JP2000299920A - Cross-linked polyethylene insulated power cable connection - Google Patents

Abstract

(57) Abstract: In a connection portion of a crosslinked polyethylene insulated power cable formed by forming a reinforcing insulator 15 by molding so as to cover a conductor connecting portion 19 and a cable insulator 5 on both sides thereof, Even if a small amount of foreign matter is involved in the interface, dielectric breakdown hardly occurs. As a result, the foreign matter management level at the time of forming the connection portion is reduced, or the connection operation can be performed without a clean room, thereby reducing the connection cost. SOLUTION: A high dielectric layer 21 made of a dielectric material having a dielectric constant of 5 to 20 is interposed between a cylindrical portion 5b of a cable insulator 5 and a reinforcing insulator 15. The thickness of the high dielectric layer 21 is reduced from the outer end to the inner end. This alleviates the electric field and reduces the effects of foreign matter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection portion of a crosslinked polyethylene insulated power cable.

[0002]

2. Description of the Related Art Crosslinked polyethylene insulated power cables (hereinafter abbreviated as CV cables) are rapidly following the path of ultra-high pressure due to their excellent insulation properties and ease of handling. In Japan, a long-distance line has already been put into practical use, and a long-distance line of 500 kV class is about to be put into practical use. Cable connection parts are indispensable for these long-distance lines, and molded connection parts have been put to practical use for connection parts of ultrahigh-voltage lines of 275 kV class or higher.

FIG. 4 shows a molded connection portion of a conventional CV cable. In the figure, 1 is a cable sheath, 3 is a cable outer semiconductive layer, 5 is a cable insulator, 7 is a cable inner semiconductive layer, 9 is a cable conductor, 11 is a conductor connection sleeve, and 13 is an inner semiconductive layer of a connection portion. , 15 are reinforcing insulators, and 17 is an external semiconductive layer of the connection portion. This mold connection is formed by the following method.

[0004] The sheath 1 at the end of the CV cable is removed, and the outer semiconductive layer 3 is removed by glass shaving to expose the cable insulator 5. Step off the cable insulator 5 and the inner semiconductive layer 7,
While exposing the conductor 1, the tip of the cable insulator 5 is cut into a tapered shape, and the surface is finished by glass shaving. The conductors 1 of the two cables are connected by a sleeve 11. After wrapping a semiconductive tape on the conductor connecting portion so as to straddle the inner semiconductive layer 7 of the two cables, the semiconductive tape is heated and crosslinked to form the connecting portion inner semiconductive layer 13. . An extrusion die is set around the conductor connection part, and the polyethylene containing the crosslinking agent is extruded from the extruder into the die to form the reinforcing insulator 15. A bridging mold is set on the outer periphery of the reinforcing insulator 15, and the reinforcing insulator 15 is cross-linked by heating and pressing. A semiconductive heat-shrinkable tube is covered so as to straddle the external semiconductive layer 3 of the two cables, and is heated and shrunk to form a connection part external semiconductive layer 17.

[0005] The connection portion thus formed has an interface between the cable insulator 5 and the reinforcing insulator 15. Although the insulator interface is physically in close contact, the physical bonding force is higher than that inside the insulator because the reinforcing insulator is formed on the already crosslinked cable insulator. Small. In addition, there is a high probability that foreign substances such as dust and dirt are caught in the insulator interface. For this reason, the above-mentioned insulator interface is the greatest weak point of the electrical characteristics of the cable connection part. Therefore, in the related art, a clean room is installed when forming a connection portion, and a series of connection work is performed therein.

[0006]

However, in the construction of long-distance tracks, connection work of several tens or hundreds of phases is required, and installing a clean room in each connection work significantly increases the construction time. This leads to a significant increase in connection costs. Furthermore, even if the connection operation is performed in a clean room, it is extremely difficult to completely prevent foreign matter having a size of about several hundred μm, which is sufficient to lower the electrical characteristics of the insulator interface.

[0007] Therefore, an object of the present invention is to improve the electrical characteristics of the interface between the cable insulator and the reinforcing insulator at the CV cable connection portion, and to reduce the total work time required for connection.

[0008]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention relates to a bridge formed by forming a reinforcing insulator so as to cover a conductor connecting portion and a tapered portion and a cylindrical portion of a cable insulator on both sides thereof. In the connection portion of the polyethylene insulated power cable, a high dielectric layer made of a dielectric material having a dielectric constant of 5 to 20 is interposed between the cylindrical portion of the cable insulator and the reinforcing insulator, and the thickness of the high dielectric layer Is thinned from its outer end to its inner end.

The thickness of the high dielectric layer is preferably such that the thickness of the outer end is at least twice the thickness of the inner end.
The thickness of the inner end of the high dielectric layer is preferably 0.5 mm or more.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 4 (conventional example) described above are denoted by the same reference numerals. The connection portion of this CV cable is formed by forming the reinforcing insulator 15 so as to cover the conductor connection portion 19 and the tapered portion 5a and the cylindrical portion 5b of the cable insulator 5 on both sides thereof. A dielectric constant of 5 between the cylindrical portion 5b and the reinforcing insulator 15.
And a high dielectric layer 21 made of a dielectric material of
The feature is that the thickness of the high dielectric layer 21 is reduced from the outer end to the inner end.

The provision of a high dielectric layer between the cable insulator and the reinforcing insulator at the connection point of the power cable can be achieved, for example, by using 72 / 69k commercially available from Raychem.
Heat shrinkable joint for V class, cold shrinkable joint commercially available from 3M, or JP-A-60-1611
This is known from a power cable connection portion and the like shown in Japanese Patent Application Laid-Open No. 5 (1993) -205. It is known that when such a high dielectric layer is provided, the electric field near the end of the reinforcing insulator is reduced, and the electrical characteristics at the interface between the cable insulator and the reinforcing insulator are improved.
FIG. 2A shows the distribution of equipotential lines when the high dielectric layer 21 is provided at the interface between the cable insulator 5 and the reinforcing insulator 15.
(B) shows the distribution of equipotential lines when a high dielectric layer is not provided at the interface between the cable insulator 5 and the reinforcing insulator 15. 7A, the electric field near the end of the reinforcing insulator 15 is reduced.

However, in the conventional connection part, the dielectric constant of the high dielectric layer is high and the thickness is uniform. As described above, the connection portion of the present invention is characterized in that the high dielectric layer 21 is made of a dielectric material having a dielectric constant of 5 to 20, and the thickness thereof is reduced from the outer end to the inner end. .

The dielectric constant of the high dielectric layer used for the commercially available connection part is 20 or more. FIG. 3A shows the distribution of equipotential lines when the dielectric constant ε of the high dielectric layer 21 provided at the interface between the cable insulator 5 and the reinforcing insulator 15 is ε = 5.
(B) shows the distribution of equipotential lines when the dielectric constant ε of the high dielectric layer 21 is 25. When the dielectric constant is higher than 20, the electric field at the end of the reinforcing insulator 15 is reduced, but on the contrary, the electric field tends to concentrate near the inner end of the high dielectric layer 21. The electric field relaxation effect cannot be obtained. When the dielectric constant exceeds 20,
Since a dielectric loss is increased, a connection portion of an ultra-high voltage cable of 154 kV or more easily causes thermal destruction due to heat generation of the high dielectric layer. Therefore, the dielectric constant of the high dielectric layer is set to 20 or less.

If the dielectric constant of the high dielectric layer is less than 5, the ratio with the dielectric constant (2 to 3) of the cable insulator and the reinforcing insulator is too small to obtain a desired electric field relaxation effect. Above.

When the thickness of the high dielectric layer is reduced from the outer end to the inner end of the high dielectric layer 21 as shown in FIG.
The voltage shared by the high dielectric layer 21 in the direction in which the electric field is applied is high on the outer end side and lower on the inner end side. That is, it is possible to make the voltage shared by the high dielectric layer have a gradient in the length direction of the high dielectric layer. As a result, a high electric field relaxation effect is obtained at the end of the reinforced insulator exposed to the highest electric field, and the concentration of the electric field near the inner end of the high dielectric layer can be suppressed. The withstand voltage characteristics can be made higher.

Further, the thickness of the high dielectric layer is preferably set so that the thickness of the thickest outer end is at least twice the thickness of the thinnest inner end. This is because if the thickness gradient is small, the desired voltage cannot be imparted to the shared voltage of the high dielectric layer.

The thickness of the high dielectric layer is preferably 0.5 mm or more at the thinnest inner end. If the thickness of the high dielectric layer is less than 0.5 mm, it becomes difficult to form the high dielectric layer in a stable manner in the circumferential direction of the cable insulator. The thickness of the high dielectric layer is 1.5 at the thickest outer end.
mm or less. If the thickness exceeds 1.5 mm, the voltage shared by the high dielectric layer increases, and particularly at the connection portion of an ultra-high voltage cable of 154 kV or more, the high dielectric layer easily becomes a base point of dielectric breakdown.

As a material for the high dielectric layer, a high dielectric resin composition obtained by blending carbon black and / or high dielectric particles with a base resin can be used. Examples of the resin used herein include rubber such as ethylene-propylene rubber and chloroprene rubber, VLDPE, polyethylene produced using a metallocene catalyst, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid. Plastics such as methyl copolymers are mentioned, and among them, those which are easy to mold into a tube or a heat-shrinkable tube and are easy to mix filler particles are preferable. In addition, as the high dielectric particles contained in the high dielectric resin composition, silicon carbide, titanium oxide, barium titanate, and other high dielectric ceramic powders can be used.

The high dielectric layer can be formed on the outer peripheral surface of the cylindrical portion of the cable insulator by a method of covering the tube or the heat-shrinkable tube, a tape winding method, or a tape winding molding method.

Further, the reinforcing insulator is formed by extrusion molding at the cable connection site as described above.
In addition, it can also be formed by covering a conductor connection portion and the outer periphery of a cable insulator at a connection site with a mold piece previously molded at a factory. In this case, the high dielectric layer may be integrally formed in advance with the interface forming portion of the reinforcing insulator.

As shown in FIG. 1, a high dielectric layer 21 is interposed between the cylindrical portion 5b of the cable insulator 5 and the reinforcing insulator 15, and the thickness of the high dielectric layer 21 is changed from the outer end to the inner end. By reducing the thickness toward the end, the electric field at the interface between the cylindrical portion 5b of the cable insulator 5 and the reinforcing insulator 15 can be made uniform. Therefore, no matter where the foreign matter exists at the interface, the concentration of the electric field near the foreign matter is reduced. This means that in the insulation design of the cable connection portion including the interface between the cable insulator and the reinforcing insulator, the size of the allowable foreign matter can be increased.

This means that the management level of foreign substances mixed during the connection work can be reduced, and as a result, the connection work can be performed easily and quickly by lowering the management level of foreign substances in the clean room. . Also, in a normal clean environment, connection work can be performed without a clean room.

[0023]

Next, examples of the present invention will be described together with comparative examples and reference examples in order to clarify the effects of the present invention. The cable used for the connection is a 275 kV, 2500 mm ² CV cable.

After heating and straightening this cable,
The outer semiconductive layer, the cable insulator, and the inner semiconductive layer were sequentially removed by an electric shaving machine and glass shaving to expose the conductor at the tip. In Examples and Comparative Examples, a heat-shrinkable tube integrated with an external semiconductive layer and a reinforced insulator was passed through the outer periphery of one of the cables, and then the conductors were connected by a compression sleeve. Thereafter, a semiconductive tape containing a cross-linking agent was wound around the conductor and the outer circumference of the compression sleeve so as to straddle the inner semiconductive layers of both cables, and was molded to form an inner semiconductive layer. Through the above steps, 14 sets of in-process products were manufactured.

On the other hand, the compositions of Nos. 1 to 7 in Table 1 were made into tapes to produce seven types of high dielectric tapes.

[Examples 1 to 6] The high dielectric tapes Nos. 1 to 5 in Table 1 were applied to the cylindrical portion of the cable insulator of the in-process connection product from the thickness a at the outer end to the thickness at the inner end. After wrapping so that the thickness becomes thin with a substantially constant gradient up to b,
Heat molding was performed for 30 minutes to form a high dielectric layer 21 as shown in FIG. The composition and thickness of the formed high dielectric layer are as shown in Examples 1 to 6 in Table 2. Next, the heat-shrinkable tube integrated with the external semiconductive layer and the reinforced insulator, which has been passed through in advance, is moved so that the conductor connection portion is located at the center, and the tube is heated and shrunk from the surroundings, thereby reinforcing the tube. The body 15 and the outer semiconductive layer 17 were formed integrally. The above connection work was performed without installing a clean room, while paying normal attention so that foreign matter does not adhere to the surface of the cable insulator or the high dielectric layer.

[Embodiments 7 and 8] Using No. 4 and No. 5 high dielectric tapes in Table 1, a cable connecting portion having a high dielectric layer 21 was formed. Embodiment 1 to 6
However, in these two examples, in order to confirm the effect of reducing the electric field with respect to the local electric field concentration, a particle diameter of 500 μm was formed on the high dielectric layer 21 at a position 30 mm from the inner end.
After adhering m copper powder, the reinforcing insulator 15 and the outer semiconductive layer 17 were formed. The connection operation was performed without installing a clean room while paying normal attention so that foreign substances other than copper powder did not adhere to the surface of the cable insulator or the high dielectric layer.

[Comparative Examples 1 to 5] Using the high dielectric tapes No. 1 and Nos. 4 to 7 in Table 1, a cable connection portion having a high dielectric layer 21 was formed. Embodiment 1 describes a method for forming a connection portion.
6, but copper powder was adhered in the same manner as in Examples 7 and 8. As shown in Table 2, Comparative Examples 1 and 2 show the case where the thickness of the high dielectric layer is uniform, Comparative Example 3 shows the case where the thickness of the high dielectric layer is too thin, and Comparative Examples 4 and 5 show the case where the thickness of the high dielectric layer is high. Are too low and too high.

REFERENCE EXAMPLE After the cable is heated and straightened, it is stripped to a predetermined size, and the outer semiconductive layer, the cable insulator, and the inner semiconductive layer are sequentially removed by an electric shaving machine and glass shaving. Then, the conductor was exposed at the tip. Next, the conductors were connected by a compression sleeve. Thereafter, a semiconductive tape containing a cross-linking agent was wound around the conductor and the outer circumference of the compression sleeve so as to straddle the inner semiconductive layers of both cables, and was molded to form an inner semiconductive layer. Next, the in-process connection product was set in an extrusion die so that the conductor connection portion was positioned at the center, and a low-density polyethylene containing a cross-linking agent was extruded to form a reinforced insulator. Then, after the sizing of the reinforcing insulator was performed by glass shaving, the semiconductive heat-shrinkable tube previously passed through was moved to the outer periphery of the reinforcing insulator, and was heated and shrunk to form an external semiconductive layer. . next,
This portion was covered with a mold, and heated by applying a constant pressure in a nitrogen atmosphere, whereby the entire connection portion was cross-linked.
The above connection work was performed in a clean room.

The 15 types of CVs manufactured as described above
An AC voltage insulation breakdown test was performed on the cable connection part. The test conditions are: initial voltage: 400 kV, step-up step: 50 kV / step, holding time: 30 minutes. Table 3 shows the test results.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

As described above, according to the present invention, it is possible to obtain a connection portion of a CV cable in which dielectric breakdown hardly occurs even if some foreign matter is caught in the interface of the insulator. Therefore, the connection operation can be easily and quickly performed without lowering the foreign matter management level at the time of forming the connection portion or without the clean room, and the connection cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a CV cable connection section according to the present invention.

FIGS. 2A and 2B show a case where a high dielectric layer is provided;
FIG. 5 is an explanatory diagram showing a distribution of equipotential lines in a connection portion when there is no connection.

FIGS. 3A and 3B are explanatory diagrams showing distribution of equipotential lines in a connection portion when the dielectric constant of a high dielectric layer is low and when the dielectric constant is high.

FIG. 4 is a sectional view showing a conventional CV cable connection portion.

[Explanation of symbols]

 3: Cable external semiconductive layer 5: Cable insulator 5a: Tapered portion 5b: Column portion 7: Cable internal semiconductive layer 9: Cable conductor 11: Conductor connection sleeve 13: Internal semiconductive layer of connection portion 15: Reinforced insulator 17: External semiconductive layer of connection portion 19: Conductor connection portion 21: High dielectric layer

Claims (3)

[Claims] 1. A connecting portion of a cross-linked polyethylene insulated power cable, wherein a reinforcing insulator is formed so as to cover a conductor connecting portion and a tapered portion and a cylindrical portion of a cable insulator on both sides thereof. A high dielectric layer made of a dielectric material having a dielectric constant of 5 to 20 is interposed between the cylindrical portion and the reinforcing insulator, and the thickness of the high dielectric layer is reduced from the outer end to the inner end. Features a crosslinked polyethylene insulated power cable connection. 2. The connection part of a crosslinked polyethylene insulated power cable according to claim 1, wherein the thickness of the outer end of the high dielectric layer is at least twice the thickness of the inner end. 3. The connection part of a crosslinked polyethylene insulated power cable according to claim 2, wherein the thickness of the inner end of the high dielectric layer is 0.5 mm or more.