JPH05325643A - Insulating composition and electric power cable - Google Patents

Abstract

PURPOSE:To provide an insulating composition capable of maintaining the excellent dielectric characteristic (tan delta), particularly even under a high temperature and a high electric field. CONSTITUTION:This is an insulating composition in which a cross linking agent of 1 to 5 parts by weight in which a very small amount of electrically conductive impurities is removed by refining, an antioxidant of 0.05 to 0.5 parts by weight in which a very small amount of electrically conductive impurities is removed by refining are added to polyolefin of 100 parts by weight and then cross-linked. A very small amount of electrically conductive impurities in an additive agent is removed by refining, thereby making it feasible to maintain the excellent dielectric characteristic even under a high temperature and a high electric field.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention provides an insulating composition capable of maintaining dielectric properties (tan δ), particularly excellent dielectric properties even under high temperature and high electric field, by a purified additive, and an insulating composition for insulating the same. It relates to a power cable used for the body.

[0002]

2. Description of the Related Art Polyolefin, for example, cross-linked polyethylene (XLPE) obtained by cross-linking polyethylene, is currently widely used as an insulator for power cables. This X
Low density polyethylene (LDPE) is generally used as polyethylene, which is the base resin of LPE, and a necessary crosslinking agent and antioxidant are added thereto. The XLPE thus obtained has good insulating properties,
In recent years, it has been applied to an ultra-high voltage power cable of 275 to 500 KV.

[0003]

However, this XLP
In the case of E, it is originally non-polar, and under normal conditions (normal temperature,
Excellent dielectric characteristics (dielectric loss tangent = tan δ) under low electric field
However, it has been clarified that the dielectric characteristics deteriorate under high temperature and high electric field. This decrease in the dielectric property causes a problem that the desired insulation property cannot be obtained in the above-mentioned ultra-high voltage power cable in which the electric field stress on the insulator becomes high.

Therefore, the present inventors have shown good tan δ at room temperature and low electric field, but ta at high temperature and high electric field.
It was inferred that the phenomenon of increasing nδ was not due to the dipole component due to the polar substance in the resin but was due to the increase of electrically conductive charge carriers under high temperature and high electric field.

As a result of various tests, as a main factor for increasing the charge carriers, a small amount of electric conductivity contained in a crosslinking agent or an antioxidant added to the base resin of XLPE is contained. It has been found that sex impurities are involved. Since this electrically conductive impurity is in a very small amount, it is at a level that cannot be detected by a method such as a usual infrared absorption method (IR) or high performance liquid chromatography (HPLC).

The present invention has been made from such a viewpoint, and by using an additive from which a trace amount of electrically conductive impurities has been removed by a refining treatment, excellent dielectric properties can be obtained even under high temperature and high electric field. The present invention provides an insulating composition that can be maintained and a power cable using the insulating composition.

[0007]

Means for Solving the Problems and Its Actions One of the present invention is to provide an insulating composition in which an additive from which a trace amount of electrically conductive impurities has been removed by a refining treatment is added to a polyolefin, or 100 parts by weight of a polyolefin are subjected to a refining treatment. 1 to 5 parts by weight of the cross-linking agent from which a trace amount of electrically conductive impurities has been removed by 0.05 to 0.5 part by weight of an antioxidant from which a trace amount of electrically conductive impurities has been removed by a purification treatment. The present invention also relates to an insulating composition, and another aspect of the present invention is a power cable using the insulating composition as an insulator.

The polyolefin used in the present invention is not particularly limited, but polyethylene, particularly low density polyethylene (LDPE) is most preferably used.

Examples of the additive used in the present invention include a crosslinking agent and an antioxidant. The cross-linking agent (PO) is not particularly limited, but includes dicumyl peroxide (DCP), α, α′-bis (t-butylperoxy).
Diisopropylbenzene, 2,5-dimethyl-2,5 di (t-butylperoxy) hexane-3,2,5-dimethyl-2,5 di (t-butylperoxy) hexane, t
-Butyl cumyl peroxide or the like can be used. The addition amount is preferably 1 to 5 parts by weight with respect to 100 parts by weight of the polyolefin. This is because if the amount is less than 1 part by weight, the desired crosslinking cannot be obtained, and if it exceeds 5 parts by weight, scorch (premature crosslinking) or the like occurs.

The antioxidant (AO) is not particularly limited, but 4,4'-thiobis- (6-
Tert-butyl-3-methylhenol), distearyl-
Thiodipropionate, n-octadecyl-3- (4 '
-Hydroxy-3 ', 5'-di-t-butylphenylpropionate and the like can be used. And the addition amount is 0.05 to 100 parts by weight of polyolefin.
0.5 parts by weight is preferred. This is because if it is less than 0.05 parts by weight, the desired antioxidant function cannot be obtained, and if it exceeds 0.5 parts by weight, a high antioxidant function cannot be obtained even if the amount is increased, which leads to an increase in cost. Because it will be. The antioxidant can be omitted depending on the application.

As the purification treatment method for removing a trace amount of electrically conductive impurities in the crosslinking agent and the antioxidant used as described above, the following method can be mentioned. In addition to the case where these are carried out alone, these two or more methods may be carried out in combination. Solvent Dissolution and Reprecipitation Purification Method This method is a method of dissolving impurities in a high-temperature solvent and then cooling and precipitating and reprecipitating the impurities to remove impurities. Purification Method by Solvent Washing This method is a method for removing impurities by washing the finely-divided additive with a solvent or deionized water in contact with stirring. Purification Method by Electrophoresis This method is a method in which an electrode is placed in a melted additive and a DC voltage or the like is applied to collect and remove impurities on the electrode side. Purification method by melting and recrystallization This method is a method of melting impurities and then recrystallizing them to remove impurities.

Of the above-mentioned purification methods, the most effective method is the dissolution and reprecipitation purification method of, and the solvent used at that time is, for example, a non-polar hydrocarbon-based solvent such as hexane, heptane, toluene, xylene and benzene. Examples of the solvent include polar hydrocarbon solvents such as methanol, isopropyl alcohol, and acetone.

The following method can be used as a measure of the specific degree of purification of the additive (crosslinking agent, antioxidant) purified in this way. When measured according to JIS-C2101 (according to the electrical insulating oil test method), 1 × 1
Electrical insulating oil 10 having an insulation resistance value of 0 ¹⁶ Ω-cm or more
That is, the insulation resistance value of the electric insulating oil when 1 g of the cross-linking agent and 0.1 g of the antioxidant are dissolved in 0 ml is 1 × 10 ¹⁴ Ω-cm or more. That is,
At this insulation resistance value of less than 1 × 10 ¹⁴ Ω-cm,
This is because the removal of a trace amount of electrically conductive impurities contained in the additive is incomplete, so that the charge carriers considerably remain. Here, the dissolution amount of the antioxidant is set to 0.1 g per 1 g of the crosslinking agent, because the addition amount of the antioxidant is usually about 1/10 of that of the crosslinking agent. Is.

In the insulating composition of the present invention, in addition to the above-mentioned crosslinking agent and antioxidant additives, other additives can be appropriately added, if necessary. These additives are also purified and used in the same manner as above.

[0015]

Example: 100 parts by weight of low density polyethylene (MI = 1, density = 0.92 g / cm ³ ) with dielectric loss tangent (tan δ) = 0.01% under high electric field at 90 ° C. and 30 KV / mm. On the other hand, 2 parts by weight of a cross-linking agent (DCP) and 0.2 parts by weight of an antioxidant (4,4′-thiobis- (6-tert-butyl-3-methylphenol)) were added to form a compound of an insulating composition. Was manufactured.

The crosslinking agent (DCP) and antioxidant (4,4'-thiobis- (6-tert-butyl-3) used here are used.
-Methylphenol)) is an ordinary commercial product, and therefore, when used, as shown in Table 1, unpurified ones and their own purification treatments (levels 1 to 4). ) Different purified products were used. That is, in the case of the cross-linking agent, DCP was dissolved in n-hexane at 50 ° C., sufficiently stirred, cooled to 0 ° C., and then precipitated and recrystallized, and recovered as a purified cross-linking agent. On the other hand, in the case of an antioxidant, 4,4'-thiobis- (6
(Tert-butyl-3-methylphenol) was dissolved in methanol at 50 ° C., sufficiently stirred, cooled to 0 ° C., and precipitated and recovered to be recovered as a purified antioxidant. Of course, the solvent of the recovered purified crosslinking agent and purified antioxidant was completely removed by drying under reduced pressure. The above-mentioned purification levels (levels 1 to 4) are obtained by changing conditions such as the amount of solvent or additive and the number of times of purification, and the higher the number of levels, the higher the degree of purification is set.

Regarding such additives having different purification levels (levels 1 to 4) and non-purified additives, JIS
-When measured according to C2101, 1 x 10 ¹⁶ Ω-c
When 100 g of an alkylbenzene oil (electrical insulating oil) having an insulation resistance value of m or more was dissolved in 1 g of a crosslinking agent and 0.1 g of an antioxidant, the insulation resistance value of the oil was measured. It was like that.

The crosslinked polyethylene (XLPE) obtained by press-molding the compound to which this additive was added into a film under the conditions of 160 ° C. × 60 minutes was tested at 90 ° C.
Dielectric loss tangent (tan) under high temperature and high electric field of 30KV / mm
When δ) was measured, it was as shown in Table 1.

[0019]

[Table 1]

From Table 1, in the XLPE (Examples 1 to 3) using the highly purified additive according to the present invention,
It is understood that the insulation resistance value of the alkylbenzene oil in which the additive is dissolved is high and the dielectric loss tangent is small. On the other hand, in XLPE using an unpurified additive (Comparative Example 1) and XLPE using an additive with a low degree of purification (Comparative Example 2), the insulation resistance value and dielectric loss tangent of the alkylbenzene oil are large. I understand.

Next, Example 2 and Comparative Example 1 in Table 1 above
When a power cable (Example 4, Comparative Example 3) using the compound of the insulating composition having the level shown in (3) as an insulator was manufactured, the results shown in Table 2 were obtained. In the case of this cable, the conductor cross-sectional area was 400 mm ² , the insulator thickness was 9 mm, and the insulator was formed by coextrusion with the inner and outer semiconductive layers. Moreover, the dielectric loss tangent of this cable is measured at 90 ° C. and 30 KV / mm.
Was performed under high temperature and high electric field.

[0022]

[Table 2]

From Table 2, it can be seen that in the power cable according to the present invention (Example 4), excellent dielectric loss tangent can be obtained. On the other hand, it is found that the power cable using the unpurified additive (Comparative Example 3) has a poor dielectric loss tangent.

[0024]

As is apparent from the above description, according to the present invention, the refined additives (crosslinking agent, antioxidant) are used, so that the dielectric property (tan δ), especially at high temperature and high electric field, is high. It is possible to provide an insulating composition capable of maintaining excellent dielectric properties even under the conditions, and an excellent power cable using the insulating composition, particularly an ultrahigh voltage power cable.

Front page continuation (72) Kenji Matsui 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Densen Co., Ltd. (72) Toshio Niwa 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Densen Ltd. In the company

Claims (4)

[Claims] 1. An insulating composition, characterized in that an additive from which a trace amount of electrically conductive impurities has been removed by refining treatment is added to polyolefin. 2. Cross-linking agents 1 to 5 from which a trace amount of electrically conductive impurities have been removed by refining 100 parts by weight of polyolefin.
An insulating composition, characterized in that 0.05 to 0.5 parts by weight of an antioxidant from which a trace amount of electrically conductive impurities has been removed by a purification treatment as in the case of parts by weight is added and crosslinked. 3. The degree of purification of the crosslinking agent and the antioxidant is 1 g of the crosslinking agent and 100 g of the electrical insulating oil having an insulation resistance value of 1 × 10 ¹⁶ Ω-cm or more. 3. The insulating composition according to claim 2, wherein the insulation resistance value of the electric insulating oil when dissolved in 0.1 g is 1 × 10 ¹⁴ Ω-cm or more. 4. A power cable using the insulating composition according to claim 1, 2 or 3 as an insulator.