JPH09129039A - Dc cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC cable in which dielectric breakdown voltage is stabilized by forming the insulator layer of the DC cable by use of a polyolefin containing a specified quantity of a synthetic absorbent. SOLUTION: An internal semiconductor layer 2, an insulator layer 3, an external semiconductor layer 4, a soft vinyl chloride resin sheath 5 are successively laminated on a copper conductor 1 to form a DC cable. As the insulator layer 3, an insulating composition containing 0.1-15wt.% of a synthetic absorbent to polyolefin is used. As the synthetic absorbent, Al2 O3 .xH2 O, 2.5MgO.Al2 O3 .xH2 O, 2MgO.6SiO2 .xH2 O or the like is used, and as polyolefin, a polyolefin synthesized with metallocene catalyst is preferably used. Thus, a DC cable in which the formation of a spatial charge can be suppressed without reducing insulating characteristic or electric characteristic to stabilize dielectric breakdown voltage can be provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a DC cable.

[0002]

2. Description of the Related Art Conventionally, as a variety of AC cables including power cables for high-voltage AC power transmission, cables made of polyolefin such as cross-linked polyethylene as an insulator have high and stable dielectric strength, water resistance, and water resistance. Chemical,
It is widely used because of its excellent solvent resistance.

Therefore, in recent years, it has been studied to use a polyolefin insulated cable having such excellent characteristics as a DC cable.

However, in this case, there are problems peculiar to direct current insulation to be solved, and above all, the problem of space charge formed in the insulator by the application of direct current voltage is expanded to the use of such a polyolefin insulated cable for direct current cables. Has become a major obstacle.

That is, in a conventional polyolefin insulated cable, when a DC voltage is applied, electronically-polarized charges (homo-charges) are generated near the conductor electrode side and the shield electrode side.
Is formed, which relaxes the electric field around the electrodes, but when a lightning impulse voltage of the opposite polarity to the direct current enters or the polarity of the direct current voltage is reversed, the electric field on the conductor electrode rises and the breakdown voltage Cause a significant decrease in In addition, it is unavoidable that impurities such as cross-linking residues, which are compounded to prevent long-term chemical deterioration and impurities such as polymerization catalyst residues, are mixed in the insulator. When polarized, it polarizes and ionizes from the one with low ionization energy to form a space charge. This space charge is called a hetero-charge, and as a result of being attracted to electrodes of opposite signs by electrostatic attraction, the electric field near the electrodes is increased and dielectric breakdown easily occurs.

Therefore, an inorganic filler such as carbon black or magnesium oxide is added, an organic acid such as maleic acid is added or grafted, and further,
Various measures have been proposed to suppress the formation and accumulation of space charges, such as adding polar monomers such as vinyl acetate.

However, carbon black is intended to enhance the conductivity and promote the disappearance of charges.
This causes deterioration of insulation resistance and insulation characteristics. Further, although magnesium oxide can trap anions such as halogen and sulfuric acid, it reionizes with a small amount of water to form a large amount of hetero charges. Furthermore, if an electric charge is to be adsorbed by an organic acid or the like, the higher-order structure is disturbed due to a large amount of polar groups, and the insulation characteristics, particularly the impulse breakdown voltage, are greatly reduced. Moreover, these are all
The effect of suppressing the formation of space charge under the high temperature where the cable is used is small, and the reliability in practical use is lacking.

[0008]

As described above, in recent years, in order to apply the polyolefin insulated cable to a DC cable, a cable has been developed in which the formation and accumulation of space charge due to the application of a DC voltage, which is a problem in this case, is suppressed. ing.
However, in reality, the effect of suppressing the formation and accumulation of space charges, particularly the effect of suppressing the charge at high temperature is insufficient, or the other electric characteristics are deteriorated, and the satisfactory results have not yet been obtained. is there.

The present invention has been made in consideration of such a conventional situation, and it is possible to sufficiently suppress the formation and accumulation of space charge in an insulator in a polyolefin-insulated cable even at a high temperature, and to prevent other insulation. It is an object of the present invention to provide a highly reliable direct current cable that does not deteriorate the characteristics and electrical characteristics.

[0010]

The direct current cable of the present invention contains 0.1 to 15% by weight of a synthetic adsorbent with respect to polyolefin.
It is characterized by comprising an insulating layer made of the insulating composition contained therein.

The polyolefin used in the present invention includes ultra low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene, high density polyethylene (HDPE) and metallocene catalyst. Polyethylene, polypropylene, polybutene-1, polymethylpentene-1, and
Examples thereof include ethylene vinyl acetate copolymer, ethylene propylene rubber, ethylene ethyl acrylate copolymer, and other ethylene copolymers. These may be used alone or in combination of two or more. May be. Moreover, you may make it use, cross-linking. In the present invention, among others, a polyolefin synthesized by a metallocene catalyst having excellent electric properties, for example,
It is preferable to use ethylene or propylene homopolymerized with the same catalyst, or ethylene or propylene copolymerized with propylene, butene, pentene, hexene, octene, or the like. Examples of such products include Engage CL8001 and Engage CL8002 (both are trade names) manufactured by Dow Chemical Company.
And so on. The polyolefin synthesized by these metallocene catalysts is a polymer having features such as narrow molecular weight distribution, uniform distribution of comonomer, and extremely small catalyst residue, as compared with polyolefins synthesized by other catalysts. .

Further, for such a polyolefin,
0.1-15 synthetic adsorbents wt% formulation is one that characterizes the _{invention, Al 2 0 3 · xH 2} O, 2.5MgO · Al 2 0
₃ xH ₂ O, Mg ₆ Al ₂ (OH) ₁₆ CO ₃ 4H ₂ O, 2MgO 6SiO _{2
· XH 2 O, Al 2 0} 3 · 9SiO 2 · xH 2 O, W a Al b Si c O
_{2 (b + c)} · xH ₂ O (W is Na, Ca, K, Ba, and
An element selected from the group consisting of Sr, a is a positive integer, b and c are positive integers of b + c, and c / b> 1)
A solid adsorbent containing Mg, Al, Si, etc. as a main element component and / or a solid adsorbent having a strong solid acid strength is preferable. That is, these synthetic adsorbents have excellent acid and / or alkali adsorbing ability and adsorb the heterocharges inside the insulator to electrically neutralize them. This effect does not change even under high temperature. Moreover, these synthetic adsorbents do not lower the insulation resistance like carbon black does, and do not ionize themselves as magnesium oxide to become a charge generation source. Further, it is less likely that the higher-order structure of the polyolefin such as an organic acid is disturbed and electrical characteristics are deteriorated. Therefore, the formation of space charges can be suppressed without deteriorating the insulation characteristics and electrical characteristics,
It is possible to stabilize the dielectric breakdown voltage. Note that the space charge source inside the insulator is not limited to either one of acid and alkali, and both are present. Therefore, in the present invention, in particular, one having both acid adsorption ability and alkali adsorption ability is preferable. It is desirable to use, or to use in combination an acid-adsorptive one and an alkali-adsorptive one. _{Incidentally, 2MgO · 6SiO 2 · xH 2} O is combines a strong acid adsorption capacity and alkali adsorption capacity, _{also, Al 2 0 3 · xH 2} O has an acid adsorption capacity and weak alkali adsorption capacity. Furthermore, 2.5MgO ・ Al ₂
0 ₃ .xH ₂ O and Mg ₆ Al ₂ (OH) ₁₆ CO ₃ 4H ₂ O have strong acid adsorbing ability, and Al ₂ 0 ₃ .9SiO ₂ .xH ₂ O has strong alkaline adsorbing ability.

In the present invention, the compounding amount of such a synthetic adsorbent is limited to the range of 0.1 to 15% by weight with respect to the polyolefin because when it is less than 0.1% by weight, the adsorption of the space charge generation source becomes insufficient. On the other hand, if it exceeds 15% by weight, the electric characteristics may be adversely affected.

The insulating composition of the present invention includes
If it is within the range that is usually used, it does not matter even if a crosslinking agent, a crosslinking aid, an antiaging agent and other additives are blended as necessary. Most of these additives serve as a space charge source, but the action of the synthetic adsorbent suppresses the formation of space charges.

As described above, in the direct-current cable of the present invention, a synthetic adsorbent which has an excellent ability to adsorb electric charges to polyolefin, does not ionize itself, and does not disturb the higher order structure of polyolefin is specified. Since it has an insulating layer made of an insulating composition blended in a sufficient amount, it has stable dielectric breakdown characteristics even at high temperatures, and is excellent in other insulating characteristics and electrical characteristics.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples.

Examples 1 to 8 Each component was uniformly mixed in the composition shown in Table 1 to obtain an insulating composition, which was used to produce a DC cable as shown in FIG.

That is, a copper conductor 1 having a diameter of 2 mm is coated with a semiconductive composition, the insulating composition, and the semiconductive composition in this order by three-layer coextrusion, and heat-crosslinked by a conventional method. An inner semiconductive layer 2 with a thickness of 0.5 mm, an insulator layer 3 with a thickness of 2 mm, and an outer semiconductive layer 4 with a thickness of 0.5 mm are formed, and a soft vinyl chloride resin is extrusion-coated on the outer side of the sheath 5 with a thickness of 1 mm. Was formed. For forming the inner semi-conductive layer 2 and the outer semi-conductive layer 4, a semi-conductive composition prepared by mixing 38% by weight of conductive carbon with an ethylene / vinyl acetate copolymer was used.

Next, for the obtained DC cables of Examples, the long-term DC breakdown voltage, impulse breakdown voltage, and reverse polarity impulse superimposed breakdown characteristics at room temperature and 90 ° C. were measured under the following voltage application conditions or evaluation methods. Examined. The results are shown in the lower column of Table 1. The number of samples in each test was 10 samples.

[DC breakdown voltage] After applying a DC voltage of -100kV for 1 hour, boost the voltage in steps of 10kV / 1 hour until breakdown. [Impulse breakdown voltage] + Apply 100kV of impulse voltage 3 times, then 20kV / 3 Boost up to breakdown in a number of steps [Reverse polarity impulse superimposed breakdown characteristic] DC voltage of 100 kV
After applying for 1 hour, 70% of the positive impulse breakdown voltage,
Impulse voltage of 80% and 90% was applied three times to measure the destruction probability. Also, in Table 1, instead of synthetic adsorbent, for comparison,
Example in which carbon black was blended (Comparative Example 1), Example in which magnesium oxide was blended (Comparative Example 2), Example in which no synthetic adsorbent was blended, and Organic acid copolymer polyethylene was used as polyolefin (Comparative Example 3) An example in which the synthetic adsorbent is not blended (Comparative Example 4) is also shown.

[0021]

[Table 1] As is clear from Table 1, the cable according to the present invention is
The DC breakdown characteristics were improved over a long period of time, and the impulse breakdown characteristics were also good. Furthermore, it has a good destruction characteristic even when impulses of opposite polarities are superimposed. In particular, these effects are remarkable in the practical temperature range of 90 ° C., which improves reliability during use.

[0022]

As described above, according to the present invention,
Space charge formation and accumulation due to direct current application in the polyolefin insulation is sufficiently suppressed even at high temperatures, and the original excellent characteristics of the polyolefin insulation cable do not deteriorate, so it has stable dielectric breakdown characteristics, In addition, it is possible to obtain a highly reliable DC cable having other excellent insulation characteristics and electric characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a DC cable of the present invention.

[Explanation of symbols]

 1 ... Conductor 2 ... Inner semiconductive layer 3 ... Insulator layer 4 ... Outer semiconductive layer 5 ... Sheath

Claims (4)

[Claims] 1. A synthetic adsorbent is added to a polyolefin in an amount of 0.1.
A DC cable comprising an insulating layer made of an insulating composition containing about 15% by weight. 2. The DC cable according to claim 1, wherein
Synthetic _{adsorbent, Al 2 0 3 · xH 2} O, 2.5MgO · Al 2 0 3 · xH 2 O, Mg 6 Al
₂ (OH) ₁₆ CO ₃ 4H ₂ O, 2MgO ・ 6SiO ₂・ xH ₂ O, Al ₂ 0 ₃
・ 9SiO ₂・ xH ₂ O, and W _a Al _b Si _c O _{2 (b + c)}・ xH
₂ O (where W is an element selected from the group consisting of Na, Ca, K, Ba, and Sr, a is a positive integer, b and c are b +
A direct current cable characterized in that c is a positive integer and is at least one selected from the group consisting of c / b> 1). 3. The DC cable according to claim 1 or 2, wherein the synthetic adsorbent has both acid and alkali adsorption capacities. 4. The DC cable according to claim 1, wherein the polyolefin is a polyolefin synthesized by a metallocene catalyst.