Bushing

Abstract

To suppress a rise in electric field of an electric field relaxation shield.SOLUTION: A bushing (10) is mounted while penetrating an opening (2) which is formed in a partition wall (1). The bushing comprises: a central conductor (11) which extends in a thickness direction of the partition wall; a first insulation part (13) which is formed on an outer periphery of the central conductor and inserted into the opening; an electric field relaxation shield (20) which is embedded in the first insulation part and provided at a position enclosing the central conductor; and a second insulation part (14) which is provided while enclosing an outer periphery of the first insulation part at the side of a top face (1a) of the partition wall in the thickness direction of the partition wall. The electric field relaxation shield includes a shield main body (21) which is provided in a cylindrical shape of which the center axis direction is in parallel with an extension direction of the central conductor. An upper end side which is one end side of the shield main body in the center axis direction is provided at a position which is held between the central conductor and the second insulation part in a direction orthogonal to the center axis direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bushing having an electric field mitigation shield embedded in an insulating material. [Background technology]

[0002] Patent Document 1 discloses a bushing that is fixed to the outer box of a switchgear, transformer, etc. Such a bushing is composed of a main circuit conductor, a shield, and epoxy resin as an insulating medium. The shield is a cylindrical conductor that covers the main circuit conductor and is positioned inside the epoxy resin. In Patent Document 1, the shield is grounded to reduce the electric field inside and outside the outer box and bushing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-326319 Summary of the Invention [Problem to be solved by the invention]

[0004] In a bushing such as that described in Patent Document 1, the electric field tends to become high at the end of the shield, and in order to alleviate the electric field at the end, a structure in which the diameter dimension of the cylindrically formed shield is increased and the distance from the main circuit conductor is lengthened is conceivable. However, with such a structure, the end of the shield approaches the creeping surface of the epoxy resin, which creates a high electric field at the creeping surface, and this causes a problem in that the electric field cannot be sufficiently alleviated.

[0005] The present invention has been made in view of the above-mentioned points, and has an object to provide a bushing that can suppress the increase in the electric field of the electric field mitigation shield. [Means for solving the problem]

[0006] A bushing of one embodiment of the present invention is a bushing that is inserted through an opening formed in a partition wall, and comprises: a central conductor extending in the thickness direction of the partition wall; a first insulating portion formed on the outer periphery of the central conductor and inserted into the opening; an electric field mitigation shield embedded in the first insulating portion and provided at a position surrounding the central conductor; and a second insulating portion provided surrounding the outer periphery of the first insulating portion on one main surface side of the partition wall in the thickness direction of the partition wall, wherein the electric field mitigation shield comprises a shield body that is provided in a cylindrical shape with a central axis direction parallel to the extension direction of the central conductor, and one end side of the shield body in the central axis direction is provided at a position sandwiched between the central conductor and the second insulating portion in a direction perpendicular to the central axis direction. Effect of the Invention

[0007] According to the present invention, a first insulating portion and a second insulating portion are provided around the central conductor, and one end side of the shield main body is embedded in the first insulating portion and covered by the second insulating portion. This makes it possible to reduce the electric field at the one end side of the shield main body by both the first insulating portion and the second insulating portion, and makes it possible to suppress an increase in the electric field in the electric field relaxation shield. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic vertical cross-sectional view of a bushing and its surrounding structure according to an embodiment of the present invention; [Diagram 2] 2A and 2B are longitudinal sectional views that diagrammatically show an example of an electric field mitigation shield. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a bushing according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiment, and can be appropriately modified and implemented without departing from the gist of the present invention. In the following drawings, some components may be omitted for convenience of explanation. In the following explanation, unless otherwise specified, "upper", "lower", "left" and "right" are based on Figs. 1 and 2. However, the orientation of each component in the following embodiment is merely an example, and can be changed to any orientation.

[0010] Fig. 1 is a schematic vertical cross-sectional view of a bushing and its surrounding structure according to an embodiment. As shown in Fig. 1, a bushing 10 is attached to an electric power device (not shown) such as a switchgear or a transformer by penetrating an opening 2 formed in a partition wall 1 constituting a housing, a bulkhead, or the like.

[0011] The partition wall 1 is made of a metal plate whose thickness direction is the vertical direction and is at ground potential or a potential slightly higher than ground potential. The partition wall 1 is formed with an upper surface 1a and a lower surface 1b as main surfaces, which are the forming surfaces on both sides in the vertical direction. The opening 2 is formed in a circular shape when viewed from the vertical direction.

[0012] The bushing 10 includes a central conductor 11 extending in the vertical direction (thickness direction of the partition wall 1), a first insulating portion 13 formed on the outer periphery of the central conductor 11, and a second insulating portion 14 provided surrounding the outer periphery in the upper half of the first insulating portion 13. The central conductor 11 is formed in a roughly cylindrical shape, and ends of a high-voltage conductor (not shown) are connected to both the upper and lower ends in FIG. 1 via a screw structure or the like.

[0013] The first insulating part 13 is formed by casting molding or the like using an insulating resin such as epoxy resin. The first insulating part 13 includes an intermediate forming part 16 inserted into the opening 2, a first forming part 17 connected to an upper part of the intermediate forming part 16 and extending upward, and a second forming part 18 connected to a lower part of the intermediate forming part 16 and extending downward.

[0014] The intermediate forming portion 16 is formed in a disk shape with an outer diameter dimension slightly smaller than the inner diameter dimension of the opening 2. When viewed in cross section as in Figure 1, the boundary position between the intermediate forming portion 16 and the first forming portion 17 is formed in an internal corner, and the boundary position between the intermediate forming portion 16 and the second forming portion 18 is also formed in an internal corner. Therefore, a step is formed between the upper surface of the intermediate forming portion 16 and the upper surface of the second forming portion 18.

[0015] The first forming portion 17 forms a portion of the first insulating portion 13 that is disposed on the upper surface 1a side (one of the main surfaces) of the partition wall 1. The first forming portion 17 is formed in a truncated cone shape that gradually reduces in diameter as it moves away from the partition wall 1. Thus, the outer peripheral surface of the first forming portion 17 is formed by a tapered surface. The lower end side of the first forming portion 17 is formed to have an outer diameter smaller than the outer diameter of the intermediate forming portion 16.

[0016] The second forming portion 18 forms a portion of the first insulating portion 13 that is disposed on the lower surface 1b side (the other main surface side) of the partition wall 1. The second forming portion 18 is provided in a shape that includes a flange portion 18a whose upper surface contacts the lower surface 1b of the partition wall 1, and a spindle portion 18b that is formed in a spindle shape whose diameter gradually decreases from the lower end of the flange portion 18a downward (away from the partition wall 1).

[0017] The flange portion 18a is formed in a roughly circular plate shape with an outer diameter dimension larger than the inner diameter dimension of the opening 2, and is provided to close the opening 2. The flange portion 18a is fixed by bolts or the like in a state where it closes the opening 2, and maintains airtightness between the upper and lower spaces sandwiching the partition wall 1. The outer dimension of the upper end side of the spindle portion 18b is smaller than the outer diameter dimension of the flange portion 18a, slightly larger than the inner diameter dimension of the opening 2, and larger than the outer diameter dimension of the lower end side of the first forming portion 17.

[0018] The second insulating portion 14 is provided on the upper surface 1a side of the partition wall 1, and is formed in a cylindrical shape that receives the first forming portion 17 of the first insulating portion 13 therein. The upper end of the second insulating portion 14 is provided at a vertical position that is roughly flush with the upper end of the first insulating portion 13, and the lower end of the second insulating portion 14 is located slightly above the lower end of the first insulating portion 13, and is disposed with a gap between it and the upper surface 1a of the partition wall 1.

[0019] The inner peripheral surface of the second insulating portion 14 is formed into a tapered surface shape according to the outer peripheral surface of the first forming portion 17 in the first insulating portion 13, and is provided so as to closely contact and make surface contact with the outer peripheral surface of the first forming portion 17. The second insulating portion 14 is formed of a resin having insulating properties, for example, a silicone resin or the like which is a resin different from that of the first insulating portion 13. A ground layer 19 which becomes a ground potential is formed on the outer peripheral side of the second insulating portion 14. By providing the second insulating portion 14 and the ground layer 19, the electric field in the gas phase portion above the surface of the second insulating portion 14 (ground layer 19) and the partition wall 1 is alleviated.

[0020] The bushing 10 of the present embodiment further includes an electric field reduction shield 20 embedded in the first insulating portion 13. The electric field reduction shield 20 is provided at a position surrounding the central conductor 11 and at a position passing through the opening 2 in the vertical direction.

[0021] The electric field mitigation shield 20 only needs to be at a lower potential than the central conductor 11, and is electrically connected to the partition wall 1 by a connection structure (not shown) and is set to the same ground potential as the partition wall 1. This reduces the concentration of the electric field between the inner periphery of the opening 2 and the surface of the first insulating part 13 in the vicinity thereof. Note that the ground layer 19 can also be set to the ground potential in the same manner as the electric field mitigation shield 20.

[0022] The electric field reduction shield 20 includes a shield body 21 that is provided in a cylindrical shape with a central axis direction parallel to the up-down direction (extension direction of the central conductor 11). The shield body 21 is provided in a shape along a truncated cone having the same central axis as the central conductor 11. More specifically, the shield body 21 is provided in a shape that reduces in diameter from the lower end side (the other end side in the central axis direction) to the upper end side (one end side in the central axis direction).

[0023] The upper end of the shield body 21 is embedded in the first forming portion 17 and disposed above the lower end position of the second insulating portion 14. Therefore, the upper end side of the shield body 21 is provided at a position sandwiched between the central conductor 11 and the second insulating portion 14 in a direction (left-right direction in FIG. 1) perpendicular to the up-down direction (central axis direction). The lower end of the shield body 21 is embedded in the second forming portion 18 and disposed near the boundary position between the flange portion 18a and the spindle portion 18b in the up-down direction.

[0024] The electric field mitigation shield 20 further includes end forming bodies 22 provided on both upper and lower sides of the shield body 21. The end forming body 22 is formed in a circular loop shape when viewed from the central axis direction. The end forming body 22 and the shield body 21 are made of a metal material such as copper or aluminum.

[0025] Next, the configuration of the shield body 21 in the electric field mitigation shield 20 will be described below with reference to Fig. 2. Fig. 2A and Fig. 2B are vertical cross-sectional views that typically show an example of an electric field mitigation shield.

[0026] In the above embodiment, the electric field mitigation shield 20 may employ a shield body 21 shown in Fig. 2A and Fig. 2B. The shield body 21 shown in Fig. 2A includes a cylindrical body 21a formed into a shape along the tapered surface of a truncated cone by a plate-like body, and a plurality of holes 21b formed in the cylindrical body 21a. The plurality of holes 21b are evenly formed in the circumferential direction (the rotation direction about the central axis of the shield body 21) and the vertical direction (the central axis direction of the shield body 21) of the cylindrical body 21a.

[0027] The shield body 21 shown in Fig. 2B includes a tube body 21c formed in the same manner as the tube body 21a in Fig. 2A, and a plurality of slits 21d formed in the tube body 21c. Each slit 21d is formed to open in an elongated hole shape, and its longitudinal direction is oriented in the extension direction of the generatrix of the truncated cone in the tube body 21c. The plurality of slits 21d are formed in a line in the circumferential direction of the tube body 21c.

[0028] 2A and 2B, the holes 21b and slits 21d can be formed to improve the adhesion between the resin forming the first insulating portion 13 and the shield body 21. This can suppress electric field concentration around the interface between the first insulating portion 13 and the shield body 21, and can prevent deterioration of insulation performance.

[0029] 2A and 2B, a method of manufacturing the shield body 21 may be exemplified by drilling holes corresponding to the holes 21b and slits 21d in a plate-like body forming the cylindrical bodies 21a and 21c. Alternatively, a manufacturing method may be exemplified by irradiating a laser on stacked metal powder to melt and solidify it, and stacking it. Compared to the conventional structure using a wire mesh, each of the above-mentioned shield bodies 21 has a higher bending strength, making it easier to prevent deformation due to the flow of resin during casting when manufacturing the first insulating part 13, and facilitating manufacturing.

[0030] 1, in the bushing 10 according to the above embodiment, the electric field tends to concentrate at the upper and lower ends of the electric field relaxation shield 20. Therefore, in the bushing 10 using the electric field relaxation shield 20, it is important to relax the electric field at both the upper and lower ends of the electric field relaxation shield 20.

[0031] In order to reduce the electric field at the upper end of the electric field reduction shield 20, in this embodiment, a second insulating portion 14 is provided. Furthermore, in this embodiment, the upper end of the shield body 21 is sandwiched between the central conductor 11 and the second insulating portion 14 in the left-right direction (radial direction). This results in an insulating portion having a thickness of the second insulating portion 14 being disposed in the direction from the upper end of the shield body 21 toward the outside in the left-right direction.

[0032] This makes it possible to suppress the electric field from concentrating on the creeping surface of the insulating portion (first insulating portion 13 and second insulating portion 14) for the gas phase portion near the upper end of the shield body 21. This makes it possible to set the diameter dimension of the upper end of the shield body 21 as large as possible while satisfying the manufacturing conditions that allow the electric field mitigation shield 20 to be embedded in the first insulating portion 13. This makes it possible to increase the distance between the upper end of the shield body 21 and the central conductor 11, thereby mitigating the electric field at the upper end.

[0033] Here, the length in the left-right direction (radial direction) at the position of the upper end of the electric field mitigation shield 20 in the first insulating part 13 will be described using the lengths L1 and L2 shown in FIG. 1. The length L1 is the length between the outer circumferential position of the upper end forming body 22 (upper end) in the electric field mitigation shield 20 and the outer circumferential position of the central conductor 11. The length L2 is the length between the outer circumferential position of the upper end forming body 22 (upper end) in the electric field mitigation shield 20 and the outer circumferential position of the first insulating part 13. In this embodiment, the length L2 is set to be 10% or more and 20% or less when the length L1 is 100% and expressed as a percentage. If the percentage is less than 10%, the length L2 becomes too small, making it difficult to mold the first insulating part 13, and if the percentage exceeds 20%, the end forming body 22 approaches the central conductor 11, making it difficult to obtain a sufficient electric field mitigation effect.

[0034] In this embodiment, the shield body 21 is formed in a shape along a truncated cone, and the lower end is formed to have a larger diameter than the upper end. In the first insulating part 13, the second forming part 18 in which the lower end of the shield body 21 is embedded has a larger diameter than the upper first forming part 17, so that the thickness of the second forming part 18 around the lower end can be ensured while increasing the distance between the lower end of the shield body 21 and the central conductor 11. Therefore, even in the lower end of the shield body 21, the distance from the central conductor 11 can be increased to relax the electric field at the lower end, and it is possible to prevent the lower end from approaching the creeping surface of the second forming part 18 to create a high electric field. The diameter of the lower end of the shield body 21 is set in consideration of the manufacturing conditions of the first insulating part 13, as well as the distance between the inner corner of the boundary between the intermediate forming part 16 and the first forming part 17 and the shield body 21.

[0035] As described above, according to the above embodiment, it is possible to reduce the electric field on the upper end side and the lower end side of the shield body 21, and the increase in the electric field in the electric field mitigation shield 20 can be suppressed.

[0036] The embodiments of the present invention are not limited to the above-mentioned embodiments, and may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way due to technological progress or a different derived technology, the present invention may be implemented using that method. Therefore, the claims cover all embodiments that may be included within the scope of the technical idea of ​​the present invention.

[0037] In the above embodiment, the hole 21b in Fig. 2A and the slit 21d in Fig. 2B are not limited to the shapes shown in the drawings, and various modifications are possible. For example, the hole 21b in Fig. 2A may be rectangular, polygonal, or elliptical instead of circular, and the slit 21d in Fig. 2B may be oval or multiple slits may be arranged in the longitudinal direction.

[0038] Furthermore, the cross-sectional shape of end portion forming body 22 in FIG. 2A and FIG. 2B and the form of the connection portion between end portion forming body 22 and shield main body 21 may be appropriately changed so as to reduce electric field concentration.

[0039] Furthermore, the ground layer 19 on the outer periphery of the second insulating portion 14 may be omitted. However, providing the ground layer 19 makes it possible to more effectively prevent the generation of a high electric field on the surface of the second insulating portion 14 .

[0040] In the above embodiment, the shield body 21 is shaped to conform to a truncated cone, but may be formed to be cylindrical. However, by forming the shield body 21 to conform to a truncated cone, the distance between the lower end of the shield body 21 and the central conductor 11 can be increased, thereby mitigating the electric field.

[0041] Furthermore, the central conductor 11 may have a constricted shape in the region surrounded by the electric field reduction shield 20 .

[0042] Moreover, the intermediate forming portion 16 may be modified to have a truncated cone shape with a tapered outer circumferential surface. [Explanation of symbols]

[0043] 1: Partition wall 1a: Top surface (one of the main surfaces) 1b: Bottom surface (other main surface) 2:Aperture 10: Bushing 11: Center conductor 13: First insulating part 14: Second insulating part 17:First forming part 18:Second forming part 19: Ground layer 20: Electric field mitigation shield 21: Shield body 21a: Cylinder body 21b: Hole 21c: Cylinder body 21d: Slit

Claims

1. A bushing is attached through an opening formed in a partition wall, a central conductor extending in a thickness direction of the partition wall; a first insulating portion formed on an outer periphery of the central conductor and inserted into the opening; an electric field reduction shield that is embedded in the first insulating portion and is provided at a position surrounding the central conductor; a second insulating portion provided on one main surface side of the partition wall in a thickness direction of the partition wall to surround an outer periphery of the first insulating portion, The electric field reduction shield includes a shield body that is provided in a cylindrical shape with a central axis direction parallel to an extension direction of the central conductor, A bushing characterized in that one end side in the central axis direction of the shield body is located at a position sandwiched between the central conductor and the second insulating portion in a direction perpendicular to the central axis direction.

2. The first insulating portion includes a first forming portion that forms a portion disposed on one main surface side of the partition wall; a second forming portion that forms a portion that is to be disposed on the other main surface side of the partition wall, The first forming portion and the second forming portion are each formed to have a shape that decreases in diameter as it moves away from the partition wall, 2. The bushing according to claim 1, wherein the shield body is shaped so that its diameter decreases from the other end side toward the one end side in the central axial direction.

3. The shield body includes a cylindrical body formed of a plate-like body, 3. The bushing according to claim 2, further comprising a plurality of holes formed in the circumferential direction and in the central axis direction of the cylindrical body.

4. The shield body includes a cylindrical body formed of a plate-like body, 3. The bushing according to claim 2, further comprising a plurality of slits formed in the cylindrical body in a circumferential direction.

5. The second insulating portion is formed in a cylindrical shape, 5. The bushing according to claim 1, wherein a ground layer having a ground potential is formed on an outer periphery of the second insulating portion.

Images