WO2011093211A1 - Crosslinked polyolefin composition, direct-current power cable, and process for construction of direct-current power line - Google Patents

Abstract

Provided is a direct-current power cable which does not suffer from deterioration in electrical characteristics even after high-temperature heat history. The direct-current power cable can be produced by using, as the insulation layer, a crosslinked polyolefin composition which comprises (1) 100 parts by mass of a polyolefin, (2) 0.1 to 5 parts by mass of carbon black, (3) 0.02 to 2 parts by mass of triallyl isocyanurate and/or trimethallyl isocyanurate, and (4) a prescribed amount of a crosslinking agent consisting of an organic peroxide.

Description

Crosslinked polyolefin composition, DC power cable and method of installing DC power line

The present invention relates to a crosslinked polyolefin composition, a DC power cable having an insulating layer formed of the crosslinked polyolefin composition (herein referred to as "DC power cable" in the present application), and a method of applying a DC power line using a DC power cable.

An extruded insulated cable (hereinafter referred to as an XLPE cable), in which an insulating layer is formed using a composition of cross-linked polyethylene (XLPE), is generally used as an AC power cable (referred to as "AC power cable" in the present application). However, there are few application examples to the high voltage DC power cable of the XLPE system cable. An oil immersion cable (OF cable, MI cable) is generally used as a high voltage DC power cable of 22 V or more.

The reason why there are few applications of XLPE cable to high voltage DC power cable is that in the case of XLPE cable, decomposition residues of dicumyl peroxide (DCP) (acetophenone, cumyl alcohol) space charge when DC high voltage is applied It is because it forms and the direct current | flow characteristic is reduced notably. Here, dicumyl peroxide (DCP) is a crosslinking agent that is widely used to crosslink polyethylene.

As a means of suppressing the above-mentioned space charge, it is practiced to incorporate certain inorganic fillers into the composition of the XLPE system. For example, Patent Document 1 describes that, in an XLPE-based cable, the direct current characteristics are improved by blending a certain type of carbon black with the composition of the XLPE-based material that forms the insulating layer.

In addition, patent document 2 describes that triallyl isocyanurate is mix | blended as a crosslinking adjuvant in an alternating current power cable. It is known that the blending amount of the crosslinking agent can be reduced by blending the crosslinking aid.

Patent Document 3 discloses that, in a direct current power cable, a resin composition obtained by blending triallyl isocyanurate and a diene polymer with polyolefin is crosslinked to form an insulator layer, and a certain amount of organic peroxide crosslinking agent is used. It is described that formation of space charge due to a crosslinking agent decomposition residue is suppressed by blending triallyl isocyanurate and a diene-based polymer while suppressing the following.

Patent No. 3602297 JP-A-57-49635 JP 2001-325834 A

By the way, the inventors evaluated the electrical characteristics of the DC power cable in which the insulating layer was formed by the composition of XLPE type which blended carbon black. As a result, it has been found that sufficient electrical characteristics can not always be obtained after adding a thermal history for a fixed time. For example, the DC breakdown characteristics evaluated after heating at 160 ° C. for 10 hours or more decreased to nearly 70% of the characteristics before heating.

In the case of mold jointing the connection portion and the end portion of XLPE cables, when the semiconductive layer and the insulating layer covering the connection portion and the end portion of the cable are heat-molded, the high temperature heat as described above History is added. For this reason, in the XLPE cable in which the direct current electrical characteristics are deteriorated after the heat history is added, the performance in the vicinity of the connection portion and the end portion is affected, which is disadvantageous for direct current power transport.

An object of the present invention is to improve the insulating material for a DC power cable disclosed in Patent Document 1 (Japanese Patent No. 3602297), and to suppress the deterioration of DC electrical characteristics due to heat history. It is to provide. That is, to provide a DC power cable of XLPE type that can be used for higher voltage power transportation.

In order to solve the above problems, the crosslinked polyolefin composition according to the present invention is a crosslinked polyolefin composition in which an organic peroxide crosslinking agent is blended with a polyolefin, and further,
(1) per 100 parts by mass of polyolefin,
(2) 0.1 to 5 parts by mass of carbon black and (3) 0.02 to 2 parts by mass of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate Do.

The direct current power cable according to the present invention is characterized in that an insulating layer is formed of the crosslinked polyolefin composition.

In the method of manufacturing a DC power line according to the present invention, the insulating layer is formed by covering the portion to which the DC power cable is connected with an insulating material and performing a heating process.

According to the present invention, it is possible to provide an XLPE-based DC power cable which can be used for higher voltage power transportation with less deterioration of DC electrical characteristics even when subjected to heat history.
The present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for the purpose of illustration only and do not limit the scope of the invention.

It is sectional drawing of the produced direct current | flow cable 10. As shown in FIG. It is sectional drawing of a cable connection part.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, although various limitations preferable for carrying out the present invention are given to the embodiments described below, the scope of the present invention is not limited to the following embodiments and the illustrated examples.

The crosslinked polyolefin composition according to the present invention comprises (1) 0.1 to 5 parts by mass of (2) carbon black with respect to 100 parts by mass of polyolefin, and (3) triallyl isocyanurate or trime as a crosslinking assistant. It comprises 0.02 to 2 parts by mass of at least one compound selected from taryl isocyanurate, and (4) a predetermined amount of an organic peroxide crosslinking agent. Here, the term "part by mass" indicates the mass ratio of each raw material to be blended, and in the following description, indicates the part by mass with respect to 100 parts by mass of polyolefin.

[Polyolefin]
Polyolefins form the basis of the crosslinked polyolefin composition according to the invention. Examples of polyolefins include low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene-vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer. A polymer, a mixture of two or more of these, and the like can be used.

〔Carbon black〕
The carbon black is preferably nano-dispersed particles having an average primary particle size of 10 to 100 nm. Such a nano-dispersed particle is to exert a space charge suppressing function.

Assuming that the number of particles in each particle diameter section is Ni and the central value of the particle diameter section is Di, the average primary particle diameter is given by the following equation.
Average primary particle size = Ni Ni · Di / Ni Ni
The carbon black having a size of 10 to 100 nm of the average primary particle diameter is an optimal value that does not disturb the crystal structure of the insulator such as polyethylene. Disruption of the crystal structure reduces the electrical performance of the insulator. If the particle size is larger than this range, the dispersion and mixing of the carbon black will be poor. If it is smaller than this, manufacture is difficult and unrealistic.

The compounding amount of carbon black is preferably 0.1 to 5 parts by mass. If the amount is less than 0.1 parts by mass, the effect of improving the direct current characteristics can not be obtained. On the other hand, if the amount is more than 5 parts by mass, the direct current characteristics deteriorate. If the amount is more than 5 parts by mass, the amount of the filler will be large, and the long extrusion characteristics will be impaired.

In the carbon black, the proportion of carbon black particles having a particle size of 300 nm or more is preferably 1% by weight or less. The lightning impulse breakdown voltage can be improved by setting the proportion of carbon black particles having a particle size of 300 nm or more to 1% by weight or less. In the impulse breakdown, the conductive protrusion is often the origin of the breakdown. When the proportion of large carbon particles having a particle diameter of 300 nm or more is large, naturally, aggregates formed by aggregation of carbon particles also become large. When the insulating layer of the cable is formed of the crosslinked polyolefin composition according to the present invention, if the aggregates present in the insulating layer become large, the aggregates are in contact with the inner semiconductive layer and the outer semiconductive layer adjacent to the insulating layer. Or the probability of proximity also increases. Such carbon aggregates in the vicinity of the inner semiconductive layer and in the vicinity of the outer semiconductive layer are considered to affect the impulse breakage of the cable.

The carbon black preferably has a ratio of oil absorption (cc / 100 g) of mineral oil to specific surface area (m ² / g) measured by BET method is 0.7 or more and 3.5 or less. Here, the BET method is one of methods of measuring the surface area of powder by vapor phase adsorption method, and is a method of determining the total surface area of a 1 g sample, that is, the specific surface area, from the adsorption isotherm. In general, nitrogen gas is often used as the adsorption gas, and the method of measuring the adsorption amount from the change in pressure or volume of the gas to be adsorbed is most frequently used. The most prominent ones representing the isotherm of multimolecular adsorption are the Brunauer, Emmett, Teller equations, called the BET equation. The BET equation is widely used for surface area determination. The amount of adsorption is determined based on the BET equation, and the surface area is obtained by multiplying the area occupied by one adsorbed molecule on the surface.

By setting the ratio of oil absorption (cc / 100 g) of mineral oil to the specific surface area (m ² / g) to 0.7 or more and 3.5 or less, leakage of space charge can be promoted. The reason will be described below.
The resistivity (specific resistance) of the crosslinked polyethylene composition is 抵抗 (Ω · m), the temperature coefficient of insulation resistance is α (1 / ° C.), the electric field coefficient (stress coefficient of insulation resistance) is β (mm / kv), If the electric field strength applied to the insulator is E (kv / mm), it is known that the following relationship is established.
ρ = ρ ₀ exp− (αT + βE) (1)

Then, when carbon black is compounded, the temperature coefficient α decreases while the electric field coefficient β increases, and the leakage of space charge in the insulator composition is promoted. The reason is that when the electric field coefficient β is increased, the resistivity ρ is decreased, so that the electric field in the high stress portion (the portion to which the strong electric field is applied) is relaxed. In addition, when the temperature coefficient α decreases, the maximum electric field Emax appearing on the shielding side decreases when the conductor temperature is high. Thus, the electric field distribution in the insulator composition moves in the direction of homogenization, and the space charge accumulation is reduced.

When the compounding amount of carbon black is increased, the distance between particles is reduced, and under a high electric field, a current flows due to tunneling between particles. For this reason, the electric field coefficient β becomes larger than necessary, which causes thermal destruction. Therefore, it is essential to reduce the resistivity ρ of the equation (1) with a small blending amount. By the way, carbon black having a large ratio of oil absorption amount to specific surface area can lower the resistivity で by a small amount, and good results can be obtained if this ratio is 0.7 or more.

On the other hand, when this ratio is larger than 3.5, the degree of aggregation of the particles is increased, the apparent (aggregate) particle diameter is increased, and the condition of mixing with a thermoplastic resin such as polyethylene becomes worse. In the case of acetylene carbon in particular, this effect is significant because the particles are linked in a chain.
In addition, when the carbon black of SAF, ISAF, I-ISAF, CF, SCF, or HAF carbon which is furnace carbon black is used, the above ratio is particularly good in the range of 0.7 to 1.5. What has been confirmed experimentally.

Furthermore, the carbon black preferably has a carbon content of 97% by weight or more. Carbon black contains impurities such as ash, O 2, H 2 and the like, and when the amount of these impurities is large, the electrical characteristics deteriorate. Therefore, the higher the carbon purity, the better.

[Crosslinking Aid]
The most characteristic point of the crosslinked polyolefin composition according to the present invention is that it contains at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate as a crosslinking assistant. The compounding ratio is 0.02 to 2 parts by mass. If the amount is less than 0.02 parts by mass, the effect of suppressing the decrease in insulation performance due to the high temperature heat history can not be obtained. On the other hand, when the amount is more than 2 parts by mass, slip and resin burn occur in the extruder when extruding the crosslinked polyolefin composition. When resin burning occurs, the resin pressure rises during extrusion, making it impossible to produce a stable DC power cable. Also, the electrical performance of the DC cable is degraded. A further preferable compounding amount of the crosslinking coagent is 0.1 to 2 parts by mass. By blending 0.1 parts by mass or more, the blending amount of the organized oxide crosslinking agent can be reduced, and the effect of suppressing resin burning in the extruder can also be obtained.

[Organic peroxide crosslinking agent]
As the organic peroxide crosslinking agent, any organic peroxide used for ordinary crosslinking may be used. For example, dicumyl peroxide (DCP), t-butylcumyl peroxide, α, α'-bis (t-butylperoxy-m-isopropyl) benzene and the like can be used. The decomposition residue of t-butylcumyl peroxide and α, α'-bis (t-butylperoxy-m-isopropyl) benzene contains, like the decomposition residue of DCP, compounds having a polar group such as a hydroxyl group. As in the case of using DCP, the above-mentioned problems occur, but the present invention can solve this problem.

The compounding quantity of the organic peroxide crosslinking agent is suitably adjusted with the kind of organic peroxide to be used, polyolefin, etc. The amount is preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass. When the blending amount of the organic peroxide crosslinking agent is too small, crosslinking is insufficient and mechanical properties and heat resistance of the insulating layer are lowered. On the other hand, when the compounding amount of the organic peroxide crosslinking agent is too large, resin extruding occurs in the extruder when extruding the crosslinked polyolefin composition. When resin burning occurs, the resin pressure rises during extrusion, making it impossible to produce a stable DC power cable. Also, the electrical performance of the DC power cable is degraded.

〔Antioxidant〕
Moreover, you may mix | blend antioxidant with a crosslinked polyolefin composition as needed. As the antioxidant, commonly used antioxidants can be appropriately selected and blended. Phenolic, phosphite and thioether anti-aging agents are preferred. In particular, 4,4′-thiobis (3-methyl-6-tert-butylphenol) has the effect of suppressing the crosslinking reaction when extruding the crosslinked polyolefin composition, and is thus preferable.
The compounding amount of the antioxidant is appropriately adjusted in consideration of the type of the antioxidant to be used and the oxidation resistance, but is preferably 0.1 to 1.0 parts by mass.

(Example)
Hereinafter, the present invention will be described in more detail based on examples.

[Power cable]
FIG. 1 is a cross-sectional view of the created DC cable 10. As shown in FIG. 1, the direct current power cable 10 is formed by sequentially forming an inner semiconductive layer 12, an insulating layer 13, an outer semiconductive layer 14, a metal shielding layer 15, and a sheath 16 outside the conductor 11. The cross-sectional area of the conductor 11 is 200 mm ² , the thickness of the insulating layer 13 is 3 mm, and the thicknesses of the inner semiconductive layer 12 and the outer semiconductive layer 14 are 1 mm.

(1) Inner semiconductive layer The inner semiconductive layer 12 is formed of ethylene-vinyl acetate copolymer, organic peroxide crosslinker (DCP), carbon black (acetylene black), antioxidant (4,4'-thiobis ( It formed using the composition (semiconductive resin composition) which mix | blended 3-methyl- 6-tert- butyl phenol)).
(2) Insulating Layer The insulating layer 13 was formed using the crosslinked polyethylene composition according to the present invention. The compounding ratio (parts by mass) of the polyolefin, carbon black, crosslinking aid and organic peroxide crosslinking agent is as shown in Tables 1 to 4.
As the polyolefin, LDPE (NUC-9026 manufactured by DOW) was used. Carbon black has a specific surface area of 140 m ² / g as measured by the BET method, an oil absorption of 114 cc / 100 g of mineral oil, a carbon content of 97.5 mass%, and an average particle size of primary particles of 18 nm and coarse particles of 300 nm or more An amount of 1% or less of furnace carbon black SA was used. The ratio of oil absorption (cc / 100 g) of mineral oil to specific surface area (m ² / g) is 0.8.
Triallyl isocyanurate or trimethallyl isocyanurate was used as a coagent.
As the organic peroxide crosslinking agent, DCP, t-butylcumyl peroxide, α, α'-bis (t-butylperoxy-m-isopropyl) benzene was used.
The above materials were kneaded with a Banbury mixer, passed through a metal screen mesh with an opening of 34 μm, and further mixed with DCP using a Henschel mixer to prepare a crosslinked polyethylene composition.
(3) Outer Semiconductive Layer The outer semiconductive layer 14 was formed using a semiconductive resin composition having the same composition as the inner semiconductive layer 12.

The compositions (1) to (3) are simultaneously extruded to the outer peripheral part of the conductor 11, and pressure heating is performed at a pressure of 10 kg / cm ² and a temperature of 280 ° C. in a nitrogen atmosphere, and an organic peroxide crosslinking agent is used as an initiator The crosslinking was advanced by the radical reaction. Subsequently, a metal shielding layer and a sheath were provided by a conventional method to prepare a DC power cable.

[Structure of cable connection portion]
The DC power line was manufactured by connecting the DC power cable 10 created by the above procedure.
A schematic cross section of the cable connection is shown in FIG. As shown in FIG. 2, the cable connection portion is formed by connecting two DC power cables 10, 10 with the conductors 11, 11 facing each other at their ends and facing each other (reference numeral 21 in the figure). The conductive layer 22, the insulating layer 23, and the outer semiconductive layer 24 are sequentially coated.

The inner semiconductive layer 22 and the insulating layer 23 are formed by sequentially winding a semiconductive tape and an insulating tape around the conductors 11 and 11 butted connected to each other to a predetermined thickness and then heating and fusing the wound tape. Be done. The outer semiconductive layer 24 is formed using a semiconductive shrink tube. The semiconductive tape and the semiconductive shrink tube were formed using the same semiconductive resin composition (before crosslinking) as the inner semiconductive layer 12 and the outer semiconductive layer 14 of the DC power cable 10. The insulating tape is obtained by extruding a crosslinked polyethylene composition (before crosslinking) of the same composition as the insulating layer 13 of the DC power cable 10 into a tape having a thickness of 0.1 mm, a width of 20 mm, and a length of 150 m by a single screw extruder. Created by doing.

[Connection method of cable]
Hereinafter, the cable connection method will be described.
First, the end portions of the two DC power cables 10 are peeled off in the order of the sheath 16, the metal shielding layer 15, the outer semiconductive layer 14, the insulating layer 13, and the inner semiconductive layer 12 in the order of a cone shape did. Next, the conductors 11, 11 of the two DC cables 10, 10 were put together and connected to form a conductor connection portion 21. Next, a semiconductive tape was wound around the conductor connection portion 21 and heated and fused to form the inner semiconductive layer 22.
Next, the insulating tape was wound around the inner semiconductive layer 22, and the outer periphery was covered with a semiconductive shrink tube. On top of this, a semiconductive shrink tube was further placed and heated to shrink.

Next, the outer periphery of the semiconductive shrink tube was coated with a gas barrier layer, and the outer periphery of the gas barrier layer was coated with a heater. Further, a cross-linked tube consisting of two halves of the mold and packing at both ends was assembled on the outside of the heater. The cross-linked tube is selected to be sufficiently longer than the distance (the range of A to C in FIG. 2) between the outer semiconductive layers 14 of the two DC power cables 10. In this embodiment, the distance between the outer semiconductive layers 14 is 760 mm, and a cross-linked tube having a length of 1150 mm covering A to D in FIG. 2 was used.
Thereafter, the internal pressure in the cross-linking tube was adjusted to 0.8 MPa with nitrogen gas, and the temperature was raised by a heater and held at 220 ° C. for 3 hours to form the insulating layer 23 and the outer semiconductive layer 24.

[Evaluation]
(1) The degree of crosslinking of the manufactured power cable was measured according to JISC 3005 4.25 by collecting a test piece from the middle portion in the thickness direction of the cable insulator.
(2) The DC breakdown voltage (kV) of the connected DC power cable was measured. The breakdown voltage was measured by raising the voltage with a step-up of -20 kV / 10 minutes from a start voltage of -60 kV for a DC power cable with a total length of 20 m including the cable connection. The conductor temperature was adjusted to 90 ° C. during energization. The DC breakdown voltage of the DC power cable before connection was an average of -320 kV.
(3) After the destruction, the connection was dismantled to identify the broken part. In the case of breakage between both ends 23A and 23A of the insulating layer 23, the broken part is A, and in the case of breakage at both ends 23A and 23A of the insulating layer 23, the broken part is B and the end 23A of the insulating layer 23 The fracture site is C if it is fractured with the end 14A of the outer semiconductive layer 14 or the fracture site if it is fractured between the end 14A of the outer semiconductive layer 14 and the end of the bridging tube. It was D.
The results are shown in Tables 1 to 4.
(4) In manufacturing a direct current power cable, the pressure of the extruded resin was measured with a 34 μm metal screen mesh portion attached to the tip of the insulating layer extruder screw. The extrusion characteristics were evaluated from the rising tendency of the resin pressure 5 hours after the start of the extrusion. The criteria for evaluation are as follows. Moreover, x was displayed for what a slip produced in the extruder and stable extrusion was not able to be performed.
-: Almost no rise in resin pressure is observed.
+: A rise in resin pressure is observed, but there is no problem at all in the production of a long cable.
++: An increase in resin pressure is observed, but a long cable can be manufactured.
+ ++: Resin pressure rise is recognized, and it is difficult to manufacture a long cable.

 
　　ＬＤＰＥ；ＤＯＷ製　ＮＵＣ－９０２６
Ａ；接続部中央、Ｂ；テープ絶縁層立上部、Ｃ；ケーブル外導処理部、Ｄ；ケーブル再加熱部

LDPE; made by DOW NUC-9026
A: Center of connection, B: Upstanding tape insulation layer, C: Outer conductor treatment section, D: Cable reheating section

 
　　ＬＤＰＥ；ＤＯＷ製　ＮＵＣ－９０２６
Ａ；接続部中央、Ｂ；テープ絶縁層立上部、Ｃ；ケーブル外導処理部、Ｄ；ケーブル再加熱部

LDPE; made by DOW NUC-9026
A: Center of connection, B: Upstanding tape insulation layer, C: Outer conductor treatment section, D: Cable reheating section

 

 

 

 

When triallyl isocyanurate is used as the crosslinking assistant (Examples 1 to 6 and 12 to 17) when the blending amount of the crosslinking assistant is in the range of 0.02 to 2 parts by mass, when trimethallyl isocyanurate is used The direct current breakdown voltage of (Examples 7 to 11) was -320 to -260 kV, and all showed excellent direct current electrical characteristics. The breakdown site was in the range of the part A or the part B, that is, the insulating layer 23 of the connection.

On the other hand, when the compounding amount of the crosslinking aid was 0.01 parts by mass (Comparative Examples 1, 5, 8 and 10), the direct current breakdown voltage was 200 or less in absolute value, and the direct current electrical characteristics were poor. The fracture site was a D portion outside the end 14 A of the outer semiconductive layer 14. The failure occurred at such a site because the direct current electrical characteristics of the insulating layer 13 of the direct current power cable were deteriorated by the heat treatment for crosslinking the crosslinked polyethylene composition to be the insulating layer 23 of the connection portion.

The blending amounts of the crosslinking agent in Example 4 and Comparative Example 1, Example 10 and Comparative Example 5, Example 13 and Comparative Example 8, and Example 16 and Comparative Example 10 are the same. However, even if the heat treatment for crosslinking the cross-linked polyethylene composition to be the insulating layer 23 of the connection portion is performed, the direct current electricity in Examples 4, 10, 13, 16 is higher than that in Comparative Examples 1, 5, 8, 10. The decrease in characteristics is small. From this result, it can be seen that the effect of preventing deterioration of the direct current electrical characteristics at the time of reheating becomes remarkable when the triallyl isocyanurate or trimethallyl isocyanurate is added in an amount of not less than 0.02 parts by mass.

In the case where the compounding amount of triallyl isocyanurate and the like is 2.5 parts by mass (Comparative Examples 2 and 6, Comparative Example 9 and Comparative Example 11), a slip is generated during the extrusion, so that a DC power cable can be manufactured. It was not.

In Comparative Example 3 in which the blending amount of carbon black is small, and Comparative Example 4 in which the blending amount of carbon black is large, the DC breakdown voltage is low and the DC electrical characteristics are not sufficient.

The comparative example 7 is an example which mix | blended m-phenylene bis maleimide as a crosslinking adjuvant. In Comparative Example 7, the cable D is broken at -160 kV. This destruction occurs because the DC electric characteristics of the insulating layer 13 of the DC power cable are deteriorated by the heat treatment for crosslinking the crosslinked polyethylene composition to be the insulating layer 23 of the connection portion. From this result, it can be seen that m? -Phenylene bismaleimide does not have an effect like triallyl isocyanurate or trimethallyl isocyanurate.

As explained above, by using the cross-linked polyethylene composition according to the present invention, it is possible to obtain a DC power cable with little deterioration in electrical characteristics even when subjected to heat history. Also, this DC power cable can be used for higher voltage DC power transportation.

In the above embodiment, as the [connection method of cable], the method of forming the insulating layer by winding the insulating tape and heating it is described, but the connection method used in the method of manufacturing the DC power line of the present invention is Any other method may be employed as long as the connecting portion is covered with an insulating material and heat treated. For example, in the method of manufacturing a direct current power line according to the present invention, a so-called extrusion molding method (EMJ) of extruding an insulating material using an extruder and heating and crosslinking it to form an insulating layer may be adopted as a connection method. it can. Further, the insulating material used to connect the cable may not have the same composition as the insulating material used for the cable insulator shown in the embodiment, as long as it is a DC insulating material.

The entire disclosure of Japanese Patent Application No. 2010-01611, filed on January 28, 2010, including the specification, claims, drawings and abstract is incorporated herein by reference.
Although various exemplary embodiments have been shown and described, the present invention is not limited to the above embodiments. Accordingly, the scope of the present invention is to be limited only by the following claims.

DESCRIPTION OF SYMBOLS 10 DC power cable 11 Conductor 12, 22 Internal semiconductive layer 13, 23 Insulating layer 14, 24 Outer semiconductive layer 14A End part 21 Conductor connection part 23A Both ends

Claims (3)

A cross-linked polyolefin composition comprising an organic peroxide cross-linking agent blended with a polyolefin,
Furthermore,
(1) per 100 parts by mass of polyolefin,
(2) 0.1 to 5 parts by mass of carbon black and (3) 0.02 to 2 parts by mass of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate Crosslinked polyolefin composition. A DC power cable comprising an insulating layer formed of the crosslinked polyolefin composition according to claim 1. A method of manufacturing a DC power line, comprising forming an insulating layer by covering and heating a portion connected to the DC power cable according to claim 2 with an insulating material.

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