JPS63301414A - Rubber plastic insulated power cable - Google Patents

Abstract

PURPOSE:To make it possible to provide the water tree deterioration preventive ability to an insulator formation material itself and to maintain its effect for a long time by forming an insulator layer with a bridged or non-bridged resin composition of a specific mixture, and making the methylmethacrylate concentration in the resin composition 0.1 to 20 wt.%. CONSTITUTION:An insulator layer is formed of only olefine-methylmethacrylate copolymer, or a bridged or non-bridged resin composition of a mixture of olefine-methylmethacrylate copolymer and polyolefine, and the methylmethacrylate concentration in the resin composition is made 0.1 to 20wt.%. In this case, as the olefine in the olefine-methylmethacrylate copolymer, ethylene, propylene, or the like is used. And the methylmethacrylate concentration means the rate of the weight equivalent to the methylmethacrylate in the copolymer to the whole composition weight. In such a composition, the water tree deteoration preventive ability of the insulator layer is made excellent and the property is maintained for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rubber-plastic insulated power cable with improved water tree deterioration.

(Prior art and its problems) As shown in FIG. 1, a rubber-plastic insulated power cable has a conductor 1, an inner semiconducting layer 2, an insulating layer 3, an outer semiconducting layer 4, a metal shielding layer 5, and a protective layer 6. It has a basic structure such as a structure in which the internal semiconductor layer 2 is sequentially provided or a structure in which the internal semiconducting layer 2 is removed from the above structure.

The material for the insulating layer may be a polyolefin with excellent electrical properties, a crosslinked polyolefin obtained by crosslinking this with a crosslinking agent such as an organic peroxide to improve heat resistance, or an ethylene-propylene copolymer. is widely used.

However, it has become clear that the long-term insulation properties of these polyolefin-based resin or rubber-insulated power cables are significantly degraded by the occurrence of water trees, and in recent years there has been a demand for the development of cables with cable structures or materials that suppress the occurrence of water trees. has been done. Measures to suppress water trees: - Change the cross-linking method from wet to dry to reduce the number of voids in the insulator layer that are the source of water trees (in this case, bow tree trees). (2) By adopting a three-layer co-extrusion method of an internal semiconductive layer, an insulating layer, and an external semiconductive layer, the protrusions at the source of water trees (in this case, internal trees and external trees) are miniaturized. ■Measures have been taken to prevent water from entering the insulator layer by providing a water-blocking layer on the cable core or under the protective layer, but none of these measures can be considered sufficient.

Also, the idea of providing the insulator-forming material itself with the ability to prevent water tree deterioration is attracting attention, and as an example, it has been proposed to use an insulating material mixed with certain additives.

However, these additives have the disadvantage that they bleed outward from the inside of the insulating layer over a long period of time, and their effects are not maintained for a long period of time.

(Means for Solving the Problems) In order to solve the above-mentioned drawbacks, the present invention uses a material that has an excellent ability to prevent water tree deterioration and that continues for a long time as an insulating material to be used for the insulating layer 3. This was done as a result of research to find out, in a rubber-plastic insulated power cable having a rubber-plastic insulating layer on the outer periphery of the conductor, the insulating layer is composed of an olefin-methyl methacrylate copolymer alone or an olefin-methyl methacrylate copolymer. It is formed of a crosslinked or non-crosslinked resin composition of a mixture of agglomerates and polyolefins, and the methyl methacrylate concentration in the resin composition is 0.1 to 20% by weight.
It is characterized by its weight.

The olefin-methyl methacrylate copolymer used in the present invention is represented by the molecular formula, and the olefins include ethylene,
There are propylene, etc. Furthermore, the concentration of methyl methacrylate in a crosslinked or non-crosslinked resin composition of an olefin-methyl methacrylate copolymer alone or a mixture of the olefin-methyl methacrylate copolymer and a polyolefin as defined in the present invention is defined as the concentration of methyl methacrylate based on the total weight of the composition. This is a value expressed as a percentage of the weight ratio corresponding to methyl methacrylate in the copolymer. The reason why the concentration of methyl methacrylate in the resin composition forming the insulator layer of the rubber-plastic insulated power cable of the present invention is set to 0.1 to 20% by weight is that 1 degree of methyl methacrylate in the resin composition is 0.1 to 20% by weight. If the amount is 1% by weight without grooves, the ability to prevent water tree deterioration is low, and if it exceeds 20% by weight, the t of the formed insulator layer will be reduced.
This is because electrical properties such as an δ and dielectric breakdown properties deteriorate. The preferred concentration is 0.5-5% by weight. In the present invention, polyolefins that can be used in combination with the olefin-methyl methacrylate copolymer include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, or Mixtures of these may be mentioned. The resin composition forming the insulating layer can be used without crosslinking, but in order to improve heat resistance, it can be made into a crosslinked product by adding a crosslinking agent such as an organic peroxide or by irradiating it with an electron beam. . Furthermore, one or more kinds of additives such as antioxidants, compounding agents, etc. may be added as necessary.

(Example) An example of the present invention will be described based on a model cable for characteristic evaluation shown in FIG. A conductor 1 with a diameter of 2 mm and a wall thickness of 0.
5111 is provided, and on the outside thereof, an ethylene-methyl methacrylate copolymer alone or a mixture of an ethylene-methyl methacrylate copolymer and polyethylene with different acrylic acid concentrations is mixed with a crosslinking agent and an antioxidant. An experiment was conducted by forming an insulating layer 3 made of a crosslinked resin composition with a thickness of 1 mm using the composition shown in Table 1, and forming an external semiconducting layer 4 with a thickness of 0.5 mm on top of the insulating layer 3 made of a crosslinked resin composition with a thickness of 1 mm. It was made into a model cable. Note that dicumyl peroxide is used as a crosslinking agent, and 44T-thiobis(3-methyl-6-
tert-butylphenol) was used.

Dielectric conditions (AC voltage 2
KV, IKH2) submerged in water for 600 days and subjected to a voltage application test to measure tanδ and bowtie in the insulator layer)
The number of IJ-occurring cells was observed using a microscope (X100).

The results are also listed in Table 1. For comparison, a model cable using a composition made of polyethylene alone mixed with a crosslinking agent and an antioxidant was evaluated as the insulating layer 3.

(Effects of the Invention) As is clear from Table 1, the rubber-plastic insulated power cable of the present invention has water in the insulating layer itself!・The quality of rubber-plastic insulated power cables has been improved because it is made of a material that has excellent ability to prevent leakage degradation and maintains its performance for a long time.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing the basic structure of a rubber-plastic insulated power cable, and FIG. 2 is a cross-sectional view of a model cable for evaluating the characteristics of the power cable of the present invention. 1. Conductor, 2. Inner semiconductive layer, 3. Rubber plastic insulator layer, 4. Outer semiconductive layer, 5. Shielding layer, 6
・Protective layer. Patent applicant: Furukawa Electric Co., Ltd. Figure 1 Figure 2 Before procedural amendment (voluntary) 1986 7J] I5 [-1 1,? Display of JG patent 117zu62-13799
No. 8 No. 2, Title of the invention Rubber plastic insulated power cable 3, Relationship to the Compensation Person Case Patent applicant residence i'li 2-6-1-4 Marunouchi, Chiyo 11-ku, Tokyo 100, Subject of amendment Drawings 5. Contents of amendment The drawings will be corrected as shown in the attached sheet. Figure 1 Figure 2

Claims (2)

[Claims] (1) In a rubber-plastic insulated power cable having a rubber-plastic insulating layer on the outer periphery of the conductor, the insulating layer is made of an olefin-methyl methacrylate copolymer alone or a mixture of the olefin-methyl methacrylate copolymer and a polyolefin. 1. A rubber-plastic insulated power cable made of a crosslinked or non-crosslinked resin composition, characterized in that the resin composition has a methyl methacrylate concentration of 0.1 to 20% by weight. (2) The rubber-plastic insulated power cable according to claim 1, wherein the crosslinked or non-crosslinked resin composition has a methyl methacrylate concentration of 0.5 to 5% by weight.