Bushing

Abstract

To provide a bushing capable of suppressing an occurrence of partial discharge on a boundary surface between an accepting part of the bushing and an insulation rubber part of an insulation plug.SOLUTION: A bushing has an inner conductor, an insulation cylinder placed on an outer periphery of the inner conductor, and an electric field relaxing member relaxing an electric field at the time of charging the inner conductor. The insulation cylinder has an accepting part to which an insulation plug can be attached. The accepting part has a first accepting surface fitted to an outer shape of a tapered insulation rubber part of the insulation plug and a columnar second accepting surface mounted continuously to a rear end of the first accepting surface. The electric field relaxing member has a conductive ring part arranged so as to surround the accepting part in the vicinity of the boundary between the first accepting surface and the second accepting surface, and a ground part grounding the ring part.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, cable termination connections such as a gas termination connection, an oil termination connection, and an air termination connection are known (see, for example, Patent Document 1). In general, a cable termination connection is formed by connecting a cable terminal portion to which a connection material is attached to a main body material (hereinafter referred to as a "bushing") having an inner conductor and a hard insulating tube arranged around the outer periphery of the inner conductor.

[0003] The bushing has a receiving portion into which a power cable or a charging cable can be attached. When a power cable or a charging cable is not attached, an insulating plug is attached to the receiving portion (see, for example, Patent Document 1). The insulating plug generally has a high-voltage electrode, an insulating rubber part, and a low-voltage electrode. The insulating plug is fixed with the insulating rubber part pressed against the inner surface of the receiving portion.

[0004] More specifically, the receiving portion has a first receiving surface on the tip side that fits the shape of the insulating rubber portion and applies a large surface pressure to the insulating rubber portion, and a second receiving surface that applies a smaller surface pressure to the insulating rubber portion than the first receiving surface (including the case where the surface pressure is zero). For example, the first receiving surface is a tapered surface that is inclined with respect to the axial direction of the bushing. The second receiving surface is a cylindrical surface having a diameter substantially the same as or slightly larger than the maximum outer diameter of the insulating rubber portion, and is connected to the rear end of the first receiving surface. The insulating rubber portion is pressed against the receiving portion with a predetermined surface pressure, thereby ensuring the insulating performance of the bushing. In the bushing, the electric field when a voltage is applied is controlled by the internal conductor, the shielding layer formed on the surface of the insulating tube, and the thickness and shape of the insulating tube. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3080331 Summary of the Invention [Problem to be solved by the invention]

[0006] When a voltage is applied to the bushing with the insulating plug attached, an equipotential distribution as shown in FIG. 1 occurs near the interface between the receiving part and the insulating rubber part. That is, the equipotential lines wrap around the area near the second receiving surface and the insulating rubber part, although the potential is small. An electric field is generated in a direction perpendicular to the equipotential lines. Therefore, an electric field according to the interval between the adjacent equipotential lines is generated at the point where the equipotential lines wrap around. On the other hand, the gap between the second receiving surface and the insulating rubber part needs to be removed toward the rear end so that no gap remains at the interface between the first receiving surface and the insulating rubber part. Therefore, the two surfaces do not come into close contact with each other, and an air layer may be present at the interface between the second receiving surface and the insulating rubber part. In this case, there is a risk of partial discharge occurring due to the air layer being present at the interface between the second receiving surface and the insulating rubber part.

[0007] An object of the present invention is to provide a bushing that can suppress the occurrence of partial discharge at the interface between the receiving portion of the bushing and the insulating rubber portion of the insulating plug. [Means for solving the problem]

[0008] The bushing according to the present invention comprises: An inner conductor; an insulating tube disposed around the outer periphery of the inner conductor; an electric field relaxation member that is embedded in the insulating cylinder and relaxes an electric field when a voltage is applied to the internal conductor; The insulating tube has a receiving portion into which an insulating plug can be attached, the receiving portion has a first receiving surface that fits the outer shape of the tapered insulating rubber portion of the insulating plug, and a cylindrical second receiving surface that is connected to a rear end of the first receiving surface, The electric field relaxation member has a conductive ring portion arranged to surround the receiving portion near the boundary between the first receiving surface and the second receiving surface, and a ground portion that grounds the ring portion. Effect of the Invention

[0009] According to the present invention, it is possible to suppress the occurrence of partial discharge at the interface between the receiving portion of the bushing and the insulating rubber portion of the insulating plug. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the equipotential distribution near the interface between the receiving part and the insulating plug in a bushing of a conventional structure. [Diagram 2] FIG. 2 is a partial cross-sectional view showing the internal structure of a cable connection termination to which a bushing according to an embodiment of the present invention is applied. [Diagram 3] FIG. 3 is an enlarged view of the vicinity of the voltage applying section. [Figure 4] FIG. 4 is a perspective view showing an example of an electric field relaxation member. [Diagram 5] 5A and 5B are diagrams showing an example of equipotential distribution when an electric field relaxation member is disposed. [Figure 6] 6A to 6C are diagrams showing an example of the equipotential distribution when the position of the ring portion is changed. [Figure 7] 7A and 7B are diagrams showing an example of equipotential distribution when the position of the ring portion is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] Fig. 2 is a partial cross-sectional view showing the internal structure of a cable connection end 1 to which a bushing 10 according to an embodiment of the present invention is applied. Fig. 3 is an enlarged view of the vicinity of a voltage-loading unit 102. Fig. 3 shows the state before an insulating plug 20 is attached. The cable connection end 1 is formed by attaching a cable terminal unit (not shown) to the bushing 10.

[0013] The cable termination 1 is a direct-connection type termination for electric power equipment such as a switchgear or a transformer that requires airtightness. In the following description, in the first bushing 10A, the upper side is referred to as the "tip side" and the lower side is referred to as the "rear side" in the drawings, and in the second bushing 10B, the right side is referred to as the "tip side" and the left side is referred to as the "rear side" in the drawings. In other words, the side toward which the member is attached is referred to as the "tip side" and the opposite side is referred to as the "rear side". Also, the end face on the tip side may be referred to as the "tip face" and the end face on the rear side as the "rear face".

[0014] The bushing 10 has a first bushing portion 10A extending in a first direction (vertical direction (up and down direction in FIG. 2)) and a second bushing portion 10B extending in a second direction (horizontal direction (left and right direction in FIG. 2)) perpendicular to the first direction. The bushing 10 is a so-called T-shaped bushing in which the second bushing portion 10B is branched and connected to the axial center of the first bushing portion 10A.

[0015] The first bushing part 10A has at one end (upper side in FIG. 2) an equipment connection part 101 to which an electric power equipment is connected, and at the other end (lower side in FIG. 2) a voltage charging part 102 to which a voltage charging cable is connected during a voltage resistance test. The second bushing part 10B has at its open end a cable connection part 103 to which a cable terminal part (not shown) is connected. Note that the voltage charging part 102 is closed by an insulating plug 20 during normal use.

[0016] The bushing 10 includes an inner conductor 11, an insulating tube 12, a shielding layer 13, an equipment-side fixing flange 14, a current-carrying-side fixing flange 15, and an electric field relaxation member 50. The inner conductor 11, the insulating tube 12, and the electric field relaxation member 50 are integrally formed by, for example, molding.

[0017] The internal conductor 11 is formed of a conductive material suitable for current flow, such as copper, aluminum, a copper alloy, or an aluminum alloy. The internal conductor 11 has a first conductor connection part (reference number omitted) that connects to a cable conductor for charging (not shown) inserted into the charging unit 102, and a second conductor connection part (reference number omitted) that connects to a cable conductor of a power cable inserted into the cable connection part 103. The first conductor connection part and the second conductor connection part each have an insertion hole for inserting a connection part (conductor connection terminal, etc.) of a cable conductor. Note that FIG. 2 shows a normal use state, and an insulating plug 20 is attached to the charging unit 102. A high-voltage side electrode 21 on the tip side of the insulating plug 20 is electrically connected to the first conductor connection part of the internal conductor 11.

[0018] The insulating tube 12 is formed of a hard plastic resin material having high mechanical strength (for example, epoxy resin or fiber reinforced plastics (FRP)). The insulating tube 12 is disposed on the outer periphery of the inner conductor 11.

[0019] The insulating tube 12 has a receiving portion 30 for receiving a charging cable (not shown) at the rear end on the charging unit 102 side. The insulating tube 12 also has a receiving portion for receiving a cable terminal at the rear end on the cable connection unit 103 side, but a description thereof will be omitted here.

[0020] The receiving portion 30 communicates with an insertion hole of the first conductor connecting portion of the internal conductor 11. The receiving portion 30 has a first receiving surface 31, a second receiving surface 32, and a third receiving surface 33. The first receiving surface 31, the second receiving surface 32, and the third receiving surface 33 have shapes that fit the outer shape of the insulating plug 20 to be attached, specifically, the outer shape of the insulating rubber portion 22.

[0021] The first receiving surface 31 has a tapered shape that reduces in diameter from the rear end to the front end. The second receiving surface 32 is connected to the rear end of the first receiving surface 31. The second receiving surface 32 is a large diameter portion formed with approximately the same diameter as the maximum inner diameter of the first receiving surface 31. The third receiving surface 33 is connected to the front end of the first receiving surface 31. The third receiving surface 33 is a small diameter portion formed with approximately the same diameter as the minimum inner diameter of the first receiving surface 31.

[0022] The shielding layer 13 is formed, for example, by a conductive paint applied to the outer circumferential surface of the insulating tube 12. The shielding layer 13 functions as a shielding section that prevents electric leakage to the outside and as an electric field mitigation section that mitigates the electric field within the bushing 10. The shielding layer 13 is formed, for example, on the entire outer circumferential surface of the insulating tube 12 from the device side fixing flange 14 to the current-carrying side fixing flange 15 in the first bushing part 10A. The shielding layer 13 is also formed, for example, on a portion of the outer circumferential surface of the insulating tube 12 excluding the end on the cable connection part 103 side in the second bushing part 10B.

[0023] The equipment side fixing flange 14 is a metal member that is arranged on the end face of the first bushing 10A on the equipment connection part 101 side (the upper side in Figure 2) of the part excluding the equipment connection part 101, and is arranged on the outer periphery of the rear end part of the equipment connection part 101.

[0024] The charging-side fixing flange 15 is a metal member disposed on the rear end surface of the insulating tube 12 in the charging section 102. The charging-side fixing flange 15 is fastened to the grounding section 52, which functions as an embedded metal fitting for the electric field relaxation member 50 embedded in the insulating tube 12, by a fixing bolt (not shown), for example.

[0025] The shielding layer 13 is electrically connected to the equipment-side fixing flange 14 and the load-side fixing flange 15. The shielding layer 13 is electrically connected to an equipment case (not shown) of the power equipment via the equipment-side fixing flange 14, and is grounded. The load-side fixing flange 15 and the electric field relaxation member 50 are also at ground potential.

[0026] In normal use, the insulating plug 20 is attached to the receiving portion 30 of the voltage-loading portion 102. The insulating plug 20 has a high-voltage electrode 21, an insulating rubber portion 22, a low-voltage electrode 23, a spring 24, and a fixing bracket 25. The high-voltage electrode 21, the insulating rubber portion 22, and the low-voltage electrode 23 are integrally formed by, for example, insert molding. Hereinafter, the member in which the high-voltage electrode 21, the insulating rubber portion 22, and the low-voltage electrode 23 are integrated is referred to as the "insulating plug main body."

[0027] The insulating rubber part 22 is formed of a rubber material such as ethylene propylene rubber (EP rubber). The insulating rubber part 22 has a first rubber part 221 that abuts against the first receiving surface 31 of the bushing 10, a second rubber part 222 that abuts against or is close to the second receiving surface 32, and a third rubber part 223 that abuts against or is close to the third receiving surface 33. The outer diameter of the second rubber part 222 is approximately the same as or slightly smaller than the inner diameter of the second receiving surface 32. The outer diameter of the third rubber part 223 is approximately the same as the outer diameter of the high voltage side electrode 21 and is approximately the same as or slightly smaller than the inner diameter of the third receiving surface 33.

[0028] The high-voltage electrode 21 is embedded in the tip of the insulating rubber part 22. The tip surface and the outer peripheral surface on the tip side of the high-voltage electrode 21 are exposed from the tip of the insulating rubber part 22, and are electrically connected to the internal conductor 11 of the bushing 10 via a separate metal member (not shown). The high-voltage electrode 21 has, for example, a convex shape that bulges toward the insulating rubber part 22 side (rear end side). It is sufficient that the surface of the high-voltage electrode 21 is conductive, and the high-voltage electrode 21 may be made conductive by applying a conductive paint to the surface of an insulating member.

[0029] The low-voltage electrode 23 is embedded in the rear end of the insulating rubber part 22. The rear end surface of the low-voltage electrode 23 is exposed from the rear end of the insulating rubber part 22. The low-voltage electrode 23 has, for example, a convex shape that bulges towards the insulating rubber part 22. A spring 24 is disposed at the rear end of the low-voltage electrode 23. The low-voltage electrode 23 is mechanically and electrically connected to a fixing bracket 25 via the spring 24. It is sufficient that the surface of the low-voltage electrode 23 is conductive, and the low-voltage electrode 23 may be made conductive by applying a conductive paint to the surface of an insulating member.

[0030] When the insulating plug 20 is attached to the receiving portion 30 of the bushing 10, the insulating plug body is inserted into the receiving portion 30 with the spring 24 placed on the low-voltage electrode 23. Next, the fixing bracket 25 is placed on the rear end face side of the low-voltage electrode 23, and the fixing bracket 25 is fastened to the current-loading side fixed flange 15 with a fixing bolt (reference number omitted). A biasing force is generated in the spring 24, and the first rubber portion 221 of the insulating rubber portion 22 is pressed against the first receiving surface 31, thereby applying a surface pressure to the interface between the first receiving surface 31 and the first rubber portion 221. As a result, the first receiving surface 31 and the first rubber portion 221 come into close contact with each other, and the insulating performance of the interface between them is ensured.

[0031] In this embodiment, an electric field relaxation member 50 is embedded in the rear end of the insulating tube 12. The electric field relaxation member 50 relaxes the electric field when a voltage is applied to the inner conductor 11 with the insulating plug 20 attached to the receiving portion 30. The electric field relaxation member 50 has a ring portion 51 and a ground portion 52, as shown in FIG.

[0032] The ring portion 51 is, for example, a ring member having a circular cross-sectional shape. The ring portion 51 is disposed in the vicinity of the boundary between the first receiving surface 31 and the second receiving surface 32 of the receiving portion 30 so as to surround the receiving portion 30. For the ring portion 51, a material having electrical conductivity, such as brass, stainless steel alloy, or aluminum alloy, can be used. Note that the electric field relaxation metal fitting 50 only needs to have electrical conductivity on its surface, and may be made electrically conductive by applying a conductive paint to the surface of a ring-shaped insulating member.

[0033] The grounding portion 52 grounds the ring portion 51. The grounding portion 52 is electrically connected to the charging side fixing flange 15, for example, to ground the ring portion 51 through the grounding portion 52. In this embodiment, the grounding portion 52 functions as an embedded metal fitting to which the charging side fixing flange 15 is fixed by fastening a bolt. In other words, the grounding portion 52 functions as a reinforcing member for fixing the charging side fixing flange 15 to the insulating tube 12, and has a female thread into which a fixing bolt is fastened.

[0034] 4, a plurality of grounding portions 52 are provided as many as fixing bolts are required, and each grounding portion 52 is fixed mechanically and electrically when inserted into ring portion 51, and extends in the axial direction. The structure in which grounding portion 52 extends in the axial direction can also serve the function of fixing load-side fixing flange 15 (fixing flange) with bolts.

[0035] In addition, there are no particular limitations on the detailed structure of electric field relaxation member 50, including the cross-sectional area and ring diameter of ring portion 51, and the number of grounding portions 52. Electric field relaxation member 50 may be designed so that equipotential lines are not formed in a wraparound manner near second receiving surface 32.

[0036] For example, the ring portion 51 may be divided into a plurality of members. In this case, it is preferable to perform a curved surface processing on the divided end faces so that the electric field does not concentrate. Also, for example, the grounding portion 52 may be formed by an embedded metal fitting and a conductive member. In this case, an embedded metal fitting having a female thread is provided at the rear end of the insulating tube 12 of the charging portion 102 and is mechanically and electrically connected to the charging side fixing flange 15 via a bolt, and the conductive member is mechanically and electrically connected to the embedded metal fitting and the ring portion 51, respectively. The conductive member may be, for example, a metal wire or a metal rod. Also, as long as the ring portion 51 can be grounded, the structure of the grounding portion 52 is not particularly limited. Also, for example, the grounding portion 52 may be formed of a conductive member, and the ring portion 51 and the charging side fixing flange 15 may be mechanically and electrically connected without the embedded metal fitting.

[0037] In the bushing 10, an electric field relaxation member 50 is disposed near the boundary between the first receiving surface 31 and the second receiving surface 32 so as to surround the receiving portion 30. This makes it possible to prevent equipotential lines from wrapping around to the second receiving surface 32 side when a voltage is applied to the internal conductor 11 with the insulating plug 20 attached to the receiving portion 30 (see Figs. 5A and 5B). Therefore, even if an air layer is present at the interface between the second receiving surface 32 and the second rubber portion 222, the occurrence of partial discharge can be prevented.

[0038] Here, the axial position of the ring portion 51 of the electric field relaxation member 50 is selected as follows from the viewpoint of facilitating design. Figures 6A to 6C and 7A and 7B are diagrams showing an example of equipotential distribution when the position of the ring portion 51 is changed.

[0039] As shown in Figures 6A and 6B, if the axial position of the ring portion 51 is displaced toward the rear end from a predetermined position, the equipotential lines are more likely to wrap around to the low voltage side, reducing the effect of suppressing electric field relaxation and possibly causing partial discharge near the interface between the second receiving surface 32 and the second rubber portion 222.

[0040] 6A, when the boundary between the first receiving surface 31 and the second receiving surface 32 is defined as a first reference S1 in the axial direction and the height of the ring portion 51 (the diameter of the cross section in the embodiment) is defined as h, the position of the rearmost end of the ring portion 51 is 1.5h from the first reference S1 to the low voltage side (rear end side). Therefore, the equipotential lines do not wrap around the interface between the second receiving surface 32 and the second rubber portion 222, and partial discharge can be suppressed.

[0041] 6B, the position of the rearmost end of the ring portion 51 is on the lower voltage side (rear end side) than the position 1.5h away from the first reference S1. Therefore, the equipotential lines wrap around the interface between the second receiving surface 32 and the second rubber portion 222, reducing the effect of suppressing the electric field relaxation, and there is a risk of partial discharge occurring near the interface between the second receiving surface 32 and the second rubber portion 222.

[0042] Therefore, as shown in Fig. 6A, it is preferable that the position of the rearmost end of the ring portion 51 is on the higher pressure side (tip side) than the position 1.5h on the lower pressure side (rear end side) from the first reference S1. More preferably, as shown in Fig. 5B, it is preferable that the position of the rearmost end of the ring portion 51 is on the higher pressure side than the first reference S1. "On the higher pressure side than the first reference S1" means that the position of the rearmost end of the ring portion 51 is on the higher pressure side (tip side) than the first reference S1.

[0043] In addition, when the axial position of the ring portion 51 is displaced toward the tip, the intrusion of equipotential lines near the interface between the second receiving surface 32 and the second rubber portion 222 can be suppressed. However, since this brings the ring portion 51 closer to the inner conductor 11, which is on the high voltage side, it is not appropriate to displace the ring portion 51 too far toward the tip than the specified position.

[0044] 6C, when the tip of the low-voltage side electrode 23 of the insulating plug 20 is set as the second axial reference S2 and the rearmost end of the ring portion 51 is located at the second reference S2, the equipotential lines can be prevented from wrapping around the interface between the second receiving surface 32 and the second rubber portion 222, and the rearmost end of the ring portion 51 is located at the limit of not getting too close to the high-voltage side inner conductor 11. In the embodiment, the rearmost end of the inner conductor 11 in the voltage applying unit 102 is located further forward than the rearmost end of the high-voltage side electrode 21 of the insulating plug 20. Therefore, even if the ring portion 51 is located further forward than the most distal end of the low-voltage side electrode 23, the distance between the ring portion 51 and the inner conductor 11 can be secured to be equal to or greater than the distance between the high-voltage side electrode 21 and the low-voltage side electrode 23.

[0045] Therefore, as shown in Fig. 6C, it is preferable that the rearmost end of the ring portion 51 is positioned on the lower pressure side (rear end side) of the second reference S2. Furthermore, it is more preferable that the frontmost end of the ring portion 51 is positioned on the lower pressure side (rear end side) of the second reference S2.

[0046] Furthermore, if the radial position of the ring portion 51 is moved away from the receiving surface, that is, if the ring diameter of the ring portion 51 is increased, the equipotential lines tend to wrap around to the low voltage side, reducing the effect of suppressing the electric field relaxation.

[0047] As shown in Figure 7A, when the position of the rearmost end of the ring portion 51 is set to the position of the second reference S2 and the position of the outermost end of the ring portion is set to a position d from the second receiving surface 32, in the embodiment, when d is 35 mm, the intrusion of equipotential lines near the interface between the second receiving surface 32 and the second rubber portion 222 can be suppressed.

[0048] On the other hand, as shown in Figure 7B, if the ring diameter is increased and ring portion 51 is positioned further outward than the position of d = 35 mm, the equipotential lines will wrap around the interface between second receiving surface 32 and second rubber portion 222, reducing the effect of suppressing electric field relaxation and, ultimately, there is a risk of partial discharge occurring near the interface between second receiving surface 32 and second rubber portion 222.

[0049] Therefore, it is preferable that the ring diameter of ring portion 51 is within a range that can suppress the equipotential lines from wrapping around the low voltage side, and in this embodiment, the position of the outermost end of ring portion 51 is located at a position 35 mm or less in the radial direction from second receiving surface 32. Furthermore, it is more preferable that the outer diameter of ring portion 51 is smaller than the outer diameter of the rear end of internal conductor 11 in voltage applying unit 102, as shown in Figures 5A and 5B.

[0050] Furthermore, increasing the cross-sectional area of ​​ring portion 51, for example by increasing the ring diameter of ring portion 51, will lead to an increase in the weight and cost of bushing 10, so ring portion 51 should be designed taking such factors into consideration.

[0051] In order to ensure the strength of the insulating tube 12, the ring portion 51 is preferably spaced from the first receiving surface 31 or the second receiving surface 32 by a radial distance of 2 mm or more.

[0052] Thus, the bushing 10 according to the embodiment has the following features either alone or in any suitable combination.

[0053] That is, the bushing 10 includes an inner conductor 11, an insulating tube 12 disposed on the outer periphery of the inner conductor 11, and an electric field relaxation member 50 that is embedded in the insulating tube 12 and relaxes an electric field when a voltage is applied to the inner conductor 11. The insulating tube 12 has a receiving portion 30 to which the insulating plug 20 can be attached, and the receiving portion 30 has a first receiving surface 31 that fits the outer shape of the tapered first rubber portion 221 (insulating rubber portion) of the insulating plug 20, and a cylindrical second receiving surface 32 that is connected to the rear end of the first receiving surface 31. The electric field relaxation member 50 has a conductive ring portion 51 that is disposed in the vicinity of the boundary between the first receiving surface 31 and the second receiving surface 32 so as to surround the receiving portion 30, and a grounding portion 52 that grounds the ring portion 51.

[0054] The bushing 10 also includes a charging-side fixed flange 15 (fixed flange) that is disposed on the rear end surface of the insulating cylinder 12, and the grounding portion 52 electrically connects the ring portion 51 and the charging-side fixed flange 15 together.

[0055] The bushing 10 is also provided with an embedded metal fitting that is disposed at the rear end of the insulating cylinder 12 and to which the load-side fixing flange 15 (fixing flange) is fixed by bolting. The embedded metal fitting functions as a grounding portion 52.

[0056] In the bushing 10, the boundary between the first receiving surface 31 and the second receiving surface 32 is defined as a first reference S1 in the axial direction, and the ring portion 51 is disposed on the high pressure side of the first reference S1.

[0057] In the bushing 10, the ring portion 51 is disposed on the low-voltage side of the second reference S2 in the axial direction, with the tip end of the low-voltage side electrode 23 of the insulating plug 20 being set as the second reference S2.

[0058] In the bushing 10, the ring portion 51 is spaced from the first receiving surface 31 or the second receiving surface 32 by a radial distance of 2 mm or more.

[0059] According to the bushing 10, the electric field relaxation member 50 is disposed in the vicinity of the boundary between the first receiving surface 31 and the second receiving surface 32 so as to surround the receiving portion 30. Therefore, when a voltage is applied to the internal conductor 11 with the insulating plug 20 attached to the receiving portion 30, it is possible to suppress the equipotential lines from wrapping around the second receiving surface 32 side (see Figs. 5A and 5B). Therefore, even if an air layer is present at the interface between the second receiving surface 32 and the second rubber portion 222, it is possible to suppress the occurrence of partial discharge. In addition, by forming the electric field relaxation member 50 with the ring portion 51 and the ground portion 52, it is possible to reduce the material required for the electric field relaxation member 50 compared to the case where the ring portion 51 and the ground portion 52 as shown in Figs. 2 and 3 are integrated into one member so that the whole is ring-shaped (cylindrical), and partial discharge can be suppressed without increasing the weight of the bushing 10 more than necessary.

[0060] 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 of the invention.

[0061] For example, in the embodiment, the present invention has been described as being applied to a bushing that is applied to a T-shaped terminal connection part that is directly connected to an equipment, but the present invention can also be applied to a bushing that is applied to a straight terminal connection part that does not have a current-carrying part.

[0062] Also, in the embodiment, a configuration has been described in which the fixing bracket 25 of the insulating plug 20 is attached to the charging-side fixed flange 15, but for example, a configuration may be used in which the charging-side fixed flange 15 is not provided and the flange portion (fixing flange) of the fixing bracket 25 is provided directly at the rear end of the insulating tube 12. In other words, the fixing bracket 25 and the charging-side fixed flange 15 may be an integral member. In this case, in the bushing 10, the fixing flange arranged on the rear end surface of the insulating tube 12 is formed by the flange portion of the fixing bracket 25, and the grounding portion 52 electrically connects the ring portion 51 and the fixing flange (fixing bracket 25).

[0063] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0064] 1 Cable termination connection 10 Bushing 11 Inner conductor 12 Insulating tube 13 Shielding Layer 14 Equipment side fixing flange 15 Loading side fixing flange 20 Insulating plug 21 High voltage electrode 22 Insulating rubber part 221 First Rubber Section 222 Second Rubber Section 23 Low voltage electrode 30 Receptor 31 First Receptor Surface 32 Second Receptor Surface 50 Electric field relaxation material 51 Ring section 52 Grounding part

Claims

1. An inner conductor; an insulating tube disposed around the outer periphery of the inner conductor; an electric field relaxation member that is embedded in the insulating cylinder and relaxes an electric field when a voltage is applied to the internal conductor; The insulating tube has a receiving portion into which an insulating plug can be attached, the receiving portion has a first receiving surface that fits the outer shape of the tapered insulating rubber portion of the insulating plug, and a cylindrical second receiving surface that is connected to a rear end of the first receiving surface, The electric field relaxation member has a conductive ring portion arranged to surround the receiving portion near the boundary between the first receiving surface and the second receiving surface, and a grounding portion that grounds the ring portion. Bushing.

2. A fixing flange is provided on a rear end surface of the insulating cylinder, The ground portion electrically connects the ring portion and the fixing flange.

2. The bushing of claim 1.

3. an embedded metal fitting disposed at a rear end of the insulating cylinder and to which the fixing flange is fixed by bolt fastening; The embedded metal fitting functions as the grounding portion.

3. The bushing of claim 2.

4. When a boundary between the first receiving surface and the second receiving surface is set as a first reference in the axial direction and a height of the ring portion is set as h, a rearmost end of the ring portion is positioned on the tip side of a position 1.5h toward the rear end from the first reference.

2. The bushing of claim 1.

5. The ring portion is disposed such that the position of the rearmost end portion is located on the tip side of the first reference point.

5. The bushing of claim 4.

6. the ring portion is disposed such that a rearmost end of the ring portion is located rearward of a tip end of the low-voltage side electrode of the insulating plug, the tip end being set as a second reference in the axial direction.

2. The bushing of claim 1.

7. The ring portion is disposed such that a position of a most distal end portion of the ring portion is located rearward of the second reference point.

7. The bushing of claim 6.

8. The ring portion is radially spaced from the first receiving surface or the second receiving surface by a distance of 2 mm or more.

2. The bushing of claim 1.

9. The ring portion has a diameter such that the position of the outermost end of the ring portion is 35 mm or less in the radial direction from the second receiving surface.

9. The bushing of claim 8.

10. The outer diameter of the ring portion is smaller than the outer diameter of the inner conductor in the vicinity of the insulating plug.

2. The bushing of claim 1.

11. The insulating plug is attached to the receiving portion. A bushing according to any one of claims 1 to 10.

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