Bushing

Abstract

To provide a bushing which can secure mechanical strength which can withstand use under high gas pressure without significantly changing the design.SOLUTION: A bushing includes: a bushing body formed of a resin material; an attachment flange which is formed integrally with the bushing body of a resin material and fastened to a device case by fixing bolts; and cylindrical embedded metal fittings each having a bolt through hole into which the fixing bolt is inserted. The attachment flange has: a flange body part whose planar view shape as seen in an axial direction is a regular hexagon and in which the embedded metal fittings are embedded near vertices of the regular hexagon; and a flange reinforcement part whose planar view shape as seen in the axial direction is a polygon including protruding parts and recessed parts formed alternately and having six-fold rotational symmetry and in which a bolt fixing surface for fastening the fixing bolts is formed protruding to the rear end side of the flange body part so as to be exposed from the recessed parts. A rounded portion having a curvature radius ranging 5 to 10 mm is provided at a connection portion between the bolt fixing surface and an outer peripheral surface of the flange reinforcement part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a bushing. [Background technology]

[0002] Conventionally, known cable terminations include gas terminations, oil terminations, and air terminations. Generally, a cable termination is formed by connecting a cable terminal, to which a connection material is attached, to a main body material (called a "bushing") that has an inner conductor and a hard insulator made of epoxy resin or the like that is placed around the inner conductor (for example, Patent Document 1).

[0003] The bushing described in Patent Document 1 is entirely made of epoxy resin and has a bushing body and a mounting flange integrally formed with the bushing body. The bushing is inserted into the equipment case of the electric power equipment and attached to the equipment case by fastening fixing bolts inserted through the mounting flange to the equipment case. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5548567 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, due to environmental considerations, dry gases and other gases are often used instead of sulfur hexafluoride gas (SF6 gas) as the insulating gas filled inside equipment. Dry gas has lower insulating performance than SF6 gas, so to obtain equivalent insulating performance, the gas pressure must be set higher. As a result, there is a concern that the equipment case may be deformed by the gas pressure, and external forces resulting from the deformation of the equipment case may act on the bushing mounting flange, causing damage to the mounting flange. In particular, in the bushing described in Patent Document 1, the mounting flange is made of epoxy resin and is easily damaged, so the structure of the mounting flange needs to be improved so that it has the mechanical strength to withstand external forces from the equipment case.

[0006] An object of the present disclosure is to provide a bushing that can ensure mechanical strength sufficient to withstand use under high gas pressure without requiring major design changes. [Means for solving the problem]

[0007] The bushing according to the present disclosure comprises: a bushing body formed of a resin material; a mounting flange formed integrally with the bushing body from the resin material and fastened to an equipment case by a fixing bolt; a cylindrical embedded fitting having a bolt through-hole through which the fixing bolt is inserted, The mounting flange is a flange main body portion having a regular hexagonal shape in a plan view as viewed from the axial direction, the embedded metal fittings being embedded near the vertices of the regular hexagon; a flange reinforcing portion formed so as to protrude from the rear end side of the flange main body portion so that a bolt fixing surface on which the fixing bolt is fixed is exposed from the recessed portion, and the flange reinforcing portion has a planar shape as viewed from the axial direction that is a six-fold rotationally symmetric polygon in which convex portions and concave portions are alternately formed, The connecting portion between the bolt fixing surface and the outer peripheral surface of the flange reinforcing portion is subjected to R processing with a curvature radius of 5 to 10 mm. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a bushing with high mechanical strength that can withstand use under high gas pressure without making major design changes. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a cable connection termination using a bushing according to an embodiment. [Figure 2] FIG. 2 is a perspective view of the bushing as viewed from the rear end side. [Figure 3] FIG. 3 is a plan view of the bushing as viewed from the rear end side. [Figure 4] 4A and 4B are enlarged views showing the fixing structure of the bushing. [Figure 5] FIG. 5 is a diagram showing the relationship between the radius of curvature of the corner of the flange reinforcing portion and the maximum stress generated in the mounting flange. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] 1 is a cross-sectional view showing a cable connection termination 1 to which a bushing 10 according to an embodiment of the present disclosure is applied. The cable connection termination 1 is a gas-filled connection termination that is applied to the connection parts of electric power equipment that requires airtightness, such as switchgear and transformers. The overall structure of the cable connection termination 1, other than the characteristic part of the mounting flange 12, is the same as that of a conventional cable connection termination, and will therefore only be briefly described.

[0012] As shown in Fig. 1, the cable termination 1 is configured by attaching a cable terminal 20 to a bushing 10. In the following description, the side of the bushing 10 into which the cable terminal 20 is inserted (the lower side in Fig. 1) will be referred to as the "rear end side," and the opposite side will be referred to as the "front end side."

[0013] The bushing 10 has a bushing body 11, a mounting flange 12, and an embedded metal fitting 33. The bushing body 11 and the mounting flange 12 are integrally formed from a hard plastic resin material with high mechanical strength (e.g., epoxy resin or fiber reinforced plastics (FRP)). In this embodiment, the bushing body 11 and the mounting flange 12 are formed from epoxy resin, and an internal conductor 13 is integrally embedded in the tip end of the bushing 10, specifically, in the tip end of the bushing body 11. The internal conductor 13 is embedded in the inner peripheral surface of the bushing body 11 by, for example, molding.

[0014] The bushing body 11 has a hollow bell shape, and accommodates the cable terminal portion 20 in the hollow portion 111. The bushing body 11 has an electric field mitigation portion 14 at its rear end. The electric field mitigation portion 14 functions as a shielding layer for the bushing 10, for example, by applying a conductive paint (not shown) to a predetermined position on the outer surface, and the conductive paint being electrically connected to the device case 60.

[0015] The mounting flange 12 is formed integrally with the bushing body 11 at the rear end side of the bushing body 11, for example, by molding. The mounting flange 12 is fastened to the rear end surface of the equipment case 60 by fixing bolts 31. The mounting flange 12 has a flange body portion 41 and a flange reinforcing portion 42.

[0016] The flange main body 41 is formed on the rear end side of the bushing main body 11 so as to protrude radially outward beyond the bushing main body 11. The outer shape of the flange main body 41 as viewed in the axial direction is larger than the inner shape of the opening 61 of the equipment case 60, so that the opening 61 of the equipment case 60 is closed by the flange main body 41. A plurality of cylindrical embedded fittings 33 (described later) for inserting the fixing bolts 31 are embedded in the flange main body 41 integrally with the flange main body 41 by, for example, molding.

[0017] The flange reinforcing portion 42 is formed to protrude from the rear end side of the flange main body 41. The structural design of the flange reinforcing portion 42 makes it possible to reduce the thickness of the flange main body 41 while ensuring the mechanical strength required of the mounting flange 12.

[0018] The bushing 10 is airtightly attached to the equipment case 60 by inserting the bushing 10 into the opening 61 of the equipment case 60 from the rear end side and bolting the mounting flange 12 to the equipment case 60 via a sealing member 62 such as an O-ring. The bushing body 11 is located inside the equipment case 60 when the bushing 10 is attached to the equipment case 60. The flange body portion 41 of the mounting flange 12 closes the opening 61 of the equipment case 60. The detailed structure of the mounting flange 12 will be described later.

[0019] The inner conductor 13 is formed of a conductive material suitable for conducting electricity, such as copper, aluminum, a copper alloy, an aluminum alloy, etc. The inner conductor 13 is disposed on the inner peripheral surface of the tip portion of the bushing body 11 and is led out from the through hole of the bushing body 11 toward the tip side.

[0020] The cable terminal portion 20 is configured by attaching connecting materials such as a conductor connection terminal 21, a stress cone 22, a compression device 23, a protective metal fitting 24, and a corrosion-resistant layer 25 to the tip portion of the power cable 50.

[0021] The power cable 50 is, for example, a 66 / 77 kV class power cable insulated with rubber or plastic, and the nominal cross-sectional area of the cable conductor 51 is 600 mm 2 The power cable 50 in this embodiment is a 66 kV 2000 mm 2 The power cable 50 includes, in order from the center, a cable conductor 51, a cable insulator 52, a cable outer semiconductive layer 53, a cable shielding layer 54, and a cable sheath 55. At the cable terminal 20, each layer is exposed by step-stripping a predetermined length from the tip of the power cable 50.

[0022] The cable terminal 20 is assembled by step-stripping the tip of the power cable 50, attaching the protective fitting 24, compression device 23, and stress cone 22 to the power cable 50, and attaching the conductor connection terminal 21 to the cable conductor 51. The tip of the assembled cable terminal 20 is inserted into a receiving opening of a bushing 10 fixed to an equipment case 60 and fixed in place, thereby attaching the cable terminal 20 to the bushing 10. Specifically, while compressing a spring (reference number omitted) of the compression device 23, the compression device 23 is bolted to the rear end surface of the mounting flange 12 of the bushing 10, and the protective fitting 24 is bolted to the rear end surface of the compression device 23. A corrosion-resistant layer 25 for waterproofing is arranged at the rear end of the protective fitting 24.

[0023] With the cable terminal 20 attached to the bushing 10, the tip of the stress cone 22 is pressed against the inner wall surface of the hollow portion 111 of the bushing body 11. The conductor connection terminal 21 is electrically connected to the inner conductor 13 via a contact 15 (e.g., a tulip contact). The cable termination 1 can be assembled relatively easily by plug-in connection.

[0024] FIG. 2 is a perspective view of bushing 10 as viewed from the rear end side. FIG. 3 is a plan view of bushing 10 as viewed from the rear end side. FIGS. 4A and 4B are enlarged views showing the fixing structure of bushing 10. FIG. 4A shows a state in which fasteners such as fixing bolts 31 and washers 32 are not disposed on mounting flange 12, while FIG. 4B shows a state in which fasteners are disposed on mounting flange 12. In FIGS. 2 and 3, connecting portion 43, which is one of the characteristic features of mounting flange 12, is indicated by hatching. Furthermore, lines indicating the internal structure of bushing 10 that appear inside the bushing 10 receiving opening on the rear end surface of flange reinforcing portion 42 have been omitted for ease of explanation.

[0025] The structure of mounting flange 12 will be described in detail with reference to Figures 2, 3, 4A, and 4B. As shown in Figures 2 and 3, mounting flange 12 has a two-stage structure consisting of a flange main body portion 41 and a flange reinforcing portion 42. Mounting flange 12 has a six-fold rotationally symmetric structure with the axial direction as the axis of rotation.

[0026] The fixing bolt 31 is fixed to a bolt fixing surface 411 on the rear end side of the flange main body 41 via a washer 32. The bolt fixing surface 411 is formed on the rear end surface of the flange main body 41. In FIG. 4B of the embodiment, the washer 32 includes both a flat washer on the front end side and a spring washer on the rear end side. The bolt fixing surface 411 is a portion where the flange reinforcing portion 42 is not formed, and is exposed from a recess 423 of the flange reinforcing portion 42.

[0027] The flange main body 41 has a regular hexagonal shape in a plan view from the axial direction. The vertices of the regular hexagon are chamfered to form curved surfaces. The outer diameter R1 of the flange main body 41 is, for example, 250 to 350 mm. The outer diameter R1 of the flange main body 41 is the diameter of the circumscribing circle of the regular hexagon, and is the same as the diagonal length of the regular hexagon that is the outer shape of the flange main body 41. The thickness t of the flange main body 41 is 30 to 50 mm.

[0028] Bolt through holes 412, through which the fixing bolts 31 are inserted, are arranged near the vertices of the regular hexagon of the flange main body 41. The bolt through holes 412 are formed by through holes in cylindrical embedded fittings 33 that are arranged on the same circumference centered in the axial direction of the bushing 10. In this embodiment, a total of 12 bolt through holes 412 are arranged, two on each of the six bolt fixing surfaces 411 of the flange main body 41.

[0029] A washer receiving portion 413 that is recessed circularly toward the tip end is formed in the bolt fixing surface 411, and a bolt through-hole 412 is connected to this washer receiving portion 413. The outer diameter of the washer receiving portion 413 is larger than the outer diameter of the washer 32, and it is possible to receive the washer 32 without the peripheral edge of the washer 32 coming into contact. The washer 32 does not come into contact with the corners of the bolt fixing surface 411 (the open end of the washer receiving portion 413), and external force is not applied during the tightening operation of the fixing bolt 31, so damage such as cracks and chips that start from the corners of the bolt fixing surface 411 can be prevented from occurring in the flange main body 41.

[0030] The bolt through-holes 412 are formed by through-holes in a cylindrical embedded metal fitting 33 embedded in the flange main body 41. The embedded metal fitting 33 is embedded in advance by molding so that the end face on the front end side is flush with the front end face of the flange main body 41 and the end face on the rear end side is flush with the front end face of the washer receiving portion 413.

[0031] The two bolt through holes 412 are arranged at symmetrical positions on the bolt fixing surface 411. Specifically, the distances from the two bolt through holes 412 to the protrusions 422 closest to each other are the same. This equalizes the stress generated in the mounting flange 12 and suppresses the maximum stress, thereby improving the mechanical strength of the mounting flange 12 as a whole.

[0032] The flange reinforcing portion 42 is formed to protrude from the rear end side of the flange main body 41. The flange reinforcing portion 42 has a substantially cylindrical trunk portion 421 and six convex portions 422 arranged in a row at equal intervals in the circumferential direction on the outer peripheral surface of the trunk portion 421. That is, the flange reinforcing portion 42 has a planar shape as viewed from the axial direction that is a six-fold rotationally symmetric polygon with the axial direction as the axis of rotation, in which the convex portions 422 and concave portions 423 are alternately formed. The convex portions 422 function as ribs, thereby increasing the mechanical strength of the mounting flange 12 without increasing the thickness of the flange main body 41 and effectively preventing deformation such as warping and twisting.

[0033] The flange reinforcing portion 42 is inscribed in the flange main body 41 in a plan view seen from the axial direction. In other words, the outer diameter R2 of the flange reinforcing portion 42 is the same as the diameter of the inscribed circle of the regular hexagon that is the shape of the flange main body 41 in a plan view. If the outer diameter of the body 421 is R3, the protruding length of the convex portion 422 is expressed as (R2 - R3) / 2. The protruding length of the convex portion 422 is not particularly limited as long as it is large enough to secure space for the bolt fixing surface 411 of the flange main body 41 even when the curvature radius of the R processing described below is set to 5 to 10 mm.

[0034] Furthermore, a rounded portion 43 is applied to connect the rear end surface of the flange main body 41 (specifically, the bolt fixing surface 411 in this embodiment) and the outer peripheral surface of the flange reinforcing portion 42. The radius of curvature of the rounded portion applied to the connecting portion 43 is 5 to 10 mm. By applying a rounded portion with a curvature radius of 5 to 10 mm to the connecting portion 43, stress concentration in the flange reinforcing portion 42 is significantly reduced compared to when a rounded portion with a curvature radius of 2 mm is applied, and the mechanical strength of the mounting flange 12 as a whole is improved.

[0035] Generally, because stress tends to concentrate in areas such as the connecting portion 43, R machining is often performed. In this embodiment, it has been discovered that not only does R machining suppress stress concentration in the connecting portion 43, but by appropriately setting the radius of curvature, the maximum stress generated in the mounting flange 12 can be reduced and the overall mechanical strength of the mounting flange 12 can be improved, and therefore the radius of curvature is set to 5 to 10 mm. This ensures mechanical strength sufficient to withstand use under high gas pressures without increasing the thickness of the flange main body 41.

[0036] Furthermore, in the embodiment, when the radius of curvature of the connecting portion 43 is set to 5 to 10 mm, the corner portions 424, 425, which are vertices of the planar shape of the flange reinforcing portion 42, are also formed in a curved shape in order to ensure space for the bolt fixing surface 411. Note that the radius of curvature of the corner portions 424, 425 does not have to be 5 to 10 mm.

[0037] FIG. 5 is a diagram showing the results of a simulation of the relationship between the radius of curvature of the connecting portion 43 and the maximum stress generated in the mounting flange 12. In FIG.

[0038] 5, by increasing the radius of curvature of the connecting portion 43, the maximum stress generated in the mounting flange 12 can be reduced. When the radius of curvature of the connecting portion 43 is 5 mm or more, the maximum stress can be reduced to 60% or less compared to when the radius of curvature is 2 mm. In particular, when the radius of curvature is 7 mm or more, the maximum stress can be reduced to 50% or less compared to when the radius of curvature is 2 mm, which is more preferable.

[0039] As shown in Figure 5, when the radius of curvature is 7 mm or greater, the effect of reducing the maximum stress is almost saturated. In other words, the maximum stress generated in the mounting flange 12 remains almost constant even when the radius of curvature is increased. Note that when the radius of curvature of the connecting portion 43 is less than 5 mm, the effect of reducing the maximum stress generated in the mounting flange 12 is small, and the effect of suppressing damage to the epoxy resin forming the mounting flange 12 is small. Furthermore, when the radius of curvature of the connecting portion 43 is greater than 10 mm, the convex portion 422 of the flange reinforcement portion 42 becomes small, reducing the effect of the convex portion 422 as a rib. Therefore, the radius of curvature of the connecting portion 43 is preferably 5 to 10 mm, and more preferably 7 to 10 mm. This increases the mechanical strength of the mounting flange 12.

[0040] As described above, the bushing 10 according to the embodiment has the following features either singly or in appropriate combination.

[0041] That is, the bushing includes a bushing body 11 made of a resin material, a mounting flange 12 formed integrally with the bushing body 11 from the resin material and fastened to an equipment case 60 by a fixing bolt 31, and a cylindrical embedded metal fitting 33 having a bolt through hole 412 through which the fixing bolt 31 is inserted. The mounting flange 12 has a flange body portion 41 having a regular hexagonal shape in a plan view from the axial direction, with the embedded metal fitting 33 embedded near the vertices of the regular hexagon, and a flange reinforcing portion 42 having a six-fold rotationally symmetrical polygonal shape in a plan view from the axial direction, with convex portions 422 and concave portions 423 formed alternately, the flange reinforcing portion 42 protruding from the rear end side of the flange body portion 41 so that bolt fixing surfaces 411 to which the fixing bolts 31 are fixed are exposed from the concave portions 423, and a connecting portion 43 between the bolt fixing surfaces 411 and the outer peripheral surface of the flange reinforcing portion 42 is rounded with a radius of curvature of 5 to 10 mm. The radius of curvature of the connecting portion 43 is preferably 7 to 10 mm.

[0042] According to the bushing 10, stress concentration in the flange reinforcing portion 42 is suppressed and the mechanical strength of the mounting flange 12 as a whole is improved, so that the mechanical strength sufficient to withstand use under high gas pressure can be ensured without making major design changes such as increasing the thickness of the flange main body portion 41.

[0043] Furthermore, in the bushing 10, a washer accommodating portion 413 that communicates with the bolt through-hole 412 and is concavely formed in the bolt fixing surface 411 and is capable of accommodating a washer 32, and the fixing bolt 31 is inserted through the bolt through-hole 412 of the embedded fitting 33 with the washer 32 interposed therebetween. The washer 32 does not come into contact with the corners of the bolt fixing surface 411 (the open end of the washer accommodating portion 413), and no external force is applied during the tightening operation of the fixing bolt 31. This prevents damage such as cracks and chips from occurring in the flange main body 41 starting from the corners of the bolt fixing surface 411, making it even more suitable for use under high gas pressure.

[0044] Furthermore, in bushing 10, two bolt through holes 412 are arranged at symmetrical positions on bolt fixing surfaces 411 exposed from each recess 423. This equalizes the stress generated in mounting flange 12 and suppresses the maximum stress, thereby improving the mechanical strength of mounting flange 12 as a whole.

[0045] In the bushing 10, the outer diameter of the flange main body is 250 to 350 mm. This allows the connecting portion 43 to be rounded with a curvature radius of 5 to 10 mm without interfering with other components (for example, the bolt through hole 412).

[0046] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist thereof.

[0047] The bushing of the present invention can be applied not only to the gas terminations of power equipment as in the embodiment, but also to a wide range of so-called prefabricated cable terminations, such as air terminations, gas terminations, and oil terminations. Furthermore, in the case of cable terminations using the bushing of the present invention, it may be not only the so-called inner cone type in which a stress cone is inserted inside the bushing as in the embodiment, but also the so-called outer cone type in which a rubber block insulator is attached to the outside of the bushing.

[0048] Furthermore, in the present invention, the term "bushing" includes not only the main body material of a cable termination connection part as in the embodiment, but also bushings for power equipment that are not cable termination connection parts, etc. In other words, the present invention can be applied to bushings in which the bushing body and mounting flange are integrally formed from an insulating material (for example, a hard plastic resin material with high mechanical strength such as epoxy resin or FRP).

[0049] In addition, in the embodiment, the bushing according to the present invention has been described as being applied to a 66 / 77 kV class cable termination connection portion, but the voltage class used is not particularly limited, and it may also be applied to a cable termination connection portion of, for example, 110 kV or 154 kV or higher.

[0050] In the embodiment, the electric field mitigation portion 14 is formed by applying conductive paint, but it may be formed by embedding a shielding metal fitting in the bushing body 11. In the case of a cable termination using the bushing according to the present invention, the connection configuration between the cable conductor 51 and the inner conductor 13 is not limited to the tulip contact type as in the embodiment, and may be, for example, a multi-contact type.

[0051] In the embodiment, the bushing 10 is described as being attached to the equipment case 60, but this is not limiting and the bushing may be attached to a sealed case. For example, the bushing may be used as a so-called epoxy seat for an outdoor termination connection, or may be attached to a test case.

[0052] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0053] 1 Cable termination 10 Bushing 11 Bushing body 12 Mounting flange 13 Inner conductor 31 Fixing bolt 32 washer 33 Embedded fittings 41 Flange body 42 Flange reinforcement 43 Continuous part 60 Equipment Case 411 Bolt fixing surface 412 Bolt through hole 422 Convex part 423 Recess 424, 425 Corner

Claims

1. a bushing body formed of a resin material; a mounting flange formed integrally with the bushing body from the resin material and fastened to an equipment case by a fixing bolt; a cylindrical embedded fitting having a bolt through-hole through which the fixing bolt is inserted, The mounting flange is a flange main body portion having a regular hexagonal shape in a plan view as viewed from the axial direction, the embedded metal fittings being embedded near the vertices of the regular hexagon; a flange reinforcing portion formed so as to protrude from the rear end side of the flange main body portion so that a bolt fixing surface on which the fixing bolt is fixed is exposed from the recessed portion, and the flange reinforcing portion has a planar shape as viewed from the axial direction that is a six-fold rotationally symmetric polygon in which convex portions and concave portions are alternately formed, The connecting portion between the bolt fixing surface and the outer peripheral surface of the flange reinforcing portion is subjected to R processing with a curvature radius of 5 to 10 mm. Bushing.

2. The radius of curvature is 7 to 10 mm.

2. The bushing of claim 1.

3. a washer receiving portion that communicates with the bolt through hole and is capable of receiving a washer is formed on the bolt fixing surface, The fixing bolt is inserted into the bolt through-hole of the embedded metal fitting via the washer.

2. The bushing of claim 1.

4. The two bolt through holes are arranged at symmetrical positions on the bolt fixing surfaces exposed from the respective recesses.

4. A bushing according to claim 1 or 3.

5. The outer diameter of the flange body is 250 to 350 mm.

4. The bushing according to claim 1 or 3.

6. The resin material is an epoxy resin.

4. The bushing according to claim 1 or 3.

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