JPS643295B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method of manufacturing rubber, plastic insulated power cables. In general, rubber or plastic power cables have an internal semiconductive layer on the conductor as necessary, and then coat the outside with rubber, a plastic insulator layer, and an external conductive layer by extrusion, and then wrap a copper tape around the outside. It is manufactured by sequentially providing a metal shielding layer and a protective sheath made of polyvinyl chloride, polyethylene, etc. However, rubber manufactured using this method,
In plastic insulated power cables, small amounts of gas and moisture generated during the manufacturing process remain in the extruded rubber and plastic insulation coating materials. That is, when an extrusion-coated insulating coating material is subjected to a crosslinking process or a cooling process, gas and moisture permeate into the coating layer and accumulate therein. Also, during use of the cable, moisture such as rainwater permeates through the protective sheath and reaches the insulator layer within the cable core. The presence of moisture in the insulator layer causes so-called water trees, which significantly reduces the insulation performance of the power cable. The present invention has been developed as a result of intensive research in view of the current situation, and as a result, it is possible to easily remove residual moisture during cable manufacturing, and the resulting cable can actively prevent moisture from entering from the outside during use. We have discovered a method for manufacturing rubber and plastic insulated power cables that has extremely practical effects. That is, the method of the present invention involves forming an internal semiconducting layer on the conductor as necessary, and applying a metal tape on at least one side of the cable core at a desired position on the outside of the cable core, which is provided with a rubber or plastic insulating layer by extrusion on the outside thereof. A laminate tape made by laminating a plastic tape such as a polyethylene tape mixed with carbon black is provided, and the plastic surface is used as the core side and is wrapped vertically to form a water-blocking layer.
The sheathed cable is then heated to 50°C or higher, usually 50°C.
By heating at ~120℃ for several hours to several tens of hours, the inside of the cable core, that is, the inside of the insulator layer,
In addition, the present invention was based on the discovery that moisture within a semiconducting layer can be easily and quickly removed. In the method of the present invention, the cable is heated to 50°C as described above.
The reason for heating above is that the moisture contained in the insulator layer and inner and outer semiconductor layers that form the cable core of rubber and plastic insulated power cables rapidly decreases when heated above 50℃. . That is, it is presumed that when heated to 50° C. or higher, the amount of saturated water that can be contained in the insulating layer and the inner and outer semiconducting layers decreases markedly, and crystallization progresses. Note that the higher the heating temperature, the shorter the heating time can be. Therefore, heating below 50°C has almost no effect. The reason why moisture and gas in the cable core can be removed quickly is that metal has a thermal conductivity hundreds of times better than rubber or plastic. By sealing a sheathed power cable with lead, aluminum, or copper tape or a laminated tape of metal tape and plastic tape placed vertically and heating it from the outside of the sheath, the moisture inside the cable core evaporates easily and the temperature rises. This is thought to be due to the fact that it passes through the low conductor gap and diffuses to the outside from the cable end. The water-blocking layer may be provided anywhere on the outside of the cable core, for example, on the outside of the external conductive layer or on the inside of the protective sheet. Note that steam, water, or the like can be used as the heating medium for the cable, since it is easy to work with. This is because, in the cable manufactured by the method of the present invention, water does not penetrate into the cable core due to the presence of the water-blocking layer. Next, examples of the present invention will be described. Example 1 When manufacturing 400m of 66kV1×250SQ CV cable, an external semiconductive layer was provided on the outside of the cable core manufactured by the usual method, and a conductive PE layer was placed on the outside of the cable core.
(50μ) / Pb (50μ) / conductive PE (50μ) laminate tape is placed vertically to form a water-shielding layer, and a water-shielding layer made of copper tape and a protective sheath made of polyvinyl chloride are provided on the outside. The rubber/plastic insulated power cable was heated by immersing it in warm water at 80° for 6 hours. Comparative Example 1 A 66kV1×250SQ cable was manufactured in the same manner as in Example 1 except that the water-blocking layer in Example 1 was not provided. Example 2 When manufacturing a 66kV1×250SQCV cable in the usual manner, PVC (100μ)/Pb (50μ)/PVC (100μ) was applied to the inner surface of the polyvinyl chloride protective sheath.
Rubber/plastic insulated power cables made by vertically lining laminate tape to form a water-blocking layer and integrated with polyvinyl chloride were steam-heated at 50°C for two days. Comparative Example 2 A 66kV1×250SQ cable was obtained in the same manner as in Example 2 except that the water-blocking layer in Example 2 was not provided. Comparative example 3 66kV1×250s QCE cable according to the usual method
When manufacturing 400m, PE (100μ)/Pb was added to the inner surface of the polyethylene (PE) protective sheath.
(50μ) / PE (100μ) laminate tape was placed vertically to form a water-blocking layer, which was integrated with a polyethylene protective sheath. Comparative Example 4 When manufacturing a 66kV1 x 250s QCE cable with a length of 400m, the cable core was heated and dried at 60℃ for 48 hours, then 40 1.2φ copper wire shielding layers were spirally wound, and a pressure tape (thickness 0.4 mm), and then a PE (100 μ)/Pb (50 μ)/PE (100 μ) laminate tape was placed lengthwise to form a water-blocking layer, which was then integrated with a polyethylene protective sheath. Table 1 shows the results of measuring and comparing the moisture content of the cable of the present invention and the cable of the comparative example.

[Table] As is clear from the above table, the comparative power cable has a higher moisture content in its cable core than the power cable of the present invention. In Comparative Example 4, a water-blocking layer was applied after heating the cable core. Therefore, the moisture content in the outer semiconducting layer is increasing. In addition, the outer semiconductive layer contains conductive carbon and is hygroscopic, so it absorbs some moisture during storage from the heating of the cable core to the water-shielding treatment, increasing its moisture content. The water content is about 0.03 to 0.05 wt%. As detailed above, according to the method of the present invention, the amount of water in the cable core is extremely small, and the presence of the water-blocking layer prevents water from entering from the outside, resulting in an excellent water-blocking effect. No trees etc. are generated. Therefore, rubber exhibits excellent insulation performance over a long period of time.
It has remarkable effects such as the ability to obtain plastic insulated power cables.

Claims (1)

[Claims] 1. Laminate tape with plastic tape laminated on at least one side of the metal tape at a desired position on the outside of the cable core, which has an internal semiconducting layer formed on the conductor as necessary and a rubber or plastic insulating layer on the outside. , forming a water-blocking layer by vertically covering the plastic surface with the core side as the core side;
A method for manufacturing a rubber or plastic insulated power cable, which comprises heating the rubber or plastic insulated power cable provided with a sheath to 50°C or higher for a certain period of time.