JPH0652728A - Electric power cable - Google Patents

Abstract

PURPOSE:To provide a stabilized electric power cable excellent in electric characteristic at high temperatures. CONSTITUTION:A copper twisted conductor 1 is covered with an inside semiconductor layer 2 incorporating hydrotalcite or a similar compound and a chelate forming agent, a crosslinked polyethylene insulator layer 3, and an outside semiconductor layer 4 incorporating hydrotalcite or a similar compound and a chelate forming agent, followed by being covered with a sheath 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable having improved high temperature electrical characteristics.

[0002]

2. Description of the Related Art Conventionally, a crosslinked polyethylene insulated cable has been widely used as a high voltage power cable. This crosslinked polyethylene insulated cable is generally constructed by forming an inner semiconductive layer, a crosslinked polyethylene insulation layer, and an outer semiconductive layer on a conductor by three-layer coextrusion, and covering the outer circumference with a jacket. It has excellent characteristics such as excellent water resistance, moisture resistance, chemical resistance, solvent resistance, high dielectric strength at room temperature and high volume resistivity, and low dielectric constant and dielectric loss tangent.

[0003]

However, the electrical characteristics of this crosslinked polyethylene insulated cable are significantly lowered when the temperature rises. For example, the AC breakdown voltage at 90 ° C is reduced by about 20 to 40% from that at room temperature. However, there is a problem that the DC insulation resistance is increased by 100 to 1000 times as much as at room temperature.

Therefore, as a result of intensive studies conducted by the present inventors to improve such high-temperature electrical characteristics, ionic impurities contained in the semiconductive layer largely contribute to the deterioration of the high-temperature electrical characteristics. I found that.

That is, generally, the semiconductive layer contains a considerable amount of conductive carbon black as a conductivity-imparting agent, but various impurities are mixed in this conductive carbon black. Among them, and elements such as cationized the Fe, Ca, Ni, Cr, Al under polar solvent such as water, Cl ^-,
Those anionized to Br ⁻ , SO ₄ ^−, etc. migrate into the insulating layer and become a charge trap, which promotes injection and accumulation of charges from the semiconductive layer. And, since this accelerating effect becomes particularly remarkable under high temperature and high electric field, as a result, tan δ at high temperature rises, promoting the thermal breakdown tendency,
It is considered that the high temperature electrical characteristics are deteriorated.

Therefore, if such migration of ionic impurities to the insulating layer can be prevented, it is considered to be an extremely effective means for improving the high temperature electrical characteristics of the cable.

The present invention has been made on the basis of such knowledge, and prevents migration of ionic impurities from the inner and outer semiconductive layers to the insulator layer, and significantly improves high-temperature electrical characteristics of a power cable. The purpose is to provide.

[0008]

A power cable of the present invention is a power cable in which an inner semiconductive layer, an insulating layer, an outer semiconductive layer, and an outer cover are formed in order on a conductor. The external semiconductive layer is characterized in that hydrotalcite or a similar compound thereof and a chelate-forming agent are mixed.

The hydrotalcite used in the present invention has the following formula [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^{x +} [A ^n- x / n mH ₂ O] ^x- (wherein , M ²⁺ is Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ ,
Divalent metals such as Zn ²⁺ , M ³⁺ is Al ³⁺ , Fe ³⁺ , Cr ³⁺ , C
o ^3+, trivalent metal such as In ^3+, A ^n- is OH ^-, F ^-, C
_{^{l -, Br -, NO 3}} -, CO 3 2-, SO 4 2-, Fe (CN) 6 3-, CH
₃ COO ^-, oxalic acid ion, n such Sarichin ion
A valent anion is shown, and x is a number satisfying 0 <x ≤ 0.33. ) Is a non-stoichiometric compound, which is naturally produced in the Ural region of the Soviet Union and Sunalm in Norway. Further, as such a compound similar to hydrotalcite, Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .3H ₂ O, Mg _4.5 Al ₂ (O
H) ₁₃ CO ₃・ 3.5H ₂ O, Mg ₆ Al ₂ (OH) ₁₆ CO ₃・ 4H ₂ O, Al
₂ O ₃ · xH ₂ O, 2.5MgO · Al ₂ O ₃ · xH ₂ O and other synthetic hydrotalcite, and Al ₂ O ₃ · Na ₂ O · 2CO
₃・ xH ₂ O, 2MgO ・ 6SiO ₂・ xH ₂ O, Al ₂ O ₃・ 9SiO ₂
XH ₂ O, Mg _0.7 Al _0.3 O _1.15 , aluminum hydroxide,
Examples thereof include aluminum silicate, magnesium silicate, and magnesium hydroxide. These may be used alone or in combination of two or more. In the present invention, use of synthetic hydrotalcite is preferable.

Such a hydrotalcite or a similar compound thereof immobilizes (traps) anions or anions and cations contained in the inner or outer semiconductive layer.
However, it has the effect of preventing the migration of these ionic impurities to the insulating layer and improving the electrical characteristics of the cable, especially at high temperatures.

On the other hand, examples of the chelating agent used in the present invention include 8-hydroxyquinoline, o-phenanthroline, 1,2-glycol, glycerin, α-benzoin oxime, EDTA and the like. They may be used alone or in combination of two or more.
In the present invention, it is preferable to use 8-hydroxyquinoline.

Such chelating agents are themselves
It has a function of immobilizing (trapping) metal ions contained as impurities in the inner or outer semiconductive layer and preventing the migration thereof to the insulating layer.

In the present invention, by using such a chelate-forming agent in combination with the above-mentioned hydrotalcite or a compound similar thereto, the respective effects can be further enhanced, and the ionic impurities contained in the inner or outer semiconductive layer can be improved. A significant effect can be obtained in preventing migration.
That is, the effect of preventing migration of ionic impurities of hydrotalcite or its similar compound and the same effect of the chelating agent can be far greater than the effects of using each alone, and the electrical conductivity of the cable can be improved. The characteristics, especially the electrical characteristics at high temperature, can be significantly improved.

The blending amount of these is appropriately determined depending on the kind of the semiconductive layer. For example, in a semiconductive layer made of a semiconductive resin composition containing a conductive carbon black, the amount of the semiconductive layer is different from that of the conductive carbon black. 0.001-10% is appropriate.

The power cable of the present invention comprises a semiconductive resin composition in which hydrotalcite or a similar compound thereof and a chelate forming agent are mixed on a conductor, an insulating resin composition such as polyethylene in which a crosslinking agent is mixed, A semiconductive resin composition in which hydrotalcite or a similar compound thereof and a chelating agent are mixed is sequentially coated by three-layer coextrusion or individual extrusion, and if necessary, crosslinked to form an internal semiconductive layer and an insulator. A layer, an outer semiconducting layer, on which
It can be obtained by providing an outer cover such as a soft vinyl chloride resin sheath.

Here, as the semiconductive resin composition in which hydrotalcite or a similar compound thereof and a chelating agent are mixed, polyethylene, ethylene / vinyl acetate copolymer (EVA), ethylene / ethyl acrylate copolymer is used. Ethylene-based copolymers such as polymers (EEA), or ethylene / vinyl acetate copolymer-polyvinyl chloride grafters (EVA-PVC grafters), chlorinated polyethylene, chlorosulfonated polyethylene, nitrile rubber, Acrylic rubber, styrene-based rubber such as styrene-butadiene rubber is used as a base resin, and a conductive carbon black such as acetylene black or furnace black is added as a conductivity-imparting agent to the base resin. Contains additives such as anti-aging agents Known what can be used with. The one using furnace black as the conductivity-imparting agent has a large amount of ionic impurities as compared with acetylene black and the like, so that the present invention is particularly effective. By the way, the content of ionic impurities in furnace black is 0.1 to 0.7%, and that of acetylene black is about 0.06%.

[0017]

In the electric power cable of the present invention, by blending hydrotalcite or a similar compound and a chelating agent in the inner or outer semiconductive layer, an insulator of ionic impurities contained in the inner or outer semiconductive layer is obtained. It is possible to suppress the transition to layers, and by such transition,
In particular, the injection and accumulation of charges from the semiconductive layer to the insulator layer, which is promoted under high temperature and high electric field, can be suppressed. Therefore, the tan δ characteristic does not deteriorate even when used at high temperatures, and the initial excellent electrical characteristics are maintained.

[0018]

EXAMPLES Next, examples will be described.

Examples 1 to 7 Each component having the composition shown in Table 1 was uniformly kneaded with a Banbury mixer to obtain a semiconductive resin composition, which was press-molded into a sheet having a thickness of 1 mm to obtain a volume resistivity. Was measured and the smoothness of the surface was examined. In addition, 1mm created in the same way
A thick sheet was bonded to one side of a 1 mm thick cross-linked polyethylene sheet and pressed together to form a composite sheet, and the tan δ temperature characteristics of these were investigated. Also, room temperature-120
After applying a heat cycle of repeating ℃ -room temperature 10 times, the temperature characteristic of tan δ was examined again. The above results are also shown in Table 1. The surface smoothness of the semiconductive sheet was evaluated by the number of spots formed on the surface.

For comparison, Table 1 also shows the results of the same evaluation of the semiconductive resin composition in which hydrotalcite or a similar compound thereof and the chelate-forming agent were individually blended.

[0021]

[Table 1] As is clear from Table 1, the semiconductive resin composition in the case of using hydrotalcite or a similar compound thereof and a chelating agent together has a longer temperature at a higher temperature than that in the comparative example in which each of them is blended alone. Stable ta after using for a long time
It has n δ characteristics.

Next, using the semiconductive resin composition of each of the above examples, a crosslinked polyethylene insulated cable as shown in FIG. 1 was manufactured as a prototype.

That is, as shown in FIG. 1, the cross-sectional area is 12 mm.
^On the copper stranded wire conductor 1 of ² , the above semiconductive resin composition, an insulating polyethylene composition in which 1.6% by weight of DCP (dicumyl peroxide is mixed with polyethylene), and the above semiconductive resin composition are sequentially formed into three layers. Coated by layer co-extrusion, heat-crosslinked by a conventional method, and 0.5 mm thick inner semiconductive layer 2, 1.
An insulating layer 3 having a thickness of 5 mm and an outer semiconductive layer 4 having a thickness of 0.5 mm were formed, and a soft vinyl chloride resin was extrusion-coated thereon to form a jacket 5 having a thickness of 1 mm.

The cables produced in the same manner as described above except that each of the obtained cables and a conventional semiconductive composition containing no hydrotalcite or a similar compound thereof and a chelating agent were used, were subjected to heat treatment of dielectric properties. The stability was compared. The results show that the example has good initial tan δ temperature characteristics even after 1 month deterioration at 90 ° C (ta within the range of room temperature to 90 ° C).
While the n δ characteristic was maintained at 0.02% or less), the conventional one has a high temperature due to long-term deterioration.
An increase in tan δ was observed, which was 0.1% at 90 ° C.

[0025]

As is clear from the above examples, the electric power cable of the present invention contains hydrotalcite or a compound similar thereto and a chelating agent in the semiconductive layer, so that the insulation at high temperature is prevented. The migration of ionic impurities from the semiconductive layer to the insulator layer, which promotes the injection and accumulation of charges into the body layer, is prevented. Therefore, it has good and stable electrical characteristics even at high temperatures, and is very useful especially when used in a high-voltage power cable.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a crosslinked polyethylene cable according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Copper stranded conductor 2 ... Inner semiconductive layer 3 ... Insulator layer 4 ... Outer semiconductive layer 5 ...

Claims (1)

[Claims] 1. A power cable in which an inner semiconductive layer, an insulator layer, an outer semiconductive layer, and a jacket are sequentially formed on a conductor, wherein the inner and / or outer semiconductive layers are hydrotal. A power cable comprising a site or a compound similar thereto and a chelating agent.