JP5697037B2 - DC power cable and method for manufacturing DC power line - Google Patents

Description

  The present invention relates to a DC power cable (hereinafter referred to as “DC power cable”) in which an insulating layer is formed of a crosslinked polyolefin composition, and a method for manufacturing a DC power line 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 examples in which the XLPE cable is applied to a DC power cable for high voltage. As a high voltage DC power cable of 22 kV 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, decomposition residues (acetophenone, cumyl alcohol, etc.) of dicumyl peroxide (DCP) are space charges when DC high voltage is applied. This is because the direct current characteristics are significantly reduced. Dicumyl peroxide (DCP) is a cross-linking agent that is commonly 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 suppressing the following and mixing the arylaryl isocyanurate and the diene polymer.

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-based composition containing carbon black described in Patent Document 1. 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 molding and joining the connection and termination of XLPE cables, when semi-conductive layer or insulation layer (hereinafter referred to as “reinforced insulation layer”) covering the connection or termination of the cable is heat-molded In addition, a high-temperature thermal history as described above is added in the vicinity thereof. 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.

  The subject of this invention is improving the insulation material for DC power cables disclosed by the said patent document 1, and implement | achieving the XLPE type DC power cable which can suppress the fall of the DC electrical characteristic by a heat history. That is, an XLPE DC power cable that can be used for higher voltage power transportation and a method for manufacturing a DC power line using the DC power cable are provided.

In order to solve the above problems, in the DC power cable according to the present invention, an insulating layer is formed with a crosslinked polyolefin composition in which an organic peroxide crosslinking agent is blended with polyolefin,
As the crosslinked polyolefin composition,
(1) For 100 parts by mass of polyolefin,
(2) 0.1 to 5 parts by mass of carbon black, and (3) 0.02 to 1.25 parts by mass of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate , and carbon black less than one quarter at a weight ratio of the amount, and so as use those formulated.
Furthermore, the carbon black includes
(A) The ratio of the oil absorption amount (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less,
(B) a carbon content of 97% by weight or more,
(C) A carbon black particle having a particle size of not less than 300 nm and having a characteristic of 1 wt% or less is used.

  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 power transportation can be provided. Moreover, the manufacturing method of the DC power line using this DC power cable is provided.
In addition, according to the present invention, the storage characteristics of the cross-linked polyolefin composition used to form the insulating layer can be improved, so that there is an advantage that the productivity of the DC power cable can be improved.

It is sectional drawing of a DC power cable. 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 DC power cable according to the present invention is a DC power cable in which an insulating layer is formed from a crosslinked polyolefin composition in which an organic peroxide crosslinking agent is blended with polyolefin.
In particular, the crosslinked polyolefin composition forming the insulating layer includes (1) 100 parts by mass of polyolefin, (2) 0.1 to 5 parts by mass of carbon black, and (3) triallyl isocyanurate or trimethallyl. A compound in which 0.02 to 1.25 parts by mass of at least one compound selected from isocyanurate is blended so that the mass ratio of the compounded amount of carbon black is ¼ or less is used. Further, as carbon black, (a) the ratio of the oil absorption amount (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less, (b) carbon content A carbon black particle having a ratio of 97% by weight or more and (c) a particle size of 300 nm or more is used in an amount of 1% by weight or less.
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 polyolefins include, for example, 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 coalescence or a mixture of two or more of these 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 compounding quantity of carbon black is 0.1-5 mass parts. 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 degraded. 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. From the viewpoint of long extrusion characteristics, the amount of carbon black is more preferably 2 parts by mass or less. This is because the greater the amount of carbon blended, the easier the resin pressure rises during extrusion.
Moreover, although the characteristic calculated | required by the carbon black to mix | blend is described below, these are the same as the characteristic prescribed | regulated in "patent 3602297 gazette (patent document 1)".

  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 amount (cc / 100 g) of mineral oil to a 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 , and H ₂ , and 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 used in the present invention is that a predetermined amount of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate is blended as a crosslinking aid. That is, the compounding quantity of a crosslinking adjuvant is 0.02-1.25 mass part with respect to 100 mass parts of polyolefin. And it is 1/4 or less by mass ratio with respect to carbon black compounding quantity.
When the blending ratio of the crosslinking aid is less than 0.02 parts by mass, the effect of suppressing the deterioration of the insulation performance due to the high temperature thermal history cannot be obtained.
In addition, the crosslinked polyolefin composition is stored in a state of being processed into pellets. However, if the amount of the crosslinking aid exceeds 1.25 parts by mass, the crosslinking aid is precipitated during storage of the pellet, and the pellet A phenomenon called blocking occurs in which the two adhere to each other. When blocking occurs, pellet feeding and feeding to an extruder are hindered, and a DC power cable cannot be manufactured normally.
By the way, in the development of the present invention, in the system where carbon black coexists, the inventor determined that the precipitation behavior of the crosslinking aid is not determined only by the blending amount of the crosslinking aid. We noticed that it affects the precipitation behavior. That is, in order to obtain a practical cross-linked polyolefin composition, it is also important to appropriately combine the cross-linking aid and carbon black from the viewpoint of long-term storage characteristics.
Specifically, even if the amount of the crosslinking aid is 1.25 parts by mass or less, when a crosslinking aid exceeding 1/4 in the mass ratio of the carbon black is mixed, The auxiliary agent precipitates and causes blocking. Therefore, the blending amount of the crosslinking aid must be less than or equal to ¼ of the blending amount of carbon black by mass ratio.
In addition, the more preferable compounding quantity of a crosslinking adjuvant is 0.1-0.5 mass part. 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. Further, from the viewpoint of the above-described long extrusion characteristics, it is desirable that the amount of carbon black is 2.0 parts by mass or less, so the amount of the crosslinking aid is 1/4 or less, that is, 0.5 parts by mass. It is more preferable to make it below.

[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 it becomes impossible to manufacture a stable DC power cable, and the electrical performance of the DC power cable is also lowered.

[Antioxidant]
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 scorch 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 part by mass. In addition, additives such as processing aids can be blended if necessary, but additives that impair the electrical performance of high voltage DC power cables such as hydrated metal oxide fillers. I can't.

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

[Power cable]
FIG. 1 is a cross-sectional view of a DC power cable 10 that has been created. 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 is composed of 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 1-3.
LDPE (DOC NUC-9026) was used as the polyolefin.
As the carbon black, “Vulcan9A32” manufactured by Cabot and “Asahi # 50HG” manufactured by Asahi Carbon Co., Ltd. were used.
Vulcan9A32 is a furnace-based carbon black, SAF, having a specific surface area of 140 m ² / g, a mineral oil absorption of 114 cc / 100 g, a carbon content of 97.5% by mass, an average of primary particles, as measured by the BET method. The particle size is 18 nm and the content of coarse particles having a particle size of 300 nm or more is 1% or less. The ratio of the oil absorption amount (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) is 0.8.
Asahi # 50HG has an average primary particle size of 85 nm and a ratio of the oil absorption (cc / 100 g) of mineral oil to the specific surface area (m ² / g) is 5.3.
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 reinforcing insulating layer 23, and the external semiconductive layer 24 are sequentially covered.

  The inner semiconductive layer 22 and the reinforcing insulating layer 23 are formed by winding a semiconductive tape and an insulating tape sequentially on the conductors 11 and 11 that are connected to each other to a predetermined thickness, and then heat-sealing the wound tape. It is formed. 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. It was produced by doing.

[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 and 11 of the two DC power cables 10 and 10 were put together and connected to form a conductor connection portion 21. Next, the semiconductive tape was wound around the conductor connection portion 21 and heat-sealed to produce the internal semiconductive 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 | bridging pipe | tube uses what is sufficiently longer than the distance (the range of AC in FIG. 2) between the external semiconductive layers 14 and 14 of the two DC power cables 10 and 10. FIG. In this example, the distance between the outer semiconductive layers 14 and 14 was 760 mm, and a bridge 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 set to 0.8 MPa with nitrogen gas, the temperature was raised with a heater, and the temperature was maintained at 220 ° C. for 3 hours, whereby the reinforcing insulating layer 23 and the external semiconductive layer 24 were formed.

[Evaluation]
(1) The degree of cross-linking of the manufactured DC power cable was measured in accordance with JIS C 3005 4.25, by taking a test piece from the middle part in the thickness direction of the cable insulator.
(2) The manufactured DC power cable was divided into two parts, one of which was a DC power cable having a total length of 20 m, and the DC breakdown voltage (kV) was measured as it was, and the DC breakdown voltage before connection was evaluated. The other DC power cable is further divided into two parts, and the divided part is subjected to connection processing, and the DC breakdown voltage (kV) is measured with a DC power cable having a total length of 20 m including the connection part. The voltage was evaluated. The DC breakdown voltage was measured by increasing the voltage in a step-up of -20 kV / 10 minutes from a start voltage of -60 kV for a DC power cable having a total length of 20 m. The conductor temperature during energization was adjusted to 90 ° C.
(3) After the destruction, the connection part was disassembled and the destruction part was specified. When breaking between both end portions 23A, 23A of the reinforcing insulating layer 23, the breaking portion is A, when breaking at both end portions 23A, 23A of the reinforcing insulating layer 23, the breaking portion is B, and the end portion 23A of the reinforcing insulating layer 23 And the end portion 14A of the outer semiconductive layer 14 are broken by C, and when the breakage is made between the end portion 14A of the outer semiconductive layer 14 and the end of the bridge tube, the broken portion is D. It was.
(4) The pellets of the produced crosslinked polyethylene composition were pressed at 120 ° C. for 2 minutes, then 10 MPa was applied and held for 10 minutes, and pressed into a 4 mm thick sheet (150 mm × 200 mm). did. This molded sheet was measured for torque for 8 hours at the test temperature of 140 ° C using an oscillating disc rheometer ASTM-100TYPE manufactured by Toyo Seiki Seisakusho Co., Ltd. The difference between the maximum torque value and the minimum torque value within the measurement time The time required to increase the 10% torque was determined. It can be determined that the longer this time, the less likely the composition is to scorch.
(5) About 500 kg of pellets of the produced crosslinked polyethylene composition are stored in a metal container containing 1.1 ton, and a heat cycle in which the surface temperature of the container is “10 ° C. × 12 hours” + “50 ° C. × 12 hours” is 3 After adding for a month, the extraction opening at the bottom of the metal container was opened and the pellets were extracted by falling under its own weight. The environmental temperature at the time of extraction was kept constant at 10 ° C. When all the pellets could be discharged, it was judged as “good”, and when the pellets were clogged in the middle and all the pellets could not be discharged, it was judged as “poor”.
(6) In producing 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 insulating layer extruder screw tip. 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.
-; Almost no increase in resin pressure is observed.
+: Although an increase in resin pressure is observed, there is no problem in producing a long cable.
++: 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.

  The evaluation results of (1) to (6) are shown in Tables 1 to 3.

  When the amount of the crosslinking aid is 0.02 to 1.25 parts by mass, when triallyl isocyanurate is used as the crosslinking aid (Examples 1 to 6 and 10 to 15), trimethallyl isocyanurate is used. (Examples 7 to 9) had a DC breakdown voltage of -320 to -260 kV, and all exhibited excellent DC electrical properties. The fracture site was the range of the reinforcing 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, 8, 11 and 13), 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 reinforcing insulating layer 23 of the connecting portion. .

  The amount of the crosslinking agent in Example 3 and Comparative Example 1, Example 9 and Comparative Example 8, Example 11 and Comparative Example 11, Example 14 and Comparative Example 13 are the same. However, even when the heat treatment for crosslinking the crosslinked polyethylene composition that becomes the reinforcing insulating layer 23 of the connection portion is performed, the direct current in Examples 3, 9, 11, and 14 is higher than that in Comparative Examples 1, 8, 11, and 13. Small decrease in electrical characteristics. 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.

  Comparative Examples 5, 7, 12, and 14 in which triallyl isocyanurate and the like are blended in excess of 1.25 parts by mass, and even if the blending amount of triallyl isocyanurate and the like is 1.25 parts by mass or less, carbon In Comparative Examples 2, 4, and 6 in which the mass ratio with respect to the black blending amount is ¼ or more, blocking occurs during the storage period, and all the pellets cannot be taken out, which indicates that the storage characteristics are poor.

In Comparative Example 2 and Comparative Example 3 in which the amount of furnace-based carbon black SAF is small, the DC breakdown voltage before connection is low, and the DC electrical characteristics are not sufficient.
Further, in Comparative Example 10 in which Asahi # 50HG is blended as carbon black, the DC breakdown voltage before connection is low and the DC electrical characteristics are sufficient even though the configuration excluding the type of carbon black is the same as in Example 7. is not. This is because Asahi # 50HG is a carbon black having a large ratio of the oil absorption amount (cc / 100 g) of mineral oil to the specific surface area (m ² / g) (5.3).

  Comparative Example 9 is an example in which m-phenylene bismaleimide is blended as a crosslinking aid. In Comparative Example 9, 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 deteriorated due to the heat treatment for crosslinking the crosslinked polyethylene composition that becomes the reinforcing 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, the DC power cable using the cross-linked polyethylene composition according to the present invention is less deteriorated in electrical characteristics even when subjected to a thermal history, and 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 has been described. 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.

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

Claims (2)

A DC power cable in which an insulating layer is formed of a crosslinked polyolefin composition in which an organic peroxide crosslinking agent is blended with polyolefin,
The crosslinked polyolefin composition;
(1) For 100 parts by mass of polyolefin,
(2) 0.1 to 5 parts by mass of carbon black, and (3) 0.02 to 1.25 parts by mass of at least one compound selected from triallyl isocyanurate or trimethallyl isocyanurate , and carbon black Formulated so that the mass ratio of the blended amount is 1/4 or less ,
Furthermore, as the carbon black,
(A) The ratio of the oil absorption amount (cc / 100 g) of the mineral oil to the specific surface area (m ² / g) measured by the BET method is 0.7 or more and 3.5 or less,
(B) a carbon content of 97% by weight or more,
(C) A DC power cable characterized by using a carbon black particle having a particle diameter of 300 nm or more and having a characteristic that the proportion of carbon black particles present is 1% by weight or less.   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 1 is connected with an insulating material and performing heat treatment.

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