JP3459079B2 - Insulation composition and power cable - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to 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 widely used at present as an insulator for power cables. This X
Low density polyethylene (LDPE) is generally used as polyethylene, which is a 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 are deteriorated under high temperature and high electric field. This deterioration of the dielectric properties poses a problem that the desired insulation properties 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 due to the increase of electrically conductive charge carriers under high temperature and high electric field.

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

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 characteristics can be obtained even at high temperatures and high electric fields. An insulating composition that can be maintained and a power cable using the insulating composition are provided.

[0007]

[Means and Solutions for Solving the Problems ]
In order to solve the above problem, the invention according to claim 1 provides a polyolefin
100 parts by weight of tin have been impregnated with a trace amount of electric conductivity due to the refining process.
1-5 parts by weight of the cross-linking agent removed from the product, and the same purification treatment
Antioxidant with trace amount of electrically conductive impurities removed by
A composition for adding 0.05 to 0.5 parts by weight to crosslink
Therefore, the degree of purification of the crosslinking agent and the antioxidant is 1 ×
Electrical insulating oil 1 having an insulation resistance value of 10 ¹⁶ Ω-cm or more
1 g of the cross-linking agent and the antioxidant
Insulation resistance of the electrical insulating oil when 0.1g of the stopping agent was dissolved
The value is 1 × 10 ¹⁴ Ω-cm or more, and
It is an edge composition. The invention according to claim 2 is claim 1
Characterized by using the above-mentioned insulating composition as an insulator
It is a power cable.

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 and the like can be used. And 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 (early 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 may be omitted depending on the application.

As the purification treatment method for removing a trace amount of electrically conductive impurities in the cross-linking agent and the antioxidant thus used, the following method can be mentioned. In addition to the case where these are performed alone, these two or more methods may be performed in combination. Solvent Dissolution and Reprecipitation Purification Method This method is a method in which an additive is dissolved in a high temperature solvent and then cooled to cause precipitation and reprecipitation to remove impurities. Purification Method by Solvent Washing This method is a method of removing impurities by washing the finely divided additive with a solvent, deionized water or the like while stirring the mixture. Purification Method by Electrophoresis This method is a method in which an electrode is put 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 thereof include solvents and 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 additives (crosslinking agent, antioxidant) thus purified. 1 × 1 when measured according to JIS-C2101 (according to electrical insulation oil test method)
Electrical insulating oil 10 having an insulation resistance value of 0 ¹⁶ Ω-cm or more
That is, when 0 g of the crosslinking agent and 0.1 g of the antioxidant are dissolved in 0 ml, the insulation resistance value of the electric insulating oil 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 amount of the antioxidant to be dissolved is 0.1 g per 1 g of the crosslinking agent, because the amount of the antioxidant added 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. In that case, Even these additives are 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 ) having a dielectric loss tangent (tan δ) = 0.01% under high electric field of 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 recrystallized by precipitation, which was recovered as a purified cross-linking agent. On the other hand, in the case of an antioxidant, 4,4'-thiobis- (6
(Tertiary 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) can be obtained by changing the conditions such as the amount of the solvent and the additive and the number of times of purification, and the higher the number of levels, the higher the degree of purification is set.

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

The cross-linked 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 30 KV / 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 and 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]

It can be seen from Table 2 that the power cable according to the present invention (Example 4) can obtain an excellent dielectric loss tangent. 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, since refined additives (crosslinking agent, antioxidant) are used, the dielectric properties (tan δ), especially high temperature and high electric field are 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyo Takahashi 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Cable Co., Ltd. (72) Hiroyuki Miyata 1-1-5, Kiba, Koto-ku, Tokyo Fujikura Electric Cable (72) Inventor Kenji Matsui 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Cable Co., Ltd. (72) Inventor Toshio Niwa 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Cable Co., Ltd. ( 56) References JP-A-60-28108 (JP, A) JP-A-1-225003 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01B 3/44 C08L 23/00 H01B 9/00

Claims (2)

(57) [Claims] 1. Purification treatment of 100 parts by weight of polyolefin
Cross-linking agents 1 to 5 from which trace amount of electrically conductive impurities are removed by
Parts by weight and trace amounts of electrically conductive impurities due to the same refining process
0.05 to 0.5 parts by weight of the removed antioxidant is added.
And a crosslinking degree of the antioxidant is 1 × 10 ¹⁶ Ω.
-100 ml electrical insulating oil with insulation resistance of -cm or more
To 1 g of the cross-linking agent and the antioxidant
Insulation resistance value of the electric insulating oil when dissolved 0.1g is 1
× 10 ¹⁴ Ω-cm or more insulating composition
Thing . 2. The insulating composition according to claim 1 as an insulator
A power cable characterized by being used.