JPH04181611A - Power cable - Google Patents

Abstract

PURPOSE:To improve anti-water-tree characteristics inside an insulation body by constructing anti-conductive layer for constituting a cable in a double construction of either a rubber having a specific composition or a plastic composition respectively. CONSTITUTION:Inner and outer semiconductive layer 2, 4 are provided on a conductor 1 and on an insulation body 3 mainly composed of a bridge polyethylene or a bridge polyethylene copolymer respectively. Those layers 2 and 4 are constructed in respective double layers, and formed in combination of a rubber including acetylene black by 30 to 80 weight part or a semiconductor layer 5a of a plastic composition, and a rubber including (Ketien black EC) by 10 to 60 weight part or a semiconductor layer 5b of a plastic composition. The layer 5b absorbs each sort of ion invading from outside, so as to prevent diffusion of ion into the insulation body 3, and smoothens the layer 5a, by using it on the interface to the insulation body 3, thus anti-water-tree characteristics into the insulation body can be improved.

Description

Detailed Description of the Invention [Industrial Application Field] This invention relates to a power cable provided with an insulator mainly composed of crosslinked polyethylene or crosslinkable polyethylene copolymer, particularly an inner semiconducting layer and an outer semiconducting layer. The present invention relates to an improved power cable having improved water resistance.

[Conventional technology]

Polyethylene or polyethylene-based copolymers have excellent insulating properties and are easy to process, so today they are widely used for power generation, especially when crosslinking improves thermal properties. Power cables using insulators mainly composed of crosslinked polyethylene or crosslinkable polyethylene copolymers have become the mainstream of power cables.

[Problem to be solved by the invention]

In cables whose insulators are made of cross-linked polyethylene or cross-linked polyethylene copolymers, trace amounts of water mixed in during manufacturing or use can cause water trees to enter the insulator due to interaction with the electric field. It is known that this deterioration phenomenon occurs when moisture is supplied, and this progresses further when moisture is supplied, significantly impeding insulation performance.

The causes of such water trees are thought to be the presence of foreign matter or voids in the polyethylene insulator, and defects at the interface between the insulator and the inner or outer semiconducting layer.
Various measures have been taken in manufacturing to reduce these.

However, even if such measures were taken, prevention of water tree was still insufficient.

In addition, some methods have been used, such as installing a metal sheath or metal water-shielding layer on the cable, or making the conductor watertight to prevent moisture itself, which causes water trees, from entering the insulator. However, there are problems in that it not only increases costs but also reduces manufacturing capacity.

The present invention aims to solve these problems of the conventional technology.

[Means to solve the problem]

The outline of the present invention is as follows.

Under these circumstances, the inventor of the present invention has made extensive studies and has researched a power cable that can prevent the water tree deterioration phenomenon in the insulator and can be manufactured using manufacturing technology and manufacturing costs that are almost the same as conventional ones. It has been found that this can be achieved by using acetylene black and Ketchen Blank EC together as a conductive layer. That is, in a power cable having a semiconducting layer on an insulator mainly composed of a polyethylene copolymer, the semiconducting layer has a two-layer structure, and one of the semiconducting layers is made of Ketjen Black EC. A power cable comprising a rubber or plastic composition containing from 30 to 80 parts by weight of acetylene black, the other semiconductive layer comprising a rubber or plastic composition containing from 30 to 80 parts by weight of acetylene black.

2) The semiconducting layer containing acetylene black is in contact with the insulator, and the semiconducting layer containing Ketjenblack EC is on the conductor side in the inner semiconducting layer and on the cable outer circumferential side in the outer semiconducting layer. The power cable according to claim 1.

[Effect]

In the power cable of the present invention, Ketjenblack EC adsorbs various ions entering from the outside and prevents ions from diffusing into the insulator, and by using an acetylene blank at the interface with the insulator, It smoothes the surface and improves the water resistance in the insulator.

[Example] As shown in FIG. 1, an example of the structure of the power cable of the present invention is as shown in FIG. However, in the inner semiconducting layer 2, a semiconducting layer 5a containing acetylene black is provided on the insulator side, a semiconducting layer 5b containing Kenochen Black EC is provided on the conductor side, and the outer semiconducting layer In No. 4, a semiconducting layer 5a containing acetylene black is provided on the insulator side, and a semiconducting layer 5b containing Ketjenblack EC is provided on the outer peripheral side of the cable. In the above, the insulator and the inner and outer semiconducting layers are extruded simultaneously using a common throat to integrate the layers,
It can be manufactured efficiently.

In the present invention, the content of acetylene black is 30 to
The reason for using 80 parts by weight is that the electric field can be relaxed with appropriate semiconductivity; if it is less than 30 parts by weight, the conductivity is insufficient, and if it exceeds 80 parts by weight, it becomes too hard, making it difficult to manufacture. This is because there is a problem.

The reason for setting the content of Ketjenblack EC to 10 to 60 parts by weight was determined from the viewpoint of securing water resistance and maintaining semiconductivity. If it is less than 10 parts by weight, the water resistance and semiconductivity will be insufficient, and if it exceeds 80 parts by weight, the mechanical properties will deteriorate and the viscosity will become too high, which is not preferable.

In carrying out the present invention, it is preferable to use a composition containing a crosslinked side in order to improve heat resistance, as in the case of conventional BoIJ ethylene. One example of this crosslinking is 2,5 dimethyl-2,5 di(t-butylperoxy)hexyne-
3. α・α” Bis(1-butylperoxo)diisopropylhenzene, peroxide-based crosslinking agents such as dicumyl peroxide, and isocyanate-based crosslinking aids such as triallylisocyanurate can be mentioned. Addition thereof The amount is V
It is preferably 1.5 to 3.0 parts by weight per 100 parts by weight of LDPE.

Crosslinking by radiation is also possible.

The power cable of the present invention can be obtained by extrusion coating the outside of a cable conductor with the composition having the above formulation and crosslinking.

The following tests were conducted to demonstrate the superiority of the power cable of the present invention.

On a conductor with a conductor cross-sectional area of 100 mm2, a polyethylene composition containing acetylene black and Ketjenblack EC was extruded and coated to a thickness of In so that the acetylene black was in contact with the insulator, and peroxide was blended. A power cable was manufactured by extrusion coating a polyethylene composition as an insulating layer to a thickness of 3 mm and crosslinking with heating.

At the same time, the unregulated power cable of the present invention and the current X
An LPE electrical cable was manufactured for comparison.

The results of evaluating the water tree density and appearance of these cables are shown in Table 1.

Table 1 The water tree test was conducted as shown in Figure 2.

In the figure, 11 is a crosslinked polyethylene sheet, and 12 is a semiconductive paint coating layer provided on the back surface of the sheet to form a ground electrode. 15 is an acetylene black filled semiconductive mixture sheet, and 16 is a Ketjen black filled semiconductive mixture sheet.

A water tank 14 is provided on the upper surface of the Ketjen black filled semiconductive mixture sheet to form a water electrode, and a 10 kV,
1k) The configuration is such that the voltage Iz can be applied from the high voltage electrode 13. After applying electricity between the electrodes for 30 days, water trees generated in the sheet 1 were observed.

Here, the number of water trees is assumed to be 100, and the relative number is shown.

From Table 1 above, in Examples 1 to 4, the effect of suppressing the occurrence of water trees is clear compared to Comparative Example 2. Comparative example 1
It can be seen that the amount of carbon filling is small and the effect of suppressing the occurrence of water trees is small.

Next, power cables were created using Example 2 and Comparative Example 2. The cable structure is a four-layer structure having an inner semiconducting layer, an insulating layer, an outer semiconducting layer filled with acetylene black, and an outer semiconducting layer filled with Ketjen black. Note that the thickness of the insulating layer is 31 mm, and the thickness of the inner and outer semiconducting layers is IN.

Each of the power cables manufactured in this manner was subjected to the following submergence charging test and compared. The results are shown in Table 2.

Table 2 From this table, it can be seen that in Example 2, compared to Comparative Example 2, the number of water trees generated after water immersion charging was smaller and the dielectric breakdown voltage was higher.

〔Effect of the invention〕

As explained above, the present invention has a two-layer structure in which the semiconductive layer is a combination of a semiconductive layer filled with acetylene black and a semiconductive layer filled with Ketjen black.
It is possible to provide an efficient power cable that is effective in suppressing the occurrence of water trees and has excellent water tree resistance without changing the conventional technology.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a power cable obtained according to the present invention, and FIG. 2 is a sectional view illustrating a water tree test method. 1: Stranded wire conductor 2: Inner semiconducting layer 3: Insulating layer 4; Outer semiconducting layer 5a: Semiconducting layer containing acetylene black 5b = Semiconducting layer containing Ketchen Black EC

Claims (1)

[Scope of Claims] 1) In a power cable having a semiconducting layer on a conductor or on an insulator mainly composed of crosslinked polyethylene or crosslinked polyethylene copolymer, the semiconducting layer has a two-layer structure, and any One of the semiconducting layers is Ketjenblack E.
A power source characterized in that the semiconductive layer is made of a rubber or plastic composition containing 10 to 60 parts by weight of C, and the other semiconductive layer is made of a rubber or plastic composition containing 30 to 80 parts by weight of acetylene black. cable. 2) The semiconducting layer containing acetylene black is in contact with the insulator, and the semiconducting layer containing Ketjenblack EC is on the conductor side in the inner semiconducting layer and on the cable outer circumferential side in the outer semiconducting layer. The power cable according to claim 1.