JPS63200419A - Resin molded bushing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a resin molded bushing in which a center conductor and a shield ring disposed outside the center conductor are integrally molded with resin. Regarding.

(Prior art) This type of resin molded bushing can relatively easily meet the various shapes required, so its practical use has recently expanded to various applications, such as oil-filled bushings with gas insulation. Used in transformers, vehicle transformers, etc. An example of a conventional configuration will now be described with reference to FIGS. 3 and 4. First, in FIG. 3, there is a central conductor 2 in which a plurality of grooves 1 constituting an airtight part are formed in the axially intermediate part of the outer periphery, and a ground terminal 3 is connected to the center conductor 2. It is constructed by integrally molding a shield ring 4 with resin 5.

Furthermore, FIG. 4 shows an example of a different conventional configuration, in which a plurality of metal round bars 6 are welded to the center conductor 2 and the resin in place of the groove 1 in the axially intermediate portion of the outer circumference of the center conductor 2. This differs from the previous one in that the adhesive area with 5 is increased to form an airtight part.

The resin 5 is made of epoxy resin mixed with silica powder, alumina, etc., and is injected into the mold with the center conductor 1 and shield ring 5 set in the mold, and then heated and hardened to mold them together. are doing.

(The source point to be solved by the invention) In the structure as described above, the conductor cross-sectional area of the center conductor 2 is smaller in the groove 1 than in other parts, so when a large current flows through the center conductor 2, the There was a risk that the temperature of the groove portion 1 would be high and the resin 5 would be locally heated and cracks would occur in the resin 5. In addition, because the center conductor 1 and the resin 5 are firmly fixed over the entire surface, it can be used in applications where load fluctuations are large and the operating temperature range is wide, such as oil-immersed transformers in steel plants or transformers for vehicles. In this case, cracks may occur in the resin 5 due to thermal stress caused by the difference in thermal expansion coefficients between the center conductor 2 and the resin 5. In this case, since there is an edge particularly in the groove 1 portion of the center conductor 2, the resin 5 corresponding to the edge
Stress tends to concentrate in certain areas. In addition, the expansion and contraction of the resin 5 near the outer periphery of the shield ring 4 and the center conductor 2 is restricted by the shield ring 4, so the stress value in this area increases, and as a result, temperature changes and load fluctuations cause the resin 5 to expand and contract. In some cases, cracks were generated in the center conductor 2 and dielectric breakdown occurred between the center conductor 2 and the shield ring 5. Furthermore, if peeling occurs between the center conductor 2 and the resin 5, there is a risk that corona discharge will occur between the center conductor 2 and the shield ring 4.

In the configuration shown in FIG. 4, which is another conventional example, since the metal round bar 6 is welded to the center conductor 2, there is a risk that the center conductor 2 will be distorted.

In addition, even in the configuration in the above direction, the center conductor 2 and the resin 5 are in a fixed state, so if there is a scratch on the outer circumference of the center conductor 2, stress will be concentrated on the part of the resin 5 corresponding to the scratch. Fatigue strength decreases and repeated thermal stress causes resin 5
There was still a risk of cracks occurring.

On the other hand, in order to prevent the occurrence of cracks in the resin 5 as described above, there is a device in which a rubber tape is wound around the outer periphery of the center conductor 2 to relieve stress on the resin 5. When used in containers, one side of the tape may penetrate into oil, causing the rubber tape to deteriorate and swell, resulting in oil leakage. Additionally, rubber tape alone cannot maintain airtightness, so it cannot be used for gas-insulated equipment.

The present invention has been made in view of the above circumstances, and its purpose is to provide a resin molded bushing that can prevent the occurrence of cracks in the resin in which the center conductor is molded, and has good airtightness without oil leakage. .

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, a center conductor and a shield ring disposed outside the center conductor are integrally molded with resin. The resin molded bushing is characterized in that a plurality of intermediate resin layers with stepwise varying coefficients of thermal expansion are provided between the center conductor and the resin.

(Function) When providing, for example, three intermediate resin layers with stepwise varying coefficients of thermal expansion between the center conductor and the resin, layers A, B, and C, the coefficients of thermal expansion should be in the following order. By arranging them, it is possible to suppress the generation of thermal stress caused by a difference in coefficient of thermal expansion and prevent the generation of cracks in the resin.

That is, the order is the center conductor, the A layer, the B layer, the C layer, and the outer resin. Thermal stress caused by the difference in thermal expansion coefficient between the outer resin layer and the middle resin layer (C layer) occurs in the C layer, the thermal stress between the C layer and the B layer occurs in the B layer, and the thermal stress between the B layer and the A layer occurs in the A layer. By absorbing each, the thermal stress generated between the A-layer and the center conductor becomes the difference in the coefficient of thermal expansion between the A-layer and the center conductor, so the thermal stress is smaller than in the conventional method and can prevent the occurrence of cracks. .

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2. First, in Fig. 1, 11 is the center conductor,
12 is a shield ring arranged concentrically outside the center of the center conductor 11 and connected to the ground terminal 13;
is an intermediate register 28 layer molded around the outer periphery of the center conductor 11,
15 is the intermediate register 25 layer molded on the outer periphery of the intermediate register 28 layer 14, 16 is the intermediate resin C layer molded on the outer periphery of the intermediate register 25 layer 15, and 17 is the center conductor 11 and the intermediate 9223 layer 14.5 layer 15. This is an outer resin in which the 0 layer 16 and the shield ring 12 are integrally molded. These intermediate 9223 layers, 14.5 layers, and 15.0 layers 16 are provided at the center in the axial direction corresponding to the shield ring 12.

Reference numeral 18 denotes an airtight part provided at one end of the outer periphery of the center conductor 11, and the outer periphery of the center conductor 11 is sandblasted over a width of about 50 cm to roughen the surface, and then an airtight resin 19 with good adhesiveness is applied on the surface. (for example, Araldite 1000 manufactured by Ciba Geigi). This airtight part 18 improves the adhesion between the center conductor 11 and the outer resin 1 on both sides of the airtight part 18 in the axial direction.
7 and maintains airtightness.

In manufacturing the bushing with the above configuration, first, the center conductor 11 is set in an intermediate resin mold (not shown), and the resin is injected and hardened. In the center,
9223 intermediate layers, 14.5 layers, and 15.0 layers 16 are sequentially provided. Further, an airtight portion 12 is provided inside the shield ring 12 of the center conductor 11 at a position that does not face it. And the shield ring 1 connected to this center conductor 11 and the ground terminal 13
2 is set in a separately prepared mold (not shown), and the outer resin 17 is injected into the mold to integrally mold the mold. The outer resin 17 is first hardened within the mold, and after being released from the mold, it is secondarily hardened.

Here, the middle 9223 layers 14.5 layers 15.0 layers 16 and the outer resin 17 are made of epoxy resin mixed with silica powder alumina, etc., and the thermal expansion coefficient of the 8 layers 14.5 layers 15.0 layers 16 is 8 layers < The blending ratio of the silica powder etc. is adjusted so that the b layer becomes the 0 layer and is smaller than the outer resin 17.

Thermal stress in the circumferential direction of the resin is greatest in the vicinity of the center conductor at -20° C., as shown by characteristic line A in FIG. 2, when there is no intermediate resin layer. On the other hand, according to the above embodiment, by providing the intermediate resin layer A layer 14.5 layer 15 and C layer YU 6, which have different thermal expansion coefficients in stages, between the center conductor 11 and the outer resin 17, First, a thermal stress of σE(α〇−αC)Δt is generated between the outer resin 17 and the intermediate resin C layer 16. Here, α0 is the thermal expansion coefficient of the outer resin 17, and αC is the thermal expansion coefficient of the intermediate resin C layer 16. Thermal stress is caused by the outer resin 1 because the coefficient of thermal expansion is α0>αC.
7 acts as a tensile stress, and acts on the intermediate resin C layer 16 as a compressive stress. Similarly, intermediate resin C layer 16 and intermediate resin layer 25 layer 1
5, tensile stress acts on layer 0 16, compressive stress acts on layer 5 15, and between intermediate 9223 layer 14 and center conductor 11, tensile stress acts on the intermediate resin layer 14 side and compressive stress acts on the center conductor 11 side. However, since the width of each resin layer is made small, the temperature difference is small, and the difference in the coefficient of thermal expansion is gradually reduced, so the generated thermal stress can be reduced.

Therefore, the thermal stress between the outer resin, the middle 9223 layer, the b layer, the 0 layer, and the center conductor is as shown by the characteristic line B in Figure 2, and the middle 9222
The thermal stress between the 23rd layer and the center conductor is reduced to about 60% (about 2.8 kg/C) of the case without the intermediate resin layer.

Generally, the tensile strength of resin molded bushings (epoxy resin) is 7 to 9 kg/m+s2, and if the reduction due to repeated fatigue is taken into account, it is approximately 4 kg/mm.
2 is the limit that can withstand thermal stress. However, in the case of this embodiment, as described above, it can sufficiently withstand the thermal stress generated in the circumferential direction.

[Effects of the Invention] As is clear from the above description, the present invention provides an airtight portion between the center conductor and the outer resin, and the thermal expansion coefficient is gradually changed from the outer resin to the center conductor except for this airtight portion. By providing a plurality of small intermediate resin layers, it is possible to suppress thermal stress between the center conductor and the resin layer, thereby preventing the occurrence of cracks in the resin. Furthermore, it is possible to provide a resin molded bushing that exhibits excellent effects such as being able to maintain airtightness by the airtight portion and having good airtightness without oil leakage.

[Brief explanation of the drawing]

Figures 1 and 2 show an embodiment of the present invention, Figure 1 is an overall sectional view, Figure 2 is a characteristic diagram of circumferential thermal stress generated in the resin, and Figure 3 is an example of a conventional configuration. 1, and FIG. 4 is a partially enlarged sectional view showing an example of a different conventional configuration. In the figure, 11 is a center conductor, 12 is a shield ring, 14 is an intermediate register 28 layer, 15 is an intermediate register 25 layer, 16 is an intermediate resin C layer, 17 is an outer resin, and 18 is an airtight part. Agent Patent Attorney Nori Ken Yudo Hiroshi Mimata Fumi II...Neni°41 Akane, /Z...Nurutozo;
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Claims (1)

[Claims] A part formed by integrally molding a center conductor and a shield ring placed outside the center conductor with resin, in which an airtight part is provided between the center conductor and the resin, and this airtight part is removed. A resin molded bushing characterized by having a plurality of intermediate resin layers whose thermal expansion coefficients are gradually smaller from the outside to the center conductor.