JPH06315218A - Bushing for cable joint - Google Patents

Abstract

PURPOSE:To downsize the joint between a bushing and a cable and to protect the conductor layer on the outer surface of bushing while isolating a shield layer. CONSTITUTION:A conductive layer 31 is formed covering the outer surface of a bushing 1 entirely. The conductor layer 31 is terminated in the vicinity of a cable joint terminal A of the bushing 1 and a shield isolating part 32 having no conductor layer 31 is formed thereat. Consequently, the shield layer 5 of the cable 3 is isolated electrically from the conductor layer 31 of the bushing 1. The isolating part allows direct securing of a protective case 19 to the bushing 1 without requiring any insulation tube or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable connecting bushing used for making an electrical connection between a cable and equipment.

[0002]

2. Description of the Related Art When connecting a high voltage device such as a gas insulated switch to a high voltage cable, the following cable connecting portion is adopted. FIG. 2 shows a vertical cross-sectional view of a conventional cable connecting bushing. As shown in the figure, the bushing 1 formed by molding epoxy resin or the like is
It is fixed to the wall surface of a device (not shown) arranged on the left side of the figure. An internal electrode 2 is provided at the center of the bushing 1 and is electrically connected to the internal conductor of the device.
Connection terminals A and B are provided above and below the bushing 1 for connecting cables, respectively. When the device is actually used, a cable for making an electrical connection with another device is connected to one of the terminals, for example, the connection terminal B.

A cable for electrical testing of equipment and cables connected to the connection terminal B is connected to the other connection terminal A. In the figure, the cable 3 connected to the connection terminal A includes a sheath 4, a shield layer 5, and a semiconductive layer 6.
And the insulator 7 is stepped off in order to expose the conductor 8.
The conductor 8 has a crimp terminal 9 and a tulip contact 10.
Are attached and electrically connected to the internal electrodes 2. In addition, the stress cone 1 is provided around the insulator 7 of the cable 3.
3 is fitted. The stress cone 13 is formed by integrally molding an insulating portion 14 made of insulating rubber or the like and a semiconductive portion 15 made of semiconductive rubber or the like.

Further, the stress cone 13 is provided with a push fitting 16
And the spring unit 18 are configured to be pressed against the inner wall surface of the bushing 1 with a certain force or more. As a result, the stress cone 13 and the bushing 1
The surface pressure is applied to the boundary surface with the required insulation characteristics. In addition, the spring unit 18 is the protective case 1.
It is configured to be sandwiched between a washer 17 supported by the step portion of 9 and the push fitting 16.

The protective case 19 is composed of a metal pipe for surrounding and protecting the end portion of the cable 3 exposed from the bushing 1. One end of the protective case 19 is fixed to the bushing 1 and the lower end thereof is the tape winding portion 2
An airtight treatment is performed between the cable 3 and the outer peripheral surface of the cable 3. A lead wire 20 is wound around the shielding layer 5 of the cable 3 and electrically connected to the protective case 19 via a washer 17. As a result, the protective case 19 is grounded and the shield layer 5 of the cable 3 is grounded. Note that, for example, the state shown in the figure is for the test cable 3
Is attached to the connection terminal A of the bushing 1, and a blind plug is attached to the other connection terminal B for electrical protection. In this state, for example, a high voltage is applied to the device through the cable 3 and various electric tests are performed.

An insulating plate 25 and a connecting tube 26 are arranged between the bushing 1 and the protective case 19. Generally, a cable for electrical test that is directly connected to the equipment is equipped with a current transformer to measure an abnormal current. At this time, if an induced current flows in the shield layer of the cable, the current flowing in the conductor of the cable and the current flowing in the shield layer cancel each other out, and the current cannot be accurately measured by the current transformer attached to the cable. For this purpose, the shielding layer of the cable is trimmed in the longitudinal direction. The insulating plate 25 is inserted for this purpose. A conductor layer 27 is formed on the outer peripheral surface of the bushing 1 to ensure safety, and is grounded via a wall surface of the device or the like.

[0007]

By the way, the above-mentioned conventional bushing for cable connection has the following problems to be solved. In the bushing having the above-described structure, when an abnormal voltage is applied between the shield layers that are cut off by the insulating plate 25, the insulation is broken on the surface portion of the insulating plate 25, and a creeping discharge occurs. Also,
When a large current flows through the shield layer during a ground fault, the current also flows through the conductor layer 27 on the outer surface of the bushing 1. Normally, the conductor layer 27 is formed by applying a conductive paint, and it is difficult to form the conductor layer 27 with a uniform thickness as a whole without unevenness. Therefore, this current may flow in a concentrated manner. In such a case, since the conductor layer 27 itself has an electric resistance, the conductor layer 27 itself may generate heat to cause discoloration or burn.

To prevent such a large current, it is preferable to connect a gapless arrester to the portion of the insulating plate 25, but in general, this type of arrester is expensive, which leads to an increase in equipment cost. In addition, it is necessary to secure the installation place. Further, when an insulating plate is inserted for cutting the edge of the cable shielding layer, there is a problem that the connecting portion between the bushing and the cable becomes large. The present invention has been made in view of the above points, and is intended for cable connection in which the conductor portion of the outer surface of the bushing is protected while the connection portion between the bushing and the cable is downsized and the shield layer is cut off. The purpose is to provide a bushing.

[0009]

The first invention of the present invention is formed by molding an insulator, has a connection terminal for receiving a cable end, and forms a conductor layer so as to cover almost the entire outer surface. However, the present invention relates to a bushing for cable connection, wherein a shield edging portion that electrically separates the conductor layer from the shield of the cable is formed near the connection terminal of the bushing. A second aspect of the present invention is characterized in that annular electrodes are formed on the edges of the conductor layer on both sides of the shield edge cut portion.

[0010]

In this bushing, a conductor layer is formed so as to cover the entire outer surface thereof. This conductor layer has an end terminating halfway in the vicinity of the cable connecting terminal of the bushing. In this portion, a shield edging portion having no conductor layer is formed. This electrically cuts off the shield layer of the cable and the conductor layer of the bushing. Moreover, by providing such an edge cut portion, it becomes possible to directly fix the protective case to the bushing without the need for an insulating cylinder or other parts. At the edge of the conductor layer, it is preferable to provide an annular electrode that relieves electrical stress and generates a uniform arc when a high voltage is applied to protect this portion.

[0011]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of a cable connecting bushing of the present invention. The configuration of the bushing 1 and the configuration of the cable 3 in the figure are the same as those of the conventional one described with reference to FIG. The protective case 19 provided here to protect the connecting portion of the cable 3 is directly fixed to the bushing 1 in this embodiment. That is,
The insulating plate 25 and the connecting tube 26 which are conventionally used for cutting the edge of the cable shielding layer are not necessary in the present invention.

Further, the conductor layer 31 is provided so as to cover the entire outer surface of the bushing 1, but in this embodiment, just at the portion of the cable connecting terminal A,
A portion where the epoxy is exposed is provided in a ring shape.
That is, the conductor layer 27 is not formed in this portion.
In the present invention, this portion is referred to as the shield edging portion 32. That is, in such a state, the conductor layer 31 and the shield layer of the cable 3 are electrically separated.
With such a shape, the insulating plate 25 and the like shown in FIG. 2 are omitted, and the total length is reduced by about 300 millimeters.

FIG. 3 shows a sectional view of an embodiment of the second invention.
In the example of the figure, in the shielding edge cutting section 32 shown in FIG.
An annular electrode 35A is formed on the edge 31A of the conductor layer 31.
Are arranged. The annular electrode 35A is composed of a rod or pipe of copper, aluminum or the like. And the annular electrode 3
The support portion 35B is attached to the 5A and is fixed to the wall surface of the device with bolts 35C or the like.

With such a structure, the annular electrode 35A acts just like an arc horn. That is, when a high voltage is applied to the shield layer of the cable 3 in the longitudinal direction, a creeping discharge is generated at the shield edging portion 32. Usually, the epoxy resin used for this type of bushing has a sufficiently strong resistance to such creeping discharge. Therefore, electrically, such an annular electrode 35A
Need not necessarily be provided. However, the creeping discharge stains the portion of the shield edge cutout 32 of the bushing 1 and impairs its appearance. Furthermore, if a large current flows due to the creeping discharge, a local large current may flow in a part of the conductor layer 31 as described above, causing discoloration or the like. The annular electrode 35A acts so as to evenly blow an arc in the shield edging portion 32 and is directly electrically connected to the device, so that a large current is prevented from flowing to the conductor layer 31. Furthermore,
When the annular electrode 35A is fixed to the wall surface of the device or the like via the support portion 35B, when various bending stresses are applied to the bushing 1 by the cable 3, the bushing 1 is mechanically supported and plays a role of protecting the bushing 1. .

The present invention is not limited to the above embodiments. The length, width, etc. of the shield edging portion 32 may be freely set according to the electrical characteristics. Further, the shape, size, etc. of the annular electrode arranged in this portion may be freely set, and the supporting portion is not particularly required unless the strength for supporting the bushing is taken into consideration.

[0016]

The cable connecting bushing of the present invention described above has a conductor layer formed so as to cover the entire outer surface of the bushing, and the conductor layer is electrically connected to the cable shielding layer in the vicinity of the connection terminal of the cable. Since the shield edging portion is formed so as to be cut off, it is not necessary to separately insert an insulating plate or the like at the portion where the cable is connected to the bushing, and the entire connection portion can be downsized.

Moreover, by shortening the length of the lower portion of the bushing, the length of the cable to be started up for connecting to the device can be shortened. Therefore, for example, when a pit is dug near the device and the cable is housed in the pit in order to prevent the cable from bending below the allowable bending radius, the pit may become unnecessary.
Further, the arrangement height of the device itself can be reduced. Further, the connecting portion between the cable and the bushing has a simple structure, which facilitates the connecting work and improves its reliability. Of course, the cost can be reduced because the number of parts is reduced. Further, the conductor layer can be protected by providing the annular electrode.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a cable connecting bushing of the first invention.

FIG. 2 is a vertical sectional view of a conventional cable connecting bushing.

FIG. 3 is a vertical sectional view of a cable connecting bushing showing an embodiment of the second invention.

[Explanation of Codes] 1 Bushing 2 Internal electrode 3 Cable 5 Shielding layer 19 Protective case 31 Conductor layer 31A Conductor layer edge portion 32 Shield edging portion

Claims (2)

[Claims] 1. A conductor is formed by molding an insulator, has a connection terminal for receiving a cable end, and has a conductor layer formed so as to cover substantially the entire outer surface of the bushing. A bushing for cable connection, characterized in that a shield edging portion for electrically separating the conductor layer from the shield of the cable is formed. 2. The bushing for cable connection according to claim 1, wherein annular electrodes are formed on the edges of the conductor layer on both sides of the shield edge cut portion.