WO2018221802A1 - Ultra-high voltage direct current power cable - Google Patents

Abstract

The present invention relates to an ultra-high voltage direct current power cable. Specifically, the present invention relates to an ultra-high voltage direct current power cable enabling the simultaneous prevention or minimization of electric field distortion, DC dielectric strength degradation and impulse breakdown strength degradation caused by the accumulation of space charge in an insulator.

Description

Ultra High Voltage DC Power Cable

The present invention relates to an ultra-high voltage direct current power cable. Specifically, the present invention relates to an ultra-high voltage DC power cable capable of simultaneously preventing or minimizing electric field distortion, a decrease in DC dielectric strength, and a decrease in impulse breakdown strength due to accumulation of space charge in an insulator.

In general, in a large power system where large capacity and long distance transmission are desired, high voltage transmission to increase the transmission voltage is essential in view of reduction of power loss, construction site problem, and transmission capacity increase.

The power transmission method can be largely divided into an AC power transmission method and a DC power transmission method. Among these, the DC power transmission method refers to the transmission of electrical energy by direct current. Specifically, the DC power transmission method first converts the AC power of the power transmission side to a suitable voltage, converts it to DC by a forward conversion device, and then sends it to the power receiver through the power transmission line. This is how you convert it.

In particular, the DC transmission method is advantageous in transporting a large amount of power over a long distance and can be interconnected with the asynchronous power system, and is widely used because DC has less power loss and higher stability than AC in long distance transmission. There is a situation.

The insulator of the (ultra) high voltage direct current transmission cable used in the DC transmission method may be formed from an insulation composition impregnated with insulating oil or an insulation composition based on a polyolefin resin, and recently, the cable may be operated at a relatively high temperature. Insulators formed of an insulating composition containing a polyolefin resin that can increase the transmission capacity and have no fear of insulating oil leakage have been widely used.

However, since the polyolefin resin has a linear molecular chain structure, it is applied to the cable insulation layer by improving mechanical and thermal properties through a crosslinking process, and the cable insulation is insulated due to the crosslinking by-products inevitably decomposed during the crosslinking process. There is a problem of accumulating space charge in the layer, and the space charge may distort the electric field in the (ultra) high voltage direct current transmission cable insulator and cause insulation breakdown at a voltage lower than the first designed breakdown voltage.

In the case of a cable used in a current type direct current transmission (LCC) that requires polarity inversion to change the direction of transmission, inorganic additives such as magnesium oxide are uniformly dispersed in the cable insulation layer in order to solve the above-mentioned problems. Inorganic additives are polarized and trap the space charge, thereby minimizing electric field distortion caused by space charge accumulation. However, in the case of voltage-type direct current transmission (VSC), polarity inversion is unnecessary, and an insulation composition with an organic additive added to optimize the electrical stress applied to the cable insulator requires precise control of the space charge content in the insulation layer. There is.

Therefore, it is possible to simultaneously prevent or minimize the electric field distortion caused by the accumulation of space charge in the insulator, the decrease of the DC dielectric strength and the decrease of the impulse breakdown strength, and is particularly suitable for use in voltage type DC power transmission (VSC). There is an urgent need for cables.

An object of the present invention is to provide an ultra-high voltage DC power cable capable of simultaneously preventing or minimizing electric field distortion caused by accumulation of space charge in an insulator, a decrease in DC dielectric strength, and a decrease in impulse breaking strength.

In order to solve the above problems, the present invention,

An ultra-high voltage DC power cable, comprising: a conductor formed by stranded wires; An inner semiconducting layer surrounding the conductor; An insulation layer surrounding the inner semiconducting layer; And an outer semiconducting layer surrounding the insulating layer, wherein the insulating layer is formed from an insulating composition comprising a polyolefin resin and a crosslinking agent, wherein the insulating layer is divided into three layers by dividing its thickness into an inner layer, a middle layer, and an outer layer. Three specific crosslinking byproducts of α-cumyl alcohol (α-CA), acetophenone (AP) and α-methyl styrene (α-MS) among the crosslinking by-products included in It provides an ultra-high voltage DC power cable, characterized in that the average value of the total content of the 3,890 ppm or less.

Here, the total content of the three specific cross-linked by-products contained in the inner layer of the insulating layer is characterized in that, 3,990 ppm or less, to provide an ultra-high voltage DC power cable.

In addition, it provides an ultra-high voltage DC power cable, characterized in that the Field Enhancement Factor (FEF), which is defined by Equation 1 below, is 140% or less.

[Equation 1]

FEF = (maximumly increased field on insulated specimen / field applied to insulated specimen) * 100

In Equation 1,

The insulating specimen is a specimen prepared by crosslinking the insulating composition forming the insulating layer and having a thickness of 120 μm,

The electric field applied to the insulated specimen is 50 kV / mm as a direct current applied to electrodes connected to the surfaces facing each other in the insulated specimen,

The maximum increased electric field in the insulated specimen is the maximum value of the increased electric field during the application of a 50 kV / mm direct current electric field to the insulated specimen for one hour.

Furthermore, the polyolefin resin provides an ultra high voltage DC power cable, characterized in that it comprises a polyethylene resin.

In addition, the crosslinking agent provides an ultrahigh voltage direct current power cable, characterized in that the peroxide crosslinking agent.

Here, the peroxide crosslinking agent is dicumyl peroxide, benzoyl peroxide, lauryl peroxide, t-butyl cumyl peroxide, di (t-butyl peroxy isopropyl) benzene, 2,5-dimethyl-2,5-di It provides an ultra-high voltage DC power cable, characterized in that it comprises one or more selected from the group consisting of (t-butyl peroxy) hexane and di-t-butyl peroxide.

In addition, the insulation composition provides an ultra-high voltage DC power cable, characterized in that it further comprises one or more additives selected from the group consisting of antioxidants, extrudability enhancers and crosslinking aids.

On the other hand, the semiconductive composition forming the inner and outer semiconducting layer provides an ultra-high voltage DC power cable, characterized in that the content of the crosslinking agent is 0.1 to 5 parts by weight based on 100 parts by weight of the base resin.

Here, the base resin is ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene methyl methacrylate (EMMA), ethylene ethyl acrylate (EEA), ethylene ethyl methacrylate (EEMA), ethylene (iso) Propyl acrylate (EPA), ethylene (iso) propyl methacrylate (EPMA), ethylene butyl acrylate (EBA) and ethylene butyl methacrylate (EBMA) To provide an ultra-high voltage DC power cable.

The ultra high voltage direct current power cable according to the present invention is an insulator by precisely controlling the content of the crosslinking agent added to the insulating composition forming the insulating layer and the specific crosslinking by-products generated during crosslinking by controlling the degree of crosslinking by appropriate modification of the base resin. It exhibits an excellent effect of simultaneously preventing or minimizing the electric field distortion, the decrease in DC dielectric strength and the impulse breakdown strength due to the accumulation of space charge in the interior.

1 schematically illustrates a longitudinal cross-sectional view of an ultra-high voltage direct current power cable.

2 is a graph showing the results of measuring the electric field increase coefficient (FEF) in the embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the present invention to those skilled in the art. Like numbers refer to like elements throughout.

Figure 1 schematically shows a longitudinal cross-sectional view of the ultra-high voltage DC power cable according to the present invention.

Referring to FIG. 1, the power cable 200 includes a conductor 210 formed by connecting a plurality of wires, an inner semiconducting layer 212 surrounding the conductor, an insulating layer 214 surrounding the inner semiconducting layer 212, Including an outer semiconducting layer 216 surrounding the insulating layer 214, and transmits power only in the cable length direction along the conductor 210, and has a cable core portion to prevent current leakage in the cable radial direction do.

The conductor 210 serves as a passage through which current flows to transmit power, and has a high conductivity to minimize power loss and a material having strength and flexibility suitable for cable production and use, for example, copper or aluminum. It may be configured as. The conductor 210 may be a circular compressed conductor compressed in a circular shape by twisting a plurality of circular small wires, and may be a flat rectangular wire 210B twisted to surround a circular center element wire 210A and the circular center element wire 210A. It may be a flat conductor having a flat rectangular wire layer 210C and having a circular cross section as a whole. The flat conductor has an advantage of reducing the outer diameter of a cable due to a relatively high drop ratio compared to a circular compressed conductor.

However, since the conductor 210 is formed by twisting a plurality of element wires, the surface thereof is not smooth, so that an electric field may be uneven, and corona discharge is likely to occur partially. In addition, when a gap is formed between the surface of the conductor 210 and the insulating layer 214 to be described later, insulation performance may be degraded. In order to solve the above problems, the inner semiconducting layer 212 is formed outside the conductor 210.

The inner semiconducting layer 212 has semiconductivity by adding conductive particles such as carbon black, carbon nanotubes, carbon nanoplates, graphite, and the like to an insulating material, between the conductor 210 and the insulating layer 214 to be described later. It prevents a sudden electric field change and stabilizes insulation performance. In addition, by suppressing non-uniform charge distribution on the conductor surface, the electric field is made uniform, and the gap between the conductor 210 and the insulating layer 214 is prevented to prevent corona discharge and insulation breakdown.

An insulating layer 214 is provided on the outer side of the inner semiconducting layer 212 to electrically insulate the outside so that current flowing along the conductor 210 does not leak to the outside. In general, the insulating layer 214 has a high breakdown voltage and should be able to be stably maintained for a long time. Furthermore, the dielectric loss is low and must have heat resistance such as heat resistance. Accordingly, the insulating layer 214 may be a polyolefin resin such as polyethylene and polypropylene, and further preferably, polyethylene resin. Here, the polyethylene resin may be made of a crosslinked resin.

An outer semiconducting layer 216 is provided outside the insulating layer 214. The outer semiconducting layer 216 is formed of a material having semiconductivity by adding conductive particles, such as carbon black, carbon nanotubes, carbon nanoplates, graphite, etc., to an insulating material like the inner semiconducting layer 212, The nonuniform charge distribution between the insulating layer 214 and the metal sheath 22 described later is suppressed to stabilize the insulating performance. In addition, the outer semiconducting layer 216 smoothes the surface of the insulating layer 214 in the cable to mitigate electric field concentration to prevent corona discharge, and also physically protects the insulating layer 214. .

The cable core part, in particular, the inner semiconducting layer 212, the insulating layer 214, and the outer semiconducting layer 216 are most concerned with electric field distortion caused by the generation, accumulation, and injection of the above-mentioned space charges and the resulting insulation breakdown. Detailed description thereof as a part will be described later.

The core part may further include a moisture absorbing layer for preventing moisture from penetrating the cable. The moisture absorbing layer may be formed between stranded wires and / or outside the conductor 210, and has a high rate of absorbing moisture penetrating into the cable and a super absorbent polymer having excellent ability to maintain an absorbing state. It is formed in the form of a powder, a tape, a coating layer or a film including SAP) serves to prevent the penetration of moisture in the cable longitudinal direction. In addition, the moisture absorbing layer may have a semiconductivity to prevent a sudden electric field change.

A protection sheath part is provided outside the core part, and a power cable installed in an environment in which water is exposed to moisture, such as the seabed, further includes an exterior part. The protective sheath and the sheath protect the cable core from various environmental factors such as moisture penetration, mechanical trauma, and corrosion, which can affect the power transmission performance of the cable.

The protective sheath portion includes a metal sheath layer 218 and an inner sheath 220 to protect the cable core portion from accidental currents, external forces or other external environmental factors.

The metal sheath layer 218 is grounded at the end of the power cable to serve as a passage through which an accident current flows in case of an accident such as a ground fault or a short circuit, to protect the cable from external shocks, and to prevent the electric field from being discharged to the outside of the cable. have. In addition, in the case of a cable installed in an environment such as a seabed, the metal sheath layer 218 is formed to seal the core part, thereby preventing foreign matter such as moisture from invading and deteriorating insulation performance. For example, the molten metal may be extruded to the outside of the core to be formed to have a seamless outer surface so that the ordering performance may be excellent. Lead or aluminum is used as the metal, and in particular, in the case of submarine cables, it is preferable to use lead having excellent corrosion resistance to seawater, and lead alloy containing a metal element to complement mechanical properties. More preferably).

In addition, the metal sheath layer 218 is coated with an anti-corrosion compound, for example, blown asphalt, etc. on the surface in order to further improve the corrosion resistance, water resistance, etc. of the cable and to improve adhesion to the inner sheath 220. Can be. In addition, a copper wire straight tape (not shown) to a moisture absorbing layer may be further provided between the metal sheath layer 218 and the core part. The copper wire direct tape consists of a copper wire and a nonwoven tape to facilitate electrical contact between the outer semiconducting layer 216 and the metal sheath layer 218, and the moisture absorbing layer absorbs moisture that has penetrated the cable. It is composed of powder, tape, coating layer or film including super absorbent polymer (SAP) that absorbs quickly and has excellent ability to maintain the absorption state. It plays a role. In addition, in order to prevent a sudden electric field change in the water absorbing layer may be configured to include a copper wire in the water absorbing layer.

The inner sheath 220 made of a resin such as polyvinyl chloride (PVC), polyethylene, etc. is formed outside the metal sheath layer 218 to improve corrosion resistance, water resistance, and the like of the mechanical trauma and heat, It can also protect the cable from other external environmental factors such as UV light. In particular, in the case of power cables laid on the sea floor, it is preferable to use polyethylene resin having excellent degree of orderability, and polyvinyl chloride resin is preferably used in an environment where flame retardancy is required.

The protective sheath portion is made of a semi-conductive nonwoven tape or the like further includes an outer sheath made of a resin such as a metal reinforcing layer for buffering the external force applied to the power cable, polyvinyl chloride to polyethylene, etc. to further improve corrosion resistance and water resistance of the power cable. And further protect the cable from mechanical trauma and other external environmental factors such as heat and ultraviolet radiation.

In addition, the power cable installed on the seabed is easy to be damaged by anchors of ships, and may be damaged by bending force due to currents or waves, friction with the sea bottom, etc. Can be.

The exterior part may include an armor layer and a serving layer. The armor layer may be made of steel, galvanized steel, copper, brass, bronze, and the like, and may be constituted by at least one layer by cross winding a wire having a circular cross section or the like. The armor layer not only serves to enhance the mechanical properties and performance of the cable, but also additionally protects the cable from external forces. The serving layer made of polypropylene yarn or the like is formed in one or more layers on the upper and / or lower portion of the armor layer to protect the cable, and the outermost serving layer is made of two or more materials of different colors. Visibility of cables laid on the sea floor can be ensured.

The above-described inner semiconducting layer 212 and outer semiconducting layer 216 have conductive particles such as carbon black, carbon nanotubes, carbon nanoplates, graphite, and the like dispersed in a base resin, and a crosslinking agent, an antioxidant, a scorch inhibitor, and the like are added. It is formed by the extrusion of the semiconducting composition added thereto.

Here, the base resin may be a olefin resin of a similar series to the base resin of the insulating composition for forming the insulating layer 214 for the interlayer adhesion between the semiconductive layers 212 and 216 and the insulating layer 214, More preferably, in consideration of compatibility with the conductive particles, olefins and polar monomers such as ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene methyl methacrylate (EMMA), ethylene ethyl acryl Elate, Ethylene Ethyl Methacrylate (EEMA), Ethylene (Iso) propyl Acrylate (EPA), Ethylene (Iso) propyl Methacrylate (EPMA), Ethylene Butyl Acrylate (EBA), Ethylene Butyl Methacrylate It is preferable to use (EBMA) or the like.

In addition, the crosslinking agent is a silane crosslinking agent, or dicumyl peroxide, benzoyl peroxide, lauryl peroxide, t-butyl cumyl peroxide, di (t-) according to the crosslinking method of the base resin included in the semiconductive layers 212 and 216. Organic peroxide crosslinking agents such as butyl peroxy isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butyl peroxy) hexane and di-t-butyl peroxide.

The semiconducting compositions forming the inner and outer semiconducting layers 212 and 216 may include 45 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 45 parts by weight, sufficient semiconducting properties may not be realized, whereas when the content of the conductive particles is greater than 70 parts by weight, the extrudability of the inner and outer semiconducting layers 212 and 216 may be deteriorated, resulting in deterioration of surface properties or cable productivity There is a problem of deterioration.

In addition, the semiconducting compositions forming the inner and outer semiconducting layers 212 and 216 may be precisely adjusted to 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. have.

Here, when the content of the crosslinking agent is greater than 5 parts by weight, the content of crosslinking by-products which are essentially generated when crosslinking the base resin included in the semiconducting composition is excessive, and the crosslinking byproducts are separated from the semiconducting layers 212 and 216. By moving into the insulating layer 214 through the interface between the layers 214 to accumulate heterocharges, the distortion of the electric field may be increased, causing a problem of lowering the dielectric breakdown voltage of the insulating layer 214. On the other hand, if less than 0.1 parts by weight of the cross-linking degree is insufficient, the mechanical properties, heat resistance and the like of the semiconducting layers (212,216) may be insufficient.

The insulating layer 214 may be, for example, a polyolefin resin such as polyethylene or polypropylene as a base resin, and may be preferably formed by extrusion of an insulating composition containing a polyethylene resin.

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

In addition, the insulating composition for forming the insulating layer 214 includes a crosslinking agent, so that the insulating layer 214 is crosslinked polyolefin (XLPO), preferably crosslinked polyethylene (XLPE) by a separate crosslinking process during or after extrusion. It can be made of). In addition, the insulation composition may further include other additives such as antioxidants, extrusion enhancers, crosslinking aids, and the like.

The crosslinking agent included in the insulating composition may be the same as the crosslinking agent included in the semiconductive composition. For example, a silane crosslinking agent, or dicumyl peroxide, benzoyl peroxide, and lauryl peroxide depending on the crosslinking method of the polyolefin. organic compounds such as t-butyl cumyl peroxide, di (t-butyl peroxy isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butyl peroxy) hexane and di-t-butyl peroxide It may be a peroxide crosslinking agent. Here, the crosslinking agent included in the insulation composition may be included in an amount of less than 1% by weight, for example, 0.1% by weight or more and less than 1% by weight based on the total weight of the insulation composition.

The present inventors have found that specific crosslinking by-products that cause space charge generation among crosslinking by-products inevitably generated during crosslinking of the insulating layer 214 include α-cumyl alcohol (α-CA), acetophenone (AP), and acetophenone (AP). ) And α-methyl styrene (α-MS), and the content of the crosslinking agent included in the insulating composition forming the insulating layer 214 is limited to less than 1 wt% and the insulating layer Degasing after crosslinking of (214) may limit the content of the specific crosslinking byproduct, and in particular, may limit the content of the specific crosslinking byproduct by position in the thickness of the insulating layer, Due to the limitation of the content, it is possible to significantly reduce the space charge generation and the electric field distortion, and consequently to prevent the decrease in the DC dielectric strength and the impulse breakdown strength of the insulating layer 214 at the same time. By experimentally it confirmed that it is possible to digest the present invention has been completed.

Furthermore, the inventors of the present invention have a problem that the degree of crosslinking of the insulating layer 214 is lowered because the content of the crosslinking agent is limited to less than 1% by weight, and as a result, the mechanical and thermal properties of the insulating layer 214 may be lowered. The present invention was completed by experimentally confirming that by increasing the vinyl group content of the base resin included in the insulating composition forming (214), a degree of crosslinking of 60% or more, for example, 60 to 70% can be achieved and solved.

In detail, the insulating layer 214 is divided into three layers of the inner layer, which is a lower layer disposed directly on the conductor 10, a middle layer disposed on the inner layer, and an outer layer disposed on the middle layer. The average value of the total contents of the three specific crosslinking by-products is adjusted to 3,890 ppm or less so that the generation of space charges in the insulating layer 214 is suppressed, thereby indicating the degree of electric field distortion in the insulating layer 214. Field Enhancement Factor (FEF) of Equation 1 is adjusted to about 140% or less, and as a result, it is possible to simultaneously prevent or minimize the reduction of the DC dielectric strength and the impulse breakdown strength of the insulating layer 214. .

[Equation 1]

FEF = (maximumly increased field on insulated specimen / field applied to insulated specimen) * 100

In Equation 1,

The insulating specimen is a specimen prepared by crosslinking the insulating composition forming the insulating layer 214 and having a thickness of 120 μm,

The electric field applied to the insulated specimen is 50 kV / mm as a direct current applied to electrodes connected to the surfaces facing each other in the insulated specimen,

The maximum increased electric field in the insulated specimen is the maximum value of the increased electric field during the application of a 50 kV / mm direct current electric field to the insulated specimen for one hour.

Furthermore, the inner layer of the insulating layer 214 is disposed directly on the conductor 210 to form a heterogeneous interface with the inner semiconducting layer 212, and is included in the inner layer because a relatively high field is applied to the insulating layer. More preferably, the total content of the three specific crosslinking byproducts is controlled to 3,990 ppm or less.

EXAMPLE

1. Manufacturing Example of Model Cable

A model cable having an insulation thickness of about 4 mm and a conductor cross-sectional area of about 400 SQ including an inner semiconducting layer, an insulating layer, and an outer semiconducting layer, wherein the crosslinking byproduct is controlled by controlling the content of the crosslinking agent added to the insulating layer and crosslinking and degassing. By controlling the amount of, by dividing the thickness of the insulating layer by the content of the cross-linked by-products of each layer / cross-linked by-product type of the inner layer, middle layer and outer layer is adjusted as shown in Table 1 below the model cable of the Examples to Comparative Examples Each manufactured. The crosslinking byproduct content was measured by taking specimens at any intermediate point in each layer.

		Crosslinked Byproduct Content (ppm)
		α-CA	AP	α-MS	total
Comparative Example 1	Inner layer	3112	1163	149	4424
	Middle layer	3037	1406	568	5011
	Outer layer	1919	1011	569	3499
	Average	2689.3	1193.3	428.7	4311.3
Comparative Example 2	Inner layer	2947	1159	181	4287
	Middle layer	2885	1443	641	4969
	Outer layer	1667	853	475	2995
	Average	2499.7	1151.7	432.3	4083.7
Comparative Example 3	Inner layer	2658	1073	261	3992
	Middle layer	2595	1378	722	4695
	Outer layer	1730	835	476	3041
	Average	2327.7	1095.3	486.3	3909.3
Example 1	Inner layer	2681	1052	257	3990
	Middle layer	2509	1278	737	4524
	Outer layer	1799	859	498	3156
	Average	2329.7	1063.0	497.3	3890.0
Example 2	Inner layer	2412	896	274	3582
	Middle layer	2359	1046	553	3958
	Outer layer	1463	540	373	2376
	Average	2078.0	827.3	400.0	3305.3
Example 3	Inner layer	2254	854	259	3367
	Middle layer	2501	1065	507	4073
	Outer layer	1593	610	394	2597
	Average	2116.0	843.0	386.7	3345.7

2. Measurement of field rise coefficient (FEF)

Comparative Examples and Examples After taking an insulating specimen having a thickness of about 120 μm from the insulation layer of each model cable, a DC electric field of 50 kV / mm was applied to the insulation specimen for 1 hour based on a pulsed electro acoustic (PEA) system. While applying, the electric field rise coefficient (FEF) of Equation 1 was measured. The measurement results are shown in Table 2 and FIG. 2 below. In order to confirm the correlation between the crosslinked byproduct content and the electric field increase coefficient, the electric field increase coefficient (FEF) was measured at the same time as the crosslinked byproduct content measurement.

	FEF (%)
Comparative Example 1	159
Comparative Example 2	157
Comparative Example 3	165
Example 1	137
Example 2	135
Example 3	132

As shown in Table 2 and FIG. 2, the insulation specimens of Comparative Examples 1 to 3, in which the content of three specific crosslinking by-products are not controlled, have an electric field increase coefficient (FEF) of 160%, indicating electric field distortion due to generation of space charge. It was found to be close to, which is expected to significantly reduce the dielectric strength.

On the other hand, in the insulating specimens of Examples 1 to 3 according to the present invention, the content of three specific cross-linked by-products is precisely controlled, thereby suppressing the generation of space charges, which results in an electric field increase coefficient (FEF) of less than 140%. The adjustment was made low and consequently the degradation of dielectric strength was expected to be minimal.

Although the present specification has been described with reference to preferred embodiments of the invention, those skilled in the art may variously modify and change the invention without departing from the spirit and scope of the invention as set forth in the claims set forth below. Could be done. Therefore, it should be seen that all modifications included in the technical scope of the present invention are basically included in the scope of the claims of the present invention.

Claims (9)

1. Ultra high voltage DC power cable,

   A conductor formed by stranding a plurality of strands;

   An inner semiconducting layer surrounding the conductor;

   An insulation layer surrounding the inner semiconducting layer; And

   An outer semiconducting layer surrounding the insulating layer,

   The insulating layer is formed from an insulating composition comprising a polyolefin resin and a crosslinking agent,

   The insulating layer is divided into three thicknesses and divided into an inner layer, a middle layer and an outer layer. Among the crosslinking by-products included in the inner layer, α-cumyl alcohol (α-CA), acetophenone (AP) and Total content of α-methyl styrene (α-MS), α-cumyl alcohol (α-CA), acetophenone (AP) and α in crosslinked by-products included in the middle layer The total content of α-methyl styrene (α-MS) and the α-cumyl alcohol (α-CA), acetophenone (AP) and α-methylstyrene (α-MS) contained in the outer layer; Ultra-high voltage direct current power cable, characterized in that the average value of the total content of α-methyl styrene;
2. The method of claim 1,

   An ultra-high voltage direct current power cable, characterized in that the total content of the three specific crosslinking by-products contained in the inner layer of the insulating layer is 3,990 ppm or less.
3. The method according to claim 1 or 2,

   Ultra-high voltage DC power cable, characterized in that the Field Enhancement Factor (FEF) is defined by Equation 1 below 140% or less.

   [Equation 1]

   FEF = (maximumly increased field on insulated specimen / field applied to insulated specimen) * 100

   In Equation 1,

   The insulating specimen is a specimen prepared by crosslinking the insulating composition forming the insulating layer and having a thickness of 120 μm,

   The electric field applied to the insulated specimen is 50 kV / mm as a direct current applied to electrodes connected to the surfaces facing each other in the insulated specimen,

   The maximum increased electric field in the insulated specimen is the maximum value of the increased electric field during the application of a 50 kV / mm direct current electric field to the insulated specimen for one hour.
4. The method according to claim 1 or 2,

   The polyolefin resin is characterized in that it comprises a polyethylene resin, ultra-high voltage DC power cable.
5. The method according to claim 1 or 2,

   The crosslinking agent is a peroxide-based crosslinking agent, ultra-high voltage DC power cable.
6. The method of claim 5,

   The peroxide crosslinking agent is dicumyl peroxide, benzoyl peroxide, lauryl peroxide, t-butyl cumyl peroxide, di (t-butyl peroxy isopropyl) benzene, 2,5-dimethyl-2,5-di (t -Butyl peroxy) hexane and di-t-butyl peroxide, characterized in that it comprises one or more selected from the group consisting of, ultra high voltage DC power cable.
7. The method according to claim 1 or 2,

   The insulation composition further comprises at least one additive selected from the group consisting of antioxidants, extrudability enhancers and crosslinking aids, ultra high voltage DC power cable.
8. The method according to claim 1 or 2,

   Semiconducting composition forming the inner and outer semiconducting layer is characterized in that the content of the cross-linking agent is 0.1 to 5 parts by weight based on 100 parts by weight of the base resin, ultra-high voltage DC power cable.
9. The method of claim 8,

   The base resin is ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene methyl methacrylate (EMMA), ethylene ethyl acrylate (EEA), ethylene ethyl methacrylate (EEMA), ethylene (iso) propyl Characterized in that it comprises one or more selected from the group consisting of acrylate (EPA), ethylene (iso) propyl methacrylate (EPMA), ethylene butyl acrylate (EBA) and ethylene butyl methacrylate (EBMA), Ultra high voltage DC power cable.

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