JPH11224543A - Dc power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the accumulation of space charge by the application of a DC high voltage by constituting an insulator by a resin composition obtained by graft polymerizing maleic anhydride with polyethylene polymerized by use of a single site catalyst. SOLUTION: Since carbonyl groups are distributed uniformly in a material by graft polymerizing maleic anhydride with polyethylene, local trap of space charge can be prevented. The influence of the cracking residue of an organic peroxide causing the accumulation of space charge can be eliminated by performing no cross-linking treatment. According to such a structure, the space charge can be reduced to improve the DC breaking strength. The graft quantity of the maleic anhydride is preferably set to 0.001-0.01 wt.%. When this ratio is too high, the fear of reducing the electric withstand voltage performance at high temperature is caused. To the resin composition, tris(2,4,di-t-buthylphenyl) phosphite is preferably blended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power cable.

[0002]

2. Description of the Related Art For long-distance, large-capacity power transmission,
DC power transmission does not have dielectric loss of an insulator as compared with AC power, and does not require equipment for compensating for ineffective components with respect to charging current.
In addition, it is considered to be advantageous from various characteristics such as high withstand voltage of the insulator and stability.

[0003] At present, an OF cable mainly made of low-viscosity insulating oil and paper is used as a high-voltage DC cable for DC transmission, but an oil supply facility or the like is required and maintenance is troublesome.

On the other hand, as a maintenance-free plastic insulated cable, a cross-linked polyethylene (XLPE) cable is widely used as an AC power cable.
Ultrahigh-voltage cables comparable to OF cables are being developed.

However, due to problems such as space charge characteristics with respect to a DC voltage, applications as a high-voltage DC cable are limited. That is, in the XLPE cable, the space charge is accumulated in the insulator by the application of a high DC voltage, and when the reverse polarity impulse is superimposed or the DC polarity is reversed, the insulation characteristics thereof are significantly deteriorated.

[0006] For the above reasons, there is a demand for the development of a solid insulated cable that replaces the conventional XLPE cable.

[0007]

It is generally considered that the higher the crystallinity, the higher the withstand voltage strength of polyethylene. However, when a DC voltage is applied, the space charge formed by injecting charges from the electrodes becomes less. It is presumed that the particles are easily trapped at the interface between the crystal and the amorphous of polyethylene. In addition, in order to withstand deformation due to heating when an overcurrent flows, etc.,
As a countermeasure, a crosslinking treatment is taken, but it is known that the decomposition residue of the organic peroxide used as a crosslinking agent increases space charge.

It is also known that an antioxidant 4,4 thiobis (3-methyl-6-t-butylphenol) (SWC) added for preventing heat aging similarly increases the space charge. .

From such a viewpoint, the present inventors have proposed that by introducing a polar group into a polymer, it is possible to improve space charge characteristics, and therefore, by grafting a specific polar group to nonpolar polyethylene, By not using an organic peroxide and not subjecting to cross-linking treatment, the influence of the decomposition residue of the cross-linking agent is eliminated, and the DC characteristics can be improved by selecting an anti-aging agent having little space charge accumulation. And proceeded with the study.

The present invention has been made in view of the above circumstances, and specifies a polar group to be introduced into polyethylene, limits the amount of graft polymerization thereof, and accumulates space charge in an insulator. In addition, in order to eliminate the influence of organic peroxide decomposition residues, the use of a single-site catalyst with good heat resistance insulates the polymerized polyethylene instead of using organic peroxides. A high-performance DC power cable was obtained by selecting an anti-aging agent that was used as a body and had low space charge accumulation.

[0011]

Means for Solving the Problems To achieve the above object, space charge accumulation was considered by using a resin composition obtained by graft-polymerizing maleic anhydride onto polyethylene polymerized using a single-site catalyst as an insulator. It was found that the DC characteristics were excellent.

That is, the present invention is a DC power cable comprising an insulator made of a resin composition obtained by graft-polymerizing maleic anhydride onto polyethylene polymerized using a single-site catalyst.

As the antioxidant to be added to the resin composition, tris (2,4, di-t-butylphenyl) phosphite is desirable.

If the grafting amount of maleic anhydride is too large, physical properties such as crystallinity may be reduced, and the electric breakdown voltage at high temperatures may be reduced.
The content is preferably 0.01 wt% or less. Conversely, if the content is too small, the effect as a charge trap becomes ineffective.
1 wt% or more is suitable.

[0015]

It is considered that the graft polymerization of maleic anhydride onto polyethylene allows carbonyl groups to be uniformly distributed in the material, thereby preventing local trapping of space charges. In addition, by not performing the crosslinking treatment, it is considered that the influence of the decomposition residue of the organic peroxide, which is an accumulation factor of the space charge, is eliminated. In addition, an anti-aging agent having a small space charge accumulation is selected. It is considered that such a configuration reduces the space charge and improves the DC breakdown strength.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A DC power cable in an embodiment is a polyethylene (s-LD) polymerized using a single-site catalyst.
A structure in which an insulator is formed using a resin composition having a specific gravity of less than 0.940 g / cm ³ obtained by graft-polymerizing maleic anhydride onto PE).

Table 1 shows examples of the present invention and comparative examples. Experimental samples consisted of various polyethylenes, 2 phr of dicumyl peroxide (DCP) as a cross-linking agent, and 0.2% of anti-aging agent tris (2,4, di-t-butylphenyl) phosphite (TBP) or SWC.
A sheet prepared by hot pressing the partially mixed product at 160 ° C. for 30 minutes was used. Evaluation of space charge accumulation is 2
After applying a voltage of 50 kV to the mm sheet, the measurement was performed by the pulse electrostatic stress method. The amount of the accumulated charge is indicated by the number +. The DC breakdown test was performed using a model cable with an insulation thickness of 2 mm.
Performed at 0 ° C.

According to the above embodiment, when forming the insulator,
0.001 wt% of maleic anhydride in polyethylene
It was found that the use of a resin composition obtained by graft polymerization of 0.01 wt% as an insulator is more excellent in DC characteristics including space charge accumulation.

If the grafting amount of maleic anhydride is too large, physical properties such as crystallinity may be reduced, and the electric withstand voltage at high temperatures may be reduced.
1 wt% or less is suitable. Conversely, if the content is too small, the effect as a charge trap becomes ineffective.
1 wt% or more is suitable.

Further, it was also found that those using TBP were superior to those using SWC as an anti-aging (oxidation) antioxidant in DC characteristics including space charge accumulation.

[0021]

[Table 1]

Explanation of words in the table Space charge accumulation amount: M indicates homo-charge accumulation, and R indicates hetero-charge accumulation.

[0023]

As described above, according to the present invention, maleic anhydride is added to polyethylene polymerized using a single-site catalyst in an amount of 0.001% by weight to 0.01% by weight.
By using an insulator obtained by blending the antioxidant tris (2,4, di-t-butylphenyl) phosphite with the graft-polymerized resin composition, it is possible to prevent space charge accumulation due to the application of a high DC voltage, and XLPE A good DC high-voltage cable can be made compared to an insulated cable.

Claims (3)

[Claims] 1. A DC power cable comprising an insulator made of a resin composition obtained by graft-polymerizing maleic anhydride onto polyethylene polymerized using a single-site catalyst. 2. The insulator according to claim 1, wherein said resin composition is prepared by blending said resin composition with an anti-aging agent, tris (2,4, di-t-butylphenyl) phosphite. 1. The DC power cable according to 1. 3. The DC power cable according to claim 1, wherein the grafted amount of the maleic anhydride is in the range of 0.001 wt% to 0.01 wt%.