JPWO2011093211A1 - Crosslinked polyolefin composition, DC power cable, and DC power line construction method - Google Patents

Abstract

Provided is a DC power cable whose electrical characteristics do not deteriorate even after a high temperature thermal history. A cross-linked polyolefin composition in which an organic peroxide cross-linking agent is blended with a polyolefin, and (1) 0.1 to 5 parts by mass of carbon black with respect to 100 parts by mass of polyolefin, and (3) A crosslinked polyolefin composition containing 0.02 to 2 parts by mass of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate, and (4) a predetermined amount of an organic peroxide crosslinking agent. By using it as an insulating layer, it is possible to obtain a DC power cable whose electrical characteristics do not deteriorate even after a high temperature thermal history.

Description

  The present invention relates to a cross-linked polyolefin composition, a DC power cable (hereinafter referred to as “DC power cable”) in which an insulating layer is formed of the cross-linked polyolefin composition, and a DC power line construction method using the DC power cable.

  An extruded insulated cable (hereinafter referred to as an XLPE cable) in which an insulating layer is formed using a crosslinked polyethylene (XLPE) -based composition is widely used for an AC power cable (hereinafter referred to as “AC power cable”). However, there are few application examples of the XLPE cable to the high voltage DC power cable. As a high voltage DC power cable of 22 V or higher, an oil immersion cable (OF cable, MI cable) is generally used.

  The reason why there are few applications of XLPE cables to high voltage DC power cables is that, in XLPE cables, the dissociation residue (acetophenone, cumyl alcohol) of dicumyl peroxide (DCP) generates space charge when DC high voltage is applied. This is because the direct current characteristics are significantly reduced. Here, dicumyl peroxide (DCP) is a cross-linking agent that is generally used to cross-link polyethylene.

  As a means for suppressing the above-mentioned space charge, a certain inorganic filler is blended in an XLPE-based composition. For example, Patent Document 1 describes that, in an XLPE cable, DC characteristics are improved by blending a certain type of carbon black in an XLPE composition that forms an insulating layer.

  Patent Document 2 describes blending triallyl isocyanurate as a crosslinking aid in an AC power cable. It is known that the amount of the crosslinking agent can be reduced by blending the crosslinking aid.

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

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

  By the way, the inventors evaluated the electrical characteristics of a DC power cable in which an insulating layer was formed with an XLPE composition containing carbon black. As a result, it was found that sufficient electrical characteristics cannot always be obtained after applying a thermal history for a certain period of time. For example, the DC breakdown characteristics evaluated after heating at 160 ° C. for 10 hours or more decreased to about 70% of the characteristics before heating.

  When joints and terminations between XLPE cables are molded joints, when heat-molding the semiconductive layer or insulation layer covering the cable connection or termination, high-temperature History is added. For this reason, in the XLPE system cable in which the DC electrical characteristics are lowered after the thermal history is applied, the performance in the vicinity of the connection part and the terminal part is affected, which is disadvantageous for DC power transportation.

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

In order to solve the above problems, a crosslinked polyolefin composition according to the present invention is a crosslinked polyolefin composition in which an organic peroxide crosslinking agent is blended with polyolefin,
(1) For 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, To do.

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

  The method for manufacturing a DC power line according to the present invention is characterized in that an insulating layer is formed by covering a portion where the DC power cable is connected with an insulating material and subjecting it to a heat treatment.

ADVANTAGE OF THE INVENTION According to this invention, even when it receives a thermal history, the fall of direct-current electrical property is small, and the XLPE-type direct-current power cable which can be used for higher voltage electric power transportation can be provided.
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 are not intended to limit the scope of the invention.

It is sectional drawing of the produced DC cable 10. FIG. It is sectional drawing of a cable connection part.

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

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

[Polyolefin]
Polyolefin is the base of the cross-linked polyolefin composition according to the present invention. Examples of the polyolefin include, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene-vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, ethylene-propylene copolymer, and ethylene-propylene-diene copolymer. A polymer, a mixture of two or more of these, and the like can be used.

〔Carbon black〕
Carbon black is preferably nano-dispersed particles having an average primary particle size of 10 to 100 nm. This is because such a nano-dispersed particle exhibits a space charge suppressing effect.

When the number of particles in each particle diameter section is Ni and the center value of the particle diameter section is Di, the average primary particle diameter is given by the following equation.
Average primary particle size = ΣNi · Di / ΣNi
Carbon black having an average primary particle size of 10 to 100 nm is an optimum value that does not disturb the crystal structure of an insulator such as polyethylene. When the crystal structure is disturbed, the electrical performance of the insulator decreases. On the other hand, if the particle size is larger than this, the dispersion and mixing of the carbon black will deteriorate. If it is smaller than this, it is difficult to manufacture and it is not practical.

  The blending 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 direct current characteristics cannot be improved. On the other hand, when the amount is more than 5 parts by mass, the direct current characteristics are deteriorated. On the other hand, if the amount is more than 5 parts by mass, the amount of the filler becomes large, and the long extrusion characteristics are 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 making the existence ratio of the carbon black particles having a particle size of 300 nm or more 1% by weight or less. In many cases of impulse destruction, the conductive protrusion becomes the starting point of destruction. When there is a large proportion of large carbon particles having a particle size of 300 nm or more, the aggregate formed by agglomeration of the carbon particles naturally increases. When the cable insulation layer is formed with the crosslinked polyolefin composition according to the present invention, when the aggregate present in the insulation layer becomes large, the aggregate contacts the internal semiconductive layer and the external semiconductive layer adjacent to the insulating layer. Or the probability of proximity increases. This is because such a carbon aggregate in the vicinity of the inner semiconductive layer and the outer semiconductive layer is considered to affect the impulse breakdown of the cable.

Carbon black preferably has a ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method of 0.7 or more and 3.5 or less. Here, the BET method is one of powder surface area measurement methods by a gas phase adsorption method, and is a method for obtaining the total surface area, that is, the specific surface area of a 1 g sample from an adsorption isotherm. Usually, nitrogen gas is often used as the adsorbed gas, and the most frequently used method is to measure the amount of adsorption from the change in pressure or volume of the gas to be adsorbed. The most prominent expression for expressing the isotherm of multimolecular adsorption is the Brunauer, Emmett, and Teller equation, called the BET equation. The BET formula is widely used for determining the surface area. The adsorption amount is obtained 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 the oil absorption amount (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) to be 0.7 or more and 3.5 or less, leakage of space charge can be promoted. Hereinafter, the reason will be described.
The resistivity (specific resistance) of the crosslinked polyethylene composition is ρ (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), It is known that the following relationship holds if the electric field strength applied to the insulator is E (kv / mm).
ρ = ρ ₀ exp− (αT + βE) (1)

  When carbon black is blended, the electric field coefficient β is increased while the temperature coefficient α is decreased, which promotes leakage of space charges in the insulator composition. This is because when the electric field coefficient β increases, the resistivity ρ decreases, and the electric field in the high stress portion (the portion where a strong electric field is applied) is relaxed. Further, when the temperature coefficient α decreases, the maximum electric field Emax that appears on the shielding side when the conductor temperature is high decreases. In this way, the electric field distribution in the insulator composition moves in a uniform direction, and the accumulation of space charge is reduced.

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

On the other hand, when this ratio is larger than 3.5, the degree of aggregation of the particles increases, the apparent particle diameter (of the aggregate) increases, and the mixing with a thermoplastic resin such as polyethylene worsens. In particular, acetylene carbon has a large influence 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 a furnace-based carbon black, is used, the above ratio is in a range of 0.7 to 1.5, and particularly good. This has been confirmed experimentally.

  Further, 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, etc. If these impurities are large, the electrical characteristics deteriorate. Therefore, the higher the purity of carbon, the better.

[Crosslinking aid]
The most characteristic point of the crosslinked polyolefin composition according to the present invention is that at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate is blended as a crosslinking aid. The compounding ratio is 0.02 to 2 parts by mass. If it is less than 0.02 parts by mass, the effect of suppressing a decrease in insulation performance due to high-temperature thermal history cannot be obtained. On the other hand, if it exceeds 2 parts by mass, slip and resin burn will occur in the extruder when the crosslinked polyolefin composition is extruded. When the resin burn occurs, the resin pressure increases during extrusion, and a stable DC power cable cannot be manufactured. In addition, the electrical performance of the DC cable also decreases. A more preferable amount of the crosslinking aid is 0.1 to 2 parts by mass. By mix | blending 0.1 mass part or more, the compounding quantity of an organic-ized oxide crosslinking agent can be reduced and the effect which suppresses the resin burning in an extruder can also be acquired.

[Organic peroxide crosslinking agent]
The organic peroxide crosslinking agent may be any organic peroxide used for ordinary crosslinking. 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 includes a compound having a polar group such as a hydroxyl group, similar to the decomposition residue of DCP. As in the case of using DCP, the above-mentioned problem occurs. However, the present invention can solve this problem.

  The amount of the organic peroxide crosslinking agent is appropriately adjusted depending on the type of organic peroxide and polyolefin used. 0.1-5 mass parts is preferable and 0.5-3 mass parts is more preferable. If the blending amount of the organic peroxide crosslinking agent is too small, crosslinking is insufficient and the 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, when the crosslinked polyolefin composition is extruded, resin burning occurs in the extruder. When the resin burn occurs, the resin pressure increases during extrusion, and a stable DC power cable cannot be manufactured. Moreover, the electrical performance of the DC power cable is also reduced.

〔Antioxidant〕
Moreover, you may mix | blend antioxidant with a crosslinked polyolefin composition as needed. As the antioxidant, a commonly used antioxidant can be appropriately selected and blended. Phenol-based, phosphite-based, and thioether-based anti-aging agents are preferred. In particular, 4,4′-thiobis (3-methyl-6-tert-butylphenol) is preferable because it has an effect of suppressing a crosslinking reaction when extruding a crosslinked polyolefin composition.
The blending amount of the antioxidant is appropriately adjusted in consideration of the kind of the antioxidant to be used and the oxidation resistance, but is preferably 0.1 to 1.0 part 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 produced DC cable 10. As shown in FIG. 1, the DC 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 on the outside of a 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 internal semiconductive layer 12 and the external semiconductive layer 14 are 1 mm, respectively.

(1) Internal semiconductive layer The internal semiconductive layer 12 comprises an ethylene-vinyl acetate copolymer, an organic peroxide crosslinking agent (DCP), carbon black (acetylene black), an antioxidant (4,4′-thiobis ( 3-methyl-6-tert-butylphenol))) and a composition (semiconductive resin composition).
(2) Insulating layer The insulating layer 13 was formed using the crosslinked polyethylene composition according to the present invention. The blending ratio (parts by mass) of polyolefin, carbon black, crosslinking aid, and organic peroxide crosslinking agent is as shown in Tables 1-4.
LDPE (DOC NUC-9026) was used as the polyolefin. Carbon black has a specific surface area of 140 m ² / g measured by the BET method, an oil absorption of 114 cc / 100 g of mineral oil, a carbon content of 97.5% by mass, an average particle size of primary particles of 18 nm, and coarse particles containing 300 nm or more. SAF, which is a furnace carbon black with an amount of 1% or less, was used. The ratio of the oil absorption (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) is 0.8.
Triallyl isocyanurate or trimethallyl isocyanurate was used as a crosslinking aid.
As the organic peroxide crosslinking agent, DCP, t-butylcumyl peroxide, and α, α′-bis (t-butylperoxy-m-isopropyl) benzene were used.
The above materials were kneaded with a Banbury mixer, passed through a metal screen mesh having an opening of 34 μm, and further DCP was mixed with a Henschel mixer to prepare a crosslinked polyethylene composition.
(3) External Semiconductive Layer The external semiconductive layer 14 was formed using a semiconductive resin composition having the same composition as the internal semiconductive layer 12.

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

[Cable connection structure]
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 connecting portion is shown in FIG. As shown in FIG. 2, the cable connecting portion connects the two DC power cables 10 and 10 so that the conductors 11 and 11 face each other at the ends (reference numeral 21 in the figure), and the periphery is connected to the inner half. In this structure, the conductive layer 22, the insulating layer 23, and the external semiconductive layer 24 are sequentially covered.

  The internal semiconductive layer 22 and the insulating layer 23 are formed by sequentially winding the semiconductive tape and the insulating tape on the conductors 11 and 11 which are connected to each other to a predetermined thickness, and then heat-sealing the wound tape. Is done. The outer semiconductive layer 24 is formed using a semiconductive shrinkable tube. The semiconductive tape and the semiconductive shrinkable tube were formed using the same semiconductive resin composition (before crosslinking) as the internal semiconductive layer 12 and the external semiconductive layer 14 of the DC power cable 10. The insulating tape is formed by extruding a cross-linked polyethylene composition having the same composition as that of the insulating layer 13 of the DC power cable 10 (before cross-linking) into a tape having a thickness of 0.1 mm, a width of 20 mm, and a length of 150 m using a single screw extruder. Created by.

[Cable connection method]
Hereinafter, the cable connection method will be described.
First, the terminal portions of the two DC power cables 10 and 10 are stripped 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, and processed into a substantially conical 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, the semiconducting tape was wound around the conductor connection portion 21 and heat-sealed to create the internal semiconducting layer 22.
Next, the insulating tape was wound around the inner semiconductive layer 22, and the outer periphery thereof was covered with a semiconductive shrinkable tube. Further, a semiconductive shrinkable tube was placed thereon and heated to shrink.

Next, the outer periphery of the semiconductive shrinkable tube was covered with a gas barrier layer, and the outer periphery of the gas barrier layer was covered with a heater. Furthermore, a cross-linked tube comprising a two-part mold and packing at both ends was assembled outside the heater. In addition, a bridge | crosslinking pipe | tube used enough long than the distance (range of AC in FIG. 2) between the external semiconductive layers 14 and 14 of the two DC power cables 10 and 10 is used. In this embodiment, the distance between the outer semiconductive layers 14 and 14 is 760 mm, and a bridge having a length of 1150 mm covering A to D in FIG. 2 is used.
Thereafter, the internal pressure in the cross-linking tube was adjusted to 0.8 MPa with nitrogen gas, the temperature was raised with a heater, and the temperature was kept at 220 ° C. for 3 hours, whereby the insulating layer 23 and the external semiconductive layer 24 were formed.

[Evaluation]
(1) The degree of cross-linking of the manufactured power cable was measured in accordance with JISC 3005 4.25, by collecting a test piece from the middle part in the thickness direction of the cable insulator.
(2) The DC breakdown voltage (kV) of the connected DC power cable was measured. With respect to a DC power cable having a total length of 20 m including the cable connection portion, the breakdown voltage was measured by increasing the voltage by a step-up of -20 kV / 10 minutes from the start voltage of -60 kV. The conductor temperature during energization was adjusted to 90 ° C. Note that the DC breakdown voltage of the DC power cable before connection was -320 kV on average.
(3) After the destruction, the connection part was disassembled and the destruction part was specified. In the case of destruction between both end portions 23A and 23A of the insulating layer 23, the destruction portion is A, and in the case of destruction at both end portions 23A and 23A of the insulating layer 23, the destruction portion is B and the end portion 23A of the insulating layer 23 is When it is destroyed between the end portion 14A of the outer semiconductive layer 14, the destruction portion is C. When it is broken between the end portion 14A of the outer semiconductive layer 14 and the end portion of the bridge tube, the destruction portion is designated. D.
The results are shown in Tables 1-4.
(4) In manufacturing the DC power cable, the extrusion resin pressure was measured at a metal screen mesh mesh portion having an opening of 34 μm attached to the tip of the insulating layer extruder screw. Extrusion characteristics were evaluated from the increasing tendency of the resin pressure when 5 hours had passed from the start of extrusion. The criteria for evaluation are as follows. In addition, “x” is shown for the case where slippage occurred in the extruder and stable extrusion could not be performed.
-: Almost no increase in resin pressure is observed.
+: Although an increase in resin pressure is observed, there is no problem in the production of long cables.
++: Increase in resin pressure is observed, but long cable can be manufactured.
++++: Increase in resin pressure is observed, making it difficult to produce long cables.

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; NUC-9026 made by DOW
A: Connection center, B: Upright portion of tape insulation layer, C: Cable external conduction processing 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; NUC-9026 made by DOW
A: Connection center, B: Upright portion of tape insulation layer, C: Cable external conduction processing section, D: Cable reheating section

  When the amount of the crosslinking aid is 0.02 to 2 parts by mass, when triallyl isocyanurate is used as the crosslinking aid (Examples 1 to 6 and 12 to 17), when trimethallyl isocyanurate is used. The DC breakdown voltages of Examples 7 to 11 were −320 to −260 kV, and all exhibited excellent DC electrical characteristics. The destruction site was the range of the insulating layer 23 of the A part or B part, that is, the connection part.

  On the other hand, when the blending amount of the crosslinking aid was 0.01 parts by mass (Comparative Examples 1, 5, 8 and 10), the DC breakdown voltage was 200 or less in absolute value, and the DC electrical characteristics were poor. The destruction site was the D portion outside the end portion 14A of the outer semiconductive layer 14. The reason why the breakage occurred in such a part is that the DC electrical characteristics of the insulating layer 13 of the DC power cable were deteriorated by the heat treatment for crosslinking the crosslinked polyethylene composition that becomes the insulating layer 23 of the connecting portion.

  The amount of the crosslinking agent in Example 4 and Comparative Example 1, Example 10 and Comparative Example 5, Example 13 and Comparative Example 8, Example 16 and Comparative Example 10 are the same. However, even when the heat treatment for crosslinking the crosslinked polyethylene composition that becomes the insulating layer 23 of the connection portion is performed, the direct current electric current in Examples 4, 10, 13, and 16 is higher than that in Comparative Examples 1, 5, 8, and 10. The deterioration of characteristics is small. From this result, it can be seen that when 0.02 parts by mass or more of triallyl isocyanurate or trimethallyl isocyanurate is blended, the effect of preventing the direct current electric characteristics from being deteriorated during reheating becomes remarkable.

  When the blending amount of triallyl isocyanurate or the like is 2.5 parts by mass (Comparative Examples 2, 6, Comparative Example 9, and Comparative Example 11), since a slip occurred during extrusion, a DC power cable can be manufactured. There wasn't.

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

  Comparative Example 7 is an example in which m-phenylene bismaleimide was blended as a crosslinking aid. In Comparative Example 7, the cable D is broken at −160 kV. This destruction occurred because the DC electrical characteristics of the insulating layer 13 of the DC power cable were deteriorated by the heat treatment for crosslinking the crosslinked polyethylene composition that becomes the insulating layer 23 of the connection portion. From this result, it can be seen that m-phenylene bismaleimide does not have an effect such as triallyl isocyanurate or trimethallyl isocyanurate.

  As described above, by using the crosslinked polyethylene composition according to the present invention, it is possible to obtain a DC power cable with little deterioration in electrical characteristics even when it receives a thermal history. Moreover, this DC power cable can be used for higher voltage DC power transportation.

  In the above embodiment, as the [cable connection method], the method of winding the insulating tape and heating and crosslinking it to form the insulating layer is explained. However, the connection method used in the method for manufacturing a DC power line of the present invention is as follows. Any other method can be adopted as long as the connection portion is covered with an insulating material and heat-treated. For example, in the method for manufacturing a DC power line according to the present invention, a so-called extrusion molding method (EMJ) in which an insulating material is extruded using an extruder and is thermally crosslinked to form an insulating layer may be employed as a connection method. it can. In addition, the insulating material used for connecting the cables 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. 2010-016111 filed on Jan. 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 invention is limited only by the following claims.

10 DC power cable 11 Conductors 12, 22 Internal semiconductive layers 13, 23 Insulating layers 14, 24 External semiconductive layer 14A End 21 Conductor connection 23A Both ends

Claims (3)

A crosslinked polyolefin composition comprising an organic peroxide crosslinking agent blended with a polyolefin,
Furthermore,
(1) For 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 A crosslinked polyolefin composition.   A DC power cable, wherein an insulating layer is formed from the crosslinked polyolefin composition according to claim 1.   A method for manufacturing a DC power line, wherein an insulating layer is formed by covering a portion to which the DC power cable according to claim 2 is connected with an insulating material and performing heat treatment.

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