WO2016133332A1

WO2016133332A1 - Power cable

Info

Publication number: WO2016133332A1
Application number: PCT/KR2016/001535
Authority: WO
Inventors: 고경로; 이주연
Original assignee: 엘에스전선 주식회사
Priority date: 2015-02-17
Filing date: 2016-02-16
Publication date: 2016-08-25

Abstract

The present invention relates to a power cable and, particularly, to an extra-high voltage underground or submarine cable. Particularly, the present invention relates to a power cable in which an insulation layer, itself, has high dielectric strength, an electric field to be applied to the insulation layer is effectively buffered, degradation of the insulation layer can be prevented during a cable connection step such that the life of the power cable is extended and simultaneously, the thickness of the insulation layer is minimized such that an outer diameter of the cable is reduced, thereby enabling flexibility, installability, workability and the like of the cable to be improved.

Description

Power cable

FIELD OF THE INVENTION The present invention relates to power cables, in particular ultra high voltage underground or submarine cables. Specifically, the present invention has a high dielectric strength of the insulating layer itself, effectively absorbs the electric field applied to the insulating layer, prevents deterioration of the insulating layer during the operation and connection of the cable, and extends its life. In order to reduce the outer diameter of the cable by minimizing the thickness of the insulating layer, the flexibility of the cable, installation, workability and the like relates to a power cable.

As an insulating layer, a power cable using a polymer insulator such as crosslinked polyethylene (XLPE) is used.However, due to a problem of forming a space charge in a DC high electric field, an ultra-high voltage DC power transmission cable is impregnated with insulating oil in a cross winding insulating paper so as to surround a conductor. Paper-insulated cables having an insulating layer are used.

The ground insulation cable includes an OF (Oil Filled) cable for circulating low viscosity insulation oil, a Mass Impregnated Non Draining (MIND) cable impregnated with high viscosity insulation oil, and the OF cable has a limitation in the transmission length of hydraulic pressure for circulation of the insulation oil. It is not suitable for long distance transmission cables, and in particular, there is a problem that it is difficult to install insulating oil circulation facilities on the seabed, which is not suitable for submarine cables.

Therefore, MIND cable is commonly used for long distance direct current transmission or subsea high voltage cable.

The MIND cable is formed by wrapping the insulating paper in a plurality of layers when forming the insulating layer, for example, using a kraft paper (Kraft paper) or a semi-synthetic laminated laminated thermoplastic resin such as kraft paper and polypropylene resin (Polypropylene) resin Can be used.

Cables impregnated with insulating oil impregnated with kraft only, in the radial direction of the inner layer of the insulating layer in the direction of the inner semiconducting layer by the current flowing through the cable conductors during cable operation (when energizing) The temperature difference occurs in the insulating layer portion in the semiconductive layer direction. Therefore, the insulating oil of the insulating layer portion of the inner semiconducting layer, which is higher in temperature, has a lower viscosity and is thermally expanded to move to the insulating layer of the outer semiconducting layer. The oil-free voids may be formed in the radially inner side, that is, the portion of the insulating layer toward the inner semiconducting layer. The deoiled voids may be shortened in the life of the cable due to the absence of the insulating oil and the electric field is concentrated to cause partial discharge, insulation breakdown, and the like.

However, when the insulating layer is formed of semi-synthetic paper, the flow of the insulating oil can be suppressed by thermal expansion of a thermoplastic resin such as a polypropylene resin which is not impregnated with oil during the operation of the cable, and the polypropylene resin has a kraft paper with an insulation resistance. Because of the larger size, even if deoiled voids are produced, the voltage sharing can be relaxed.

In addition, since the polypropylene resin is not impregnated with the insulating oil, it is possible not only to prevent the insulating oil from flowing in the radial direction of the cable due to gravity, but also according to the impregnation temperature at the time of cable manufacture or the operating temperature at the time of cable operation. Since thermal expansion expands surface pressure on kraft paper, the flow of insulating oil can be further suppressed.

On the other hand, Japanese Laid-Open Patent Publication Nos. 2010-097778, 2013-098136, 2011-216292, etc., suppresses the formation of the deoiling voids and at the same time avoids the concentration of the electric field directly above the conductor and directly under the sheath. In this case, the optimum insulation design, that is, it is difficult to realize the desired resistance of the insulation layer and minimize the thickness of the insulation layer, and thus, there is a problem that the life of the cable is shortened or the thickness of the insulation layer is increased due to the decrease in insulation strength. . Furthermore, since the resin such as polypropylene constituting the semi-synthetic paper is susceptible to heat, the insulation layer may be deteriorated by heat generated during welding in the cable connecting process, particularly in the case of soft connection, which may further shorten the life of the cable.

Therefore, the insulation strength of the insulation layer is high, the electric field applied to the insulation layer is effectively buffered, and the degradation of the insulation layer can be prevented during the operation and connection of the cable, thereby extending the life and There is an urgent need for power cables that can minimize the thickness and reduce the outer diameter of the cable, thereby improving the flexibility, installation, workability, and the like of the cable.

The present invention provides a power cable that can improve the flexibility, installation, workability, etc. of the cable because the insulation strength is high and the life can be extended to minimize the thickness of the insulation layer to reduce the outer diameter of the cable. For the purpose of

In addition, an object of the present invention is to provide a power cable capable of suppressing deterioration of an insulating layer from external heat during a cable connecting step and extending the life of the cable.

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

Conductor; An inner semiconducting layer surrounding the conductor; An insulation layer surrounding the inner semiconducting layer and having an inner insulation layer, an intermediate insulation layer, and an outer insulation layer sequentially stacked; An outer semiconducting layer surrounding the insulating layer; A metal sheath layer surrounding the outer semiconducting layer; And a cable protection layer surrounding the metal sheath layer, wherein the inner insulating layer and the outer insulating layer are each formed of kraft paper impregnated with insulating oil, and the intermediate insulating layer is formed of a semi-synthetic paper impregnated with insulating oil. The semi-synthetic paper includes a plastic film and kraft paper laminated on at least one surface of the plastic film, and based on the total thickness of the insulating layer, the thickness of the inner insulating layer is 1 to 10%, and the thickness of the intermediate insulating layer. Is at least 75%, the thickness of the outer insulation layer is 5 to 15%, and the resistivity of the inner insulation layer and the outer insulation layer is less than the resistivity of the intermediate insulation layer, provides a power cable.

Here, the electric power cable, characterized in that the maximum impulse electric field value of the inner insulating layer is smaller than the maximum impulse electric field value of the intermediate insulating layer.

And, it provides a power cable, characterized in that the maximum impulse electric field value of the intermediate insulating layer is 100 kV / mm or less.

In addition, the thickness of the plastic film, characterized in that 40 to 70% of the total thickness of the semi-synthetic paper, provides a power cable.

The thickness of the outer insulation layer is greater than that of the inner insulation layer.

Furthermore, the thickness of the outer insulation layer is 1.25 to 3 times the thickness of the inner insulation layer, provides a power cable.

On the other hand, the thickness of the inner insulating layer is 0.1 to 2.0 mm, the thickness of the outer insulating layer is 1.0 to 3.0 mm, the thickness of the intermediate insulating layer is 15 to 25 mm, provides a power cable. .

And, the thickness of the kraft paper of the inner insulating layer and the outer insulating layer is greater than the thickness of the kraft paper of the semi-synthetic paper, provides a power cable.

In addition, the thickness of the semi-synthetic paper is 70 to 200 ㎛, and the thickness of the kraft paper of the inner insulating layer and the outer insulating layer is 50 to 150 ㎛, it provides a power cable.

On the other hand, the conductor is made of copper or aluminum, it is a circular compression conductor compressed after the circular element wire in a multi-layer on the flat conductor or circular center line consisting of a multi-layered flat element wire on the circular center line, characterized in that the power cable to provide.

In addition, the plastic film is provided with a polypropylene homopolymer resin, it provides a power cable.

In addition, the insulating oil provides a power cable, characterized in that the high viscosity insulating oil having a kinematic viscosity of 60 ℃ or more than 500 centistokes.

On the other hand, the cable protection layer is characterized in that it comprises an inner sheath, a bedding layer, a metal reinforcing layer and an outer sheath, provides a power cable.

Here, the cable protective layer further provides a power cable, characterized in that it further comprises an outer wire and the outer serving layer.

The power cable according to the present invention exhibits an excellent effect of simultaneously achieving the desired dielectric strength and minimization of the insulation layer through precise control of the structure and thickness of the insulation layer.

In addition, the power cable according to the present invention exhibits an excellent effect of extending the life of the cable by suppressing deterioration of the insulating layer by heat during the connection process of the cable by controlling the thickness of each layer of the insulating layer.

Figure 1 schematically shows the cross-sectional structure of one embodiment of a power cable according to the present invention.

FIG. 2 schematically illustrates a longitudinal cross-sectional structure of the power cable shown in FIG. 1.

3 is a graph schematically illustrating a process in which an electric field is buffered inside an insulation layer of a power cable according to the present invention.

FIG. 4 schematically illustrates a cross-sectional structure of a semisynthetic paper forming an intermediate insulation layer of the power cable shown in FIG. 1.

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 invention to those skilled in the art. Like numbers refer to like elements throughout.

1 and 2 schematically show cross-sectional and longitudinal cross-sectional structures of one embodiment of a power cable according to the invention, respectively.

As shown in FIGS. 1 and 2, the power cable according to the present invention includes a conductor 100, an inner semiconducting layer 200 surrounding the conductor 100, and an insulating layer 300 surrounding the inner semiconducting layer 200. , An outer semiconducting layer 400 surrounding the insulating layer 300, a metal sheath layer 500 surrounding the outer semiconducting layer 400, a cable protection layer 600 surrounding the metal sheath layer 500, and the like. can do.

The conductor 100 is a movement path for electric current for transmission, and has high electrical conductivity to minimize power loss, and has high purity copper (Cu), aluminum (Al), etc. having appropriate strength and flexibility required for use as a conductor of a cable. In particular, it may be made of a linkage line having a high elongation and a high conductivity. In addition, the cross-sectional area of the conductor 100 may be different depending on the amount of power transmission, the use of the cable.

Preferably, the conductor 100 may be composed of a circular compression conductor compressed by placing a flat element wire in multiple layers on a flat conductor or a circular center line composed of multiple flat angle wires on a circular center line. Since the conductor 100 made of a flat conductor formed by a so-called keystone method has a high conductor area ratio, it is possible to reduce the outer diameter of the cable and to form a large cross-sectional area of each element wire. It is economical to reduce.

The inner semiconducting layer 200 suppresses uneven charge distribution on the surface of the conductor 100, alleviates electric field distribution from inside the cable, and removes a gap between the conductor 100 and the insulating layer 300 to partially discharge To suppress dielectric breakdown, etc.

The inner semiconducting layer 200 may be formed by, for example, a transverse winding of carbon paper treated with conductive carbon black on insulating paper, and the thickness of the inner semiconducting layer 200 may be about 0.2 to 1.5 mm.

The insulation layer 300 includes an inner insulation layer 310, an intermediate insulation layer 320, and an outer insulation layer 330, and the inner insulation layer 310 and the outer insulation layer 330 are the intermediate insulation. It is made of a material having a lower resistivity than the layer 320, so that the inner insulating layer 310 and the outer insulating layer 330 are each formed by a current flowing through the conductor 100 when the cable is operated. An electric field buffering function for suppressing application of an electric field directly above the conductor 100 or directly below the metal sheath layer 500 is performed, and further, a function for suppressing deterioration of the intermediate insulating layer 320.

3 is a graph schematically illustrating a process in which an electric field is buffered inside an insulation layer of a power cable according to the present invention. As shown in FIG. 3, a high electric field is applied directly on the conductor 100 and directly under the metal sheath layer 500 by buffering an electric field in the internal insulating layer 310 and the external insulating layer 330 having a relatively low resistivity. In addition, the deterioration of the intermediate insulating layer 320 can be suppressed by controlling the maximum impulse electric field applied to the intermediate insulating layer 320 to 100 kV / mm or less.

Here, the impulse electric field means an electric field applied to the cable when an impulse voltage is applied to the cable. In addition, the inner electric field E _i and the outer electric field E _{o of} each of the inner insulation layer 310, the intermediate insulation layer 320, and the outer insulation layer 330 may be calculated by Equation 1 below.

[Equation 1]

In Equation 1,

U _o is the rated voltage of the cable,

D _io is the outer diameter of each insulating layer,

d _ii is the internal diameter of each insulating layer.

Therefore, as shown in FIG. 3, the maximum impulse electric field value of the internal insulation layer is designed to be smaller than the maximum impulse electric field value of the intermediate insulation layer so that the high electric field does not act directly on the conductor or directly under the sheath. The maximum impulse electric field applied to 320 is an inner electric field E _i of the intermediate insulating layer 320, and the inner electric field E _i is controlled to be 100 kV / mm or less, thereby deteriorating the intermediate insulating layer 320. Can be suppressed.

Therefore, the high electric field is suppressed from being applied to the inner insulation layer 310 and the outer insulation layer 330, particularly, a cable connection member vulnerable to an electric field, and further, the degradation of the intermediate insulation layer 320 is suppressed, thereby preventing the insulation. The degradation of the dielectric strength and other physical properties of the layer 300 can be suppressed, and as a result, the shortening of the life of the cable can be suppressed.

According to an embodiment of the present invention, the inner insulating layer 310 and the outer insulating layer 330 may be formed by transversely kraft paper made of kraft pulp and impregnated with an insulating oil, respectively. The insulating layer 310 and the outer insulating layer 330 may have a lower resistivity and a higher dielectric constant than the intermediate insulating layer 320. The kraft paper can be prepared by washing the kraft pulp with deionized water in order to remove the organic electrolyte in the kraft pulp to obtain good dielectric loss tangent and permittivity.

The intermediate insulating layer 320 may be formed by transversely winding a semi-synthetic paper having kraft paper laminated on an upper surface, a lower surface, or both of the plastic film and impregnating insulating oil. The intermediate insulating layer 320 formed as described above has a higher resistivity and a lower dielectric constant than the inner insulating layer 310 and the outer insulating layer 330 since the plastic film is included, and has a high resistivity of the intermediate insulating layer 320. This makes it possible to reduce the outer diameter of the cable.

In the semi-synthetic paper forming the intermediate insulating layer 320, the plastic film prevents the insulating oil impregnated in the insulating layer 300 from moving toward the outer semiconductive layer 400 due to heat generation during operation of the cable. The production of deoiled voids due to the movement of the insulating oil can be suppressed, and as a result, electric field concentration and insulation breakdown by the deoiled voids can be suppressed. Here, the plastic film may be made of a polyolefin resin such as polyethylene, polypropylene, polybutylene, fluorine resin such as tetrafluoroethylene-hexafluoro polypropylene copolymer, ethylene-tetrafluoroethylene copolymer, Preferably it may be made of a polypropylene homopolymer resin excellent in heat resistance.

In addition, the semi-synthetic paper may be 40 to 70% of the total thickness of the plastic film. When the thickness of the plastic film is less than 40% of the total thickness of the semi-synthetic paper, the resistivity of the intermediate insulating layer 320 may be insufficient, so that the outer diameter of the cable may increase, whereas when the thickness of the plastic film is greater than 70%, the intermediate insulating layer 320 This may cause a problem in which a high field is applied.

The inner insulating layer 310 may have a thickness of 1 to 10% of the total thickness of the insulating layer 300, and the outer insulating layer 330 may have a thickness of 5 to 15% of the total thickness of the insulating layer 300. The intermediate insulating layer 320 may have a thickness of 75% or more of the total thickness of the insulating layer 300. As a result, the maximum impulse electric field value of the inner insulation layer 310 may be lower than the maximum impulse electric field value of the intermediate insulation layer 320. If the thickness of the inner insulation layer is increased more than necessary, the maximum impulse electric field value of the inner insulation layer 310 is larger than the maximum impulse electric field value of the intermediate insulation layer 320, and the cable outer diameter is increased. Will occur. In addition, the outer insulating layer 330 preferably has a sufficient thickness than the inner insulating layer, which will be described later.

In the present invention, the internal insulating layer 310 and the external insulating layer 330 having a small resistivity are provided to prevent the high electric field from being applied directly above the conductor 100 and directly below the metal sheath layer 500. By designing the thickness of the intermediate insulating layer 320 with high resistivity to 75% or more, the cable outer diameter can be reduced.

As such, the inner insulation layer 310, the intermediate insulation layer 320, and the outer insulation layer 330 constituting the insulation layer 300 each have the precisely controlled thickness, so that the insulation layer ( 300 may have a desired dielectric strength while minimizing the outer diameter of the cable. In addition, the most efficient buffering of the electric field applied to the insulating layer 300 to suppress the high electric field is applied directly above the conductor 100 and directly below the metal sheath layer 500, in particular, the cable connection vulnerable to the electric field The insulation strength of a member and other physical property fall can be avoided.

Preferably, the thickness of the outer insulation layer 330 is greater than the thickness of the inner insulation layer 310, for example, the thickness of the inner insulation layer 310 is 0.1 to 2.0 mm, the outer insulation layer The thickness of the 330 may be 1.0 to 3.0 mm, and the thickness of the intermediate insulating layer 320 may be 15 to 25 mm.

Since the heat generated during soft connection for the cable connection according to the present invention is applied to the insulating layer 300 to melt the plastic film of the semi-synthetic paper forming the intermediate insulating layer 320, the plastic from the heat In order to protect the film, it is necessary to sufficiently secure the thickness of the outer insulating layer 330, and it is preferable to be formed thicker than the thickness of the inner insulating layer 310, the thickness of the outer insulating layer 330 It may be 1.5 to 30 times the thickness of the internal insulating layer 310.

In addition, the thickness of the semi-synthetic paper forming the intermediate insulating layer 320 may be 70 to 200 ㎛, the thickness of the kraft paper forming the inner and outer insulating

layers

310, 320 may be 50 to 150 ㎛.

The thickness of the kraft paper forming the inner and outer insulating

layers

310 and 320 is greater than that of the kraft paper constituting the semi-synthetic paper.

If the thickness of the kraft paper forming the inner and outer insulating layers (310,320) is too thin, the strength is insufficient and can be damaged during the transverse winding and the number of the transverse windings to form the insulating layer of the desired thickness increases the productivity of the cable On the other hand, if the thickness of the kraft paper is excessively thick, the total volume of the gap between the kraft paper during the transverse winding of the kraft paper is reduced, which may take a long time when the insulating oil is impregnated, and the content of the insulating oil impregnated is lowered so that the desired insulation It may be difficult to implement the history.

Since the insulating oil impregnated in the insulating layer 300 is fixed without being circulated like the insulating oil used in the OF cable, a high viscosity insulating oil having a relatively high viscosity is used. The insulating oil may perform a lubrication role to facilitate the movement of the insulating paper when the cable is bent, as well as the function of implementing the desired dielectric strength of the insulating layer 300.

The insulating oil is not particularly limited, but should not be oxidized by heat in contact with copper and aluminum constituting the conductor 100, and an impregnation temperature, for example, 100, may be used to facilitate the impregnation of the insulating layer 300. It should have a sufficiently low viscosity above ° C, whereas it should have a sufficiently high viscosity so that it does not flow down at the operating temperature of the cable, for example 80 to 90 ° C. For example, a high viscosity with a kinematic viscosity of 60 ° C or above 500 centistokes. Insulating oil, in particular, naphthenic insulating oil, polystyrene insulating oil, mineral oil, at least one insulating oil selected from the group consisting of alkyl benzene or polybutene synthetic oil, heavy alkylate and the like can be used.

In the process of impregnating the insulating layer 300 with the insulating oil, the kraft paper constituting the inner insulating layer 310, the intermediate insulating layer 320 and the outer insulating layer 330 are formed to a desired thickness, respectively And semi-wound each of the semi-synthetic papers, and vacuum-dried to remove residual moisture, foreign matters, etc. of the insulating layer 300, and a predetermined time in the insulating oil heated to an impregnation temperature, for example, 100 ~ 120 ℃ under a high pressure environment After impregnation for a second time, followed by slow cooling.

The outer semiconducting layer 400 suppresses the uneven charge distribution between the insulating layer 300 and the metal sheath layer 500 to mitigate electric field distribution, and the insulating layer may be formed from various types of metal sheath layers 500. 300) to physically protect.

The outer semiconducting layer 400 may be formed by, for example, a transverse winding of carbon paper treated with conductive carbon black on insulating paper and metallization paper laminated with aluminum thin film on kraft paper, and the thickness of the outer semiconducting layer 400 is about 0.1 to 1.5 mm. In particular, the metallized paper may have a plurality of perforations to facilitate the impregnation of the insulating oil of the insulating layer 300 disposed under the outer semiconducting layer 400.

The metal sheath layer 500 equalizes the electric field inside the insulation layer 300, prevents the electric field from going out of the cable, and provides an electrostatic shielding effect, and provides a ground fault or a ground through the ground at one end of the cable. It acts as a return of fault current in the event of a short circuit accident, promotes safety, protects the cable from shocks, pressures, etc. outside the cable, and improves the cable's orderability and flame retardancy.

The metal sheath layer 500 may be formed by, for example, soft psi made of a lead alloy. As the metal sheath layer 500, the soft sheath has a relatively low electrical resistance, which serves as a shield for a large current, and may further improve the order, mechanical strength, and fatigue characteristics of the cable when formed as a seamless type. have.

In addition, the soft psi is a surface of the anti-corrosion compound, for example, in order to further improve the corrosion resistance, water resistance of the cable and the adhesion between the metal sheath layer 500 and the cable protection layer 600, Blown asphalt, or the like.

The cable protection layer 600 may include, for example, an inner sheath 610, a metal reinforcement layer 630, bedding layers 620 and 640 disposed above and under the metal reinforcement layer 630, and an outer sheath 650. Here, the inner sheath 610 improves the corrosion resistance, the degree of ordering of the cable, and performs a function of protecting the cable from mechanical trauma, heat, fire, ultraviolet rays, insects or animals. The inner sheath 610 is not particularly limited, but may be made of polyethylene having excellent cold resistance, oil resistance, chemical resistance, and the like, or polyvinyl chloride having excellent chemical resistance, flame resistance, and the like.

The metal reinforcement layer 630 may serve to protect the cable from mechanical shock, and may be formed of galvanized steel tape to prevent corrosion, and the galvanized steel tape may be coated with an anticorrosion compound on its surface. . In addition, the bedding layers 620 and 640 disposed above and below the metal reinforcing layer 630 may function to buffer shocks, pressures, and the like from the outside, and may be formed by, for example, a nonwoven tape.

The outer sheath 650 has substantially the same functions and characteristics as the inner sheath 610, and fires in submarine tunnels, land tunnel sections, etc. are used in the region because they are dangerous factors that greatly affect the safety of personnel or facilities. The outer sheath of the cable is applied to polyvinyl chloride excellent in flame retardant properties, the cable outer sheath of the pipe section can be applied to polyethylene with excellent mechanical strength and cold resistance.

In addition, when the cable is a submarine cable, the cable protection layer 600 may further include, for example, an outer serving layer 670 made of an iron sheath 660, polypropylene yarn, or the like. The outer wire sheath 660, the outer serving layer 670 may perform a function of additionally protecting the cable from the sea current, reefs and the like.

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

Conductor;

An inner semiconducting layer surrounding the conductor;

An insulation layer surrounding the inner semiconducting layer and having an inner insulation layer, an intermediate insulation layer, and an outer insulation layer sequentially stacked;

An outer semiconducting layer surrounding the insulating layer;

A metal sheath layer surrounding the outer semiconducting layer; And

A cable protective layer surrounding the metal sheath layer,

The inner insulating layer and the outer insulating layer are each formed of kraft paper impregnated with insulating oil, and the intermediate insulating layer is formed of semi-synthetic paper impregnated with insulating oil, and the semi-synthetic paper is formed on at least one surface of the plastic film and the plastic film. Including laminated kraft paper,

Based on the total thickness of the insulating layer, the thickness of the inner insulating layer is 1 to 10%, the thickness of the intermediate insulating layer is 75% or more, the thickness of the outer insulating layer is 5 to 15%,

And the resistivity of the inner insulation layer and the outer insulation layer is smaller than that of the intermediate insulation layer.
The method of claim 1,

And the thickness of the outer insulation layer is greater than the thickness of the inner insulation layer.
The method according to claim 1 or 2,

The thickness of the inner insulation layer is 0.1 to 2.0 mm, the thickness of the outer insulation layer is 1.0 to 3.0 mm, the thickness of the intermediate insulation layer is 15 to 25 mm, power cable.
The method according to claim 1 or 2,

Wherein the thickness of the outer insulation layer is 1.5 to 30 times the thickness of the inner insulation layer.
The method of claim 1,

And the thickness of the kraft paper of the inner insulation layer and the outer insulation layer is larger than the thickness of the kraft paper of the semi-synthetic paper.
The method of claim 1,

The maximum impulse electric field value of the inner insulation layer is less than the maximum impulse electric field value of the intermediate insulation layer.
The method of claim 1,

And the maximum impulse electric field value of the intermediate insulation layer is 100 kV / mm or less.
The method according to claim 1 or 2,

Wherein the thickness of the plastic film is 40 to 70% of the total thickness of the semisynthetic paper.
The method according to claim 1 or 2,

The thickness of the semi-synthetic paper is 70 to 200 ㎛, the thickness of the kraft paper of the inner insulating layer and the outer insulating layer is 50 to 150 ㎛, power cable.
The method according to claim 1 or 2,

The conductor is made of an interlocking line or aluminum, characterized in that the circular compression conductor compressed after the circular element wire in a multi-layer on a flat conductor or circular center line consisting of a multi-layered flat element wire on a circular center line, characterized in that the compressed.
The method according to claim 1 or 2,

Wherein said plastic film is formed of a polypropylene homopolymer resin.
The method according to claim 1 or 2,

Wherein said insulating oil is a high viscosity insulating oil having a kinematic viscosity of 60 [deg.] C. or more at 500 centistroke or more.
The method according to claim 1 or 2,

Wherein said cable protection layer comprises an inner sheath, a bedding layer, a metal reinforcement layer and an outer sheath.
The method of claim 13,

The cable protective layer is characterized in that it further comprises a wire sheath and an outer serving layer, power cable.