Fuse

Abstract

PURPOSE: To provide a fuse that fully utilizes the arc-extinguishing performance of an arc-extinguishing silicone portion and does not reduce insulation resistance after an interruption operation.SOLUTION: A conductor 7 is provided with alternating fusion portions 71A to 71D and non-fusion portions 73A to 73E. The non-fusion portions 73A to 73E are formed with recesses 8 that extend in a second direction Y intersecting a first direction X in which the non-fusion portions 73A to 73E are aligned and have openings 8A on one surface 7A of the plate surface of the conductor 7. The recess 8 has a V-shaped cross-sectional shape when viewed from the second direction Y, the length of the opening 8A of the recess 8 measured in the first direction X is 2 to 4 mm, the depth from the opening surface of the opening 8A to the bottom of the recess 8 is 0.4 to 1 mm, and an arc-extinguishing silicone portion S does not completely fill the recess 8.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuse in which a space within a case housing a plate-shaped conductor having one or more fusible portions and a pair of non-fusible portions on either side of the fusible portion is filled with a filler material that acts as an arc-extinguishing agent. [Background technology]

[0002] 3 and 4 of JP 2022-126059 A (Patent Document 1) disclose a conventional fuse having a plate-shaped conductor having at least one fusion portion and a pair of non-fusion portions on both sides of the fusion portion, a case for accommodating the conductor, arc-extinguishing sand filled in the space in the case, recesses 131 provided in each of the pair of fusion portions, extending in a second direction intersecting the first direction in which the pair of fusion portions are arranged, and having an opening on one surface of the plate surface of the conductor, and an arc-extinguishing silicone portion formed by filling the recesses 131 with arc-extinguishing silicone 140. The cross-sectional shape of the recess 131 when viewed from the second direction is U-shaped. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-126059 A Summary of the Invention [Problem to be solved by the invention]

[0004] Fuses that use both arc-extinguishing sand and an arc-extinguishing silicone part for arc-extinguishing, such as the fuses shown in Figures 3 and 4 of Patent Document 1, have higher arc-extinguishing performance than fuses that use only arc-extinguishing sand for arc-extinguishing. However, it was found that after the arc is extinguished, carbonized silicone material remains in and around the melted part of the conductor, causing the insulation resistance to be lower than the standard value when the insulation resistance and withstand voltage are measured after the melting operation.

[0005] An object of the present invention is to provide a fuse which allows the arc-extinguishing performance of the arc-extinguishing silicone portion to be fully exhibited and which does not cause the insulation resistance after an interruption operation to become smaller than a specified value. [Means for solving the problem]

[0006] The fuse that is the subject of improvement in the present invention is a fuse with a rated voltage of 250 V or more and a rated current of 5 A or more, comprising a plate-shaped conductor having at least one fusible portion and a pair of non-fusible portions on either side of the fusible portion, a case for accommodating the conductor, arc-extinguishing sand filled in the space within the case, recesses provided in each of the pair of non-fusible portions, extending in a second direction intersecting the first direction in which the pair of non-fusible portions are arranged, and having an opening on one of the plate surfaces of the conductor, and an arc-extinguishing silicone portion formed by filling the recesses with viscous arc-extinguishing silicone and hardening it, the fuse having a rated voltage of 250 V or more and a rated current of 5 A or more.

[0007] The inventor found that the cause of the decrease in insulation resistance after the cutoff operation of the fuse described in Patent Document 1 is the shape of the arc-extinguishing silicone part. The carbide formed by carbonizing at least a part of the arc-extinguishing silicone part with heat of 1000°C or more generated when an arc occurs needs to be discontinuous and not excessively attached in the length direction, and ideally should be applied only to the inside of the recess. However, in the past, there has been no consideration of the effect of the shape of the recess and the amount of arc-extinguishing silicone filled in the recess on the resistance value of the fuse, or the effect of the presence of carbide that appears after the arc occurs. For example, if the cross-sectional shape of the recess is U-shaped, as in the fuse of Patent Document 1, the path that flows during normal current flow, not during cutoff, becomes longer, resulting in an increase in resistance value and an increase in watt loss. In addition, if the cross-sectional shape of the recess is U-shaped, the internal volume becomes large, so if the arc-extinguishing silicone is filled too much with the intention of improving the arc-extinguishing performance, the problem of the amount of carbide that causes the decrease in insulation resistance after cutoff increases too much occurs. In particular, in applications where fuses with a rated voltage of 250V or more and a rated current of 5A or more are used, any decrease in insulation resistance after interruption must be absolutely avoided.

[0008] The recess used in the fuse of the present invention has a V-shaped cross-sectional shape when viewed from the second direction. The length of the opening of the recess measured in the first direction is 2 to 4 mm, and the depth from the opening surface of the opening to the bottom of the recess is 0.4 to 1 mm, and it is preferable that the arc-extinguishing silicone part does not completely fill the recess. In this way, the arc-extinguishing silicone part fits into the V-shaped cross-section of the recess, so that the coating is of appropriate length and depth, and the path during normal current flow can be shortened, so that an increase in resistance and an increase in watt loss can be suppressed. If the length of the opening measured in the first direction is shorter than 2 mm and the depth from the opening surface of the opening to the bottom of the recess is shallower than 0.4 mm, the arc-extinguishing performance is not substantially improved. If the length of the opening measured in the first direction is longer than 4 mm and the depth from the opening surface of the opening to the bottom of the recess is deeper than 1 mm, the path during normal current flow becomes longer, resulting in an increase in resistance and an increase in watt loss. Furthermore, if the arc-extinguishing silicone portion completely fills the recess, the creepage distance of the carbide surface that appears after the arc is extinguished becomes shorter, which causes a decrease in insulation resistance.

[0009] According to the present invention, it is possible to suppress the formation of a conductive path due to a carbonized layer formed in the vicinity of the fusion portion, to fully utilize the arc-extinguishing performance of the arc-extinguishing silicone part, to prevent the insulation resistance after the interruption operation from becoming smaller than specified, and to keep the loss during normal current flow small.

[0010] The viscosity of the arc-extinguishing silicone before curing and the amount of the arc-extinguishing silicone filled into the recess are preferably determined so that the top of the surface facing the opening of the arc-extinguishing silicone does not exceed the opening. In this way, the decrease in the creepage distance after carbonization can be suppressed.

[0011] The arc-extinguishing silicone part preferably has a shape that is convex toward the opening, and if the arc-extinguishing silicone part has such a shape, it is possible to suppress a decrease in the creepage distance after carbonization.

[0012] The amount of arc-extinguishing silicone filled into the recess is preferably at least half the volume of the recess, under the condition of the present invention that the arc-extinguishing silicone does not completely fill the recess. This amount makes it possible to suppress a decrease in insulation resistance after carbonization of the arc-extinguishing silicone without decreasing the arc-extinguishing performance.

[0013] The viscosity μ of the arc-extinguishing silicone before curing is preferably 50 (Pa s)≦μ≦300 (Pa s). By using such a silicone resin, the shape of the arc-extinguishing silicone part can be made to be convex toward the opening.

[0014] The arc-extinguishing silicone is preferably a silicone having a heat resistance of at least 250° C. This type of silicone material is inexpensive and can reduce the increase in the price of the fuse. [Brief description of the drawings]

[0015] [Figure 1] 1A is a plan view of the fuse of the present embodiment, FIG. 1B is a cross-sectional view of the fuse, and FIG. 1C is a vertical-sectional view of the fuse. [Diagram 2] 2 is an enlarged view of a main portion of the fuse of the present embodiment. FIG. [Diagram 3] 13(A) to 13(C) are diagrams showing the state of application of the arc-extinguishing silicone to the recessed portion in three test examples in which the state of application of the arc-extinguishing silicone to the recessed portion was changed, the insulation resistance after interruption, and the state of the label affixed to the surface of the cylinder due to heat generation during interruption. [Figure 4] 11A and 11B are diagrams showing examples of shapes of the arc-extinguishing silicone part in the recess. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1(A) is a plan view of a fuse 1 of this embodiment, FIG. 1(B) is a cross-sectional view of the fuse 1 of this embodiment, and FIG. 1(C) is a vertical cross-sectional view of the fuse 1 of this embodiment. The fuse 1 of this embodiment includes an insulating cylindrical body 5 filled with arc-extinguishing sand 3, and an outer container 15 including a pair of cap-shaped electrodes 9 and 11 fitted to both ends of the cylindrical body 5 and electrically connected to a conductor 7 constituting a fuse element. The cylindrical body 5 is integrally molded from ceramic. The cap-shaped electrodes 9 and 11 include bottom wall portions 9A and 11A facing the openings 51 and 53 of the cylindrical body 5, and cylindrical peripheral wall portions 9B and 11B extending upright from the peripheral edges of the bottom wall portions 9A and 11A.

[0017] The conductor 7 is integrally formed by pressing a long and narrow metal plate for a fuse made of silver or copper. The conductor 7 is configured by alternately arranging 2 to 15 fusion parts 71A to 71D having a predetermined width (specifically, 0.1 to 2 mm) and 5 non-fusion parts 73A to 73E (parts having a lower electrical resistance than the fusion parts 71A to 71D and being less likely to melt than the fusion parts) having a width (specifically, 2 mm) longer than the width of the fusion parts 71A to 71D in the longitudinal direction of the conductor 7, i.e., in the first direction X [FIG. 1(C)].

[0018] The four fusible parts 71A to 71D are arranged in a state inclined, i.e., oblique, with respect to an imaginary center line extending in the first direction X. As shown in an enlarged view in FIG. 2, each of the five non-fusible parts 73A to 73E includes a recess 8 having an opening 8A on one surface 7A of the plate surface of the conductor 7, which extends in a second direction Y intersecting with the first direction X in which the non-fusible parts 73A to 73E are arranged, and an arc-extinguishing silicone part S formed by filling the recess 8 with viscous arc-extinguishing silicone. The arc-extinguishing silicone part S does not completely fill the recess 8. In this embodiment, the arc-extinguishing silicone part S has a shape that is convex toward the opening 8A of the recess 8. The viscosity of the arc-extinguishing silicone before hardening and the amount of filling into the recess 8 are determined so that the top of the surface of the arc-extinguishing silicone part S facing the opening 8A does not exceed the opening 8A. In this embodiment, the volume of the arc-extinguishing silicone part S is 1 / 2 or more of the internal volume of the recess 8. These conditions are preferred application conditions found by the inventor through testing in order to enable the arc-extinguishing silicone part S to fully exert its arc-extinguishing function and to prevent a decrease in insulation resistance due to the presence of carbonized parts of the silicone that appear after arc extinguishing.

[0019] The preferred arc-extinguishing silicone used in this embodiment has a viscosity μ before curing of 100 (Pa·s)≦μ≦300 (Pa·s), and is a silicone having a heat resistance of 250°C or higher. An example of a silicone-based material that satisfies this condition is a silicone-based material sold by ThreeBond Co., Ltd. under the product number "1209" [viscosity 140 (Pa·s)]. When a silicone resin with this viscosity is used, the shape of the arc-extinguishing silicone part S can be made convex toward the opening 8A, and the carbonized arc-extinguishing silicone is less likely to form a continuous conductive path.

[0020] The carbonized layer formed by carbonizing at least a part of the arc-extinguishing silicone part S with heat of 1000°C or more generated when an arc occurs needs not to be too thick in the length direction, and is ideally applied to the inside of the recess. If the cross-sectional shape of the recess is U-shaped as in the fuse of Patent Document 1, the path through which the current flows during normal current flow, not during interruption, becomes longer, resulting in an increase in resistance value during current flow and an increase in watt loss. In contrast, in the fuse 1 of this embodiment, the cross-sectional shape of the recess 8 when viewed from the second direction Y is V-shaped. As a result of various tests conducted by the inventors, it was found that in the case of a fuse with a rated voltage of 250V or more and a rated current of 5A or more, the length of the opening 8A of the recess 8 having a V-shaped cross-sectional shape is preferably 2 to 4 mm, and the depth of the recess 8 is preferably 0.4 to 1 mm. When the recess 8 is provided under such conditions, the shape of the arc-extinguishing silicone part S becomes deeper as it moves away from the non-melting parts (73A to 73E). By using the recess 8 of this shape, the amount of the arc-extinguishing silicone can be gradually reduced closer to the fusion part that melts due to the arc. As a result, according to this embodiment, it is possible to suppress the formation of a conductive path due to a carbonized layer formed in the vicinity of the fusion part, allowing the arc-extinguishing performance of the arc-extinguishing silicone part S to be fully exhibited, and also to prevent the insulation resistance after the interruption operation from becoming smaller than the specified value.

[0021] FIG. 3 shows photographs of the state of application of the arc-extinguishing silicone to the recesses of test examples (A) to (C) in which the opening length of the V-shaped recess 8 is 3 mm and the depth is 0.7 mm, and the state of application of the arc-extinguishing silicone is changed, the insulation resistance after interruption, and the state of the label attached to the surface of the cylindrical body 5 changed due to heat generation during interruption. In test example (A) of FIG. 3, the arc-extinguishing silicone is applied to the crest side of the recess, in test example (B) the inside of the recess is filled with the arc-extinguishing silicone almost to the full, and in test example (C) the arc-extinguishing silicone is filled to about half the depth of the recess. In all of these test examples, the interruption results when a current of 1000 V and 10000 A was passed were good. However, the insulation resistance after interruption was not measurable in test example (A) at 0.1 MΩ or less, was small at 0.8 MΩ in test example (B), and was sufficiently large at 2000 MΩ in test example (C) [corresponding to the embodiment]. Also, looking at the change in the label indicating the heat generation state, the label turned black in both test examples (A) and (B), but there was almost no change in the label in test example (C). What can be seen from these test examples is that the provision of an arc-extinguishing silicone part improves interrupting performance and makes it possible to limit the amount of heat generated during interruption, that providing an arc-extinguishing silicone part in the recess with a V-shaped cross section increases the insulation resistance after extinguishing the arc, and that the insulation resistance can be increased by appropriately adjusting the amount of arc-extinguishing silicone part provided in the recess with a V-shaped cross section.

[0022] In addition, when tests were performed by changing the viscosity of the interrupting silicone and the amount of filling into the recess, it was confirmed that, as in the above test example (C), when the length of the recess 8 used in the fuse of this embodiment measured in the first direction (X direction) of the opening 8A is 2 to 4 mm, and the depth from the opening surface of the opening 8A to the bottom of the recess 8 is 0.4 to 1 mm, and the arc-extinguishing silicone part does not completely fill the recess, the insulation resistance does not become too small. In addition, although it varies depending on the type of arc-extinguishing silicone, it was also confirmed that even with arc-extinguishing silicone other than the arc-extinguishing silicone used in this embodiment, as long as the viscosity μ before curing is 50 (Pa·s)≦μ≦300 (Pa·s), it is possible to form an arc-extinguishing silicone part having a shape that is convex toward the opening as shown in FIG. 4.

[0023] Although the insulation resistance will not necessarily decrease if the length of the recess is outside the range of 2 to 4 mm and the depth is outside the range of 0.4 to 1 mm, the probability of the insulation resistance decreasing increases, and therefore, in this embodiment, these numerical ranges are deliberately limited.

[0024] In this embodiment, the above-mentioned specific arc-extinguishing silicone is used, but it goes without saying that other arc-extinguishing silicones can be used as long as they have the same viscosity and arc-extinguishing performance as the above-mentioned specific arc-extinguishing silicone.

[0025] In the above embodiment, recesses 8 are provided in all of the non-fusible portions 73A to 73E, and arc-extinguishing silicone portions S are formed in all of the recesses 8. However, it is of course possible to adopt a configuration in which recesses 8 are provided only in a pair of non-fusible portions located on either side of one fusible portion, and arc-extinguishing silicone portions S are formed in these recesses 8. [Industrial Applicability]

[0026] According to the present invention, it is possible to suppress the formation of a conductive path due to a carbonized layer formed in the vicinity of the fusion portion, thereby allowing the arc-extinguishing performance of the arc-extinguishing silicone part to be fully exhibited, and also to prevent a decrease in insulation resistance after the breaking operation. [Explanation of symbols]

[0027] 1. Fuse 3. Arc-extinguishing sand 5 Cylinder 7 Conductors 71A to 71D Melting point 73A to 73E Non-melting parts 9,11 Cap-shaped electrode

Claims

1. a plate-shaped conductor having at least one fusion portion and a pair of non-fusion portions on both sides of the fusion portion; A case that houses the conductor; Arc-extinguishing sand filled in the space within the case; a recess provided in each of the pair of non-fusible portions, extending in a second direction intersecting a first direction in which the pair of non-fusible portions are arranged, and having an opening on one surface of a plate surface of the conductor; an arc-extinguishing silicone portion formed by filling the recess with arc-extinguishing silicone and curing the same; A fuse having a rated voltage of 250V or more and a rated current of 5A or more, the recess has a V-shaped cross-sectional shape when viewed from the second direction, the length of the opening measured in the first direction is 2 to 4 mm, and the depth from the opening surface of the opening to the bottom of the recess is 0.4 to 1 mm; A fuse, wherein the arc-extinguishing silicone portion does not completely fill the recess.

2. 2. The fuse according to claim 1, wherein the viscosity of the arc-extinguishing silicone before curing and the amount of the arc-extinguishing silicone filled into the recess are determined so that the top of the surface of the arc-extinguishing silicone portion facing the opening does not extend beyond the opening.

3. 3. The fuse according to claim 2, wherein the arc-extinguishing silicone portion has a shape that is convex toward the opening.

4. 4. The fuse according to claim 1, wherein the volume of the arc-extinguishing silicone portion is at least half the internal volume of the recess.

5. 5. The fuse according to claim 4, wherein the viscosity μ of the arc-extinguishing silicone before curing is in the range of 50 (Pa·s)≦μ≦300 (Pa·s).

6. 6. The fuse according to claim 5, wherein the arc-extinguishing silicone is a silicone having a heat resistance of 250[deg.] C. or higher.

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