JPS6367403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting crosslinked polyethylene insulated cables.

Cross-linked polyethylene insulated cables are increasingly being applied to high-voltage power transmission lines in recent years. Along with this, reliability is also required for cable connections, and for this reason, a mold connection method has been widely adopted in which a reinforcing insulating layer of rubber or plastic applied to the conductor connection part is heated under pressure to integrate it with the cable insulating layer. There is. Conventionally, this connection method involves forming a reinforcing insulating layer on the conductor connection by winding or casting polyethylene containing a crosslinking agent or crosslinked polyethylene into a tape, and then heating the layer to a temperature higher than the crosslinking temperature. After that, the conductive layer was wrapped with semiconductive tape and then the whole was heated and molded into a single piece.A waterproof protective tube was placed on the outside and the ends were wrapped with waterproof tape. According to this connection method, moisture and decomposed gas remain in the reinforcing insulating layer due to the decomposition of the crosslinking agent when the semiconductive tape and semiconductive tape containing a crosslinking agent are crosslinked during molding, resulting in the cable being used for a long time. Inside, there was a defect that caused insulation to deteriorate and cause partial discharge.

The present invention aims to eliminate the above-mentioned drawbacks and provide a cable connection method that has an excellent water-shielding effect and does not cause insulation deterioration over time, and an embodiment illustrating this will be described below.

In the figure, 1 is a cable conductor connecting pipe, and 2 is an internal semiconducting layer formed by winding a semiconductive tape containing a crosslinking agent applied over both cable conductors separated from the conductor connecting pipe. Examples include ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, polymer blends of two or more of these copolymers, and one or more of these copolymers and polyethylene. A conductive carbon black such as acetylene black is added to a base polymer selected from the group consisting of a polymer blend of Crosslinking agents such as dicumyl peroxide, bis(t-butylperoxyisopropyl)
A compound containing an organic peroxide such as benzene is made into a film by T-dying, calendar inflation, etc., and the film is slit to an appropriate width. 4 is an insulating layer formed by winding a polyolefin insulating tape containing a cross-linking agent applied on the conductor connection portion, and 5 is an insulating layer formed by winding a single metal or a laminate tape of metal and plastic with adhesive applied on the insulating layer. A water-blocking layer formed by pasting it twice or covering it with a heat-shrinkable tube that has water-blocking properties;
Reference numeral 6 denotes a protective layer applied thereon, and in the present invention, after the cable end coating to be connected is stripped in stages and the exposed conductors are compressed and connected with the connecting pipe 1, a crosslinking agent is applied from the outer periphery to both cable conductors. An internal semiconductive layer 2 made of a compounded semiconductive tape is formed, an insulating layer 4 made of a polyolefin insulating tape of the same quality as the cable insulating layer is formed thereon, and the internal semiconductive layer 2 and the insulating layer 4 are heated. After fusing, the insulating layer is further dried under vacuum at a temperature of 50°C to 120°C to completely remove moisture and decomposition gas generated by decomposition of the crosslinking agent during heating of the semiconductive layer 2 and the insulating layer 4. A water-blocking layer 5 is applied on the water-blocking layer 4, and then a protective layer 6 is provided around the outer periphery of the water-blocking layer 5 to form a connection portion. In the figure, 7 is a water-shielding layer within the cable, and 8 is a tape-wrapped layer applied to the end of the protective layer 6.

Next, specific examples of the present invention will be explained.

Strip the terminal coating layer of a 154KV CV cable (conductor 800mm ² ) to expose the conductor, connect it with compression sleeve 1, and then apply HFDJ0580 (manufactured by Nippon Unicar) semi-conducting conductor over the conductor connection part and over the cable conductor. An internal semiconductive layer 2 is prepared by wrapping a polyethylene compound tape to a thickness of 20 mm, and then a crosslinkable polyethylene compound tape of HFDJ4201 (manufactured by Nippon Unicar) is wrapped on top of this semiconductive layer 2 to a thickness of 28 mm. The insulation layer 4 is formed by winding the insulation layer 4, and then the insulation layer 4 is heated to a heater temperature of 210°C using a mold.
After heating and fusing at ℃ for 5 hours, it was cooled and further heated to 80℃.
Immediately after vacuum drying for 48 hours, the insulating layer 4 was covered with adhesive-coated lead and conductive polyethylene laminate tape in a vertical manner to form a water-blocking layer 5 to form a connection part. The connection part thus constructed and the connection part constructed without the vacuum drying process as a comparative example were immersed in warm water at 80°C for 6 months and then taken out and subjected to an AC dielectric breakdown test. When compared, the withstand voltage value of the connection part of the comparative example was reduced by 40 to 60% compared to the withstand voltage value of the cable connection part according to the present invention.

In addition, compared to the comparative example without vacuum drying after molding, the moisture content of the insulating layer was 0.05 to 0.2%.
The moisture content of the insulating layer according to the present invention, which was vacuum dried after molding, was 0.01% or less.

As described above, according to the present invention, it is possible to obtain a cable connection portion that has an excellent water-shielding effect and does not suffer from water absorption and insulation deterioration over time.

[Brief explanation of drawings]

The figure is a sectional view of a main part of a cable connection section for explaining one embodiment of the present invention. 1: Conductor connection part, 2: Internal semiconductive layer, 3: Semiconductive layer of cable, 4: Insulating layer, 5: Water shielding layer, 6:
protective layer.

Claims (1)

[Claims] 1 Strip off the cable end coating to be connected, connect the exposed conductor, form an internal semiconductive layer and an insulating layer made of polyolefin insulating tape on the outer periphery, heat-fuse, and then heat-dry at a predetermined temperature. Or a cable connection method characterized by heating and vacuum drying and forming a water-blocking layer on the insulating layer after drying.