Power cable

Abstract

The objective of the present invention is to provide a structurally stable power cable capable of assuring a high but acceptable current during alternating current transmission by minimizing alternating current resistance by suppressing the skin effect. In addition, according to the power cable of the present invention, a reinforcing string is embedded in a central insulator to assure structural stability of the power cable by preventing problems such as breakage and shrinkage of the central insulator in manufacturing and use environments of the power cable.

Description

power cable

[0001] The present invention relates to a power cable with reduced skin effect. Specifically, the present invention relates to a power cable that is structurally stable and capable of securing a high allowable current during AC transmission by minimizing AC resistance through suppressing the skin effect.

[0002] When alternating current (AC) flows through a conductor used in a power cable, the direction of the current changes according to the frequency, and consequently, an induced electromotive force is generated internally, which hinders the flow of current. As a result, the skin effect occurs, in which the AC resistance increases at the center of the conductor and relatively decreases at the surface of the conductor.

[0003] This skin effect increases as the frequency increases, and because the alternating current is concentrated on the surface of the conductor due to the skin effect, the allowable current that the conductor can transmit decreases when the cross-sectional area is the same.

[0004] Conventional power cables have applied a technology to suppress the skin effect by combining multiple conductor strands to form the cable conductor and insulating the surface of each strand to inhibit current flow between them; however, with the trend toward larger cross-sectional areas of cable conductors, the level of suppression of the skin effect in conductors with large cross-sectional areas has not been sufficient.

[0005] Therefore, there is an urgent need for structurally stable power cables that can secure high allowable current during AC transmission by sufficiently suppressing the skin effect and minimizing AC resistance.

[0006] The present invention aims to provide a power cable capable of securing a high allowable current during AC transmission by minimizing AC resistance through sufficient suppression of the skin effect.

[0007] In addition, the present invention aims to provide a structurally stable power cable in the manufacturing and usage environment of the cable.

[0008] To solve the above problem, the present invention,

[0009] A power cable is provided comprising: a cable center member; an inner semiconducting layer surrounding the cable center member; an insulating layer surrounding the inner semiconducting layer; an outer semiconducting layer surrounding the insulating layer; a metal shielding layer surrounding the outer semiconducting layer; and a jacket layer surrounding the metal shielding layer, wherein the cable center member comprises a central insulator and a conductor surrounding the central insulator, the conductor comprises a plurality of conductor wires, at least some of the plurality of conductor wires are insulating coated conductor wires coated with an insulating material, and the central insulator comprises a reinforcing string and an insulating polymer surrounding the reinforcing string.

[0010] Herein, a power cable is provided characterized in that the elastic modulus of the reinforcing string is 30% or more of the elastic modulus of the conductor wire.

[0011] In addition, the above reinforcing string provides a power cable characterized by including fiber yarn.

[0012] And, the power cable is provided, characterized in that the reinforcing string comprises at least one of aramid fiber, glass fiber, basalt fiber, ceramic fiber and silica fiber.

[0013] Furthermore, a power cable is provided characterized in that the fineness of the reinforcing string is 1500 denier or higher.

[0014] Meanwhile, the above insulating polymer is an insulating elastic polymer, and the elastic modulus of the insulating elastic polymer is 1 MPa or more, thereby providing a power cable.

[0015] Herein, the power cable is provided, characterized in that the insulating elastic polymer comprises at least one of silicone rubber, EPDM (Ethylene Propylene Diene Monomer), polychloroprene rubber, polyurethane rubber, fluoroelastomer, and LSR (Liquid Silicone Rubber).

[0016] In addition, the above-mentioned insulating polymer provides a power cable characterized by including a cross-linked material.

[0017] Meanwhile, a power cable is provided characterized in that the tensile strength of the central insulator is 2 MPa or more.

[0018] In addition, a power cable is provided characterized in that the elastic modulus of the central insulator is 5 MPa or higher.

[0019] Furthermore, a power cable is provided characterized in that the heat resistance temperature of the central insulator is 180°C or higher.

[0020] In addition, a power cable is provided characterized in that the outer diameter of the central insulator is 3 mm to 15 mm.

[0021] In addition, a power cable is provided characterized in that the roundness of the central insulator is 10% or less.

[0022] Furthermore, a power cable is provided characterized in that the elastic modulus of the central insulator is 1000 MPa or less.

[0023] Meanwhile, a power cable is provided that further includes a reinforcing tape wrapping the central insulator.

[0024] Herein, a power cable is provided characterized in that the reinforcing tape is a watertight tape.

[0025] In addition, the coating of the insulating coated conductor wire is an enamel coating, and the remaining portion of the plurality of conductor wires is a non-conductor wire, thereby providing a power cable.

[0026] In addition, the present invention provides a power cable characterized in that the conductor comprises a plurality of fan-shaped segments formed by stranding the plurality of conductor wires, and the cable center member has a structure in which the center insulator and the plurality of segments arranged around the center insulator are combined together.

[0027] Herein, the power cable is provided, wherein the segment comprises a plurality of stranded layers in which the plurality of conductor wires are stranded, and the stranding direction of the conductor wires in each stranded layer is the same in the plurality of stranded layers.

[0028] In addition, a power cable is provided characterized in that the direction of combination of the plurality of segments is the same as the direction of the conductor strands of the stranded layer.

[0029] And, the present invention provides a power cable characterized in that the cable center member further comprises a paper string provided between the outer end of the segment and the outer end of an adjacent segment.

[0030] Meanwhile, the present invention provides a power cable further comprising a binding layer provided between the cable center member and the inner semiconducting layer and surrounding the cable center member, wherein the binding layer comprises: a first binding layer surrounding the cable center member; and a second binding layer surrounding the first binding layer and compensating for non-uniformity on the outer surface of the cable center member.

[0031] Additionally, the present invention provides a power cable characterized by further comprising: a semiconducting tape layer disposed between the outer semiconducting layer and the metal shielding layer and wrapping the outer semiconducting layer; and a binding tape layer disposed between the metal shielding layer and the jacket layer and wrapping the metal shielding layer.

[0032] Herein, the binding tape layer comprises: a semiconducting watertight tape layer; and an aluminum laminate tape layer wrapping the semiconducting watertight tape; and a power cable is provided.

[0033] Meanwhile, a power cable is provided that further includes an outermost semiconducting layer that surrounds the jacket layer and serves as a means for testing the jacket layer.

[0034] According to the power cable of the present invention, by introducing a central insulator into the cable center member to sufficiently suppress the skin effect, AC resistance is minimized, thereby securing a high allowable current during AC transmission.

[0035] In addition, according to the power cable of the present invention, by embedding a reinforcing string in the central insulator, problems such as breakage or shrinkage of the central insulator in the manufacturing and usage environment of the power cable can be prevented, thereby ensuring the structural stability of the power cable.

[0036] In addition, according to the power cable of the present invention, the heat resistance temperature of the central insulator is set to 180°C or higher, thereby preventing damage to the central insulator during the extrusion and crosslinking processes of the insulation layer surrounding the cable central member, and thus further improving structural stability.

[0037] FIG. 1 schematically illustrates one embodiment regarding the cross-sectional structure of a power cable according to the present invention.

[0038] Figure 2 is an enlarged view of the cable center member in Figure 1.

[0039] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art. Throughout the specification, the same reference numerals indicate the same components.

[0040] FIG. 1 schematically illustrates one embodiment regarding the cross-sectional structure of a power cable according to the present invention, and FIG. 2 is an enlarged view of the cable center member in FIG. 1.

[0041] Referring to FIG. 1, the power cable (1000) according to the present invention may be an ultra-high voltage cable and may include a cable center member (100) which is a passage for the flow of current, an inner semiconducting layer (200) which surrounds the cable center member (100) and evenly distributes the charge on the surface of the conductor to make the electric field uniform, an insulating layer (300) which surrounds the inner semiconducting layer (200), an outer semiconducting layer (400) which surrounds the insulating layer (300) and makes the distribution of electric field lines between the inner semiconducting layer (200) equipotential to improve the insulation strength of the insulating layer (300), a metal shielding layer (500) which surrounds the outer semiconducting layer (400), and a jacket layer (600) which surrounds the metal shielding layer (500).

[0042] The inner semiconducting layer (200) and the outer semiconducting layer (400) may each be formed from a semiconducting composition in which a conductive filler such as carbon black, carbon nanotubes, carbon nanoplates, carbon nanoflakes, and metal particles is mixed with an olefin copolymer such as ethylene vinyl acetate (EVA), ethylene atelacylate (EEA), or ethylene butyl acrylate (EBA); the insulating layer (300) may include a polyethylene homopolymer, a random or block copolymer of ethylene with propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or a combination thereof, and the inner semiconducting layer (200), the insulating layer (300), and the outer semiconducting layer (400) may be cross-linked after extrusion to improve physical properties such as heat resistance, mechanical properties, and electrical properties.

[0043] The metal shielding layer (500) can perform the function of grounding the fault current when a line fault occurs, such as in a cable or junction box.

[0044] As illustrated in FIG. 1, the metal shielding layer (500) may be a metal wire shielding layer composed of a plurality of metal wires and a metal tape wound transversely on the outer side of the plurality of metal wires, but is not limited thereto, and a metal sheath shielding layer configured to wrap around the entire outer semiconducting layer (400) may also be applied. The metal wire shielding layer is flexible and relatively lightweight, while the metal sheath shielding layer has high overall mechanical strength and can provide excellent resistance to external impact or wear. The metal sheath shielding layer may have a corrugated structure or a smooth structure; the corrugated structure provides high flexibility, which is advantageous in environments where bending occurs frequently, and the smooth structure has the advantage of being easy to manufacture and install and easy to maintain.

[0045] In addition, the jacket layer (600) may include polyethylene, polyvinyl chloride, polyurethane, etc., and is preferably made of polyethylene resin, for example, and is more preferably made of high-density polyethylene (HDPE) resin when considering mechanical strength.

[0046] As illustrated in FIG. 1, the power cable (1000) may further include a semiconducting tape layer (510) that is positioned between the outer semiconducting layer (400) and the metal shielding layer (500) and wraps around the outer semiconducting layer (400). The semiconducting tape layer (510) can perform the function of protecting the outer semiconducting layer (400) and the insulation layer (300) by relieving the mechanical pressure applied to the outer semiconducting layer (400) due to the pressure generated during the manufacture of the metal shielding layer (500). Additionally, for a power cable placed in an environment requiring watertight performance, a watertight tape may be applied as the semiconducting tape layer (510). The watertight tape may be a swellable tape coated with a material that expands upon contact with moisture, but is not limited thereto.

[0047] Additionally, the power cable (1000) may further include a binding tape layer (520) that is positioned between the metal shielding layer (500) and the jacket layer (600) and wraps around the metal shielding layer (500). By applying the binding tape layer (520), the structure of the metal shielding layer (500) can be stably maintained. In the case of a power cable placed in an environment requiring watertight performance, the binding tape layer (520) may be composed of a semiconducting watertight tape layer and an aluminum laminated tape layer (laminated foil) that wraps around the semiconducting watertight tape layer. The semiconducting watertight tape is a semiconducting swelling watertight tape that can delay the penetration of water, and the aluminum laminated tape is positioned to wrap around the semiconducting swelling watertight tape to block moisture penetration from the circumferential direction of the power cable, thereby protecting the metal shielding layer (500). The above aluminum laminate tape is in the form of a thin aluminum tape coated with a semiconductive material, and can economically and effectively provide a moisture barrier function in the circumferential direction of the cable.

[0048] Furthermore, the power cable (1000) may additionally include an outermost semiconducting layer (700) surrounding the jacket layer (600). The outermost semiconducting layer (700) may be provided as a means to test the jacket layer (600), enabling the inspection of the insulation characteristics of the jacket layer (600) when necessary during processes such as cable production, transportation, laying, connection, and line operation. The condition of the jacket layer (600) can be evaluated by using the outermost semiconducting layer (700) as one electrode and the metal shielding layer (500) or aluminum laminate tape as the other electrode to inspect whether current flows.

[0049] The outermost semiconducting layer (700) can be formed by semiconducting extrusion or by applying a graphite coating. When the semiconducting extrusion process is applied, the cable can achieve an excellent appearance and has the advantage of low resistance, whereas when the graphite coating is applied, it has the economic advantage of requiring low material costs and simple process conditions.

[0050] The cable center member (100) may include a center insulator (120) and a conductor (110) surrounding the center insulator (120). The conductor (110) may include a plurality of conductor wires (112), at least some of the plurality of conductor wires (112) may be insulated coated conductor wires (113) with an insulating material coated on the surface of the conductor wires, and the remaining portion may be non-conductive wires (114) without an insulating material coated on the surface of the conductor wires. In particular, the insulating material coating of the insulated coated conductor wires (113) may be an enamel coating.

[0051] The skin effect can be reduced by making all of the plurality of conductor wires (112) into insulating coated conductor wires (113), but preferably, a structure is applied in which some of the plurality of conductor wires (112) are made into thin conductor wires (114) and insulating coated conductor wires (113) are arranged around thin conductor wires (114) to suppress direct contact between thin conductor wires (114), thereby allowing the skin effect to be sufficiently minimized without configuring all of the conductor wires (112) into insulating coated conductor wires (113).

[0052] The above conductor (110) may further reduce the skin effect by applying a split conductor comprising a plurality of segments (111). As an example thereof, as shown in FIG. 2, the conductor (110) may include a plurality of fan-shaped segments (111) formed by twisting a plurality of conductor wires (112) comprising a plurality of conductor wires (114) and a plurality of insulating coated conductor wires (113), and the cable center member (100) may have a structure in which the center insulator (120) is provided in the center and the center insulator (120) and a plurality of segments (111) arranged around the center insulator (120) are combined together.

[0053] Each of the above segments (111) may be composed of a plurality of stranded wire layers. For example, a plurality of stranded wire layers may be formed by placing a conductor wire (112) at the center of one segment (111), arranging conductor wires (112) to surround the conductor wire (112) placed at the center to form a first stranded wire layer, arranging conductor wires (112) to surround the first stranded wire layer to form a second stranded wire layer, and arranging conductor wires (112) to surround the second stranded wire layer to form a third stranded wire layer. The number of stranded wire layers may increase or decrease depending on the conductor cross-sectional area.

[0054] Each conductor wire (114) forming the stranded wire layer is positioned so that its surroundings are adjacent to an insulating coated conductor wire (113), thereby suppressing direct contact between the conductor wires (114) and minimizing the skin effect.

[0055] The above conductor (110) may have a uni-direction type in which the conductor wires of each strand layer are stranded in the same direction in multiple strand layers, but is not limited thereto, and the conductor wires of each strand layer may have a bi-direction type in which at least one of the multiple strand layers is stranded in a different direction. For example, in the case of a conductor having first to fifth strand layers, the first to fifth strand layers may all have a right stranding direction and be of a uni-direction type, or the second strand layer may have a left stranding direction and the remaining strand layers may have a right stranding direction and be of a bi-direction type. However, preferably, it may be of a uni-direction type, and more preferably, the direction of the segments may also be the same as the direction of the strand layer, and in this case, Ks may be reduced.

[0056] Here, Ks is a factor related to the AC resistance component due to the skin effect, and can be calculated by measuring the AC resistance of a conductor according to CIGRE TB 894 and applying the measured AC resistance to the standard IEC 60287-1-1. For a conductor with the same cross-sectional area, if the Ks value is large, the AC resistance increases and the AC allowable current decreases, and conversely, if the Ks value is small, the AC resistance decreases and the AC allowable current increases.

[0057] The conductor wires (112) of each segment (111) generate mutual inductance when AC current is applied, and the mutual inductance generates an induced electromotive force in the conductor wires (112). In the case of the bi-direction type, the induced electromotive force generated by a stranded wire layer with a Z-direction direction in an adjacent stranded wire layer and the induced electromotive force generated by a stranded wire layer with an S-direction direction in an adjacent stranded wire layer are in opposite directions, so stranded wire layers with different stranded directions can act as factors that hinder the actual flow of current.

[0058] That is, the bi-direction type has greater interference between conductor wires (112) than the uni-direction type, so the flow of AC current is not smooth, resulting in a relatively large Ks value and increased AC resistance, which can lead to a smaller allowable current in a conductor with the same cross-sectional area. Therefore, it may be advantageous to apply the uni-direction type to the segment (111) in terms of power cable operation.

[0059] The following describes the results of experiments to derive Ks values ​​for the Uni-direction type and Bi-direction type, respectively.

[0060] Two Cu 2250mm² test conductors were prepared by placing a central conductor in the center and combining the central conductor with multiple segments. At this time, each segment of the test conductor was configured to include five stranded wire layers. The stranded wire layers of test conductor 1 were designed as a uni-direction type with an SSSSS twist direction, whereas the stranded wire layers of test conductor 2 were designed as a bi-direction type with an SZSSS twist direction; for test conductor 1, the Ks value was calculated to be 0.297, and for test conductor 2, the Ks value was calculated to be 0.391.

[0061] Here, Ks is a factor related to the AC resistance component due to the skin effect, which can be calculated by measuring the AC resistance of a conductor according to the method of CIGRE TB 894 and applying the measured AC resistance to the standard IEC 60287-1-1.

[0062] As such, it was confirmed that the Ks value of test conductor 1, in which the twist direction of the conductor wire (112) in each stranded layer is the same, is smaller than the Ks value of test conductor 2, in which the twist direction of the conductor wire (112) in each stranded layer is different, and thus it was experimentally confirmed that applying a uni-direction type is advantageous in terms of AC current operation when the area of ​​the conductor is the same.

[0063] The cable center member (100) may include a center insulator (120) positioned in the center. For example, the center insulator (120) may be positioned in the center, and the plurality of segments (111) may be positioned around the center insulator (120) to combine the center insulator (120) and the plurality of segment divided conductors.

[0064] In the case of the existing cable center member (100), a center conductor or an insulating coated center conductor was applied to the center instead of a center insulator. In this case, the mutual inductance generated between the center conductor and each segment generated an induced electromotive force and acted as a factor that hindered the flow of current.

[0065] Accordingly, the present invention can reduce AC resistance by reducing the Ks value by applying a central insulator (120) instead of a conventional central conductor, thereby eliminating current interference factors occurring between the central conductor and each segment (111), and thus can secure a larger allowable current compared to a conductor having the same cross-sectional area.

[0066] The above-mentioned central insulator (120) may include an insulating polymer (122). For example, the insulating polymer (122) may be composed of polypropylene, polystyrene, polyurethane, silicone rubber, EPDM (Ethylene Propylene Diene Monomer), polychloroprene rubber, fluoroelastomer, LSR (Liquid Silicone Rubber), polybutadiene rubber, etc.

[0067] In particular, the insulating polymer (122) preferably includes a flexible material to ensure stability against bending in an environment where the power cable (1000) is wound onto a drum or laid out, and the insulating polymer (122) may be an insulating elastic polymer. An insulating elastic polymer may refer to an insulating polymer that simultaneously possesses insulating properties and elastic properties.

[0068] When manufacturing a cable center member, a tensile force may be applied to the center insulator (120) during the process of combining the center insulator (120) and a plurality of segments (111) surrounding the center insulator (120). If the center insulator (120) is formed only from an insulating polymer (122), a problem may occur in which the center insulator (120) breaks due to the tensile force. Alternatively, the power cable (1000) may be manufactured with the center insulator (120) excessively tensed due to the tensile force, and during the process of using it, the tensile center insulator (120) may contract and be drawn inward relative to the end surface of the power cable (1000) conductor.

[0069] Accordingly, the present invention embeds a reinforcing string (121) inside the insulating polymer (122) to prevent the breaking of the central insulator (120) during the cable central member assembly process and to prevent the central insulator (120) from being pulled in due to shrinkage when using the finished cable.

[0070] The elastic modulus of the reinforcing string (121) may be 30% or more of the elastic modulus of the conductor wire (112). For example, the conductor wire (112) may be composed of copper or aluminum, and the reinforcing string (121) may be composed of fiber yarn, and in particular, may be composed of a material including at least one of aramid fiber, glass fiber, basalt fiber, ceramic fiber, and silica fiber. Preferably, the reinforcing string (121) may be provided with aramid fiber, which is advantageous for processing.

[0071] The fineness of the reinforcing string (121) may be 1500 denier or more. Here, fineness indicates the thickness of the fiber, and denier is a unit representing the density of the fiber in terms of weight per unit length, where 1 denier means the thickness of a thread that can travel 9,000m per 1g. If the fineness of the reinforcing string (121) is lower than 1500 denier, it may be difficult to sufficiently compensate for the problem of the insulating polymer (122) being excessively stretched, and the central insulator (120) may break or be damaged during tension.

[0072] The above reinforcing string is formed to have sufficient bonding strength with the insulating polymer so that even when tensile force is applied to the central insulator, the surface of the reinforcing string does not separate from the insulating polymer and maintains the bond.

[0073] The elastic modulus of the central insulator (120) to which the reinforcing string (121) is applied may be 5 MPa or more. If the elastic modulus of the central insulator (120) is less than 5 MPa, the central insulator (120) may be excessively stretched during the above assembly process, and when the power cable (1000) is manufactured with the central insulator (120) being excessively stretched in this way, the central insulator (120) inside the power cable (1000) may contract during the process of use, such as winding the power cable (1000) onto a drum for storage and transport, and unwinding the power cable (1000) from the drum to lay it in an environment containing various bends, and a problem may occur in which the central insulator (120) is drawn inward relative to the end cross-section of the conductor of the power cable.

[0074] When the central insulator (120) shrinks and is drawn into the inside of the power cable, a void space is created in the center of the conductor at the end of the power cable, which may cause defects during intermediate connection of the power cable, and if the shrinkage is severe, a problem may arise where a certain portion of the end of the power cable must be cut. In addition, there is a possibility that the central insulator will have continuous shrinkage force when the power cable is used, and defects may occur due to additional shrinkage during use. Therefore, it is advantageous to minimize the shrinkage of the central insulator (120), and preferably, the depth to which the central insulator shrinks relative to the end of the power cable can be 15 mm or less.

[0075] Additionally, the elastic modulus of the center insulator (120) may be 1000 MPa or less, and if the elastic modulus of the center insulator (120) exceeds 1000 MPa, workability may be significantly reduced in the process of combining multiple segments and the center insulator when manufacturing the cable center member.

[0076] Additionally, the tensile strength of the central insulator (120) may be 2 MPa or more. If the tensile strength of the central insulator (120) is less than 2 MPa, it may break or be damaged because it cannot withstand the tensile force applied to the central insulator (120) during the process of joining with the segment (111).

[0077] The characteristics, such as the elastic modulus and tensile strength of the above-mentioned central insulator, are determined by measuring the central insulator of a composite structure in which the reinforcing string is embedded in an insulating polymer.

[0078] The above-mentioned central insulator (120) may include a material having a heat resistance temperature of 180°C or higher to withstand the temperature rise during the cross-linking process of the insulating layer (300). The heat resistance temperature may be the temperature at which the properties or shape of the central insulator (120) are deformed when the temperature is raised from room temperature, and the heat resistance temperature of the central insulator (120) material can be measured by conducting a Hotset test according to standard IEC 60811-507 at a temperature condition of 180°C to determine if it satisfies 180°C or higher. If the heat resistance temperature of the central insulator (120) is less than 180°C, the shape of the central insulator (120) may be deformed due to the temperature rise that occurs during the process of extruding and cross-linking the insulating layer (300) to the cable central member (100), and the overall structural stability of the combined cable central member (100) may decrease.

[0079] The central insulator (120) may be positioned at the center of the plurality of segment combined structures to improve the overall structural stability of the cable center member (100). To this end, the central insulator (120) may be a cylindrical string structure, and the roundness of its cross-section may be 10% or less. Roundness may refer to the ratio of the cross-section deviating from a geometric circle, and the measurement of roundness may be performed by a known method. If the roundness exceeds 10%, the arrangement of the segments (111) may not be aligned in a circular manner, and the structural stability of the entire power cable (1000) may be reduced.

[0080] Additionally, in order for the central insulator (120), which is a cylindrical string structure, to withstand the pressure applied by the multiple segments (111) surrounding it and maintain a circular shape when combined with the multiple segments (111), if the insulating polymer (122) included in the central insulator (120) is an insulating elastic polymer, the elastic modulus of the insulating elastic polymer may be 1 MPa or more. If the elastic modulus of the insulating elastic polymer is less than 1 MPa, the central insulator (120) may be excessively deformed by pressure during the process of combining the central insulator (120) with the multiple segments (111), and the arrangement of the segments (111) may not be aligned in a circular shape.

[0081] The outer surface of the insulating polymer may have a smooth shape. This prevents the generation of dust caused by friction between the central insulator and the segment during the assembly process of the cable central members or the use of the finished cable, which would otherwise occur if the surface of the central insulator were not smooth.

[0082] The insulating polymer (122) may be made of various insulating elastic polymer materials, for example, the insulating elastic polymer may be composed of silicone rubber, EPDM (Ethylene Propylene Diene Monomer), polychloroprene rubber, polyurethane rubber, fluoroelastomer (Viton), and LSR (Liquid Silicone Rubber). More preferably, EPDM (Ethylene Propylene Diene Monomer) may be included to satisfy conditions such as flexibility, heat resistance temperature, tensile strength, and elastic modulus. Additionally, to supplement tensile strength and elastic modulus, the insulating polymer (122) may include a cross-linked material.

[0083] The outer diameter of the central insulator (120) may be 3 to 15 mm. If the outer diameter of the central insulator (120) is less than 3 mm, the central insulator (120) may not sufficiently fill the center of the combined structure with the plurality of segments (111), making it difficult to maintain a circular combined structure, and if the outer diameter of the central insulator (120) is greater than 15 mm, the overall diameter of the power cable (1000) may become larger than necessary.

[0084] The cable center member (100) may further include a reinforcing tape (131) that wraps around the center insulator (120). Additionally, it may further include a second reinforcing tape (132) disposed between the first reinforcing tape (131) that wraps around the center insulator (120) and an adjacent segment (111).

[0085] The first reinforcing tape (131) and the second reinforcing tape (132) may be composed of, for example, non-woven tapes and may contribute to improving the structural stability of the cable center member (100). In particular, in environments where watertightness is required, the first and second reinforcing tapes (131, 132) may be implemented as watertight tapes, and, for example, a PET swelling watertight tape that absorbs moisture and expands may be applied.

[0086] Additionally, to enhance watertightness in environments where the above watertightness is required, a watertight tape (not shown), for example, a swelling watertight tape made of polyethylene terephthalate (PET) material, may be additionally inserted between the plurality of stranded wire layers constituting each segment (111) to block moisture from moving in the longitudinal direction of the cable center member (100).

[0087] Meanwhile, the cable center member (100) may further include a paper string (140) provided between the outer end of a segment (111) and the outer end of an adjacent segment (111). The outer end of the segment (111) may refer to a portion that meets the arc of the fan-shaped segment (111) and either of the two radii. The cross-sectional shape of the paper string (140) is not limited. For example, the cross-sectional shape of the paper string (140) may be circular, semicircular, triangular, pyramidal, etc.

[0088] A paper string (140) provided between the outer ends of the segments (111) can strengthen the structural stability of the cable center member (100). In the absence of the paper string (140), when the insulation layer (300) is extruded, the inner semiconducting layer (200) may penetrate between the outer ends of the segments (111), and consequently, the interface between the inner semiconducting layer (200) and the insulation layer (300) may become uneven, thereby reducing the dielectric strength. On the other hand, when the paper string (140) is provided as in the embodiments, the structural stability of the cable center member (100) is strengthened, and the inner semiconducting layer (200) cannot penetrate into the space between the outer ends of the segments (111), thereby preventing a reduction in dielectric strength.

[0089] Additionally, referring to FIG. 1, the power cable (1000) may additionally include a binding layer (150) that surrounds the cable center member (100) and is provided between the cable center member (100) and the internal semiconducting layer (200).

[0090] Specifically, the binding layer (150) may include a first binding layer that wraps around a cable center member (100) by winding the combined plurality of conductor wires (112) together, and a second binding layer that wraps around the first binding layer and performs a cushioning and protection function for the outer surface of the cable center member (100).

[0091] The first binding layer can be implemented with a general tape such as a nonwoven fabric, and a watertight tape can be applied in environments where watertightness is required. For example, watertightness performance can be provided to the power cable (1000) to minimize the recovery range when water penetrates the power cable (1000) or the connection box connecting the power cable (1000). In this case, the first binding layer can be configured with a semiconductive swelling watertight tape so that when water penetrates, it expands to block the gap between the cable center member (100) and the internal semiconductive layer (200), thereby minimizing the progression of water.

[0092] The second binding layer is made of a material having stronger mechanical properties than the first binding layer, thereby strongly additionally binding the cable center member (100) bound by the first binding tape, thereby stably maintaining the structure of the cable center member (100) and compensating for the non-uniformity of the outer surface of the cable center member (100), so as to minimize the phenomenon in which the inner semiconducting layer (200) penetrates between conductor wires or segments during the extrusion process of the insulation layer (300) and surface non-uniformity of the inner semiconducting layer (200) occurs. The second binding layer may be formed, for example, as an STB tape (Semi-conducting Tetron Tape) having stronger mechanical properties than a swelling watertight tape.

[0093] The cable center member (100) according to the present invention can achieve excellent effects that ensure high allowable current during AC transmission and structural stability by sufficiently suppressing the skin effect through the application of the previously described material and structure.

[0094]

[0095] [Example]

[0096]

[0097] 1. Measurement of Ks value based on whether center insulation is applied

[0098]

[0099] Specimens of a cable center member including a center structure were manufactured according to the design described in Table 1 below, and DC resistance, AC resistance, and Ks values ​​were measured. The AC resistance was measured according to the method of CIGRE TB 894, and the Ks value was calculated by applying the measured AC resistance to the standard IEC 60287-1-1.

[0100] Example 1 has a conductor cross-sectional area of ​​2200 mm² and a central insulator is applied as the central structure; Example 2 has a conductor cross-sectional area of ​​3500 mm² and a central insulator is applied as the central structure; Comparative Example 1 has a conductor cross-sectional area of ​​2250 mm² and a central conductor (50 mm² stranded wire) is applied as the central structure; Comparative Example 2 has a conductor cross-sectional area of ​​2500 mm² and a central conductor (50 mm² stranded wire) is applied as the central structure; and Comparative Example 3 has a conductor cross-sectional area of ​​3000 mm² and a central conductor (225 mm² stranded wire) is applied as the central structure. Examples 1 and 2, and Comparative Examples 1 to 3 all use a uni-direction type conductor. When a central insulator is applied as the central structure, the conductor cross-sectional area is the cross-sectional area excluding the central insulator, and when a central conductor is applied as the central structure, the conductor cross-sectional area is the cross-sectional area including the central conductor.

[0101]

[0102] Conductor Cross-sectional Area (mm²) Center Structure Type DC Resistance (Ω / m, 20℃) AC Resistance (Ω / m) Ks Value Example 1 2200 Center Insulator Uni-direction 8.16 4.E-06 8.70 3.E-06 0.197 Example 2 3500 Center Insulator Uni-direction 5.09 0.E-06 5.8 4.E-06 0.194 Comparative Example 1 2250 Center Conductor 50 mm² Uni-direction 7.76 2.E-06 8.8 1.E-06 0.292 Comparative Example 2 2500 Center Conductor 50 mm² Uni-direction 7.04 0.E-06 8.28 0.E-06 0.297 Comparative Example 3 3000 Center Conductor 225 mm²Uni-direction5.837.E-068.988.E-060.513

[0103]

[0104] As indicated in Table 1 above, it can be confirmed that the conductors of Examples 1 and 2, to which the central insulator is applied, have lower Ks values ​​than the conductors of Comparative Examples 1 to 3, to which the central conductor is applied. Referring to Examples 1 and 2, when a central insulator is applied as the central structure of the conductor, the DC resistance and AC resistance decrease as the cross-sectional area of ​​the conductor increases, whereas referring to Comparative Examples 1 to 3, when a central conductor is applied as the central structure of the conductor, the DC resistance decreases as the cross-sectional area of ​​the conductor increases, whereas the AC resistance does not change significantly or actually increases.

[0105] In particular, there is a recent demand for a body with a surface area of ​​3000 mm² or more. In Example 2, the Ks value related to the skin effect was calculated to be lower compared to Example 1, and the AC resistance was measured to be lower, confirming that the AC allowable current was significantly increased. On the other hand, in Comparative Example 3, the Ks value related to the skin effect was calculated to be higher compared to Comparative Example 2, and the AC resistance was measured to be increased, confirming that the AC allowable current was decreased.

[0106]

[0107] 2. Experiments based on the material of the central insulator

[0108]

[0109] 1) Preparation Example

[0110] Power cable samples containing a core insulator made of a material having the properties listed in Table 2 below were manufactured, and tests were conducted to determine whether the core insulator of each power cable sample was shrunk or damaged. The manufacturing examples in Table 2 were set to have the same cable structure and manufacturing conditions, except that a core insulator made of a different material was applied to each. The power cable sample included a cable core member comprising six segments and a core insulator with an outer diameter of 8 mm, and the conductor cross-sectional area excluding the core insulator was set to 3500 mm². A power cable sample with a cable insulation outer diameter of 126.8 mm was manufactured by performing extrusion and cross-linking insulation operations including an inner semiconducting layer, an insulating layer, and an outer semiconducting layer.

[0111]

[0112] Classification Core Insulator Material Elastic Modulus (MPa) Tensile Strength (MPa) Hotset (180 ℃) Shrinkage Length (mm) Core Insulator Damage Example 3 Cross-linked EPDM, aramid yarn 108 24 Passed 3X Comparative Example 4 Soft silicone rubber 42 Passed 19X Comparative Example 5 HDPE 700 20 Rejected Unmeasurable O Comparative Example 6 Non-cross-linked EPDM 51 Rejected Unmeasurable O

[0113]

[0114] 2) Methods for evaluating physical properties

[0115] The elastic modulus of the center insulator was averaged after 10 center insulator specimens of each example and comparative example were prepared according to the ASTM D638 standard.

[0116] The tensile strength of the center insulator was measured in accordance with Clause 19 of Standard KS C 3004, in the string state of the center insulator.

[0117] The Hotset test was conducted by testing the material of the core insulator at a temperature of 180°C in accordance with the standard IEC 60811-507 to determine whether it passed or failed.

[0118] The shrinkage length of the center insulator was measured by applying the bending test method of Section 12.4.3 of the standard IEC 62067, by repeatedly winding and unwinding the power cable samples of each example and comparative example onto a drum with a radius of 1.5 m, which is smaller than 20 times the outer diameter of the insulation, and then measuring the depth to which the center insulator has shrunk in the end section of the power cable sample.

[0119] Whether the core insulator was damaged was determined by applying the bending test method of Section 12.4.3 of the standard IEC 62067. Each power cable sample of the example and comparative example was wound and unwound repeatedly on a drum with a radius of 1.5 m, which is smaller than 20 times the outer diameter of the insulation. When the power cable sample was disassembled, it was determined to be defective if there was thermal deformation, cracks, or damage to the core insulator.

[0120] As described in Table 2 above, the power cable sample of Example 3, in which the core insulator is composed of an insulating polymer and a reinforcing string and has appropriate elastic modulus, tensile strength, and heat resistance temperature, was confirmed to have a shrinkage length of the core insulator minimized to 15 mm or less and damage suppressed.

[0121] On the other hand, in Comparative Example 4, the power cable sample in which the elastic modulus of the central insulator was below the standard caused the central insulator to shrink excessively, and in Comparative Example 5, the power cable sample in which the heat resistance temperature of the central insulator was less than 180°C caused the central insulator to melt and be damaged during the cross-linking process of the insulation layer surrounding the cable central member, and in Comparative Example 6, in which the tensile strength of the central insulator was below the standard, the central insulator broke due to tensile force during the joining process of the cable central members.

[0122] Although this specification has been described with reference to preferred embodiments of the present invention, those skilled in the art may modify and change the present invention in various ways without departing from the spirit and scope of the present invention as described in the claims below. Therefore, if a modified embodiment basically includes the components of the claims of the present invention, it should be considered to be included within the technical scope of the present invention.

Claims

1. Cable central member; An inner semiconducting layer surrounding the above cable center member; An insulating layer surrounding the above-mentioned internal semiconducting layer; An outer semiconducting layer surrounding the above insulating layer; A metal shielding layer surrounding the above outer semiconducting layer; and It includes a jacket layer surrounding the metal shielding layer, and The above cable center member includes a center insulator and a conductor surrounding the center insulator, and The above conductor comprises a plurality of conductor wires, and at least some of the plurality of conductor wires are insulating coated conductor wires coated with an insulating material. A power cable characterized in that the above-described central insulator comprises a reinforcing string and an insulating polymer that surrounds the reinforcing string.

2. In Paragraph 1, A power cable characterized in that the elastic modulus of the reinforcing string is 30% or more of the elastic modulus of the conductor wire.

3. In Paragraph 1, A power cable characterized in that the above reinforcing string includes fiber yarn.

4. In Paragraph 3, A power cable characterized in that the reinforcing string comprises at least one of aramid fiber, glass fiber, basalt fiber, ceramic fiber, and silica fiber.

5. In Paragraph 3, A power cable characterized by the fact that the fineness of the reinforcing string is 1500 denier or higher.

6. In Paragraph 1, A power cable characterized in that the insulating polymer is an insulating elastic polymer, and the elastic modulus of the insulating elastic polymer is 1 MPa or more.

7. In Paragraph 6, A power cable characterized in that the above insulating elastic polymer comprises at least one of silicone rubber, EPDM (Ethylene Propylene Diene Monomer), polychloroprene rubber, polyurethane rubber, fluoroelastomer, and LSR (Liquid Silicone Rubber).

8. In Paragraph 1, A power cable characterized in that the insulating polymer comprises a cross-linked material.

9. In Paragraph 1, A power cable characterized by the tensile strength of the central insulator being 2 MPa or more.

10. In Paragraph 1, A power cable characterized by the elastic modulus of the central insulator being 5 MPa or higher.

11. In Paragraph 1, A power cable characterized by the heat resistance temperature of the central insulator being 180°C or higher.

12. In Paragraph 1, A power cable characterized in that the outer diameter of the central insulator is 3 mm to 15 mm.

13. In Paragraph 1, A power cable characterized by the roundness of the central insulator being 10% or less.

14. In Paragraph 1, A power cable characterized in that the elastic modulus of the central insulator is 1000 MPa or less.

15. In Paragraph 1, A power cable characterized by further including a reinforcing tape wrapping the central insulator.

16. In Paragraph 15, A power cable characterized in that the above reinforcing tape is a watertight tape.

17. In Paragraph 1, The coating of the above-mentioned insulating coated conductor wire is an enamel coating, and A power cable characterized in that some of the remaining parts of the plurality of conductor wires are non-conductor wires.

18. In Paragraph 1, The above conductor includes a plurality of fan-shaped segments formed by stranding the plurality of conductor wires, and A power cable characterized in that the cable center member is a structure in which the center insulator and the plurality of segments arranged around the center insulator are combined together.

19. In Paragraph 18, The above segment includes a plurality of stranded layers in which the plurality of conductor wires are stranded, and A power cable characterized in that the stranding direction of the conductor wires in each stranded layer is the same in multiple stranded layers.

20. In Paragraph 19, A power cable characterized in that the direction of association of the plurality of segments is the same as the direction of the conductor strands of the stranded layer.

21. In Paragraph 18, A power cable characterized in that the cable center member further comprises a paper string provided between the outer end of the segment and the outer end of an adjacent segment.

22. In Paragraph 1, It further includes a binding layer provided between the cable center member and the inner semiconducting layer and surrounding the cable center member, and The binding layer above is, A first binding layer surrounding the cable center member; and A power cable characterized by including a second binding layer that surrounds the first binding layer and compensates for the non-uniformity of the outer surface of the cable center member.

23. In Paragraph 1, A semiconducting tape layer disposed between the outer semiconducting layer and the metal shielding layer and surrounding the outer semiconducting layer; and A power cable characterized by further including a binding tape layer disposed between the metal shielding layer and the jacket layer and wrapping the metal shielding layer.

24. In Paragraph 23, The above binding tape layer is, Semiconductive watertight tape layer; and A power cable characterized by including an aluminum laminate tape layer wrapping the above-mentioned semiconducting watertight tape.

25. In Paragraph 1, A power cable characterized by further including an outermost semiconducting layer that surrounds the jacket layer and serves as a means for testing the jacket layer.

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