuse 1 , so that each one of said melting members 4', 4", 4"', 41V, 4V, 4V1in the melting assembly 4 is at least almost completely surrounded by said filling particles 8.

[0040] In accordance with the proposed invention, said throughout passage 200 within said casing 2 of the fuse 1 is cylindrical (Fig. 3), so that its transversal crosssection is a regular circle, and a melting assembly 4 is inserted within said throughout passage 200 in the casing 2 of the fuse 1, wherein said melting assembly 4 consists of six symmetrically arranged and equally with regard to each other spaced melting members 4', 4", 4"', 4IV, 4V, 4V1, which are arranged on diagonals of a Active hexagon, inscribed in a circle, defining a circumferential border of said circular transversal cross-section of the throughout passage 200 in a casing 2 of the fuse 1. Each one of said melting members 4', 4", 4"', 41V, 4V, 4V1is spaced apart from the circumferential wall of said throughout passage 200 and is not in contact with said wall, so that that between each melting member 4’, 4", 4'", 41V, 4V, 4V1and said wall also said filling particles 8 can be present. The invention also proposes that each one of said knife blade contacts 5, 5' is uniformly conceived, namely that the blade 51, 51' and the attaching member 52, 52') of the knife blade contact 5, 5' are formed as perpendicularly with regard to each other extending arms of an uniform T-profile, namely as a web and a flange of a T- profile, wherein the circumferential silhouette of the attaching member 52, 52' of the knife blade contact 5, 5' is a regular hexagon, the diagonal of which is shorter than the diameter of said throughout passage 200 in the casing 2 of the fuse 1.

[0041] In one of the embodiments of the invention (Fig. 2), an arc extinguishing barrier 49, 49' is formed on the surface of each one of said melting members 4', 4", 4"', 41V, 4V, 4V1in the area either between each neighboring weak areas 40, 40', 40" or between the attaching member 52, 52' of the knife blade contact 5, 5' and the nearest weak area 40, 40', 40", wherein such barrier 49, 49' is shaped as a continuous convex rib, extending in a transversal direction with regard to said longitudinal geometric axis 20 of the throughout passage 200 within the casing 2 of the fuse 1. Such barrier 49, 49’ consists of a fireproof material, in particular of high-temperature resistant silicone. Whenever the nominal value of the fuse 1 is overcome, and said melting members 4', 4", 4'", 41V, 4V, 4V1start melting, by which gases are generated within said passage 200 and electric arc may start burning in said weak area 40, 40’, 40”. Said barriers 49, 49’ may substantially slow down progression of electric arc along said passage 200 and may essentially contribute to extinguishing of the electric arc within a reasonable time period.

[0042] In a further embodiment of the invention (Fig. 7 and 8) it is foreseen that each one of said melting members 4', 4", 4'", 41V, 4V, 4VIin the melting assembly 4 is formed as a strip, which is its longitudinal direction easily deformable, namely extendable or shrinkable, and which consists of electric conductive metallic material having pre-determined melting temperature and electric resistance. In such case, the melting member 4', 4", 4'", 41V, 4V, 4VIcomprises straight terminal areas 44’, 44”, which extend in a longitudinal direction od said throughout passage 200 within the casing 2 of the fuse 1 and are coplanar with regard to each other, as well as a corrugated central area 48, which is arranged between them and which consists of a sequence of deflections 45 and indentations 46, 46’, which are rectangular in profile and have the same dimensions with regard to each other, namely a predetermined width C and height B, and which moreover extend equidistantly and in parallel with each other. In general, between two neighboring deflections 45 there is an indentation 46, 46’, or vice versa. Each one of said areas 40, 40’, 40” comprises a sequence of throughout openings 41, 41’, 41” of mutually equal shape and characteristic dimension D, which are equidistantly spaced apart from each other at a distance d, wherein said characteristic dimension D is smaller than the width C of said deflections 45 and indentations 46, 46’. Said weak areas 40, 40’, 40” are however formed on just some of all disposable deflections 45, or on just some of all disposable indentations 46, 46’, and are consequently, with regard to said longitudinal geometric axis 20 of the throughout passage 200 within said casing 2 of the fuse 1, always formed only on the one side of each melting member 4', 4", 4"', 41V, 4V, 4V1of the complex melting assembly 4 of the fuse 1.

[0043] The thickness A of the metallic plate or a strip, of which each melting member 4', 4", 4"', 41V, 4V, 4V1in the melting assembly 4 is formed, is selected within the range

[0044] 0,04 mm A 0,5 mm, the width d of each one of said bridges 42', 42" between each neighboring throughout openings 41, 41', 41" in each one of said weak areas 40, 40', 40" is selected within the range

[0045] 0,1 mm d 0,5 mm, said height B of deflections 45, as well as of indentations 46, 46’, is determined in dependency on said thickness A of the metallic strip, of which each one of said melting members 4', 4", 4'", 41V, 4V, 4V1is formed, such that the following condition is fulfilled 10 x A <. B 40 x A and said width C of deflections 45, as well as of indentations 46, 46', is determined in dependency on said thickness A of the metallic strip, of which each one of said the melting members 4', 4", 4"', 4,v, 4V, 4V1is formed, such that the following condition is fulfilled

[0046] 1,0 x D C 2,0 x D.

[0047] Such concept of the melting member allows integration of the fuse in electric circuits, in which essential variations of electric voltage occur, and melting members 4', 4", 4"', 41V, 4V, 4V1are exposed to heating and cooling, which results in extension and shrinking thereof, which then leads to essential mechanical stresses and consequently even to disabling of interconnection between the melting member 4', 4", 4"', 41V, 4V, 4V1and the belonging knife blade contact 5, 5’.

[0048] In according to a further embodiment of the invention, at least one of both longitudinal edges 510, 510’ on the blade 51, 51’ of the knife blade contact 5, 5 is on its both sides inclined and slanted, by which, during installation of the fuse 1 into an electric circuit, knife blade contacts 5, 5’ are easier insertable into corresponding fork-shaped contacts in the electric circuit.

[0049] Moreover, a further aspect of the invention proposes two alternative embodiments of knife blade contacts 5, 5’ in the fuse according to the invention are foreseen, which may support integration of the fuse 1 into a high-performance electric circuit, in which at least occasionally essential forces may occur as a consequence of the electric current and which generate serious mechanical loadings on the electric conductors, and are also transmitted via said knife blade contacts 5, 5’ of the fuse 1. In the first alternative embodiment according to said aspect, said blade 51, 51 ’ of each knife blade contact 5, 5’ is furnished with a transversally extending U-shaped recess 55, which is directed from one longitudinal edge 510, 510’ of the blade 51, 51’ towards the other longitudinal edge 510, 510’ of the blade 51, 51’ and is in such extent spaced apart from the attaching member 52, 52’ of the knife blade contact 5, 5’ that a screw or a similar connecting means is insertable there-into due to establishing of a detachable mechanical interconnection between the knife blade contact 5, 5’ and a corresponding electric conductor of an electric circuit, into which the fuse 1 is to be integrated.

[0050] In the second alternative embodiment according to said aspect, said blade 51, 51’ of each knife blade contact 5, 5’ is furnished with a longitudinally extending U- shaped recess 55, which is directed from the free terminal portion of the blade 51, 51 ’ towards the attaching member 52, 52’ of the blade 51, 51 ’ and is in such extent spaced apart from the attaching member 52, 52’ of the knife blade contact 5, 5’ that a screw or a similar connecting means is insertable there-into due to establishing of a detachable mechanical interconnection between the knife blade contact 5, 5’ and a corresponding electric conductor of an electric circuit, into which the fuse 1 is to be integrated.

[0051] Such concept of the electric fuse 1 with said cylindrical throughout passage, with a hexagonally arranged complex melting assembly, as well as with knife blade contacts 5, 5’ in accordance with anyone of previously discussed embodiments, as soon as integrated into an electric circuit, enables a long-term and reliable protection of a heavy duty direct current (DC) electric circuit, in which the electric voltage values should be within the range of at least 1000 - 1500 V, even despite to occasional switching-off or switching-on said electric circuit, and also despite to essential variations of the electric voltage within said electric circuit, in which such fuse 1 is integrated. Moreover, such fuse 1 is capable of withstanding the forces which are generated by such electric current within each relevant electric conductor and also to any other mechanical loads, which may occur in such heavy duty electric conductors, which are intended for transmission of e.g. 100 kA or even higher electric current. In each case, during operation of such fuse 1, all electrical, mechanical and thermal loadings are uniformly distributed among all disposable melting members 4', 4", 4"', 41V, 4V, 4V1within said complex melting assembly 4, which are then, each per se, capable to withstand to proportional part of electric and thermal loadings, which may occur within an electric circuit, in which said electric fuse 1 is integrated.

Claims

CLAIMS1. Electric fuse (1) with knife blade contacts (5, 5') and a complex melting assembly (4), comprising at least- a tubular casing (2), which consists of electric insulating material and is in at least two of its corner areas (21, 22, 23, 24) furnished with a throughout bore (210, 220, 230, 240), extending in parallel with a central longitudinal geometric axis (20) of the casing (2) as such, wherein said casing (2) is on each one of its terminal areas furnished with a flat and smooth front surface (251, 252), and wherein said front surfaces (251, 252) are arranged in parallel with each other and perpendicularly with regard to said central longitudinal geometric axis (20) of the casing (2) as such;- covering plates (3, 3'), which are formed of a sufficiently rigid and electric conductive metallic material, and each one of them is tightly matching placed onto a belonging front surface (251, 252) of the casing (2), by which the throughout passage (200) within said tubular casing (2), namely the cross-section of said internal throughout passage (200) in said tubular casing (2), is completely covered, wherein said covering plates (3, 3') are interconnected with each other by means of attaching elements, which are inserted in said throughout bores (210, 220, 230, 240) in said comer areas (21, 22, 23, 24) of the casing (2) and simultaneously extend through correspondingly arranged bores in said covering plates (3, 3'), and wherein each one of said covering plates (3, 3') is furnished with a central passage (31) of a pre-determined shape, as well as with at least two further throughout bores (33, 33"), which are arranged adjacent to the lastly mentioned passage and are adjusted for passing of attaching means (35', 35") there-through;- two knife blade contacts (5, 5'), consisting of a sufficiently rigid electric conductive metallic material, wherein each one of said knife blade contacts (5, 5')is arranged on the one of both opposite terminal portions (201, 202) of the casing (2) of said fuse (1), and wherein each one of said knife blade contacts (5, 5') comprises, on the one hand, a blade (51, 51'), which is conceived as a straight and suitable rigid bearing member of a pre-determined thickness, width and length, and on the other hand an attaching member (52, 52'), which is conceived as a flange, adjusted for resting on a belonging covering plate (3, 3') and furnished with at least two throughout bores (53', 53"), which are arranged coaxially with said throughout bores (33', 33") on the belonging covering plate (3, 3'), so that said knife blade contacts (5, 5') are inserted through said central passages (31) in said covering plates (3, 3'), the previously mentioned pre-determined shape of which is adjusted to the shape of the external silhouette of the transversal cross-section of the blade (51, 51') of each knife blade contact (5, 5'), while the attaching members (52, 52') thereof are arranged within the passage (200) in the casing (2) of the fuse (1) and are each per se by means of suitable connecting means (35', 35"), which are inserted in said throughout bores (53', 53") and in said throughout bores (33', 33") in covering plates (3, 3'), connected with each belonging connecting plate (3, 3'), and wherein said blades (51, 51') of the knife blade contacts (5, 5') are arranged coaxially with each other and in the same plane, and protrude out from the casing (2) of the fuse (1) apart from each other,- a melting assembly (4), consisting of several single melting members (4', 4", 4'", 41V, 4V, 4V1), each of them consists of electric conductive material and is properly weakened in order to allow transmission of the electric current below a predetermined nominal value, wherein said melting assembly (4) is arranged within the interior of said throughout passage (200) in the casing (2) of the fuse (1), and wherein the first terminal portion (44') of each melting member (4', 4", 4'", 41V, 4V, 4V1) is mechanically connected with the attaching member (52) of the first knife blade contact (5) and is such also electrically connected there-with, while the residual terminal portion (44") of each melting member (4', 4", 4'", 41V, 4V, 4V1) ismechanically connected with the attaching member (52') of the second knife blade contact (5') and is such also electrically connected there- with; and moreover also- a suitable amount of granulated solid filling particles (8), consisting of non- metallic fireproof electric insulating material, which is suitable for extinguishing of the electric arc, wherein said filling particles (8) are inserted within said throughout passage (200) within the casing (2) of the fuse (1), so that each one of said melting members (4', 4", 4"', 41V, 4V, 4V1) in the melting assembly (4) is at least almost completely surrounded by said filling particles (8), characterized in that, said throughout passage (200) within said casing (2) of the fuse (1) is cylindrical, so that its transversal cross-section is a regular circle, wherein a melting assembly (4) is inserted within said throughout passage (200) in the casing (2) of the fuse (1), which consists of six symmetrically arranged and equally with regard to each other spaced melting members (4', 4", 4"', 41V, 4V, 4V1), which are arranged on diagonals of a hexagon, inscribed in a circle of said circular transversal crosssection of the throughout passage (200) in a casing (2) of the fuse (1), and wherein each one of said melting members (4', 4", 4"', 41V, 4V, 4V1) is spaced apart from the circumferential wall of said throughout passage (200), and in that each one of said knife blade contacts (5, 5') is uniformly conceived, namely that the blade (51, 51') and the attaching member (52, 52') of the knife blade contact (5, 5') are formed as perpendicularly with regard to each other extending arms of an uniform T-profile, namely as a web and a flange of a T- profile, wherein the circumferential silhouette of the attaching member (52, 52') of the knife blade contact (5, 5') is a regular hexagon, the diagonal of which is shorter than the diameter of said throughout passage (200) in the casing (2) of the fuse (1).

2. Fuse (1) according to Claim 1, characterized in that an arc extinguishing barrier (49, 49'), consisting of a fireproof material, in particular of high-temperature resistant silicone, is formed on the surface of each one of said melting members (4', 4", 4"', 41V, 4V, 4V1) in the area either between each neighboring weak areas (40, 40', 40") or between the attaching member (52, 52') of the knife blade contact (5, 5') and the nearest weak area (40, 40', 40"), wherein said barrier is shaped as a continuous convex rib, extending in a transversal direction with regard to said longitudinal geometric axis (20) of the throughout passage (200) within the casing (2) of the fuse (1).

3. Fuse (1) according to Claim 1 or 2, characterized in that each melting member (4', 4", 4'", 41V, 4V, 4V1) in said melting assembly (4) is formed as a strip, which is its longitudinal direction easily deformable, namely extendable or shrinkable, and which consists of electric conductive metallic material having predetermined melting temperature and electric resistance, and comprises straight terminal areas (44’, 44”), extending in a longitudinal direction od said throughout passage (200) within the casing (2) of the fuse (1) and being coplanar with regard to each other, between which there is a corrugated central area (48), consisting of a sequence of deflections (45) and indentations (46, 46’), which are rectangular in profile and have the same dimensions with regard to each other, namely a predetermined width (C) and height (B), and which moreover extend equidistantly and in parallel with each other, so that between two neighboring deflections (45) an indentation (46, 46’) is available, or vice versa, wherein each weak area (40, 40’, 40”) comprises a sequence of throughout openings (41, 41 ’, 41”) of mutually equal shape and characteristic dimension (D), which are equidistantly spaced apart from each other at a distance (d), wherein said characteristic dimension (D) is smaller than the width (C) of said deflections (45) and indentations (46, 46’), and wherein said weak areas (40, 40’, 40”) are formed on just some of all disposable deflections (45), or on just some of all disposable indentations (46, 46’), and are consequently, with regard to said longitudinal geometric axis (20) of thethroughout passage (200) within said casing (2) of the fuse (1), always formed only on the one side of each melting member (4', 4", 4"', 41V, 4V, 4V1) of the complex melting assembly (4) of the fuse (1).

4. Fuse (1) according to Claim 3, characterized in that the thickness (A) of the metallic plate or a strip, of which each melting member (4', 4", 4"', 41V, 4V, 4vl) in the melting assembly (4) is formed, is selected within the range0,04 mm A 0,5 mm, the width (d) of each one of said bridges (42', 42") between each neighboring throughout openings (41, 41', 41") in each one of said weak areas (40, 40', 40") is selected within the range0,1 mm d 0,5 mm, said height (B) of deflections (45), as well as of indentations (46, 46’), is determined in dependency on said thickness (A) of the metallic strip, of which each one of said melting members (4', 4", 4'", 41V, 4V, 4V1) is formed, such that the following condition is fulfilled10 x A S B 40 x A and said width (C) of deflections (45), as well as of indentations (46, 46'), is determined in dependency on said thickness (A) of the metallic strip, of which each one of said the melting members (4', 4", 4'", 41V, 4V, 4V1) is formed, such that the following condition is fulfilled1,0 2,0 x D.

5. Fuse (1) according to anyone of Claims 1 - 4, characterized in that at least one of both longitudinal edges (510, 510’) on the blade (51, 51’) of the knife blade contact (5, 5) is on its both sides inclined and slanted.

6. Fuse (1) according to anyone of Claims 1 - 4, characterized in that said blade (51, 51’) of each knife blade contact (5, 5’) is furnished with a transversally extending U-shaped recess (55), which is directed from one longitudinal edge (510, 510’) of the blade (51, 51’) towards the other longitudinal edge (510, 510’) of the blade (51, 51 ’) and is in such extent spaced apart from the attaching member (52, 52’) of the knife blade contact (5, 5’) that a screw or a similar connecting means is insertable there-into due to establishing of a detachable mechanical interconnection between the knife blade contact (5, 5’) and a corresponding electric conductor of an electric circuit, into which the fuse (1) is to be integrated.

7. Fuse (1) according to anyone of Claims 1 - 4, characterized in that said blade (51, 51 ’) of each knife blade contact (5, 5’) is furnished with a longitudinally extending U-shaped recess (55), which is directed from the free terminal portion of the blade (51, 51 ’) towards the attaching member (52, 52 ’) of the blade (51, 51 ’) and is in such extent spaced apart from the attaching member (52, 52’) of the knife blade contact (5, 5’) that a screw or a similar connecting means is insertable thereinto due to establishing of a detachable mechanical interconnection between the knife blade contact (5, 5’) and a corresponding electric conductor of an electric circuit, into which the fuse (1) is to be integrated.

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