JP2681158B2 - Power cable - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power cable.

(Prior Art) (Problems to be Solved by the Invention) With the recent increase in transmission voltage, polyolefin power cables up to 275 kV class have come into practical use.

However, the insulation thickness increases as the voltage of the polyolefin power cable increases, which impedes cable winding, transportation, and facilities, and a reduction in insulation thickness is desired.

In other words, it is required to make the insulation thickness as thin as possible by improving the dielectric strength of the polyolefin insulator.

In particular, since polypropylene or ethylene-propylene copolymer has slightly different properties from polyethylene, it is not possible to follow all the methods adopted for polyethylene.

The present invention aims to obtain an excellent high voltage power cable by using this material as a result of pursuing an electric power cable in which this polypropylene or ethylene-propylene copolymer is used as a main material.

(Means for Solving the Problems) The present invention has been made to achieve the above objects, and the outline thereof is as follows.

An electrical insulating composition mainly composed of polypropylene or an ethylene / propylene copolymer grafted with an antioxidant by an organic peroxide, and when this is used as an insulating layer outside a conductor, improvement in dielectric strength is achieved. I found something remarkable.

Thus, the antioxidant used here is preferably a thiobisphenol type or a vinyl group-containing phenol type, and the addition amount is suitably 0.1 to 5 parts by weight with respect to 100 parts by weight of polypropylene or ethylene / propylene copolymer. .

(Function) Although the molecule is cross-linked by the organic peroxide, it was found that the antioxidant is grafted to the polyolefin chain prior to the cross-linking when a specific antioxidant coexists.

Listed as such antioxidants are thiobisphenol-based ones, 4,4'-thiobis- (6-tert-butyl-
3-methylphenol), 4-4-thiobis- (6-tert-butyl-O-cresol), 2,2-thiobis- (6-
Tert-butyl-4 methylphenol) and the like.
Further, a phenol-based antioxidant having a vinyl group and represented by the following chemical formula is also an antioxidant which is easily grafted.

These antioxidants polypropylene or ethylene
The following mechanism is considered for the grafting to the propylene copolymer.

(Thiobisphenol antioxidant) (Vinyl group-containing phenolic antioxidant) The addition amount of the antioxidant for grafting is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of polypropylene or ethylene-propylene copolymer. If it is less than 0.1 parts by weight, the withstand voltage performance is not improved and the thermal deterioration is caused. The effect of prevention does not rise. When it exceeds 25.0 parts by weight, the dielectric properties of the insulator are deteriorated and the crystallinity of the polypropylene or the ethylene / propylene copolymer is deteriorated due to grafting, resulting in poor withstand voltage performance.

Examples of the organic peroxide used for grafting the antioxidant and crosslinking the polypropylene or the ethylene / propylene copolymer include dicumyl peroxide (DCP) and α-
α'-Bis (t-butylperoxy) diisopropylbenzene, t-butylcumyl peroxide, 2.5 dimethyl-2.5 di (t-butylperoxy) hexane-
(3) etc. are listed.

When used as an uncrosslinked insulator, the addition amount is equimolar to 1/4 mol with respect to the number of moles of the added amount of antioxidant, and when it is used as a crosslinked insulator, it is necessary to further increase it.

The reason why the withstand voltage performance is improved by grafting the antioxidant as described above is considered as follows.

(1) Suppression of acceleration of traveling electrons in crystal during dielectric breakdown due to some inhibition of crystallinity of polypropylene or ethylene / propylene copolymer (2) Electron due to aromatic ring having electron resonance structure contained in antioxidant Suppression of acceleration Further, as organic peroxides used for grafting of antioxidants, dicumyl peroxide (DCP), α, α '
-Bis (t-butylperoxy) diisopropylbenzene, t-butylcumyl peroxide, 2.5 dimethyl-
2.5 di- (t-butylperoxy) hexane, 2.5 dimethyl-2.5 di- (t-butylperoxy) hexane-
(B) etc. are listed. When used as an uncrosslinked insulator, the amount added is equivalent to the number of moles of the antioxidant added.
It is 1/4 mol, and when it is used as a cross-linked insulator, it is necessary to further increase it.

(Example) Next, an example of the present invention will be described.

Examples 1 and 2 A polypropylene having a density of 0.953 and MI = 0.5 was kneaded with a predetermined amount of an antioxidant and DCP to prepare a mixture. As the antioxidant, one having the following formula was used in the range of 1.0 to 5.0 parts by weight.

Moreover, DCP was made into 1/2 mol with respect to the antioxidant.

Comparative Example 1 Same as Example 1 except that no antioxidant was added.

Comparative Examples 2 and 3 The same as Example 1 except that the amount of the antioxidant used was less than 0.1 parts by weight and more than 5.0 parts by weight.

Examples 3 to 5 The same as Examples 1 and 2 except that the following formula was used as the antioxidant.

The amount of DCP added is 1/2 mol of the antioxidant.

Comparative Examples 4 and 5 The same as Example 3 except that the amount of the antioxidant used was less than 0.1 parts by weight and more than 5.0 parts by weight. In order to see the characteristics of these examples and comparative examples, a recessed sheet sample for fracture test and a 1 mm thick sheet for dielectric property measurement as shown in FIG. 1 were press-crosslinked at 180 ° C. for 30 minutes.

With respect to each sample, a breakdown test by a standard impulse (1 × 40 μs) voltage and a dielectric loss tangent (tan δ) measurement by AC 50 Hz were performed with the electrode configuration shown in FIG.

In FIG. 1, 1 is a sample, 2 is a conductive paint on the upper and lower surfaces of the sample, 3 is insulating oil, 4 is an electrode, and the thickness of the recess is 200 to 300.
μm, effective diameter of recess is 10 mmφ.

When the antioxidant was analyzed by solvent extraction, no antioxidant was detected in the extraction solvent, which confirmed that the antioxidant was grafted to polypropylene.

Next, in the present invention, a power cable was produced in which each of the insulators of Examples 2 and 5 and Comparative Example 2 in Table 1 above was used as an insulating layer outside the conductor. The cable structure has a conductor cross section of 250 m
It is a three-layer structure having m ² , an insulating layer thickness of 9 mm, an inner semiconductive layer and an outer semiconductive layer.

Table 2 shows the results of the destructive test of each of the above cables by the commercial frequency (AC) voltage and the standard impulse (Imp) voltage.

(Effect of the invention) According to the present invention, as is apparent from the above-mentioned comparative test, the withstand voltage performance is remarkably improved by grafting polypropylene or ethylene-propylene copolymer, unlike the case where the antioxidant is simply added. You can

[Brief description of the drawings]

FIG. 1 is a schematic view showing a destructive test method for an admixture sheet.

Claims (1)

(57) [Claims] 1. A polypropylene or ethylene / propylene copolymer, wherein 1 to 5 parts by weight of a thiobisphenol-based or vinyl group-containing phenol-based antioxidant is added to 100 parts by weight of the polypropylene, and the polypropylene is added with an organic peroxide. A power cable having an insulating layer in which an ethylene / propylene copolymer is grafted with the antioxidant.