JPH07170644A - Stress cone for prefabricated joint - Google Patents

Abstract

PURPOSE:To prevent electric destruction by winding a non-linked insulation rubber material in the longitudinal direction around a section whose electric field is high, and winding the insulation rubber material laterally around a section whose electric field is low before heating, pressing and link formation, at the time of winding the non-linked insulation rubber material to form a stress cone. CONSTITUTION:A stress cone 11 which is brought into contact with the connection part of a high voltage conductor is formed by winding a piece of non-linked insulation tape. Around a section 11a whose electric field is high, a piece of insulation tape 12 is wound longitudinally so that the adhesive surface of the tape 12 may be flush radially with the high voltage conductor. Around a section 11b whose electric field is relatively low, the insulation tape 12 is wound in the lateral direction so that the adhesive surface of the tape 12 may be flush with the axial direction of the high voltage conductor. By winding a piece of conductive rubber tape, a semi-conductive layer 13 is formed. The stress cone 11 and the semi-conductive layer 13 is heated and pressed for cross-link formation. It is thus possible to manufacture an excellent product in withstand voltage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to stress cones, and more particularly to stress cones for prefabricated joints.

[0002]

2. Description of the Related Art A stress cone for a prefabricated joint is formed by winding an uncrosslinked rubber tape horizontally to form a raw material, which is housed in a mold, heated, pressed and crosslinked. That is, the material has a large number of layers in the circumferential direction, and this layered structure remains even after crosslinking.

[0003]

Therefore, even in the stress cone after cross-linking, there is a possibility that minute gaps and poor adhesion are present in the gaps between the layers, and if the gaps and the direction of the electric field match, This may result in electrical breakdown of the stress cone. FIG. 4 is an enlarged vertical sectional view showing a part of a conventional stress cone for a prefabricated joint, in which 1 is a layer formed by a wound tape and 2 is a gap between the layers 1 and The symbol E indicates the direction of the electric field. When the gap 2 and the direction E of the electric field coincide with each other as described above, the gap 2 becomes a discharge space as shown by arranging x marks in the figure, and electrical breakdown occurs. FIG. 5 is a diagram showing the relationship between the size of the discharge space in the electric field direction (unit: μm) and the electric field intensity Es (unit: kV / mm) that causes electrical breakdown. In the figure, curve A is in air and curve B is The figure shows each in steam. From this figure, it can be seen that the larger the discharge space, the lower the electric field strength Es of the electric breakdown.

The present invention has been made under the above circumstances, and provides a stress cone for a prefabricated joint which is less likely to cause electrical breakdown.

[0005]

The stress cone for a prefabricated joint of the present invention is such that when a material formed by winding an uncrosslinked insulating rubber strip is crosslinked, the direction of the electric field in the crosslinked material. It is characterized in that large voids, poor adhesion portions, etc. are not generated.

[0006]

In the stress cone for a prefabricated joint of the present invention having the above-mentioned structure, a large void in the direction of action of the electric field,
There is no possibility of electrical breakdown because no adhesion failure part or the like occurs.

[0007]

The present invention considers the causes of the above electrical breakdown,
It is based on the result of the consideration. That is, when the material is configured as shown in FIGS. 2A and 2B, for example, even if there is a minute gap or a portion having poor adhesion between the materials, these are different from the direction of the electric field. It utilizes that it does not match and does not cause electrical breakdown.

In the method of constructing the material shown in FIG. 2 (a), the tape 3 is made so that its width is vertical and so-called vertical winding is performed to construct the material. This material is heated and pressed to crosslink it to form a stress cone. In this stress cone, the gap 4 of the tape 3 is perpendicular to the direction E of the electric field as shown in FIG. 2a. Therefore, even if there is a minute void or a poorly adhered portion 5 in the gap 4, a large discharge space is not formed by them, and the stress cone is not electrically broken.

In the method of constructing the material shown in FIG. 2 (b), the material is constructed by winding a thin string-like uncrosslinked rubber string 6. This material is heated and pressed to crosslink it,
Use as a stress cone. In this stress cone, since the rubber string 6 is wound to form the material, even if there is a minute gap or a poor adhesion portion 7 between the strings 6 after the cross-linking, they are in the direction E of the electric field. However, since they are scattered in a random manner, there is no possibility of forming a large discharge space. In these figures, the X mark indicates the discharge space.

FIG. 1 (a) is a longitudinal sectional view of an embodiment of the present invention invented based on the knowledge of FIG. 2 (a). In this figure, the portion 1 of the stress cone 11 where the electric field strongly acts
1a is formed by vertically winding the tape 12, and the portion 11b that acts relatively weakly is formed by horizontally winding the tape 12. In the figure, 13 indicates a semiconductive layer formed by winding a conductive rubber tape. In this embodiment, as in the case described with reference to FIG. 2 (a) above, electrical breakdown is unlikely to occur at the portion 11a. Also, part 11b
Since the applied electric field is weak, there is no risk of electrical breakdown even if it is constructed by winding the tape horizontally like the conventional stress cone. In this embodiment, since the lengthwise winding portion 11a of the tape which is difficult to manufacture is minimized, the manufacturing cost does not increase.

FIG. 1B, in which the same parts as those in FIG. 1A are denoted by the same reference numerals, is a longitudinal sectional view of an embodiment of the present invention invented based on the knowledge of FIG. 2B. In this figure, the entire stress cone 11 is formed by winding a thin rubber cord 16 as shown in FIG. 2 (b). In this embodiment, electrical breakdown is unlikely to occur in the entire stress cone in the same manner as described with reference to FIG. 2 (b) above.

Instead of winding the thin string-shaped rubber to form the material, an injection mold may be applied to form the material. 3 (a) is a perspective view of an extrusion die for injection molding, FIG.
(B) is a schematic diagram of the rubber cord filled in the mold at the time of the injection molding. At the time of injection molding, an extrusion die 21 having a large number of small openings 21a as shown in FIG. 3 (a) is used, and the inside of the mold (not shown) is evacuated to vacuum prior to molding. The uncrosslinked rubber extruded from the small opening 21a of the extrusion die 21 into the mold is filled into the mold while being bent as indicated by 26 in FIG. 3 (b). Therefore, there is no risk of electrical breakdown of the stress cone in the same manner as described with reference to FIG.

As described above, in the stress cone for the Brehab joint of the present invention, there is no possibility of causing electrical breakdown due to minute voids between layers, a portion having poor adhesion, and the like, which are seen in the conventional stress cone.

[0014]

As apparent from the above, in the stress cone for prefabricated joint of the present invention, after the material is crosslinked by heating and pressurization, stress is applied between the layers of the uncrosslinked rubber constituting the material. Since no large voids or poor adhesion portions are formed in the direction of the electric field acting on the cone, there is no risk of electrical breakdown.

[Brief description of drawings]

FIG. 1A is a vertical sectional view of an embodiment of the present invention, and FIG.
Is a vertical cross-sectional view of another embodiment.

2A is a cross-sectional view of an example of a method of constructing a stress cone material, and FIG. 2B is a cross-sectional view of another example.

FIG. 3A is a perspective view of an extrusion die used to form a stress cone material by injection molding, and FIG. 3B is a schematic view of a rubber cord filled in the mold at the time of injection molding.

FIG. 4 is an enlarged vertical sectional view showing a part of a conventional stress cone for a prefabricated joint.

[Fig. 5] Size of discharge space in the direction of electric field (unit: μm)
3 is a diagram showing the relationship between the electric field strength Es (unit: kV / mm) that causes electrical breakdown.

[Explanation of symbols]

 1 --- Layer formed by wound tape 2 --- Gap between layers 3,12-Tape 4 --- Tape layer 5 --- Void or poor adhesion site 6, 16, 26-Rubber cord 11 --- Stress cone 11a-Part where the electric field acts strongly 11b-Part where the electric field acts weakly 13 --- Semiconductive layer

Claims (4)

[Claims] 1. When a material formed by winding a strip of uncrosslinked insulating rubber is crosslinked, a large void in the direction of action of an electric field, a poor adhesion portion, etc. are prevented in the crosslinked material. A stress cone for prefabricated joints. 2. An uncrosslinked rubber tape is adopted as the uncrosslinked insulating rubber strip, and a portion of the material on which a strong electric field acts is formed by longitudinal winding of the uncrosslinked rubber tape,
The stress cone for a prefabricated joint according to claim 1, wherein the portion on which the weak electric field acts is formed by laterally winding the tape of the uncrosslinked rubber. 3. The stress cone for a prefabricated joint according to claim 1, wherein a thin string of uncrosslinked rubber is adopted as the strip of the uncrosslinked insulating rubber, and a raw material is formed by winding the string. . 4. Instead of winding the uncrosslinked rubber cord,
The prefabricated joint according to claim 3, wherein the material is formed by injecting uncrosslinked rubber by injection through an extrusion die having a large number of small openings into a molding die that has been evacuated in advance. Stress cone.