JPS62157612A - Electrical insulation composition and power cable using the same - 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 <Industrial Application Field> The present invention relates to an electrical insulating composition with excellent water resistance and a power cable using the same as an insulator.

<Prior Art> In recent years, cross-linked polyethylene (XLPE) has been widely used as an insulator for power cables because of its excellent electrical properties and processability, as well as its low cost.

However, in the case of cross-linked polyethylene, although the initial 21J1 electrical properties are excellent, when electricity is applied in a submerged state, deterioration due to so-called water tree occurs, resulting in a decrease in insulation performance.

This water tree is said to be caused by water acting on abnormal electric field areas such as foreign objects, voids, and electrode irregularities in the insulator. The reason why water trees tend to occur in cross-linked polyethylene is thought to be because cross-linked polyethylene is hydrophobic and water tends to concentrate in abnormal electric field areas.

Therefore, in order to suppress the occurrence of water trees in cross-linked polyethylene, it has been considered to introduce a hydrophilic substance to prevent water from concentrating in the abnormal electric field area.

From this point of view, conventionally, cross-linked polyethylene
For example, it has been proposed to blend ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polyethylene glycol (PEG), and the like.

<Problems to be Solved by the Invention> However, even with these blends of EVA, EEASPEG, etc., it is still insufficient for power cables that are used under severe conditions such as constant flooding.

Therefore, the present inventors conducted extensive research on the water tree suppression effect of various substances, and found that the addition of ethylene-methyl methacrylate copolymer (E-MMA) was extremely effective compared to the previously proposed product. I discovered something.

The present invention was invented based on this result.

Means for Solving the Problems and Their Effects One of the aspects of the present invention is a composition comprising polyethylene and an ethylene-methyl methacrylate copolymer (E-MMA), and a composition having a methyl methacrylate content ( One example is an electrical insulation composition in which M M A %) is 0.5 to 10% by weight, and the other is an electric power cable using this composition as an insulator.

Here, the methyl methacrylate content (M
MA%) was set at 0.5 to 10% by weight because if it was less than 0.5% by weight, a sufficient water tree suppression effect could not be obtained;
This is because, if the content exceeds % by weight, the initial dielectric breakdown characteristics and dielectric properties will deteriorate.

This composition may be crosslinked before use in order to prevent fluidity at high temperatures. The crosslinking method is not particularly limited, but organic peroxide (dicumyl peroxide; DC
Chemical crosslinking using P, etc.), silane crosslinking, irradiation crosslinking, etc. can be applied. Further, an anti-aging agent or other additives as required may be added to this composition. Moreover, it is of course possible to add it in combination with the above-mentioned EVA, EEA, PEG, and other additives having a water tree inhibiting effect.

<Example> Examples ■~■ As shown in Table 1, low density polyethylene (M1=1.
2), E-MMA (manufactured by Sumitomo Chemical Co., Ltd., Acrift, MI=7, MMA%=18%) was added in various proportions, and DPC2 as a crosslinking agent was added to 100 parts by weight of this mixture.
, 0 parts by weight, 4,4'-thiobis-(
0.3 parts by weight of 6-tertiary methyl-3-methylphenol) was added and kneaded to obtain a composition (Examples ① to ②).

Also, for comparison, those without E-MMA or EV
A (MI=2, VA%=15%) and EEA (MI=2
, EA%=15%) as VA% and EA for the composition.
% was added to 2%, and compositions were prepared in which the same crosslinking agent and anti-aging agent as above were added (Comparative Examples ① to ②).

Each of the above compositions was press-molded under conditions of 180'CX for 10 minutes, and the following tests were conducted. The gel fraction after press molding after each test and drying by immersion in xylene at 80℃ for 24 hours was 85.
% or more, the crosslinking was sufficient.

+1) Water tree test As shown in Figure 1 (a paint layer 2 of conductive paint is provided on the bottom surface of the test sample 1 with a thickness of 5 mm to serve as a grounding electrode, and a water tank 3 is provided on the top surface of the test sample 1). A water electrode was formed, and the structure was such that a voltage of 10 KV and IKHz could be applied thereto. After applying the above voltage for 30 days, the sample was boiled and the water tree was observed.

The occurrence density of water trees of 50μ or more was observed and expressed as a relative number to the number of occurrences of 100 in the sample of Comparative Example ① (X L PE only case).

(2) Dielectric dissipation tangent (tan δ) measurement test A voltage of 1Kv, 50H2 (7) was applied to the immmm-t, and the measurement was performed using a Schering-Blinoge.

The above test results are also listed in Table 1.

Example ■ Power cables were made using the compositions of Example ■ and Comparative Examples ■ and ■ shown in Table 1 as insulators. The cable structure is a three-layer product with a conductor cross-sectional area of 200 mm2, an insulation thickness of 3 mm, an internal extruded semiconductive layer, and an external extruded semiconductive layer.

Table 2 shows the results of determining the AC breakdown voltage of each cable after the submergence electrification described below.

The water immersion test was conducted by pouring water into the cable conductor, applying a voltage of I KHz, 10KHz in warm water at 70℃ for 90 days, and then determining the AC breakdown voltage under the condition of step-up of 5Kv/30 minutes. .

Table 2 <Effects of the Invention> As is clear from the above explanation, the present invention allows polyethylene to have a predetermined methyl methacrylate content (MMA%).
) and ethylene-methyl methacrylate copolymer, it is possible to obtain an excellent electric insulating cord that has a great effect of inhibiting the generation of water, and this composition can also be used as an insulator for power cables. This makes it possible to provide a cable with excellent water resistance.

[Brief explanation of drawings]

Figure 1 is a schematic explanatory diagram of the water tree test method/1...
Test sample, 2... Coating layer of conductive paint, 3... Water tank (water electrode),

Claims (2)

[Claims] (1) Consists of polyethylene and ethylene-methyl methacrylate copolymer (E-MMA), and the methyl methacrylate content (MMA%) in the composition is from 0.5 to
10% by weight of an electrically insulating composition. (2) The insulator provided on the conductor is made of polyethylene and ethylene-methyl methacrylate copolymer,
and methyl methacrylate content (MMA
%) is 0.5 to 10% by weight.