JPS58212007A - Semiconductive composition for power cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductive composition provided on the outer periphery of a conductor and/or the outer periphery of an insulator of a power cable.

The smoothness and adhesion of the interface between the semiconducting layer and the insulator of a cross-linked polyethylene insulated cable are important for the reliability of a cable, and if there is any irregularity at the interface, a localized high electric field is formed, which can cause damage during corona discharge or flooding. Water tree deterioration occurs and the electrical characteristics of the cable deteriorate.

To address this problem, studies have been conducted from the viewpoint of manufacturing methods and materials for semiconductive layers, and extruded semiconductive layers have been developed to replace semiconductive cloth tapes, which tend to have a lot of fuzz. .

Looking at the materials for extruded semiconductive layers, there are those whose base polymer is ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer, and those whose base polymer is a mixture of ethylene propylene rubber and high-density polyethylene. has been known for a long time.

Sometimes, semiconductive compositions whose base polymer is a mixture of ethylene propylene rubber and high-density polyethylene are manufactured in tandem by arranging an internal semiconducting layer extruder and an insulator extruder in series to produce electrical cables in tandem. The internal semiconducting layer is less susceptible to damage and deformation, and since it uses a polymer with a structure similar to that of an insulator, the interface has good smoothness and adhesion.

Cross-linked polyethylene insulated cables with such a semiconductive layer have a greatly improved breakdown voltage, but water treeing can occur if electricity is applied for a long period of time under severe deterioration conditions such as water seepage inside the cable. There is a problem that this occurs frequently and the breakdown voltage decreases.

The present invention solves the problems of the prior art described above.
The object of the present invention is to provide a semiconductive composition that can improve the water resistance of electrical cables.

That is, the semiconductive composition of the present invention is made of medium-low density polymerized low-density polyethylene (density 0.915-o, 930t/c
It is characterized by being composed of 100 parts by weight of a mixture of ethylene propylene rubber and medium-low density polyethylene with a mixing ratio of 20 to 50% by weight (r/l) and 40 parts or more of a conductivity imparting material. That is.

As a result of various studies on improving water resistance, the present inventor obtained experimental results showing that the desired objective was achieved when medium-low density polyethylene was used as a mixture with ethylene propylene rubber, and the present inventor has arrived at the present invention. It was.

Unlike conventional low-density polyethylene, medium-low density polyethylene is an ethylene-α-olefin copolymer with no long chain branching and a linear molecular structure. This α
Olefins include those with 4 or more carbon atoms, such as butene-1
, 4-methylpetene-1, hexene-1, octene-1
etc. are used.

As estimated from the molecular shape, low-density polyethylene obtained by medium-to-low specific polymerization shows almost the same physical properties as high-density polyethylene, but its density is slightly different from that of high-density polyethylene, so its density is comparable to that of conventional low-density polyethylene. be.

Of course, the density can be increased by changing the amount of α-olefin, but if the density is increased, the water resistance will be the same as when high-density polyethylene is used, and the optimal density is 0.915 to 0.930 t. /cr/l.

The mixing ratio of medium-low pressure type legal low density polyethylene to 100% by weight of the mixture must be 20 to 50% by weight, and if it is less than 20% by weight, sufficient mechanical strength cannot be obtained.
When an insulator is extruded and coated on the outer periphery, the semiconductive layer is likely to be damaged or deformed.

If it exceeds 50% by weight, water resistance will deteriorate.

Carbon blacks such as channel black, furnace black, and acetylene black are typical examples of conductivity-imparting materials that impart conductivity to the above-mentioned mixture. It is necessary to add 40 parts by weight or more of the conductivity imparting agent to 100 parts by weight of the mixture; if it is less than 40 parts by weight, the desired conductivity cannot be obtained.

The semiconductive composition thus obtained is prepared in the same manner as conventional compositions by mixing necessary additives such as antiaging agents and processing aids.

Examples of the present invention will be described below along with comparative examples.

A semiconducting composition obtained by blending various components as shown in Table 1 is extrusion coated onto a stranded copper conductor having a cross-sectional area of 150 to form an internal semiconducting layer, followed by a low density coating. polyethylene(
Density 0.9209Aa% MI 1.0 )1 [10
parts by weight, dicumyl peroxide, and 0.25 parts by weight of an antioxidant are extrusion coated to form an uncrosslinked insulator layer, and an internal semiconducting layer is formed on the outer periphery of the insulator composition. The outer semiconducting layer was formed by extrusion coating a semiconducting layer of the same composition as the material, followed by heat crosslinking to obtain a crosslinked polyethylene insulating capeple.

Water was poured into the conductor of this cable to submerge the cable, and then an AC heart pressure of 50H2, 15Kv was applied between the conductor and the water electrode. The water temperature is 90℃, and the number of days for charging is 18.
Month.

After the electrification was completed, the insulator was spirally cut to a thickness of 0.5 fi, boiled and stained with a methylene blue aqueous solution, and then the number of water trees generated at the interface between the insulator and the internal semiconductive layer was observed using a microscope. The results are shown in the lower column of Table 1.

6-Table 1 (Containing amount is heavy needle part) As can be seen from Table 1, when medium-low pressure polymerized low-density polyethylene is used, the number of water trees generated is significantly lower than when high-density polyethylene is used. ing. However, when the blending ratio of medium-low-pressure legal low-density polyethylene to ethylene propylene comb is outside the scope of the present invention (6), or when the density of medium-low-pressure polymerization low-density polyethylene is outside the scope of the present invention. (Comparative Example 2) shows no significant effect.

The reason why the semiconductive layer made of low-density polyethylene produced by medium-low pressure polymerization has excellent water resistance is not yet clear, but the lower density of the semiconducting resin makes it more flexible, which makes it more compatible with ethylene propylene rubber. It is estimated that this is due to the increase in

As explained above, according to the present invention, it is possible to obtain a semiconductive composition for a power cable that has a 1-minute I-mechanical strength and excellent water tree resistance.

Procedural amendment (voluntary) 1. Indication of the case 1982 Patent No. 95519
No.: 1, Title of invention: Semi-conductive composition for electrical cable
□a Person making the amendment 100 Detailed explanation of the invention of the specification to be amended.

Contents of correction Table 1 on page 7 of the specification is amended as follows.

2-

Claims (1)

[Claims] 1. Ethylene propylene rubber with an i degree of 0.915 to 0.
40 parts by weight or more of a conductivity-imparting material is added to 100 parts by weight of a mixture of 930 t/crll medium-low-pressure polymerized low-density polyethylene and the mixing ratio of medium-low-pressure polymerized low-density polyethylene is 20 to 50% by weight. A semiconductive composition for an electric cable, characterized by comprising: 2. The semiconductive composition for an electrical cable according to claim 1, wherein the conductivity imparting material is carbon black.