JPH11228763A - Insulation composition and power cable prepared by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition having excellent water tree resistance by mixing a crosslinked polyethylene with a poly-N-vinylacetamide in a specified ratio. SOLUTION: There is provided a composition comprising a crosslinked polyethylene and 0.1-10.0 wt.% poly-N-vinylacetamide represented by the formula. This composition is used in the internal and external semiconductive layers of a power cable as well as in the insulation layer of a power cable. The crosslinked polyethylene used is a hydrophobic polymer obtained by subjecting a low-density polyethylene, a high-density polyethylene, or the like to crosslinking by irradiation with high-energy electron beams or γ-rays, silane graft water crosslinking, chemical crosslinking, or the like and easily suffers from water deposition by dielectric condensation on a non-uniform electric field part which acts as a point of the generation of water tree. On the contrary, the poly-N-vinylacetamide is a hydrophilic thermoplastic polymer and makes it difficult for water to condense and deposit on a point of the generation of water tree on the hydrophobic polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating composition, and more particularly to an insulating composition having excellent water tree resistance.

[0002]

2. Description of the Related Art Conventionally, a power cable has a structure in which an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a metal shielding layer, and an anticorrosion layer (sheath) are sequentially formed on a conductor such as a copper wire. Consists of

The insulating layer forming the power cable requires a polymer material having a high dielectric breakdown voltage as a material for forming the insulating layer. Conventionally, polyethylene and the like have been often used as a material meeting this demand. In particular,
Crosslinked polyethylene (hereinafter referred to as "XLPE")
(Abbreviated as "abbreviated") has improved heat resistance above the melting point of polyethylene and is most commonly used as an insulator for power cables.

[0004]

However, a power cable using such XLPE as an insulator (hereinafter abbreviated as "CV cable") causes water tree deterioration due to the presence of moisture and the action of an electric field. There is a disadvantage that it is easy. This water tree degradation is caused by the operating electric field of the distribution class CV cable, 1.0 kv / mm to 3.0 kv.
/ Mm even when used in a relatively low electric field. In particular, when a CV cable is used as a distribution cable used under water, there is a problem in that a shielding layer such as a metal coating is rarely provided.

Accordingly, an object of the present invention is to solve such a problem and to provide an insulating composition having excellent water tree resistance. It is another object of the present invention to provide a power cable using the insulating composition.

[0006]

An object of the present invention is to provide an insulating composition comprising 0.1% by weight to 10.0% by weight of a poly N-vinylacetamide represented by the following general formula (I) based on XLPE. And a power cable using this insulating composition.

[0007]

Embedded image

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
As described above, the insulating composition of the present invention is characterized in that XLPE contains poly N-vinylacetamide represented by the above general formula (I) (hereinafter abbreviated as “PNVA”). Is what you do.

[0009] As the XLPE used here, those generally used as insulators of conventional CV cables can be used. For example, low density polyethylene (LDP)
E) or a method obtained by cross-linking high-density polyethylene (HDPE) by irradiation with high-energy electron beam or γ-ray, silane graft water cross-linking method, chemical cross-linking method, or the like. be able to. Since the XLPE obtained in this manner is a hydrophobic polymer, moisture is dielectrically condensed and deposited on irregular portions (foreign matter, voids, protrusions, etc.) of the electric field which is a starting point of water tree. Cheap. For this reason, water trees are likely to occur.

On the other hand, as the PNVA represented by the above general formula (I), for example, those manufactured by Showa Denko can be used. This PNVA is a thermoplastic polymer.

The P represented by the above general formula (I)
NVA is a hydrophilic polymer. Such a hydrophilic polymer makes it difficult for the hydrophobic polymer to condense and precipitate water at the starting point of water tree generation. From this, an insulating composition having excellent water tree resistance can be obtained by uniformly dispersing and containing PNVA, which is a hydrophilic polymer, in the XLPE, which is a hydrophobic polymer.

In such an insulating composition comprising XLPE containing PNVA, the content of PNVA with respect to the XLPE is 0.1% by weight to 10.0% by weight.
It is said. Preferably, it is 0.5% by weight to 5.0% by weight. When the content of the PNVA is less than 0.1% by weight, sufficient water tree resistance cannot be obtained. When the PNVA is contained in an amount exceeding 10.0% by weight, X
Inconveniences such as deterioration of electrical characteristics such as dielectric characteristics of LPE occur.

The PNVA represented by the general formula (I) is
It is used to improve the water tree resistance of the material forming the insulating layer of the power cable, but is also included in the material forming the extruded inner semiconductive layer and the extruded outer semiconductive layer. Can be used. This PNV
A can be used alone for each of these sites, but can also be used for two or all of the sites simultaneously.

[0014] The insulating composition comprising PNVA in such XLPE contains 0.1% by weight of the PNVA.
PNVA, which is a hydrophilic polymer, is a hydrophobic polymer.
Since dielectric condensation of water at the starting point of the occurrence of water trees inside the PE is suppressed to prevent water from condensing and precipitating, excellent water tree resistance can be obtained.

[0015] The power cable of the present invention is XLPE.
Characterized by using the above insulating composition containing PNVA. To manufacture a power cable using such an insulating composition, a method of sequentially forming an inner semiconductive layer, an insulating layer, and an outer semiconductive layer on a conductor by three-layer extrusion coating or the like is performed. When manufacturing such a power cable, the insulating layer is made of XLP.
It is composed of an insulating composition containing 0.1% to 10.0% by weight of PNVA with respect to E.

[0016] Such a power cable is a PPE to XLPE.
Since the insulating composition containing NVA is used, it is excellent in water-resistant tree performance. That is,
The power cable is less likely to cause water tree degradation.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. LDPE (MI = 3.0 g / 10 min, density 0.92
g / cm3), 0.00% by weight of PNVA,
0.07% by weight, 0.10% by weight, 1.00% by weight, 1
After melt-blending 0.0% by weight and 15.0% by weight, respectively, 2.0 parts by weight of DCP and 0.2 parts by weight of an antioxidant were added as a cross-linking agent. A sheet-shaped insulating composition having a ratio of about 80% and a thickness of 5 mm was prepared and used as a test sample.

As shown in FIG. 1, a ring-shaped dam was provided on the test sample 1 to form a water electrode 2. Further, a conductive paint was applied to the bottom surface of the test sample 1 to provide a coating layer, which was used as a ground electrode 3. Then, a voltage of 10 kV and 1 kHz was configured to be applied from the voltage electrode 4, and the above electrode was applied for 30 days to perform a water immersion test. After completion of the test, the number of water trees (boat trees) generated inside the test sample and the dielectric loss tangent (tan δ) of each of the test samples were measured. Table 1 shows the results.

[0019]

[Table 1]

From Table 1, it was found that in Examples 1 to 3, the number of boat title trees generated was small. On the other hand, in Comparative Example 1 or Comparative Example 2 in which the content of PNVA with respect to XLPE was less than 0.1% by weight,
As a result, a large number of boat titleries were generated, and a sufficient effect on the water resistant tree performance was not obtained. Also, PNV
In Comparative Example 3 in which A was contained in excess of 10.0% by weight, the result was that the dielectric loss tangent (tan δ) was large as compared with Examples 1 to 3, which are preferable contents.

From these results, it is found that XLPE
It was confirmed that the inclusion of VA can improve the water-resistant tree performance of XLPE. Further, it became clear that it was important to set the content in a preferable range of 0.1% by weight to 10.0% by weight.

[0022]

As described above, the insulating composition of the present invention reacts with XLPE with the P represented by the above general formula (I).
Since NVA is contained in an amount of 0.1% by weight to 10.0% by weight, it is difficult for water to be condensed and precipitated at the time of generation of the water tree of the XLPE, so that it can have good water tree resistance. . In addition, since a power cable using this insulating composition has excellent water tree resistance, for example, when using this as a power distribution cable, a shielding layer such as a metal coating is not provided. In both cases, a power cable having excellent water tree resistance when used under water can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an inundation charging test.

[Explanation of symbols] 1 ... test sample, 2 ... water electrode

Claims (2)

[Claims] 1. A method according to claim 1, wherein the poly (N-vinylacetamide) represented by the following general formula (I)
An insulating composition, characterized in that the composition comprises from 1% by weight to 10.0% by weight. Embedded image 2. A power cable using the insulating composition according to claim 1.