JPS6343209A - Electrically insulating material - Google Patents

Abstract

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

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to electrical insulation based on polyolefin for medium and high voltages of about 10 kV or higher, which has additives to retard the occurrence of water trees, particularly in cables and conductors. Regarding materials.

[Conventional technology]

A phenomenon called "electrochemical treeing (ECT)" or "water treeing" develops in electrically loaded polyolefin insulation materials.

This phenomenon, which is particularly important with regard to the operational safety of medium-high voltage cables insulated with synthetic resins, gives rise to dendritic formations, so-called ECT structures.

The visual appearance of ECT structures, which can be particularly contrasted and observed in detail by appropriate coloring, is highly variable.

Basically, it can be divided into two types:

“vented tree 1”
s) : Originating from the surface of the insulating material and spreading into the inside of the insulating material.

"bow-tie trees"
): Something that occurs inside the insulation material.

The mechanism of ECT generation has not been clarified so far.

However, it is generally believed that the generation of ECT structures requires an electric field and the presence of a polar liquid, especially water.

Therefore, the ECT structure is also called a water tree. Where water trees occur, there are always impurities, agglomerated mixtures, cavities, gaps,
It seems to be a defect location such as a crack or an interface, but
Only a portion of them produces water trees. In the case of insulating materials manufactured on a large industrial scale, dendritic structures extend in the direction of the electric field from defective locations that cannot be completely removed.

ECT structures imply local deterioration of the insulating material, thereby causing damage to the insulating material, especially with respect to the electrical breakdown strength. Many experiments have therefore already been carried out to prevent or at least retard the growth of water trees. In this case, in particular additives are added to the insulating layer.

Additives suitable for effectively and permanently inhibiting ECT generation, ie water tree formation, include the following:

Barbylic acid and 2-thiobarbylic acid and derivatives thereof (West German Patent Application No. 3202828, US Pat. No. 4,458,044 or JP-A-Sho 5)
(See Publication No. 8-13307).

Water-soluble alkali and alkaline earth metal phosphates and hydrolysable phosphoric esters (German patent application no. 3202896, U.S. Pat. No. 458129)
(See specification No. 0 or JP-A-58-133701)
.

Substances with a certain particle size and agglomeration size that are adsorbingly active for heavy metal ions or that bind heavy metal ions in ion exchange (West German Patent Application No. 33189)
88, US Pat. No. 4,623,755, or Japanese Patent Application Laid-open No. 60-3805).

Alcolade of magnesium, calcium and aluminum (West German Patent Application No. 3,321,268, US Pat. No. 4,574,111 or JP-A-60
(Refer to Publication No.-10504).

Potassium and sodium stannate and titanium oxysulfate (West German patent application no. 3503998)
(See the specification or Japanese Patent Application Laid-Open No. 183808/1983).

Derivatives of pyrimidines and hexahydropyrimidines (see German Patent Application No. 3,516,971).

Although each of the above substances has been found to be effective in retarding the development of water trees, a further set of important properties are required for practical use in electrical insulation, particularly cable and conductor insulation. They must have, in particular, thermal oxidative stability, sufficient mechanical stability, low dielectric losses, optical transparency and storage stability as easy-to-process insulating compounds. Particular attention should be paid to dielectric loss.

This is because dielectric loss increases when additives are present in the insulating material.

[Problem that the invention seeks to solve]

The object of the invention is to satisfy the practical requirements in all respects,
The object of the present invention is to provide an electrical insulation material of the type mentioned at the outset, in which an effect of retarding the occurrence of ECT and low dielectric losses is achieved.

[Means for solving problems]

This object is achieved according to the invention if the electrical insulation consists of an ethylene copolymer or a polymer blend of polyethylene and an ethylene copolymer with polar co-components, in which case the polar co-components in the copolymer or in the polymer blend are The amount is 1 to 5% by weight and is achieved by the insulation containing as an additive 0.1 to 1.5% by weight of pyrogenic silicic acid, based on the weight of the copolymer or polymer blend.

[Effect]

As will be explained in more detail below, in the case of the electrical insulation material according to the invention consisting of a special polyolefin containing silicic acid produced by pyrolysis, dielectric losses can be avoided by using this special polyolefin; The excellent action of silicic acid in delaying the development of ECT is not adversely affected.

This is quite surprising and could never have been predicted.

West German Patent Application Publication No. 33189, which was already pointed out earlier.
No. 88 as well as U.S. Pat. No. 4,623,755, it has been found that polyolefin-based electrical insulation materials have uniform distribution and adsorptive activity towards heavy metal ions as additives to retard the occurrence of water trees. Alternatively, substances with a particle size of up to 50 μm or an agglomerate size of up to 100 μm that bind heavy metal ions in ion exchange can be used in a 0.
It is known to charge from 0.05 to 10% by weight.

In this case, aluminum oxides and aluminum oxide hydrates and/or aluminum silicates with a large active surface can be used as additives, but it is advantageous for the electrical insulation to contain pyrogenic and/or precipitated silicic acids. It is.

In the case of known insulation materials, polyolefins are used as a basis, ie in reticulated or non-reticulated form. In particular polyethylene and reticulated polyethylene are used. However, at the same time ethylene copolymers, such as ethylene-propylene copolymers (EPR), ethylene-vinyl acetate copolymers (EVA) and ethylene-alkyl acrylate copolymers (for example ethylene-ethyl acrylate and butyl acrylate copolymers), and It is also possible to use ethylene-propylene-dieneter polymers and mixtures (blends) of these ethylene copolymers and terpolymers with polyolefins, especially polyethylene and polypropylene.

By the way, only one of the many possible compositions obtained from the above-mentioned ECT retardant additive and insulating material, namely pyrogenic silicic acid (as an additive to retard the occurrence of water trees) and special polyolefins, It could never have been foreseen that a composition consisting of and would meet the requirements regarding ECT retardation and low dielectric loss particularly markedly. These special polyolefins are ethylene copolymers with polar co-components and polymer blends consisting of polyethylene and ethylene copolymers of this type. The amount of polar co-components in the copolymer and in the polymer blend is in each case 1 to 5% by weight, preferably 2 to 4% by weight.

If a polymer blend is used, it advantageously contains 80-90% polyhydrene and 1% ethylene-copolymer.
0 to 20% by weight, the amount of both components of the mixture being 100%. Advantageously, the amount of ethylene copolymer is about 15% by weight. In this case, the ethylene copolymer may contain from 10 to 45% by weight of polar co-components.

When the ethylene copolymer is used alone, it contains 1 to 5% by weight of the polar co-component as detailed above. This amount can also be applied when using mixtures of ethylene copolymers containing varying amounts of polar co-components.

The same is true for ethylene-copolymers in polymer blends.

The polar co-component of the ethylene-copolymer must be sufficiently thermally and hydrolytically stable under the manufacturing and operating conditions of the electrical insulation according to the invention.

The polar co-component is therefore generally vinyl acetate, vinyl alcohol, acrylonitrile, alkyl acrylate or alkyl maleate. Particularly preferred polar cocomponents of the ethylene copolymers are methyl acrylate, ethyl acrylate or butyl acrylate. In this case, the ethylene copolymer is ethylene-butyl acrylate copolymer (E
BA) is particularly preferred.

The pyrogenic silicic acid contained in the electrical insulation material according to the invention is a synthetic product. In other words, this is, for example, oxyhydrogen flame (
It is produced when silicon tetrachloride is hydrolyzed at a temperature of about 1000°C. Pyrolytic silicic acid (chemical composition SiO□), which exists in a highly dispersed state, that is, in a finely distributed state,
It is characterized by being radiographically amorphous rather than crystalline.

The amount of the ECT retardant additive, i.e. the pyrolytic silicic acid, in the electrical insulation material according to the invention is 0°1-1.5% by weight, based on the weight of the ribolimer blend as already described.
It is. Advantageously, this amount is between 0.3 and 1 kg by weight, especially about 0.
．． It is 5% by weight. The pyrolytic silicic acid is added to the insulation material. However, in the case of cables and conductors, additives can be added not only to the actual insulating layer but also to the boundary layer, that is to say to the inner and/or outer conductive layer.

In addition to cables and conductors, the electrical insulation according to the invention can also be used in sockets and cable fittings. The polyolefin that is the base of the insulating material is generally reticulated, but it can also be used in a non-reticulated state. Reticulation can advantageously be carried out with peroxides or with energetic radiation. It is also possible to add customary additives to the insulation, such as oxidation stabilizers.

〔Example〕

The present invention will be further explained in detail based on examples.

4.4゛-thiobis(6-tert,
-butyl-3-methyl-phenol) and dicumyl peroxide as a reticulating agent, and about 25% by weight of this polyethylene and butyl acrylate (polar co-component). containing ethylene-butyl acrylate (EBA) (in this case the EBA content of the polymer blend is 15
% by weight) to produce plates with a thickness of 3 mm. The production was carried out by compaction at a pressure below 2 atmospheres and at elevated temperatures, resulting in a reticulation of the insulation. A portion of the plate material has a high specific surface area (e.g. approx. 300 m
''/g) of silicic acid, which is commercially available under the trade name of Aerosil (^eros tl), produced by a high-pyrolysis method.
It was mixed in at a concentration of 5% by weight. Next, the plate-shaped test piece was electrically loaded at 10 kV and 150 Hz. In this case both surfaces were brought into direct contact with a 3% sodium chloride solution heated to 70°C. The loading time was 130 hours.

The experimental results show that plate specimens containing pyrolytic silicic acid do not have E CT fjI structures after electrical loading, whereas this is true for specimens without silicic acid additives. do not. As already mentioned, for electrical reasons as well as ECT delay, the dielectric constant, tan δ
It is also important that there is as little as possible.

The results of the conducted experiments are shown below.

Absolute &ECTt'% tanδLDPE
100%+ None 15.10-' Aerosil 0.5% LDPE 85χ/EBA15χ+ None 5
．． 10-'Aerosilua, 5% JAN δ values for all specimens were 40.
Insulating materials made of polymer blends of polyethylene and ethylene copolymers, such as EBA, are superior to insulating materials made only of polyethylene because they have lower dielectric loss than insulating materials made only of polyethylene. ing. Therefore, the electrical insulation material according to the present invention, which is generally made of a special polyolefin containing silicic acid produced by high-pyrolysis method, not only has a small dielectric loss (ECT
It is clear that the occurrence of cancer can be effectively and permanently suppressed.

Claims (1)

[Claims] 1) An electrical insulation material based on a polyolefin for medium and high pressures containing additives that retard the occurrence of water tree, the insulation material being an ethylene copolymer or a polyethylene and ethylene copolymer having a polar co-component. wherein the amount of polar co-component in the copolymer or polymer blend is from 1 to 5% by weight, and the insulating material is made of pyrolytic silicic acid, based on the weight of the copolymer or polymer blend. Electrical insulation material based on polyolefin, characterized in that it contains .1 to 1.5% by weight as additives. 2) Electrical insulation material according to claim 1, characterized in that the electrical insulation material consists of a polymer blend consisting of 80-90% by weight of polyethylene and 20-10% by weight of an ethylene-copolymer with polar co-components. 3) Electrical insulation material according to claim 2, characterized in that the amount of ethylene-copolymer in the polymer blend is about 15% by weight. 4) The electrical insulating material according to any one of claims 1 to 3, characterized in that the amount of the additive is 0.3 to 1% by weight. 5) The polar co-component of the ethylene copolymer is vinyl acetate,
Any one of claims 1 to 4, characterized in that it is vinyl alcohol, acrylonitrile, a kind of alkyl acrylate, or alkyl maleate.
Electrical insulation materials as described in Section. 6) The electrical insulating material according to claim 5, wherein the polar co-component is methyl acrylate, ethyl acrylate or butyl acrylate.