JPH03122908A - Electrically insulated cable - Google Patents

Abstract

PURPOSE:To suppress the generation of water tree in an electrically insulated cable by having an electric insulating layer made of the admixed composition of an ethylene polymer and an ethylene-alpha-olefinic copolymer or made of its cross-linked admixed composition. CONSTITUTION:For the insulator of a cable is used an admixed composition of 95 to 50 pts.wt. of an ethylene polymer and 5 to 50 pts.wt. of an ethylene- alpha-olefinic copolymer having 0.89 to 0.91g/cm<3> in density or is used an admixed composition comprised by cross-linking the former. The ethylene polymer being used means low-density polyethylene, intermediate-density polyethylene or high-density polyethylene, while also the ethylene-alpha-olefinic copolymer means the copolymer of such alpha-olefin as ethylene and butene-1,4- methylpentene-1, hexene-1, octane-1 and the like. This results in the improvement of water tree resistance of the cable without damaging another characteristic of the insulator, such as the extrusion processibility thereof.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electrically insulated cable having an electrically insulating material capable of greatly suppressing water trees generated in the insulator of a polyethylene or cross-linked polyethylene insulated cable. It is related to.

[Prior Art] Polyethylene and crosslinked polyethylene have a high degree of electrical insulation and are therefore frequently used as electrical insulators for electric wires and cables.

However, when a couple made of this type of insulator is used in a wet or flooded state, electrochemical deterioration called so-called water tree occurs, resulting in a significant reduction in electrical performance.

That is, the general structure of a high-voltage insulating couple is, as shown in the figure, an internal semiconducting layer 2 on a conductor 1, an insulator 3 on its outer periphery, and a layer between the insulator 3 and a protective coating 5. Although it has a structure in which an outer semiconducting layer 4 is provided, a bowtie-shaped water tree occurs inside the insulator 3, and an interfacial water tree occurs from the inner semiconducting layer 2 or the outer semiconducting layer 4, resulting in the worst case. In some cases, it may even penetrate the insulator layer 3 and cause dielectric breakdown.

Therefore, in order to prevent the occurrence of water trees, we have introduced hydrophilic polar groups into the polyethylene and crosslinked polyethylene that serve as insulators, carefully controlled the quality of the resin, and created a clean room for electric wires and couples. Various efforts have been made to improve manufacturing technology.

[Problem to be solved by the invention J However, despite repeated efforts in various fields, we have not yet reached the stage where the occurrence of the above-mentioned water tree can be completely eliminated, and efforts are being made to take measures to prevent its occurrence. is currently being considered.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide a novel electrically insulated cable having an insulator capable of suppressing the occurrence of water trees to a large extent.

[Means for Solving the Problems 1] The present invention uses ethylene polymer 9 as a cable insulator.
5-50 parts by weight and density 0.89-0, 91 g/cx
A blended composition containing 5 to 50 parts by weight of the ethylene-α olefin copolymer No. 3 or a blended composition obtained by crosslinking this is used.

The ethylene polymer used here refers to low density polyethylene, medium density polyethylene, and high density polyethylene.
In addition, ethylene-α olefin copolymer is ethylene and butene-1,4-methylpentene-1, hexene-1,
A copolymer of α-olefin such as octene-1, which has an effect of suppressing the occurrence of water tree, is 0.89 to 0.91 g.
/cm3, and by incorporating it, the reliability of electrically insulated cables made of ethylene polymers is significantly improved.

If the amount of the ethylene-α olefin copolymer mixed is less than 5 parts by weight, it is too small to suppress the generation of water trees.
Moreover, if the amount is more than 50 parts by weight, the extrusion appearance of the blended composition will be poor.

When crosslinking the composition according to the present invention, methods include adding an organic peroxide represented by dicumyl peroxide and heating, or copolymerizing an unsaturated silane compound in the presence of water and a silanol condensation catalyst. A method of crosslinking with ionizing radiation and a method of crosslinking with ionizing radiation can be used.

Further, there is no problem in adding antioxidants, lubricants, etc. to the composition of the present invention.

[Example] The present invention will be described below with reference to Examples.

0.7no internal semiconducting layer on 100+m2 annealed copper stranded wire
After extrusion forming to a thickness of
+ extrusion coating, and an outer semiconductive layer was further extruded to a thickness of 0.7 rm. In Table 1, the test materials containing dicumyl peroxide were crosslinked by heating using nitrogen gas as a heating medium.

The electrically insulated cable thus obtained was immersed in water at 90° C. and an AC voltage of 18 kV was applied for 6 months. After completing the task, we investigated the number of water trees that occurred on the insulator. In addition, the extrusion processability of this composition was determined based on the appearance of the cable.

The evaluation results are shown in the lower part of Table 1.

It can be seen that Examples 1 to 4 having compositions within the range specified by the present invention have less occurrence of water trees and have good extrusion processability. On the other hand, Comparative Example 1 using ethylene polymer alone
In addition, when the density of the ethylene-α-olefin copolymer is high, as shown in Comparative Example 3, water trees occur frequently.Comparative Example 4 shows that water trees occur the most. Although the amount of ethylene-α olefin copolymer is small, the extrusion processability is deteriorated due to the presence of too much ethylene-α olefin copolymer.

[Effects of the Invention As described above, according to the electrically insulated cable according to the present invention,
Water resistance can be greatly improved compared to conventional examples without impairing other properties such as extrusion processability, and the reliability in actual installation can be improved, which is of great significance.

[Brief explanation of drawings]

The figure is a sectional view showing a specific configuration of an insulated cable. 1: conductor, 2: internal semiconducting layer, 3: Insulator, 4: outer semiconducting layer, 5: Protective coating.

Claims (1)

[Claims] (1) Ethylene polymer 95-50 parts by weight and density 0.89
An electrically insulating cable comprising an electrically insulating layer comprising a blended composition or a crosslinked blended composition of 5 to 50 parts by weight of an ethylene-alpha olefin copolymer of ~0.91 g/cm^3.