WO2018236013A1 - DC power cable - Google Patents

Abstract

The present invention relates to a DC power cable. Specifically, the present invention can simultaneously prevent reduction of direct current dielectric strength and deterioration of impulse breakdown strength due to space charge accumulation, reduction of the extrudability of an insulating layer and the like, and reduction of manufacturing cost DC power cable.

Description

 【Specification】

 Title of the Invention

 DC power cable

TECHNICAL FIELD

 The present invention relates to DC power: cables. Specifically. Disclosed are a direct current (DC) capacitor capable of simultaneously preventing a decrease in direct current insulation resistance due to space charge accumulation and a reduction in impulse breakdown strength, Power cable.

 BACKGROUND ART [0002]

 Reduced power losses in large power systems where large capacity and long distance transmission are generally required. From the point of view of construction paper problem and increase of transmission capacity, it is essential that high-pressure transmission is carried out to increase transmission voltage.

 The power transmission system can be divided into AC transmission system and DC transmission system, and DC transmission system refers to the transmission of electric energy to DC. Specifically, in the DC transmission method, first, the AC power of the transmission side is changed to an appropriate voltage, converted into a DC by a net converting device, and then sent to a power receiving side through a transmission line. On the power receiving side, DC power is converted back to AC power by an inverse converter.

Especially. The DC transmission method is advantageous for long-distance transportation of a large amount of electric power and is capable of interconnection of an asynchronous electric power system, and is widely used because it has less power loss and stability than DC in long-distance transmission It is true. However, there is a problem that the insulation characteristic of the insulator is remarkably lowered when the temperature of the cable transducer rises or when the negative polarity or the polarity reversal occurs when the transmission is progressed using the high voltage DC transmission cable , Which is known to be due to the accumulation of long-life space charge without trapping or discharging a single charge in the insulator.

 The space charge described above can distort the electric field within the high-voltage DC transmission cable insulator and cause dielectric breakdown at a voltage lower than the initially designed breakdown voltage.

 In order to solve the problem of the direct current dielectric strength and the lowering of the breakdown voltage of the cable due to the accumulation of the space charge, aluminum silicate is added to the insulating base resin constituting the insulating layer of the cable. A technique of adding inorganic particles such as calcium silicate, calcium carbonate, and magnesium oxide has been used.

 However, the above-mentioned space charge accumulation is inevitably generated by the crosslinking of the charge injected into the insulating layer from the conductor of the cable, the crosslinking by-product which is inevitably generated by the crosslinking of the insulating layer, and the semiconductive layer in contact with the insulating layer A crosslinking byproduct carried into the insulating layer, a polar monomer contained in the base resin forming the semiconductive layer and transferred into the insulating layer, and the like. Therefore, simply by adding the inorganic particles to the insulating layer The space charge accumulation and thus the problem of the direct current dielectric strength and the destruction voltage can not be sufficiently solved.

In order to solve the above problem, when the content of the inorganic particles added to the insulating layer is increased, the inorganic particles act as impurities to reduce the extrudability of the insulating layer. In addition, IMPORTANT FEATURES There is a problem of lowering the degree. Due to such a problem, the thickness of the insulation layer in the DC power cable is determined by the impulse strength rather than the breakdown voltage of the cable, which increases the outer diameter of the cable, which is a problem in terms of manufacturing and economics. In addition, the thickness of the insulation layer of the DC power cable is determined by the bridging breakdown voltage and the impulsive strength of the cable, which increases the outer diameter of the cable, which is a problem in terms of manufacturing and economics.

 Therefore, it is possible to simultaneously prevent a decrease in the DC insulation strength due to space charge accumulation and a decrease in the impulse breakdown strength, and the DC power Cables are in desperate need.

 DETAILED DESCRIPTION OF THE INVENTION

 [Technical Problem]

 It is an object of the present invention to provide a direct current power cable capable of simultaneously preventing a decrease in direct current dielectric strength due to space charge accumulation and a decrease in impulse breakdown strength.

 Further, the present invention aims to provide a DC power cable capable of reducing the manufacturing cost without deteriorating the extrudability of the flaky layer or the like.

 [Technical Solution]

 In order to solve the above problems,

A direct current power cable comprising: a conductor; An inner semiconductive layer surrounding the conductor; An insulating layer surrounding the inner semiconductive layer; An outer semiconductive layer surrounding the insulating layer; And the outer half Wherein the inner semiconductive layer or the outer semiconductive layer is formed from a semiconductive composition comprising a copolymer resin of an olefin and a polar monomer as a base resin and conductive particles dispersed in the resin, Based on the total weight of the copolymer resin, is 18% or less by weight based on the total weight of the copolymer resin, and the insulating layer is composed of a poly resin as a base resin and a resin selected from the group consisting of aluminosilicate, calcium silicate, calcium carbonate, magnesium oxide, carbon Nanotubes and graphite, wherein the content of the non-dopant is 0: 01 to 10 parts by weight based on 100 parts by weight of the base resin of the insulating layer (F ield Enhancement Factor: E \) of the insulating layer defined by the following equation (2) 7 < / RTI > to 140%.

 &Quot; (2) "

 FEF = (maximum applied electric field in specimen / electric field applied to specimen) * 100

 In Equation (2)

 The sample is an insulating film formed from an insulating composition having a thickness of 120 and forming the insulating layer, and a semi-conductive film formed from the semi-conductive composition, each of which is bonded to the upper and lower surfaces of the insulating film, Including the specimen,

 The electric field applied to the specimen was a 50 kV / ivil direct electric field applied to the insulating film for 1 hour,

The electric field which is maximally increased in the specimen is applied to the insulation film by a DC electric field Is the maximum value among the electric field values increased for one hour.

 Here, the insulating composition or the semi-conductive composition further comprises a crosslinking agent. Wherein the content of the crosslinking agent is 0.1 to 5 parts by weight based on 100 parts by weight of the base resin.

 Also. Wherein the polar monomer comprises an acrylate monomer.

 And wherein the inorganic filler comprises an oxide magnet.

 Further, the inorganic filler is surface-modified with at least one surface modifier selected from the group consisting of vinylsilane, stearic acid, oleic acid, and aminopolysiloxane.

 On the other hand, the copolymer resin can be selected from the group consisting of ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene methyl methacrylate (EMMA), ethylene ethyl acrylate (EEA), ethylene ethyl methacrylate (EE A) (1) selected from the group consisting of ethylene (iso) propyl acrylate (EPA), ethylene (iso) propyl methacrylate (EPA), ethylene butyl acrylate (EBA) and ethylene butyl methacrylate

I

And more than two types of cables are provided.

 Here, the content of the conductive particles is 35 to 70 parts by weight based on the weight of the base resin 100.

On the other hand, the cross-linking agent is a peroxide-based cross-linking agent. Herein, the peroxide-based crosslinking agent may be at least one selected from the group consisting of dicumyl peroxide, benzoyl peroxide, lauryl peroxide, _t -butyl cumyl peroxide, di ( _t -butylperoxyisopropyl) benzene, 2,5-dimethyl- (? -Butylperoxy) nucleic acid and di-t-butyl peroxide. The present invention relates to a direct current power cable,

 The present invention also provides a direct current power cable, wherein the polyolefin resin as the base resin of the insulating layer comprises a polyarylene resin.

 On the other hand, the insulating composition can be prepared by reacting 2,4-diphenyl-4-methyl-1-pentene, 1,4-hydroquinone, And a hydroquinone derivative, wherein the content of the scorch retarder is 0.1 to 1.0 part by weight based on 100 parts by weight of the base resin .

 here. Characterized in that the scorch retarder comprises 2,4-diphenyl-4-methyl-1-pentene.

 【Effects of the Invention】

 The direct current power cable according to the present invention precisely controls the base resin and the degree of crosslinking of the semiconductive layer and also adds a precisely controlled amount of inorganic particles to the inside of the insulating layer, And the deterioration of the impulsive fracture strength can be prevented in the verb.

Further, the present invention reduces the amount of inorganic particles contained in the after-treatment layer to suppress the accumulation of space charge, thereby suppressing the deterioration of the extrudability of the insulating layer or the like caused by the inorganic particles And further, it is possible to suppress the increase in the thickness of the insulating layer and to reduce the manufacturing cost of the cable.

 BRIEF DESCRIPTION OF THE DRAWINGS

 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically illustrates a cross-sectional structure of an embodiment of a power cable according to the present invention.

 2 schematically shows a cross-sectional structure of another embodiment of a power cable according to the present invention.

 FIG. 3 is a graph showing the volume resistivity of the insulating specimen according to the temperature in the embodiment. FIG.

 Fig. 4 shows FT-IR evaluation results for an insulation + semi-conductive sample in the embodiment.

 Figure 5 shows the PEA evaluation results for an insulating + semi-conducting sample in the example.

 Mode for carrying out the invention J

 Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are being presented so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Like reference numerals throughout the specification denote like elements.

1 is a schematic cross-sectional view of an embodiment of a DC power cable according to the present invention; As shown in Fig. 1, a DC power cable 100 according to the present invention includes an inner semiconductive layer 12 surrounding a conductor 10, a conductor 10 surrounding the inner semiconductive layer 12, A shield layer 18 covering the outer semiconductive layer 16 and covering the outer semiconductive layer 16 and made of metal sheath or neutral wire to provide an electrical shielding and short circuit current return path, A cover 20 surrounding the layer 18, and the like.

 FIG. 2 is a schematic cross-sectional view of a DC power cable according to another embodiment of the present invention, schematically showing a cross-sectional structure of a submarine cable.

 2, the DC power cable 200 according to the present invention includes the conductor 10, the inner semiconductive layer 12, the insulating layer 14, and the outer semiconductive layer 16, Since it is similar to the actual example, repetitive I description is omitted.

 A metal sheath made of lead is used to prevent the insulation performance of the insulation layer 14 from being deteriorated if foreign substances such as external water enter the outer semiconductive layer 16. Called i 'soft serve' (30).

 Furthermore, a sheath 32 made of a resin such as polyethylene or the like is provided on the outside of the soft tissue 30, and a bed layer 34 is provided so as not to be in direct contact with water. A wire sheath 40 may be provided on the bedding layer 34. The wire sheath 40 is provided on the outer side of the cable so as to enhance the mechanical strength to protect the cable from the external environment of the seabed.

At the outer periphery of the wire sheathing 40, that is, at the outer periphery of the cable, (42). The jacket 42 is provided on the outer side of the cable to protect the inner structure of the cable 200. In particular, in the case of a submarine cable, the core 42 has excellent weather resistance and mechanical strength that can withstand undersea environments such as seawater. For example, the jacket 42 may be made of polypropylene yarn or the like.

 The center conductor 10 may be formed of a single wire made of copper, aluminum, preferably copper, or a twisted wire associated with a plurality of wires, and the diameter of the center conductor 10, the diameter of the wire constituting the twisted wire, Can be different depending on the transmission voltage, the use, etc. of the DC power cable including the DC power cable, and can be suitably selected by a person skilled in the art. E.g. In the case where the DC power cable according to the present invention is used in applications such as seabed cable which requires installation flexibility and flexibility, the center conductor 10 is preferably formed by twisted wire having excellent flexibility rather than disconnection.

The inner semiconductive layer 12 is disposed between the center conductor 10 and the insulating layer 14 to remove the air layer inducing interlayer delamination between the center conductor 10 and the insulating layer 14 , Mitigate local electric field concentration, and so on. On the other hand, the outer semiconductive layer 16 functions to uniformly apply an electric field to the insulating layer 14, to localize local field concentration, and to protect the cable insulation layer from the outside. Normal. The inner semiconductive layer 12 and the outer semiconductive layer 16 are formed by dispersing conductive particles such as carbon black, carbon nanotubes, carbon nanoplate, and graphite in a base resin and further adding a crosslinking agent, an antioxidant, Is formed by the extrusion of the added semi-conductive composition. Here, the base resin uses a series of olefin resins similar to the base resin of the insulating composition forming the insulating layer 14 for adhesion between the semiconductive layers 12 and 16 and the insulating layer 14 Olefin and a polar monomer such as ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), and the like are more preferably used in consideration of compatibility with the conductive particles. (EMMA), ethylene ethyl acrylate (EEA), ethylene ethyl methacrylate (EEMA), ethylen (iso) propyl acrylate (EPA), ethylene (iso) propyl methacrylate ), Ethylene butyl acrylate (EBA), ethylene butyl methacrylate (EBMA), or the like is preferably used.

 The cross-linking agent may be a silane-based cross-linking agent or dicumylperoxide benzoyl peroxide, lauryl peroxide, t-butyl cumyl peroxide, di ( butylperoxy) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) nucleic acid, di-t-butyl peroxide and the like.

As a base resin contained in the semi-conductive composition forming the inner semiconductive layer 12 and the outer semiconductive layer 16, a copolymer resin of an olefin and a polar monomer and / or a polar monomer is contained in the semiconductive layer 12 The charge accumulation of space in the permeable layer 14 is further increased by moving to the inside of the insulating layer 14 through the interface of the layer 14 and the crosslinked byproducts 12, Is transferred into the insulating layer 14 through the interface between the semiconductive layer 12 and the insulating layer 14 so as to accumulate heterocharges in the insulating layer 14, By abstaining The dielectric breakdown voltage of the insulating layer 14 may be lowered. Specifically, in the direct current power cable according to the present invention, the semiconductive composition for forming the semiconductive layer 12 has a content of the notarization resin of the olefin and the polar monomer of about 60 to 70 wt. , The content of the polar monomer may be controlled to 1 to 18% by weight, preferably 1 to 12% by weight, based on the total weight of the copolymer resin.

 When the content of the polar monomer is greater than 18% by weight, the space charge accumulation of the insulating layer 14 is significantly accelerated. On the other hand, when the content of the polar monomer is less than 1% by weight, The extrudability of the semiconductive layers 12 and 16 is lowered and the semiconducting properties may not be realized.

 In the DC power cable according to the present invention, the semi-conductive composition for forming the semiconductive layer 12 may contain 0.1 to 5 parts by weight, preferably 0.1 to 1.5 parts by weight, based on 100 parts by weight of the base resin, Can be precisely controlled.

If the content of the crosslinking agent is more than 5 parts by weight, the content of the crosslinking by-products which are essential in the crosslinking of the base resin contained in the semi-conductive composition is excessive, and the crosslinking by- A problem that the dielectric breakdown voltage of the insulating layer 14 is lowered by increasing the distortion of the electric field by moving into the insulating layer 14 through the interface between the insulating layers 14 and accumulating heterocharges Whereas if it is less than 0.1 part by weight, the mechanical properties and heat resistance of the semiconductive layers 12 and 16 may be insufficient due to the non-crosslinked degree of crosslinking. In the direct current power cable according to the present invention, the semi-conductive composition for forming the inner and outer semi-conductive layers (12, 14) contains 35 to 70 parts by weight of conductive particles such as carbon black based on 100 parts by weight of the base resin . When the content of the conductive particles is less than 35 parts by weight, the layered semiconducting property can not be realized. On the other hand, when the amount of the conductive particles exceeds 70 parts by weight, the extrudability of the inner and outer semiconductive layers 12 and 14 is lowered, There is a problem that the productivity of the cable is deteriorated.

The insulating layer 14 is made of polyethylene, for example, as a base resin _. . A polyolefin resin such as polypropylene, and may be formed by extrusion of an insulating composition preferably comprising a polyethylene resin and inorganic particles.

 The polyethylene resin may be an ultra low density polyethylene (ULDPE), a low density polyethylene (LDPE), a linear low density polyethylene (LLDPE), a medium density polyethylene (MDPE), a high density polyethylene (HDPE), or a combination thereof. The polyethylene resin may be a single polymer, a random or block copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-pentene, 1-nuchene or 1-octene, or a combination thereof have.

 The inorganic particles include nano-sized aluminum silicate, calcium silicate, calcium carbonate, magnesium oxide. Carbon nanotubes, graphite, or the like can be used. However, in view of the impulse strength of the insulating layer 14, magnesium oxide is preferable as the inorganic particles. The oxidized magenet can be obtained from natural ore but can also be prepared from phosphorus synthetic materials using magnesium salt in seawater, and it is also possible to supply the material with high purity and stable quality and physical properties.

The magnesium oxide has a crystal structure of a face-centered cubic structure, Depending on the method, it can have various forms, purity, crystallinity, physical properties and the like. Specifically, the magnesium oxide is divided into cubic, terrace, rod, porous, and spherical calc, and can be variously used depending on their specific physical properties. By forming a potential well at the boundary between the base resin and the inorganic particles, the charge transfer and the accumulation of space charge can be suppressed.

 In addition, the nanocarbon particles and carbon nanotubes including the graphite may have various shapes, and space charges generated in the ultra-high voltage DC transmission cable can be removed while maintaining insulation performance, and high voltage direct current It is possible to minimize the drop in the insulation voltage which causes insulation breakdown at a voltage lower than the breakdown voltage initially designed for the transmission cable insulation. Particularly, the partially carbonized graphene nanofibers are not electrically connected to each other by the remaining PAN structure, so that they are insulated. However, since some graphite structure sufficiently polarizes by an external electric field, space charge is removed It can serve as a trap site.

 Such inorganic particles including magnesium oxide exhibit an effect of suppressing charge transfer and space charge accumulation by forming a potential well (potent alloy) at the interface between the base resin and the inorganic particles when an electric field is applied to the cable.

The dielectric constant of the inorganic particles is generally larger than that of the base resin. For example, the dielectric constant of magnesium oxide as the inorganic nanoparticles is about 10, while the dielectric constant of low density polyethylene (LDPE) as the base resin is about 2.2 to 2.3. therefore. And the inorganic nanoparticles are added to the base resin. The dielectric constant of the base resin should be higher than that of the base resin.

 However, when the size of the inorganic particles is nano-scale, for example, 1 nm to 100 nm, preferably 1 nm to 100 nm, the dielectric constant of the insulating composition may be lower than that of the base It is experimentally confirmed that the phenomenon of reducing the dielectric constant of the resin occurs and the impulse breakdown voltage is also increased.

 When the size of the inorganic particles is nanoscale, the reason why the dielectric constant of the insulating composition is lower than the dielectric constant of the base resin is unknown, but is predicted as a result of the so-called nanoffect, It is predicted that the size of the inorganic particles is controlled by the nanoscale, thereby stabilizing the interface inside the base resin.

 That is, since the size of the inorganic particles is controlled to be nanoscale, the dielectric constant of the insulating composition containing the inorganic particles is reduced, and the impurity breakdown voltage of the insulating layer formed from the insulating composition is too small, An effect of prolonging the life span may be caused.

 Accordingly, the dielectric constant of the insulating composition according to the present invention may be 1% or more, preferably 2% or more, and more preferably 5% or more, of the dielectric constant reduction rate (%) defined by the following equation (1).

 [Equation 1]

 (%) = [(A-b) / a] * 100

In the above equation (1) a is the permittivity of the base resin,

 and b is the dielectric constant of the precursor composition.

 The inorganic nanoparticles may have a shape such as a terrace, a cubic, a rod, an edge-less, and the like. In view of the interface stability within the base resin, A cubic shape is preferable.

Preferably, the inorganic particles including the oxidized magnet are surface-modified with vinylsilane, stearic acid, oleic acid, aminopolysiloxane, and the like. In general, inorganic particles such as magnesium oxide are hydrophilic with high surface energy, while base resins such as polyethylene are hydrophobic with low surface energy, so that inorganic particles of magnesium oxide are dispersed in a base resin such as polyethylene The dispersibility is not good. Electrical properties can also be detrimental. Thus, the ^it to surface modification of inorganic particles such as wet oxidation magnesite is preferred to solve this problem.

If no surface modification of inorganic particles such as a magnesium oxide, inorganic particles and poly Sikkim between the base resin of ethylene round (gap) blossomed degrade the mechanical properties, as well as the dielectric _breakdown? The electrical insulation properties such as strength may be lowered. On the other hand, since inorganic particles such as magnesium oxide are surface-modified with vinylsilane or the like, they show better dispersibility with respect to base resins such as polyethylene and exhibit improved electrical properties. A hydrolyzate such as vinylsilane is chemically bonded to the surface of magnesium oxide or the like by the condensation reaction to form a surface-modified inorganic particle. As a result, the silane group of the inorganic particles surface-modified with the vinyl silane or the like can counteract the base resin such as polyethylene, thereby ensuring excellent dispersibility. The inorganic particles such as magnesium oxide may have a single crystal or polycrystal form and may be included in the insulating composition in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the base resin. If the content of the inorganic particles is less than 0.01 part by weight, the effect of reducing the space charge accumulation can be divided into a plurality of layers, and if the content is more than 10 parts by weight, the impulse strength, mechanical properties and continuous extrudability can be deteriorated.

 Also, since the insulating composition forming the insulating layer 14 includes a crosslinking agent, the insulating layer 14 can be made of a crosslinked polyolefin (XLPO) by extrusion or by a separate crosslinking process after extrusion. Preferably made of crosslinked polyethylene (XLPE).

 The cross-linking agent included in the insulating composition may be the same as the cross-linking agent included in the semi-conductive composition. For example, the cross-linking agent may be a silane-based cross-linking agent or a dicumylperoxide, benzoyl peroxide, Di (t-butylperoxy) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) Based cross-linking agent. Here, the crosslinking agent contained in the insulating composition may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the base resin.

 In addition, the insulating composition may further include other additives such as an antioxidant, a heat resistant extrudability improving agent, a scavenger, a scorch inhibitor, and a crosslinking assistant.

Especially. An amine antioxidant as the antioxidant; Thioester-based antioxidants such as dialkyl esters, distearyl thiodipropionate, and dilauryl thiodipropionate; (2, 4-di-t-butylphenyl) 4,4'-biphenylene diphosphite, 2'2'-thiodiethylbis- [3- 4-hydroxyphenyl) -propionate], pentaerythrityl- (4-hydroxyphenyl) propionate], 4,4'-thiobis (2-methyl-6-t-butylphenol), tetrakis- [3- Bis (3-t-butyl-4-hydroxy-5-methylphenyl) propionate] ), And mixtures thereof. The antioxidant may be used in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the base resin.

 As the heat resisting agent, there may be mentioned diphenylamine and acetone compound, zinc 2-mercaptobenzimidazoate, 4,4'-bis (α, α-dimethylbenzyl) diphenylamine, pentaerythritol- Pentaerythritol-tetrakis- (beta -lauryl-ciopropionate, 2, 3-di-tert- butyl-4-hydroxy- (3,5-ditert.butyl-4-hydroxyphenyl) -propionate], distearyl-esters of β, β '-cyodipropionic acid, and 2'-cyanoethylene bis [3- , Wherein the heat resisting agent may be used in an amount of 0.1 to 2 parts by weight based on the weight of the base resin.

 As the ion scavenger, an aryl-based silane or the like may be used. Here, the ion scavenger may be used in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the base resin, .

The scorch retarder enhances the crosslinking efficiency of the cross-linking agent and improves the scorch resistance resistance. For example, 2,4-diphenyl-4-methyl- (1-methyl-1-pentene), 1,4-hydroquinone, and hydroquinone derivatives. Specifically, 2, 4-diphenyl-4-methyl-1-pentene can be used. The content of the scorch retarder may be 0.1 to 1.0 parts by weight, preferably 0.2 to 0.8 parts by weight based on 100 parts by weight of the base resin. When the content of the scorch retarder is less than 0.1 part by weight, the effect of accelerating the crosslinking is small. When the content of the scorch retarder is more than 1.0 part by weight, the crosslinking efficiency is decreased.

 The inventors of the present invention have found that, in the DC power cable according to the present invention, the electric field applied to the insulating layer 14 by the accumulation of space charge in the insulating layer 14 is distorted, The designed DC insulation breakdown voltage and insulation breakdown voltage of the cable can be maintained at the same level when the electric field enhancement factor (FEF) of the insulation layer 14 defined by Equation 2 is 100 to 140% The present invention has been completed.

 &Quot; (2) "

 FEF = (maximum applied electric field in specimen / electric field applied to specimen) * 100

 In Equation (2)

 Wherein the specimen comprises an insulating film formed from an insulating composition having a thickness of 120 and forming the insulating layer, and a semi-conductive film formed from the semi-conductive composition, each of which is bonded to an upper surface and a lower surface of the insulating film, And,

 The electric field applied to the specimen was a 50 kV / mm direct electric field applied to the insulating film for 1 hour,

The electric field which is maximally increased in the specimen is applied to the insulation film by a DC electric field Is the maximum increase of the electric field value for 1 hour.

 That is, when the electric field distortion degree (FEF) of the insulating layer 14 exceeds 140%, the inventors of the present invention have found that the space charge accumulation in the insulating layer 14 is excessively distorted and the electric field is largely distorted, And that the dielectric breakdown voltage is rapidly lowered.

 Further, by precisely controlling the content of the inorganic particles contained in the insulating layer 14 and the contents of the polar monomers and the cross-linking agent contained in the half-width full-length rods 12 and 16, the electric field distortion of the insulating layer 14 (FEF) can be precisely controlled.

 The jacket layer 20 may include polyethylene, polyvinyl chloride, polyurethane, and the like. For example, the jacket layer 20 may be formed of a polyethylene resin. Since the jacket layer 20 is disposed at the outermost portion of the cable, And more preferably made of a high-density polyethylene (HDPE) resin. The jacket layer 20 may contain a small amount of additives such as carbon black, for example, 2 to 3% by weight to realize the hue of the DC electric power cable. For example, the jacket layer 20 may have a thickness of 0.1 to 8 mm Thickness.

[Examples] 1. Production Example

1) Manufacturing of insulation + semi-conducting specimen for PEA and FT-IR evaluation

β For PEA (pulsed electro-acoustic) evaluation, Insulating thin film and insulating + antireflective thin film were used to fabricate each of the specimens. Phil B

beta

 (a) Insulating thin-film fill S (b) Insulation + Semi-

The insulating thin film was prepared by thermally compressing an insulating composition comprising magnesium oxide, a peroxide crosslinking agent and other additives surface-treated with vinylsilane as polyethylene resin inorganic particles at 120 ^° C for 5 minutes and drying at 180 ^° C After stirring for 8 minutes, the mixture was aged ^at 120 ^° C and cooled again at room temperature. The thickness of the fabricated insulating thin film was about 120.

On the other hand, the insulation + semi-conductive thin film is obtained by heat-compressing an insulating composition containing polyethylene resin, magnesium oxide surface-treated with vinylsilane as inorganic particles, peroxide crosslinking agent and other additives at 120 ^° C for 5 minutes, Conductive composition comprising butyl acrylate (BA), a cross-linking agent, and other additives is heated and pressed at 120 ^° C for 5 minutes to form a semi-conductive film, Adhered to the front and back sides of the film and remelted at 120T for 5 minutes to thermally bond with each other, then crosslinked at 18CTC for 8 minutes, then aged at 12CTC, and then cooled at room temperature. The thicknesses of the insulating films and the semi-conductive films produced were about 120 and about 50, respectively.

Here, the semi-conductive composition comprises a semi-conductive film formed of a semi-conductive composition (SC-a) having a content of butyl acrylate (BA) of 17% by weight based on the total weight of the resin, A semi-conductive film made of a semi-conductive composition (SC-b) having a content of 3% ≪ / RTI > thin films were prepared.

 In addition, for FT-IR evaluation, a thicker film was produced, and the thickness of the insulating film or the insulating thin film was 20 Å and the thickness of the semi-conducting film was 1 麵. In addition, the insulation + anti-conducting thin film was obtained by bonding a semi-conductive film to only one side of the insulating film and cutting the cross section into a 1 mm thick microcrome. Each of the insulation thin film, the insulation + semi-conductive (SC-a) thin film and the insulation + semi-conductive (SC-b) thin film was degassed by vacuum and 7 The film was also removed.

2) Manufacturing example of model cable for impulsive fracture test

 For the model cable fabrication for the impuls breakdown test, the insulation compositions A and B of Table 1 below were prepared, respectively. The unit of the content shown in Table 1 below is parts by weight.

[Table 1]

- Base resin: Low density polyethylene resin (LG Chem, LE2030; Density: 085 0.95 kg / m ^! ; Melt Index (MI): 1-2)

- Inorganic particles: Magnesium oxide surface-modified with vinylsilane (average particle diameter: 200 nm) - Crosslinking agent: Dicumyl peroxide

 - Antioxidant: Tetrakis (2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphate Also provided is an insulating layer composed of the insulating composition A or B, wherein the semiconductive composition SC -a) to the semi-conductive composition (SC-b) and the outer semiconductive layer, respectively, model cables A to D each having an insulation thickness of 4 mm and a conductor cross-sectional area of 400 sq were prepared. Specific constructions of the inner semiconductive layer, the insulating layer and the outer semiconductive layer of the model cables A to D are shown in Table 2 below.

[Table 2]

2. Property evaluation

1) FT-IR evaluation for insulation + semi-conducting specimens

Insulating film and half between the conductive film in order to determine whether or not the implementation of the acrylate and cross-linking by-products over the 64 scans at 4 cm ¹ resolution eu 4000 to 650 cm ^"1 in the spectra l data collected. FT-IR evaluation was performed with a Varian 7000e instrument equipped with a microscope and MCT detector. The evaluation result is as shown in Fig.

(A), insulation + semi-conductive (SC-a) thin film (c) and insulation + semi-conductive (SC-a) films as a film without removal of crosslinked byproducts by degassing as shown in FIG. b) thin film (e) are cross-linked whereas the 1694.3 cm ^"1 blood represents one of acetophenone of the by-product is greater observation, the insulating thin film as the film is crosslinked by-product is removed by degassing (b), insulating + (SC-a) thin film (d) and the insulating + semi-conductive (SC-b) thin film (f) were not observed to show a peak of 1694.3 cm- ¹ indicating acetophenone, The insulating thin film (a, b) without the semi-conducting film was not observed at 1735.6 cm- ¹ indicating the acrylate resin while the insulating semi-conducting thin film (c, d , e, f) has been observed in the 1735.6 ατΓ ¹ represents an acrylate resin peak, in particular half (SC-a) thin film having a relatively high acrylate content in the semiconducting film as compared to an insulation + semiconducting (SOb) thin film having a relatively low acrylate content in the entire film. cm ^{< -1 &} gt ^; was large, it was confirmed that the transition of the acrylate resin from the semiconductive film to the insulating film was large.

2) Evaluation of heterogeneous charge, space charge and electric field distortion for insulation + semi-conductive sample The insulation thin film made according to the PEA evaluation sample preparation example PEMpulsed electro-acoustic evaluation was performed on the specimen (a), the specimen (b) consisting of the insulating + semi-conducting (SC-a) thin film and the specimen (c) consisting of the insulating + semi-conducting . Specifically, an electrode is formed on both sides of the film, and a DC electric field of 50 kV / 虜 is applied for 1 hour in a galvanic field, followed by shorting for 1 hour. When a DC electric field is applied and short- The charge density was measured using a program. The measurement result is as shown in Fig.

 In the graph of FIG. 5 showing the charge density over time, an integral value representing an electric field was calculated, and a maximum value among the integrated values was selected to calculate the field distortion degree (FEF) of the equation (2). The results of the field measurement and the electric field distortion (FEF) calculations for the specimens (a), (b) and (c) over time are shown in Table 3 below. The values shown in Table 3 below are kV / mm representing the electric field values except where otherwise indicated.

[Table 3]

도 5에 도시된 바와 같이， 상기 시편 ( a)는 이에 포함된 무기입자가 전극으로 부터 상기 필름 내부에 이동하는 전하를 트램 ( t rap)하고. 또한 반도전 필름과 결합 되어 있지 않기 때문에, 상기 반도전 필름의 가교시 발생한 가교부산물이 절연 박 막 필름쪽으로 이동하지 않아 이종전하 (heterocharge)가 형성되지 않고, 반도전 필 름의 부틸아크릴레이트 (BA)가 절연 박막 필름쪽으로 이동하지 않으므로, DC 전계가 인가된 ( a) 및 DC 전계 인가가 중단된 (b)에서 공간전하의 축적이 미미한 것으로 확인되었고, 이에 따라 전계 I왜곡도 (FEF)도 낮은 것으로 확인되었다.

As shown in FIG. 5, the specimen (a) trams the charge in which the inorganic particles contained therein move into the film from the electrode. Further, since it is not bonded to the semi-conductive film, crosslinking by-products generated during crosslinking of the semi-conductive film do not migrate toward the insulating thin film film, heterocharging is not formed, and butyl acrylate (BA It was confirmed that the accumulation of the space charge was insignificant in the case of (a) in which the DC electric field was applied and in the case of (b) in which the DC electric field application was interrupted and thus the electric field I distortion degree (FEF) Respectively.

On the other hand, in the test pieces (b) and (c), the crosslinked byproducts or butyl acrylate (BA) of the antireflective thin film migrate toward the insulating thin film and a hetero electric charge is generated near the interface between the insulating thin film and the semi- As a relatively large amount of space charge is accumulated in the vicinity of the interface between the sustained thin film and the semi-conductive thin film, the electric field distortion (BA) content of specimen (b) was relatively higher than that of specimen (c) with relatively low content of butylacrylate (BA) (FEF) was also found to be relatively large.

3) Evaluation of volumetric resistivity change according to impulsive breakdown voltage and temperature

 In order to measure the impulse breakdown voltage of the model cables A to D, an impulse voltage generator was used to measure an impulse breakdown voltage by applying an impulse voltage of 300 kV. Specifically, the impulse breakdown voltage was measured at an initial applied voltage of 300 kV to 20 kV The breakdown voltage was measured at the breakdown of the specimen and the measurement results (breakdown probability 0%) are shown in Table 4 below.

Then, the collected specimen on the insulating layer of the cable model A and model cable C 25 ^° C. Resistivity was measured at 50 ^° C, 70 ^° C and 90 ^° C, respectively, and the measurement results are shown in FIG.

[Table 4]

상기 표 4에 나타난 바와 같이, 무기입자를 포함하는 모델 케이블 A 및 모델 케이블 B의 경우, 직류 전기장 하에서 상기 무기입자가 분극화되고, 분극화된 무기 입자가 공간전하를 트랩 ( t rap)할 수 있을 뿐만 아니라, 상기 무기입자는 상기 절연 층에 고르게 분산되어 있으므로, 공간전하 축적 및 이로 인한 국부적인 전계왜곡을 방지하여, 높은 임펄스 파괴전압이 구현되었다. 반면, 무기입자를 포함하지 않는 모델 케이블 c 및 모델 케이블 D의 경우, 절연체 내부에 공간전하 축적에 의한 전 계왜곡이 유발되어, 결과적으로 임필스 파괴전압이 크게 저하된 것으로 확인되었 다.

As shown in Table 4, the model cable A and the model In the case of the cable B, under the direct electric field, the inorganic particles are polarized, the polarized inorganic particles can trap (trap) the space charge, and the inorganic particles are uniformly dispersed in the insulating layer, And the local field distortion caused thereby, and a high impulse breakdown voltage is realized. On the other hand, in the case of the model cable C and the model cable D which do not contain inorganic particles, electric field distortion due to the accumulation of space charge is induced in the insulator, and consequently, the impulse breakdown voltage is significantly reduced.

In addition, as shown in FIG. 3, the model cable A including the inorganic particles in the insulating layer effectively restrains the accumulation of the space charges, and as the temperature increases, the volume resistivity is maintained at the maximum, . Model cables without inorganic particles (:) were found to be highly dependent on temperature due to the rapid decrease in volume resistivity at 70 and 90 ^° C due to the accumulation of space charge.

 It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the following claims. Change will be possible. It is therefore to be understood that the modified embodiments are included in the technical scope of the present invention, basically including the constituents of the claims of the present invention.

Claims

Claims:  [Claim 1]  As a direct current power cable,  Conductor;  An inner semiconductive layer surrounding the conductor;  An insulating layer surrounding the inner semiconductive layer;  An outer semiconductive layer surrounding the insulating layer; And  And an outer sheath surrounding the outer semiconductive layer,  Wherein the inner semiconductive layer or the outer semiconductive layer is formed from a semiconductive composition comprising a copolymer resin of an olefin and a polar monomer as a base resin and conductive particles dispersed in the resin,  The content of the polar monomer is 18% by weight or less based on the total weight of the copolymer resin,  Wherein the insulating layer comprises at least one inorganic particle dispersed in the resin and dispersed in the resin and selected from the group consisting of aluminum silicate, calcium silicate, calcium carbonate, oxide magnes, carbon nanotubes and graphite, Lt; RTI ID = 0.0 >  The content of the inorganic particles is 0.01 to 10 parts by weight based on 100 parts by weight of the base resin of the insulating layer, Wherein the electric field distortion factor (FEF) of the insulation layer defined by the following formula (2) is 100 to 14W. &Quot; (2) "  FEF = (maximum applied electric field in specimen / electric field applied to specimen) * 100  In Equation (2)  Wherein the specimen comprises an insulating film formed from an insulating composition having a thickness of 120 and forming the insulating layer, and a semi-conductive film formed from the semi-conductive composition, each of which is bonded to an upper surface and a lower surface of the insulating film, I am a psalmist.  The electric field applied to the specimen is a 50 kV / ivil direct electric field applied to the insulating film for 1 hour.  The electric field maximally increased in the specimen is the maximum electric field value increased during one hour when the DC electric field is applied to the insulating film.  [Claim 2]  The method according to claim 1,  Wherein the insulating composition or the semi-conductive composition further comprises a crosslinking agent, and the content of the crosslinking agent is 0.1 to 5 parts by weight based on 100 parts by weight of the base resin. DC power cable.  [3]  3. The method according to claim 1 or 2,  Wherein the polar monomer comprises an acrylate monomer. Claim 4 3. The method according to claim 1 or 2,  Wherein the inorganic particles comprise magnesium oxide. DC power cable.  [Claim 5]  3. The method according to claim 1 or 2,  Characterized in that the inorganic particles are surface-modified by at least one surface modifying agent selected from the group consisting of vinyl silane, stearic acid, oleic acid and amino polysiloxanes. DC power cable.  [Claim 6]  3. The method according to claim 1 or 2,  The copolymer resin may be at least one selected from the group consisting of ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene methyl methacrylate (EMMA), ethylene ethyl acrylate (EEA), ethylene ethyl methacrylate (EEMA) ) Propyl acrylate (EPA), ethylene (iso) propyl methacrylate (EPMA). (EBA), ethylene butyl acrylate (EBA), and ethylene butyl methacrylate (EBMA).  Claim 71  The method according to claim 6,  Wherein the content of the particles is 35 to 70 parts by weight based on 100 parts by weight of the base resin. 8. 3. The method of claim 2,  Wherein the cross-linking agent is a peroxide-based cross-linking agent. 9]  9. The method of claim 8,  The peroxide-based cross-linking agent is selected from the group consisting of dicumyl peroxide, benzoyl peroxide, lauryl peroxide, t-butyl cumyl peroxide, di (t-butylperoxyisopropyl) benzene, 2,5- t-butylperoxy) nucleic acid and di-t-butyl peroxide. DC power cable.  Claim 10  3. The method according to claim 1,  Characterized in that the polyolefin resin as the base resin of the insulation layer comprises a polyethylene resin.  Claim 11  3. The method according to claim 1 or 2,  The insulating composition may be selected from the group consisting of 2,4-di phenyl-4-methyl-1-pentene, 1,4-hydroquinone, A quinone derivative, and a scorch inhibitor, wherein the content of the scorch retarder is 0.1 to 1.0 parts by weight based on 100 parts by weight of the base resin.  [12] 12. The method of claim 11, Wherein the scorch retarder comprises 2,4-diphenyl-4-methyl-1-pentene.