JPH0250562B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an oil-filled power cable, particularly an oil-filled power cable suitable for ultra-super high voltage power transmission. [Conventional technology] Ultra-super high voltage (UHV) overhead power transmission lines of 750 kV or more have been realized for the purpose of long-distance high-power transmission, but underground cable lines that can be connected to this system have not yet been developed. Conventional low-hydraulic OF cables or high-hydraulic OF cables insulated with low-loss cellulose paper (or kraft paper) cannot be used in these systems because of the temperature increase caused by dielectric loss in the cables. Since the power transmission capacity of cables is limited by dielectric loss, research has been carried out for more than 20 years to apply very low loss synthetic materials to OF cables. [Problems to be solved by the invention] However, non-polar plastic films such as polyethylene and polypropylene with excellent dielectric properties swell significantly in aromatic hydrocarbon oils that are currently widely used. They were not successful in putting it into practical use. The application of synthetic materials made from fibers of these fibers to cables has also been considered, but this has not been put to practical use for the same reason. Furthermore, attempts have been made to reduce the swelling in oil by laminating these with cellulose paper, but although the swelling in the length direction could be suppressed, the swelling in the thickness direction could not be suppressed. The present invention solves the problems of the prior art described above, and aims to provide a power cable whose power transmission capacity can be significantly increased by using an insulating film with low dielectric loss. [Means for Solving the Problems] The oil-filled power cable of the present invention has an insulating layer around the conductor made of a mixed resin of a non-polar thermoplastic resin and a tetrafluoroethylene-ethylene copolymer. It is constructed by winding a laminated film of a film and cellulose paper in which the content ratio of thermoplastic resin/tetrafluoroethylene-ethylene copolymer is 85/15 to 20/80. In the present invention, the non-polar thermoplastic resin is
Refers to thermoplastic resins that do not contain polar groups such as halogen, carbonyl group, hydroxyl group, carboxyl group, or ester group in the molecule, including polyethylene, polypropylene, polybutene-1, poly-4 methylpentene-1, as well as ethylene and propylene. , copolymers with butene, pentene, and hexene. These can be used alone or in combination of two or more. Although such non-polar thermoplastic resins have very good electrical properties, they swell to a large extent in oil. In the present invention, a tetrafluoroethylene-ethylene copolymer is mixed in order to eliminate this swelling. The weight ratio of non-polar thermoplastic resin/tetrafluoroethylene-ethylene copolymer is 85/15 to 20/80.
If the content of the tetrafluoroethylene-ethylene copolymer is less than 15% by weight, swelling in oil will be large, and if it exceeds 80% by weight, it will be difficult to obtain the desired dielectric properties. Become. Furthermore, fluorine-containing resins other than the tetrafluoroethylene-ethylene copolymer cannot be used because they have problems either in compatibility with non-polar thermoplastic resins or in dielectric properties. Mixing of the non-polar thermoplastic resin and the tetrafluoroethylene-ethylene copolymer and film forming are usually carried out using an extruder equipped with a T-die set at 270°C or higher, and when laminating with cellulosic paper, film forming is performed. It is preferable to carry out these processes at the same time in order to prevent the mixed resin from being separated again. The main purpose of laminating with cellulose paper is to improve oil impregnation and strength, and the film may be laminated on either one or both sides.
Furthermore, it may be used after being subjected to surface treatment such as embossing. Furthermore, the film may be uncrosslinked or crosslinked, and examples of the crosslinking method include crosslinking by irradiation with ionizing radiation such as electron beams. [Example] As shown in each example in Table 1, various components were
Using an extruder (L/D = 28m/m) set at cylinder 1 = 300℃ and cylinder 2 = 80℃, it was kneaded and formed into a film with a thickness of 100 to 150μ and a density of 0.72g/m. cm, laminated with cellulose paper with airtightness of 5000G/sec. In addition, although Example 5 is an example of a film alone without laminating cellulose paper, in this case, in order to improve oil impregnation, a film was used whose surface was embossed. The evaluation results for the oil resistance and dielectric properties of the film are shown in the lower column of Table 1. As is clear from Table 1, Examples 1 to 5 within the scope of the present invention are excellent in both oil resistance and dielectric properties. On the other hand, in Comparative Example 1, the tetrafluoroethylene-ethylene copolymer alone was laminated with cellulose paper. It has excellent oil resistance but poor dielectric properties. In Comparative Example 2, polyethylene was used alone, but it completely dissolved in dodecyl bezene oil at 100°C. Comparative Example 3 is a product in which polypropylene is laminated with cellulose paper, and although the dielectric properties are very good, it swells greatly in oil and partially dissolves. [Effect of the invention]

[Table] As explained above, according to the present invention, it is possible to realize an oil-filled power cable having an insulating layer made of a non-polar thermoplastic resin, thereby significantly increasing the power transmission capacity. becomes possible.

Claims (1)

[Claims] 1. An oil-filled power cable having an insulating layer on the outer periphery of the conductor and having this insulating layer impregnated with insulating oil,
The insulating layer is made of a mixed resin of a non-polar thermoplastic resin and a tetrafluoroethylene-ethylene copolymer.
Weight ratio of ethylene copolymer is 85/15 to 20/80
An oil-filled power cable characterized in that it is constructed by winding a film or a laminate film of the film and cellulose paper. 2. The oil-filled power cable according to claim 1, wherein the non-polar thermoplastic resin is selected from polyethylene, polypropylene, polybutene-1, and poly-4-methylpentene-1. .