JPS598216A - Polyolefin insulated power cable with semiconducting layer - 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 polyolefin insulated capeple having a semiconducting layer coated on a conductor or on an insulator.

Polyolefin-insulated power cables, especially high-voltage power cables, are coated with polyolefin on the center conductor and insulator for the purpose of preventing corona deterioration in the gaps that exist between the center conductor and the insulator, and between the insulator and the shielding layer. A semiconducting layer consisting of a coating layer of a semiconducting plastic mixture is provided (ζ).
This semiconductive layer is coated with a semiconductive composition whose main component is polyethylene or a polymer mainly composed of ethylene, and carbon black is added to the base polymer to impart conductivity. It is formed by

However, in conventional electric cables having a semi-conductive layer, if a small amount of moisture infiltrates due to cross-linking with water vapor or use in a flooded environment, the protrusions of the semi-conductive layer may enter the insulator. This has the disadvantage that water trees extending in the direction of the electric field, so-called inner conductor trees or outer ring trees, are generated, and the insulation properties of the cable are significantly reduced.

In view of the above points, the inventor conducted extensive research to develop an electrical cable with excellent water resistance, and found that carbon particles aggregated in the protrusions that form the starting point of the inner guide tree or outer ring tree. Furthermore, it was revealed that in conventional semiconducting compositions, there are many carbon particles because the carbon black is not evenly mixed into the base polymer during the mixing process. did.

As a result of further investigation, we found that the paste polymers are ethylene vinyl acetate copolymer and ethylene propylene rubber (EPM).
, EPDM, etc.) and mix it with the necessary amount of carbon black to obtain conductivity.
The present invention was completed based on the discovery that a semiconductive composition having a high shear during kneading and having no carbon particles at all was obtained due to the effect of adding ethylene propylene rubber.

That is, the present invention provides a semiconductive composition comprising ethylene-vinyl acetate copolymer, ethylene propylene rubber, and carbon black as main components, and in which the blend ratio of ethylene propylene rubber to the base polymer is 10 to 40% by weight. This invention relates to a polyolefin insulated cable having a semiconductive layer formed by covering a polyolefin insulator, and is mainly intended for cables whose main components are polyethylene, crosslinked polyethylene, or ethylene copolymer as the polyolefin insulator.

More specifically, by making the semiconducting composition have the above composition, a compound having no carbon particles can be obtained, and the semiconducting layer formed by extrusion coating the same has no protrusions and is very smooth. Since it is a surface, there is no occurrence of inner conductor trees or outer ring trees, which are the drawbacks of conventional power cables, and it is possible to provide a power cable with stable insulation properties even after long-term use.

In the present invention, the combination of base polymers was limited to ethylene vinyl acetate copolymer and ethylene propylene rubber because other polymer combinations would have a large number of carbon particles and would not provide the desired protrusion-free semiconductive layer. It's for a reason. Furthermore, the reason why the blending ratio of ethylene propylene rubber is set to 10 to 40% by weight is because the effect of adding ethylene propylene rubber cannot be obtained if it is less than 10% by weight, and if it exceeds 40% by weight, the material becomes hard. This is because extrusion becomes difficult. The amount of carbon black is not particularly limited, and is usually added in an amount of 15 to 80 parts by weight in order to obtain the required conductivity. Of course, it goes without saying that processing aids such as crosslinking agents, anti-aging agents, and zinc stearate can be added if necessary.

EXAMPLES Below, the present invention will be specifically explained with reference to Examples and Comparative Examples.

(Note 1) Carbon black: Acetylene black (Note 2)
) Crosslinking agent Nijicumyl peroxide (Note 3) Anti-aging agent: 4-4' thiobis6tertiary methyl 3-methylphenol (Note 4) Processing aid Zinc nistearate (Note 5) Carbon pieces: 100 times the belt surface The number of carbon particles per myb2 of 1 or more is represented by X, 0.1 to 1.0 is represented by Δ, and less than 0.1 is represented by ○.

*In this example, the cable was not obtained because the material was too hard and difficult to extrude coat.

The semiconductive compositions having the compositions shown in Table 1 are mixed in a bumper mixer, and the resulting compound is extruded into a tape shape with a thickness of 0.7 m and a width of 30 mm using an extruder with a diameter of 80 mm. Workability and carbon spots on the tape surface were measured. Next, a stranded wire conductor with a cross-sectional area of 150 ruL2 was coated with the obtained compound by extrusion, and polyethylene (density 0.92, melt index 1.0
A composition obtained by adding 2.0 parts by weight of dicumyl peroxide and 0.2 parts by weight of an antiaging agent (4-4'thiobis-6-tert-butyl-3-methylphenol) was extrusion coated. An insulating layer having a thickness of about 2 layers was provided, and then the crosslinking reaction was completed to obtain a crosslinked polyethylene capacitor having a semiconductive layer.

Immerse lOm of each of these cables in water at 70°C, and while constantly supplying water to the stranded conductors, conduct ACI.
After applying OKV (50 Hz) for 6 months, it was taken out and the presence or absence of water trees originating from the semiconductive layer, so-called internal trees, was observed.

The above results are also listed in Table 1.

As is clear from the examples, only when a certain ratio of ethylene vinyl acetate copolymer is blended as the base polymer, it is possible to prevent the generation of water trees from the target semiconductive layer and to obtain a conductive material with excellent long-term insulation properties. If the blending ratio of ethylene propylene rubber is less than 10% by weight, there will be no effect of adding carbon particles, and internal trees will occur (Comparative Example 1).
and 2) If it exceeds 40% by weight, the material becomes too hard and difficult to extrude, making it impractical. (Comparative Example 3) Therefore, the blending ratio of ethylene propylene was 10 to 40.
When the amount is % by weight (Examples 1 to 5), an electric cable having the desired tree resistance can be obtained.

On the other hand, when this combination was changed to other polymers (Comparative Examples 4 to 11), there were many carbon particles,
Good results cannot be obtained because internal trees occur.

The above example is an example of a power cable having a so-called inner semiconducting layer coated on a central conductor as a semiconducting layer, but in the present invention, a so-called outer conductive caple having the above composition coated on an insulator is used. Cables with layers also have similar effects.

As described above, the electrical cable of the present invention having a semiconducting layer coated on a conductor or an insulator has no protrusions on the semiconducting layer, so even if it is used for a long period of time under water, there will be no damage from the semiconducting layer. It is a power cable that does not generate water trees and has excellent long-term insulation properties, and its industrial value is extremely large from the viewpoint of supply reliability.

Written amendment to the procedure by Kazuo Wakasugi, Commissioner of the Patent Office1, Indication of the case, Patent Application No. 116021 of 1982, Title of the invention, Polyolefin insulating capeple with semiconductive layer, 3,
Relationship with the person making the amendment Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (21
8) President of Sumitomo Electric Industries, Ltd. Tetsube 4, Agent address: 6, Sumitomo Electric Industries, Ltd., 1-1-3 Shimaya, Konohana-ku, Osaka, Column 7 for detailed explanation of the invention in the specification subject to amendment , Details of the amendment (1) In the fourth line of page 4 of the specification, "protrusion" is corrected to "pu".

(2) Page 4, line 12 of the specification Correct "protrusion" to "irregularity due to bumps".

(3) Page 8, line 18 of the specification Correct "protrusion" to "irregularity due to bumps".

Claims (1)

[Claims] (1) The semiconductive layer coated on the conductor or insulator contains ethylene-vinyl acetate copolymer, ethylene propylene rubber, and carbon black as main components, and the blend ratio of ethylene propylene rubber to the base polymer is 10
1. A polyolefin insulating capeple having a semiconductive layer, characterized in that it is formed from a semiconductive composition containing 40% by weight of a semiconductive composition.