BRIEF DESCRIPTION OF THE INVENTION
Technical Field
[0001] The present invention relates to an internal strength member for an overhead transmission line, and an overhead transmission line including the same. More particularly, the present invention relates to an internal strength member, for an overhead transmission line, which is capable of achieving low-sag characteristics of an overhead transmission line, has bending resistance enough to suppress damage to the internal strength member when the overhead transmission is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line, and is capable of suppressing corrosion of conductor wires arranged around the internal strength member of the overhead transmission line and reducing total resistance of the overhead transmission line to improve a power transmission rate; and an overhead transmission line including the same.
Background Art
[0002] Methods of supplying power to cities, factories, etc. from a power plant via a substation include an overhead transmission method using an overhead transmission line connected via iron towers and an underground transmission method using an underground transmission line buried underground. The overhead transmission method occupies about 90% of domestic transmission methods.
[0003] Conventionally, an aluminum conductor steel reinforced (ACSR) overhead transmission line manufactured by twisting a plurality of strands of aluminum alloy conductors around an outer circumference of an internal strength member is generally used as an overhead transmission line to achieve high tension characteristics.
[0004] However, a sag ratio of the ACSR overhead transmission line is high due to a heavy weight of a steel core used as the internal strength member, and increasing the weight of an aluminum conductor to increase a power transmission rate of the overhead transmission line is limited. Many attempts have been made to manufacture a lightweight overhead transmission line having an internal strength member formed of a fiber reinforced composite material so as to reduce the sag

ratio of the overhead transmission line or increase a power transmission rate versus the same sag ratio.
[0005] FIG. 1 is a schematic cross-sectional view of an overhead transmission line with an internal strength member including a fiber-reinforced composite material, according to the related art.
[0006] As illustrated in FIG. 1, the overhead transmission line according to the related art includes an internal strength member 10 and conductor wires 20 arranged around the internal strength member. To achieve high tension characteristics, the internal strength member 10 may include a core part 11, and an anti-corrosion layer 12 suppressing corrosion of the conductor wires 20 due to bimetallic corrosion, i.e., galvanic corrosion, between the core part 11 and the conductor wire 20.
[0007] In particular, an aluminum conductor composite core (ACCC) overhead transmission line is disclosed, as an example of a conventional overhead transmission line with the internal strength member including the fiber reinforced composite material, in Korean Laid-Open Patent Publication Nos. 2007-0014109 and 2014-0053398 and Korean Registered Patent No. 1046215.
[0008] The ACCC overhead transmission line includes an internal strength member having an inner core formed by impregnating a carbon fiber-reinforced material with epoxy resin and an outer core formed on an outer circumferential surface of the inner core by impregnating glass fiber reinforced material with epoxy resin. The outer core functions as the anti-corrosion layer 12.
[0009] Here, the inner core and the outer core of the internal strength member are integrally formed by simultaneously impregnating a plurality of carbon fibers used to form the inner core and a plurality of glass fibers used to form the outer core with epoxy resin, and pultruding the carbon fibers and the glass fibers.
[0010] Japanese Unexamined Patent Application Publication Nos. 1998-321047 and 1994-103831 disclose techniques for reducing total resistance of an overhead transmission line while suppressing corrosion of the conductor wire 20 by using a

fiber-reinforced plastic material as the core part 11 and a metal material as the anti-corrosion layer 12.
[0011] However, in the internal strength member or the overhead transmission line including the same disclosed in the above-described Korean and Japanese prior art documents, the core part 11 and the anti-corrosion layer 12 behave together and thus part of a bending force applied to the internal strength member when the overhead transmission line is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line may be applied to the anti-corrosion layer 12 having relatively low hardness, thereby damaging the anti-corrosion layer 12.
[0012] Accordingly, an internal strength member, for an overhead transmission line, which is capable of achieving low-sag characteristics of an overhead transmission line, has bending resistance enough to suppress damage to the internal strength member when the overhead transmission is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line, and is capable of suppressing corrosion of conductor wires arranged around the internal strength member of the overhead transmission line and reducing total resistance of the overhead transmission line to improve a power transmission rate; and an overhead transmission line including the same are in urgent demand.
DETAILED DESCRIPTION OF THE INVENTION
Technical Problem
[0013] The present invention is directed to an internal strength member, for an
overhead transmission line, which is capable of achieving low sag characteristics
of an overhead transmission line and has bending resistance enough to suppress
damage to the internal strength member when the overhead transmission line is
wound around a bobbin, a drum, or a pulley to manufacture or install the overhead
transmission line; and an overhead transmission line including the same.
[0014] The present invention is directed to an internal strength member, for an
overhead transmission line, which is capable of suppressing corrosion of conductor

wires arranged around the internal strength member, and an overhead transmission line including the same.
[0015] The present invention is directed to an internal strength member, for an overhead transmission line, which is capable of reducing total resistance of an overhead transmission line to improve a power transmission rate, and an overhead transmission line including the same.
Technical Solution
[0016] According to an aspect of the present invention, there is provided an internal strength member for an overhead transmission line, comprising: a core part including a resin matrix and a plurality of reinforcing fibers which are at least partially impregnated with the resin matrix, the core part continuously extending in a lengthwise direction of the internal strength member; an anti-corrosion layer configured to cover the core part, and formed of a material having electrical conductivity; and a fine gap formed between the core part and the anti-corrosion layer, wherein the fine gap causes the core part and the anti-corrosion layer to behave separately when a bending force is applied to the internal strength member for an overhead transmission line.
[0017] According to another aspect of the present invention, there is provided the internal strength member, wherein the internal strength member has a parameter X which is in a range of 0.1 to 0.8 on a certain cross section thereof, the parameter X being defined by Equation 1 below.
a. [Equation 1]
b. X=(Dcore/1.23)αx(Agap/Acore)β,
[0018] wherein α is 0.9, β is 0.86, Dcore represents an average diameter of the core part on a certain cross section of the internal strength member, Agap represents a total cross-sectional area of the fine gap on the cross section, Acore represents a cross-sectional area of the core part on the cross section, and the parameter X is a value rounded to two decimal places.

[0019] According to other aspect of the present invention, there is provided the
internal strength member, wherein a diameter of the core part on a certain cross
section of the internal strength member is in a range of 5 to 11 mm, a cross-sectional
area of a hollow part of the anti-corrosion layer is in a range of 15 to 103 mm2, and
a total cross-sectional area of the fine gap is in a range of 0.15 to 7.1 mm2.
[0020] According to other aspect of the present invention, there is provided the
internal strength member, wherein the anti-corrosion layer is formed of a metal
material having an electrical conductivity of 55 to 64 %IACS.
[0021] According to other aspect of the present invention, there is provided the
internal strength member, wherein the metal material comprises an aluminum
material.
[0022] According to other aspect of the present invention, there is provided the
internal strength member, wherein the anti-corrosion layer has a thickness of 0.3 to
2.5 mm.
[0023] According to other aspect of the present invention, there is provided the
internal strength member, wherein the core part has a tensile strength of 140 kgf/mm2
or more, a modulus of elasticity of 110 GPa or more, and a coefficient of thermal
expansion (CTE) of 2.0 µm/m°C or less.
[0024] According to other aspect of the present invention, there is provided the
internal strength member, wherein the core part is formed of fiber reinforced plastic
obtained by impregnating reinforcing fiber with a thermosetting resin matrix,
wherein the content of the reinforcing fiber is 50 to 90% by weight based on the
total weight of the core part.
[0025] According to other aspect of the present invention, there is provided the
internal strength member, wherein the thermosetting resin matrix comprises: at least
one base resin selected from the group consisting of an epoxy-based resin, an
unsaturated polyester resin, bismaleide resin, and a polyimide resin; and a curing
agent, a curing accelerator, and a releasing agent.
[0026] According to other aspect of the present invention, there is provided the
internal strength member, wherein the epoxy-based resin comprises diglycidyl ether

bisphenol-A epoxy resin, multifunctional epoxy resin, and diglycidyl ether bisphenol-F resin.
[0027] According to other aspect of the present invention, there is provided the internal strength member, wherein, with respect to 100 parts by weight of the base resin, the thermosetting resin matrix comprises: 70 to 150 parts by weight of an acid anhydride-based curing agent or 20 to 50 parts by weight of an amine-based curing agent, as the curing agent; 1 to 3 parts by weight of an imidazole-based curing accelerator or 2 to 4 parts by weight of boron triflouroethylamine-based curing accelerator, as the curing accelerator; and 1 to 5 parts by weight of the releasing agent.
[0028] According to other aspect of the present invention, there is provided the internal strength member, wherein the reinforcing fiber comprises a high-strength continuous fiber having a diameter of 3 to 35 µm, and has a tensile strength of 140 kgf/mm2 or more and a coefficient of thermal expansion close to 0 or less. [0029] According to other aspect of the present invention, there is provided the internal strength member, wherein the reinforcing fiber comprises at least one fiber selected from the group consisting of carbon fiber, glass fiber, organic synthetic fiber, boron fiber, ceramic fiber, aramid fiber, alumina fiber, silicon carbide fiber, and polybenzoxazole fiber.
[0030] According to other aspect of the present invention, there is provided the internal strength member, wherein the reinforcing fiber is surface-treated with a coupling agent.
[0031] According to other aspect of the present invention, there is provided an overhead transmission line comprising: the internal strength member of claim 1 or 2; and a conductor arranged around the internal strength member, the conductor being obtained by uniting a plurality of aluminum alloys or aluminum wires. [0032] According to other aspect of the present invention, there is provided the overhead transmission line, wherein a surface hardness reinforcement layer is formed on surfaces of the aluminum alloys or the aluminum wires.

Advantageous Effects
[0033] An internal strength member, for an overhead transmission, according to the present invention is advantageous in that low sag characteristics of an overhead transmission line can be achieved by forming a fine gap between a core part and an anti-corrosion layer to make the core part and the anti-corrosion layer having different hardness and flexibility behave separately, and the internal strength member has bending resistance enough to suppress damage to the anti-corrosion layer when the overhead transmission line is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line. [0034] The internal strength member, for an overhead transmission, according to the present invention is advantageous in that the anti-corrosion layer covering the core part can suppress bimetallic corrosion, i.e., galvanic corrosion, of conductor wires due to a contact between the core part and the conductor wires. [0035] Furthermore, the internal strength member, for an overhead transmission, according to the present invention is advantageous in that the anti-corrosion layer covering the core part is formed of a material having high electrical conductivity, e.g., a metal, and thus total resistance of the overhead transmission line can be reduced to improve a power transmission rate.
Description Of The Drawings
[0036] FIG. 1 is a schematic cross-sectional view of an overhead transmission line
according to the related art.
[0037] FIG. 2 is a schematic cross-sectional view of an internal strength member,
for an overhead transmission line, according to an embodiment of the present
invention.
[0038] FIG. 3 is a schematic cross-sectional view of an overhead transmission line
including the internal strength member of FIG. 2, according to an embodiment of
the present invention.
Mode of The Invention
[0039] Hereinafter, exemplary embodiments of the present invention will be described in detail. The present invention is, however, not limited thereto and may be embodied in many different forms. Rather, the embodiments set forth herein are

provided so that this disclosure will be thorough and complete, and fully convey
the scope of the invention to those skilled in the art. Throughout the specification,
the same reference numbers represent the same elements.
[0040] FIG. 2 is a schematic cross-sectional view of an internal strength member,
for an overhead transmission line, according to an embodiment of the present
invention.
[0041] As illustrated in FIG. 2, an internal strength member 100, for an overhead
transmission line, according to the present invention may include a core part 110,
an anti-corrosion layer 120 covering the core part 110, and a fine gap 130 formed
between the core part 110 and the anti-corrosion layer 120.
[0042] The core part 110 may continuously extend in a lengthwise direction of the
internal strength member 100. When an overhead transmission line including the
internal strength member 100 and conductor wires arranged around the internal
strength member 100 is installed between iron towers, a tensile force is applied
thereto in the lengthwise direction of the internal strength member 100. Thus, the
core part 110 may be formed to continuously extend in the lengthwise direction of
the internal strength member 100 so as to secure sufficient tensile strength.
Preferably, the core part 110 has an average surface roughness value of 0 to 2.33
µm.
[0043] The core part 110 may be fiber-reinforced plastic formed by impregnating
reinforcing fabric with a thermosetting resin matrix. The thermosetting resin matrix
may be formed by adding an additive, such as a curing agent, a curing accelerator,
or a releasing agent, to base resin such as epoxy-based resin, unsaturated polyester
resin, bismaleide resin, or polyimide resin, and preferably, epoxy resin.
[0044] In particular, the epoxy resin may include diglycidyl ether bisphenol-A
epoxy resin, multifunctional epoxy resin, diglycidyl ether bisphenol-F resin, or the
like, or preferably, a mixture of these three types of epoxy resins. Heat resistance,
bending characteristics and flexibility may be more improved when the mixture of
the three types of epoxy resins is used than when diglycidyl ether bisphenol-A
epoxy resin is used alone.

[0045] The curing agent may include an acid anhydride-based curing agent such as methyl tetrahydrophthalic anhydride (MTHPA), tetrahydrophthalic anhydride (THPA), hexahydrophthalic anhydride (HHPA), or nadic methyl anhydride (NMA), or preferably, methyl tetrahydrophthalic anhydride or nadic methyl anhydride; or an amine-based curing agent which is a liquid curing agent, e.g., a alicyclic polyamine-based compound such as menthane diamine (MDA) or isophoronediamine (IPDA) or an aliphatic amine-based compound such as diaminodiphenyl sulfone (DDS) or diaminodiphenylmenthane (DDM). [0046] The content of the acid anhydride-based curing agent may be 70 to 150 parts by weight and the content of the amine-based curing agent may be 20 to 50 parts by weight with respect to 100 parts by weight of the base resin. When the content of the anhydride-based curing agent is less than 70 parts by weight or the content of the amine-based curing agent is less than 20 parts by weight, the thermosetting resin matrix may be insufficiently cured and thus heat resistance thereof may deteriorate. When the content of the anhydride-based curing agent is more than 150 parts by weight or the content of the amine-based curing agent is more than 50 parts by weight, the unreacted curing agent may remain in the thermosetting resin matrix and act as an impurity and thus heat resistance and other physical properties thereof may deteriorate.
[0047] The curing accelerator accelerates the curing of the thermosetting resin matrix through the curing agent. An imidazole-based curing accelerator is preferably used when the curing agent is the acid anhydride-based curing agent, and a boron trifluride ethylamine-based curing accelerator is preferably used when the curing agent is the amine-based curing agent.
[0048] The content of the imidazole-based curing accelerator may be 1 to 3 parts by weight and the content of the boron triflouride ethylamine curing accelerator may be 2 to 4 parts by weight with respect to 100 parts by weight of the base resin. When the content of the imidazole-based curing accelerator is less than 1 part by weight or the content of the boron triflouride ethylamine curing accelerator is less than 2 parts by weight, a completely cured thermosetting resin matrix cannot be obtained. In contrast, when the content of the imidazole-based curing accelerator

is greater than 3 parts by weight or the content of the boron triflouride ethylamine curing accelerator is greater than 4 parts by weight, a curing time decreases due to a high reaction rate and thus the viscosity of the thermosetting resin matrix sharply increases, thereby lowering workability.
[0049] The releasing agent reduces friction against a molding die during the molding of the thermosetting resin matrix, thereby facilitating a molding process. For example, zinc stearate or the like may be used.
[0050] The content of the releasing agent may be 1 to 5 parts by weight with respect to 100 parts by weight of the base resin. When the content of the releasing agent is less than 1 part by weight, the workability of the thermosetting resin matrix may be reduced. In contrast, when the content of the releasing agent is greater than 5 parts by weight, the workability of the thermosetting resin matrix cannot be further improved and manufacturing costs increase.
[0051] The reinforcing fiber impregnated in the thermosetting resin matrix may include, for example, carbon fiber formed of amorphous carbon, graphite carbon, metal coated carbon, or the like; glass fiber formed of E-glass, A-glass, C-glass, D-glass, AR-glass, R-glass, S1-glass, S2-glass, or the like; synthetic organic fiber such as polyamide, polyethylene, paraphenylene, terephthalamide, polyethylene terephthalate, polyphenylene sulfide, polyacrylate, ultra-high molecular polyethylene, or the like; boron fiber; ceramic fiber; aramid fiber such as Kevlar; alumina fiber; silicon carbide fiber; polybenzoxazole fiber; or the like, and may preferably include carbon fiber.
[0052] The reinforcing fiber may be a high-strength continuous fiber having a diameter of 3 to 35 µm, and may have a tensile strength of 140 kgf/mm2 or more and a thermal expansion coefficient close to zero or less. When the diameter of the fiber is less than 3 µm, the fiber is difficult to manufacture and thus is not economical. When the diameter of the fiber is greater than 35 µm, the tensile strength of the fiber may greatly reduce. [0053] The reinforcing fiber may be surface-treated to improve compatibility with the base resin of the thermosetting resin matrix. A coupling agent to be used to surface-treat the reinforcing fiber is not particularly limited as long as it can process a surface of high-strength fiber. For example, the coupling agent may include a

titanate-based coupling agent, a silane-based coupling agent, a zirconate-based coupling agent, or the like. One of the coupling agents may be used alone or a combination including two or more of the foregoing coupling agents may be used. [0054] A plurality of reactors are introduced on the surface of the reinforcing fiber which is surface-treated with the coupling agent. The reactors react with polymer resin and thus prevent aggregation of the fiber, thereby removing bubbles or a defect affecting physical properties of a final product. Accordingly, interfacial bonding between the high-strength fiber and the thermosetting resin and the dispersibility of the high-strength fiber may be improved.
[0055] The content of the reinforcing fiber may be 50 to 90% by weight based on the total weight of the core part 110 and thus the density of fiber-reinforced plastic wires forming the core 110 may be 2.0 g/cm3 or less. When the content of the reinforcing fiber is less than 50% by weight, the strength of the fiber-reinforced plastic wires forming the core part 110 may greatly reduce. In contrast, when the content of the reinforcing fiber is greater than 90% by weight, the aggregation of the reinforcing fiber may increase and bubbles or cracks may occur in the core part 110, thereby greatly deteriorating physical properties and workability of the core part 110. [0056] As described above, the core part 110 including the fiber-reinforced plastic wire produced by impregnating the reinforcing fiber in the thermosetting resin matrix may have a diameter of 5 to 11 mm, a tensile strength of 200 kgf/mm2 or more, a modulus of elasticity of 110 GPa or more, a coefficient of thermal expansion (CTE) of 2.0 µm/m °C or less, and glass transition temperature Tg of about 205 °C or more.
[0057] In particular, since the fiber-reinforced plastic wire cannot achieve mechanical properties, such as tensile strength and a linear expansion coefficient, of the core part 110 required at the glass transition temperature Tg or higher, the glass transition temperature Tg may be understood to mean a maximum temperature at which the fiber-reinforced plastic wire can be used.
[0058] In the internal strength member 100 for an overhead transmission line according to the present invention, the anti-corrosion layer 120 is configured to suppress bimetallic corrosion, i.e., galvanic corrosion, of the conductor wires to be

arranged around the internal strength member 100 due to a contact between the core part 110 and the conductor wires.
[0059] In detail, the anti-corrosion layer 120 is formed covering the core part 110, and is preferably formed covering an outer surface of the core part 110 continuously extending in the lengthwise direction of the internal strength member 100, thereby minimizing corrosion of the conductor wires caused by a potential difference due to the penetration of electrolytes into the core part 110 and the conductor wires. [0060] The anti-corrosion layer 120 may be formed of a metal material having high electrical conductivity, preferably, a metal having an electrical conductivity of 55 to 64 %IACS, and more preferably, an aluminum material that is the same as the conductor wires arranged around the internal strength member 100. When the anti-corrosion layer 120 is formed of a metal material having high electrical conductivity, electric current may be conducted between the anti-corrosion layer 120 and the conductor wires arranged around the internal strength member 100 and thus the total resistance of an overhead transmission line may be reduced and thereby additionally increase a power transmission rate.
[0061] Here, the anti-corrosion layer 120 may have a thickness of 0.3 to 2.5 mm. When the thickness of the anti-corrosion layer 120 is less than 0.3 mm, the bending characteristics, heat resistance, corrosion resistance, etc. of the internal strength member 100 may be reduced and deteriorated by an external force, and an effect of reducing the total resistance of the overhead transmission line may be low. In contrast, when the thickness of the anti-corrosion layer 120 is greater than 2.5 mm, the internal strength member 100 is difficult to manufacture, and a diameter of the core part 110 decreases versus the same external diameter of the internal strength member 100. Thus, the tensile strength of the internal strength member 100 may decrease and low sag characteristics may not be achieved.
[0062] The anti-corrosion layer 120 may be formed through conform extrusion of a metal rod such as an aluminum rod or by welding a metal tape such as an aluminum tape. In particular, since the anti-corrosion layer 120 may be formed through conform extrusion of an aluminum rod, the anti-corrosion layer 120 may be formed to be long and thereby improve the productivity and facilitate the

formation and adjustment of the fine gap 130. Further, when the anti-corrosion layer 120 is formed through conform extrusion, the anti-corrosion layer 120 may be formed having a continuously formed surface with no joints such as welded portions. Accordingly, it is possible to prevent the occurrence of galvanic corrosion, caused by breakage of the joints due to bending stress applied to the internal strength member 100 during the manufacture or installation of the internal strength member 100 or an overhead transmission line including the same or after the installation thereof.
[0063] As illustrated in FIG. 2, in the internal strength member 100 according to the present invention, the fine gap 130 may be formed between the core part 110 and the anti-corrosion layer 120. The anti-corrosion layer 120 and the fine gap 130 may be formed by extruding a metal material in the form of a tube. In detail, the anti-corrosion layer 120 may be obtained by forming a metal material, which covers the core part 110 and as an internal diameter greater than the external diameter of the core part 110, in a tubular shape by extrusion and gradually reducing a diameter of the tubular shape, and a size of the fine gap 130 may be adjusted. [0064] Accordingly, heat generated during the conform extrusion of the aluminum rod to form the anti-corrosion layer 120 may be suppressed from being transferred to the core part 110 to prevent deterioration of the core part 110. Furthermore, when bending stress is applied to the internal strength member 100 for an overhead transmission line, the core part 110 and the anti-corrosion layer 120 behave separately due to the fine gap 130 and thus a greater part of the bending stress is applied to the core layer 110 including the fiber reinforced plastic wire material having relatively high tensile strength and an elongation rate of less than 2%, thereby achieving low sag characteristics of the overhead transmission line. At the same time, stress to be applied to the anti-corrosion layer 120 formed of an aluminum material having relatively low tensile strength and an elongation rate of 15% or more may be minimized to suppress damage to the internal strength member 100 when the overhead transmission line is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line.

[0065] The inventors of the present application experimentally determined that an effect obtained through the separate behaviors of the core part 110 and the anti-corrosion layer 120 due to the fine gap 130 may significantly vary depending on a total cross-sectional area of the fine gap 130 and that a total cross-sectional area of the fine gap 130 required to achieve the effect may vary according to the diameter of the core part 110.
[0066] In particular, the correlation among the diameter of the core part 110, the total cross-sectional area of the fine gap 130, and the behaviors of the core part 110 and the anti-corrosion layer 120 according to the diameter of the core part 110 and the total cross-sectional area of the fine gap 130 was analyzed to derive a parameter X defined by Equation 1 below so as to predict behaviors of the core part 110 and the anti-corrosion layer 120 by a force applied to the internal strength member 100 during the manufacture or installation of the internal strength member 100 or the overhead transmission line, and the parameter X was limited to be in a range of 0.1 to 0.8, thereby completing the present invention.
[0067] In detail, the parameter X includes, as key variables, an average diameter of the core part 110 closely related to a normal load applied to an inner surface of the anti-corrosion layer 120 due to the core part 110, and a cross-sectional area of the core part 110. The parameter X further includes, as a key variable, the total cross-sectional area of the fine gap 130 greatly influencing a contact between the core part 110 and the anti-corrosion layer 120 in the lengthwise direction of the internal strength member 100. In addition, the parameter X includes correction coefficients α and β determined by taking into account circularity, cylindricity, surface roughness, etc. of an outer surface of each of the core part 110 and the inner surface of the anti-corrosion layer 120.
a. [Equation 1]
b. X=(Dcore/1.23)αx (Agap/Acore)
[0068] In Equation 1 above, α is 0.9, β is 0.86, Dcore represents an average diameter of the core part 110 on a certain cross section of the internal strength member 100, Agap represents the total cross-sectional area of the fine gap 130 on the cross-section

of the internal strength member 10, and Acore represents the cross-sectional area of the core part 110 on the cross section of the internal strength member 100.
[0069] The parameter X is a value rounded to two decimal places. Agap and Acore described above may be measured using a device capable of measuring an area or calculated using Dcore and the internal diameter of the anti-corrosion layer 120, and may be rounded to four decimal places. π is set to 3.14 when Agap and Acore are calculated using the internal diameter of the anti-corrosion layer 120.
[0070] In detail, Agap described above may be the difference between a cross-sectional area of a hollow part of the anti-corrosion layer 120 and the cross-sectional area of the core part 110. The cross-sectional area of the hollow part of the anti-corrosion layer 120 may be a cross-sectional area of the hollow part of the anti-corrosion layer 120 which is in the tubular shape having the hollow part. The core part 110 may be provided only at a side of the hollow part of the anti-corrosion layer 120. There may be a structure slightly protruding from or recessed in a surface of the core part 110 and/or the inner surface of the anti-corrosion layer 120. Accordingly, Agap may more exactly represent a degree of the fine gap 130 more than a thickness of the fine gap 130.
[0071] Here, when the parameter X is less than 0.1, the total cross-sectional area of the fine gap 130 between the core part 110 and the anti-corrosion layer 120 is insufficient and thus the core part 110 and the anti-corrosion layer 120 behave together. Thus, the overhead transmission line does not have low sag characteristics, and the anti-corrosion layer 120 may be damaged when the overhead transmission line is wound around a bobbin, a drum, or a pulley to manufacture or install the overhead transmission line. In contrast, when the parameter X is greater than 0.8, the external diameter of the internal strength member 100 may increase insufficiently and the internal strength member 100 may be structurally unstable.
[0072] For example, the diameter of the core part 110 on a certain cross-section of the internal strength member 100 may be about 5 to 11 mm, the hollow part of the

anti-corrosion layer 120 may have a cross-sectional area of about 15 to 103 mm2, and the fine gap 130 may have a total cross-sectional area of about 0.15 to 7.1 mm2.
[0073] An intermediate anti-corrosion layer (not shown) may be additionally formed to a thickness of about 50 µm between the anti-corrosion layer 120 and the core part 110. The intermediate anti-corrosion layer may suppress bimetallic corrosion, i.e., galvanic corrosion, of the anti-corrosion layer 120 due to a contact between the core part 110 and the anti-corrosion layer 120. For example, the intermediate anti-corrosion layer has a greater ionization tendency than the metal material used to form the anti-corrosion layer 120 and thus may be formed of a metal material, such as zinc (Zn) or magnesium (Mg), which may act as a sacrificial anode, or a polymer composite material including the metal material. [0074] FIG. 3 is a schematic cross-sectional view of an overhead transmission line including the internal strength member 100 of FIG. 2, according to an embodiment of the present invention.
[0075] As illustrated in FIG. 3, the overhead transmission line according to the present invention may be formed by arranging a conductor, which is obtained by uniting a plurality of aluminum alloys or aluminum wires 200, around the internal strength member 100.
[0076] The aluminum wires 200 may be formed of 1000 series aluminum such as 1050, 1100, or 1200 aluminum, and has a tensile strength of about 15 to 25 kgf/mm2 and an elongation rate of less than about 5% before the aluminum wires 200 are heat treated and has a tensile strength of about 9 kgf/mm2 and an elongation rate of about 20% or more after the aluminum wires 200 are heat treated. [0077] The aluminum wires 200 each have a trapezoidal cross section and thus a space factor of the conductor is remarkably higher than that of a conductor of aluminum wires each having a round cross section of an overhead transmission line according to the related art, thereby maximizing a power transmission rate and efficiency of the overhead transmission line. For example, the space factor of the conductor including the aluminum wires having the round cross section according to the related art is about 75%, whereas the space factor of the conductor including

the aluminum wires 200 having the trapezoidal cross section may be about 95% or
more.
[0078] The aluminum wires 200 may be formed having the trapezoidal cross
section through conform extrusion or wire drawing using a trapezoidal dice. When
the aluminum wires 200 are formed through conform extrusion, they are naturally
heated in an extrusion process and thus need not be additionally heat treated. In
contrast, when the aluminum wires 200 are formed by wire drawing, they may be
additionally heat treated subsequently.
[0079] Since the aluminum wires 200 are heat treated during the conform extrusion
or are heat treated subsequently after being drawn, stress-concentrated regions
formed inside an aluminum structure due to twisting of the aluminum wires 200
when extruded or drawn may be untangled. Accordingly, the electrical conductivity
of the aluminum wires 200 may be improved, and thus, a power transmission rate
and efficiency of the overhead transmission line may be improved.
[0080] The cross sectional area and number of the aluminum wires 200 may be
appropriately selected according to the size of the overhead transmission line. For
example, the aluminum wire 200 may have a cross-sectional area of 3.14 to 50.24
mm2, and when the aluminum wire 200 having the trapezoidal cross section is
converted into an aluminum wire having the same cross-sectional area and a round
cross section, a cross section of the resultant aluminum wire may have a diameter
of 2 to 8 mm.
[0081] The number of the aluminum wires 200 may be, for example, in a range of
12 to 40. Preferably, the aluminum wires 200 may have a multilayer structure
including eight aluminum wires at an inner layer and twelve aluminum wires at an
outer layer.
[0082] As described above, the aluminum wires 200 may be heat treated to improve
electrical conductivity. When the aluminum wires 200 are heat treated, the
aluminum wires 200 are softened and thus the surfaces thereof become vulnerable
to scratches. Thus, a large number of scratches may be generated on the surfaces
of the aluminum wires 200 due to external pressure or impact during the
manufacture, delivery, or installation of the overhead transmission line.

Accordingly, corona discharge may occur during an operation of the overhead transmission line, thereby causing high frequency noise.
[0083] Accordingly, a surface hardness reinforcement layer may be formed on the surfaces of the aluminum wires 200 to suppress generation of scratches on the surfaces thereof. Preferably, a thickness of the surface hardness reinforcement layer may be 5 µm or more, and may be preferably greater than 10 µm and less than or equal to 50 µm. If the thickness of the surface hardness reinforcement layer is less than 5 µm, the surface hardness of the aluminum wires 200 cannot be sufficiently improved and thus a large number of scratches may be generated on the surfaces of the aluminum wires 200 due to external pressure or impact during the manufacture, delivery, or installation of the overhead transmission line. In contrast, if the thickness of the surface hardness reinforcement layer is greater than 50 µm, the surface hardness reinforcing layer may be locally broken or may crack when the overhead transmission line is bent, for example, during the winding thereof around a bobbin.
[0084] Further, when the surface hardness reinforcement layer is formed on the surfaces of the aluminum wires 200, the tensile strength of the overhead transmission line may be additionally improved and thus a sag ratio thereof may be additionally decreased.
[0085] The surface hardness reinforcement layer may be formed on the surfaces of all the aluminum wires 200 of the overhead transmission line, preferably, on the surfaces of outermost aluminum wires 200 among the aluminum wires 200, and more preferably, on an outer surface forming an outer circumferential surface of the overhead transmission line among the surfaces of the outermost aluminum wires 200.
[0086] The surface hardness reinforcement layer is not particularly limited as long as it can suppress generation of scratches by improving the hardness of the surfaces of the aluminum wires 200. For example, the surface hardness reinforcement layer may include an aluminum oxide film formed by anodizing or a film plated with nickel (Ni), tin (Sn), or the like.

[0087] In detail, a method of anodizing the surfaces of the aluminum wires 200 may include cleaning to remove organic contaminants such as grease from the surfaces of the aluminum wires 200, rinsing to clean the surfaces of the aluminum wires 200 with clean water, etching to remove an aluminum oxide remaining on the surfaces of the aluminum wires 200 with sodium hydroxide or the like, desmutting to dissolve and remove alloy components remaining on the surfaces of the aluminum wires 200 after the etching, rinsing to clean the surfaces of the aluminum wires 200 with clean water, anodizing performed by applying 20 to 40 V to form a dense and stable aluminum oxide film on the surfaces of the aluminum wires 200, rinsing to clean the surfaces of the aluminum wires 200 with clean water, drying the surfaces of the aluminum wires 200 with air at room temperature, etc. [0088] When the surface hardness reinforcement layer includes an aluminum oxide film formed by anodizing, the aluminum oxide film has high insulating characteristics and thus power consumption may be reduced due to an effect of insulation achieved between the aluminum wires 200, and joule heat generated during transmission of power may be quickly discharged into the atmosphere due to high radiation properties of the aluminum oxide film, thereby increasing current capacity.
[0089] Alternatively, the surface hardness reinforcement layer may be additionally coated with polymer resin such as fluororesin. The polymer resin gives a super water-repellent effect to the aluminum oxide film, and thereby the adsorption of dust or contaminants in the air onto a surface of the overhead transmission line or the accumulation of snow or the formation of ice on the surface of the overhead transmission in winter may be suppressed.
[0090] The surface hardness reinforcement layer may include both the aluminum oxide film formed by anodizing and the film plated with nickel (Ni), tin (Sn), or the like. When the surface hardness reinforcement layer includes both the aluminum oxide film and the plated film, the aluminum oxide film may be first formed and then the plated film may be formed on the aluminum oxide film. A ratio between thicknesses of the aluminum oxide film and the plated film may be in a range of about 3: 1 to 5: 1.

[0091] When the ratio between the thicknesses of the aluminum oxide film and the plated film is in the range of about 3: 1 to 5: 1, the hardness of the surfaces of the aluminum wires 200 may be sufficiently improved by the aluminum oxide film which is relatively thick and has a higher surface hardness improvement effect, and the surface hardness reinforcement layer may be effectively suppressed from locally cracking or being damaged, when the overhead transmission line is bent, e.g., during the winding thereof around a bobbin or the like, due to the plated film which is formed as an outer side of the surface hardness reinforcement layer and is not likely to locally cracking or being damaged.
[0092] [Examples]
1. Preparation Example
[0093] Samples of an internal strength member (length: 60 mm) as shown in Table 1 below were prepared.

[0094] Test of Physical Properties
a. Evaluation of behaviors of core part and anti-corrosion layer [0095] Whether a core part and an anti-corrosion layer behave separately was evaluated according to behaviors between the core part and the anti-corrosion layer, i.e., a degree of a fine gap between the core part and the anti-corrosion layer, by removing the anti-corrosion layer by 10 mm from an end portion of each of the samples of the internal strength member according to examples and comparative examples, installing only the anti-corrosion layer on a tensile tester jig, and measuring a maximum load applied while the core part was moved by 10 mm from an aluminum tube by applying a force in an upward direction by a round object smaller than a diameter of the core part.
a. Flexibility Test
[0096] Ten sufficiently long samples of the internal strength member according to
the examples and the comparative examples were bent to a radius of curvature
which was 85 times the diameter of the core part, and the number of broken samples
was recorded.
[0097] A result of the evaluation of physical properties is as shown in Table 2
below.

[0098] As shown in Table 2 above, in each of the samples of the internal strength member according to Examples 1 to 15 of the present invention, a parameter X defined by Equation 1 above was in a range of 0.1 to 0.8. Thus, it was determined that the core part and the anti-corrosion layer behaved separately by a force corresponding to a bending stress and applied to the samples of the internal strength member during the manufacture or installation of the samples of the internal strength member or an overhead transmission line including the same or after the installation thereof. Accordingly, it was determined that the samples of the internal strength member had high flexibility.
[0099] In contrast, each of the samples of the internal strength member according to Comparative examples 1, 4, and 7 had a parameter X less than 0.1, and it was determined that the core part and the anti-corrosion layer behaved together and thus the anti-corrosion layer was damaged when bent. Each of the samples of the internal strength member according to Comparative examples 2, 3, 5, 6, 7 and 8 had a parameter X greater than 0.8, and it was determined that although the core part and the anti-corrosion layer behaved separately, the core part and the anti-corrosion layer were easily separated from each other due to an excessive degree of a fine gap therebetween during the manufacture or installation of the samples of the internal

strength member or an overhead transmission line including the same, and total external diameters of the samples increased unnecessarily.
[0100] While the present invention has been described above with respect to exemplary embodiments thereof, it would be understood by those skilled in the art that various changes and modifications may be made without departing from the technical conception and scope of the present invention defined in the following claims. Thus, it is clear that all modifications are included in the technical scope of the present invention as long as they include the components as claimed in the claims of the present invention.

CLAIMS
We claim that:
1. An internal strength member for an overhead transmission line, comprising:
a core part including a resin matrix and a plurality of reinforcing fibers which are at least partially impregnated with the resin matrix, the core part continuously extending in a lengthwise direction of the internal strength member;
an anti-corrosion layer configured to cover the core part, and formed of a material having electrical conductivity; and
a fine gap formed between the core part and the anti-corrosion layer,
wherein the fine gap causes the core part and the anti-corrosion layer to behave separately when a bending force is applied to the internal strength member for an overhead transmission line.
2. The internal strength member of claim 1, wherein the internal strength
member has a parameter X which is in a range of 0.1 to 0.8 on a certain cross section
thereof, the parameter X being defined by Equation 1 below.
[Equation 1]
X=(Dcore/1.23)αx(Agap/Acore)β,
wherein α is 0.9, β is 0.86, Dcore represents an average diameter of the core part on a certain cross section of the internal strength member, Agap represents a total cross-sectional area of the fine gap on the cross section, Acore represents a cross-sectional area of the core part on the cross section, and the parameter X is a value rounded to two decimal places.
3. The internal strength member of claim 1 or 2, wherein a diameter of the core
part on a certain cross section of the internal strength member is in a range of 5 to
11 mm,

a cross-sectional area of a hollow part of the anti-corrosion layer is in a range of 15 to 103 mm2, and
a total cross-sectional area of the fine gap is in a range of 0.15 to 7.1 mm2.
4. The internal strength member of claim 1 or 2, wherein the anti-corrosion layer is formed of a metal material having an electrical conductivity of 55 to 64 %IACS.
5. The internal strength member of claim 4, wherein the metal material comprises an aluminum material.
6. The internal strength member of claim 4, wherein the anti-corrosion layer has a thickness of 0.3 to 2.5 mm.
7. The internal strength member of claim 1 or 2, wherein the core part has a tensile strength of 140 kgf/mm2 or more, a modulus of elasticity of 110 GPa or more, and a coefficient of thermal expansion (CTE) of 2.0 µm/m°C or less.
8. The internal strength member of claim 7, wherein the core part is formed of fiber reinforced plastic obtained by impregnating reinforcing fiber with a thermosetting resin matrix,
wherein the content of the reinforcing fiber is 50 to 90% by weight based on the total weight of the core part.
9. The internal strength member of claim 8, wherein the thermosetting resin
matrix comprises:
at least one base resin selected from the group consisting of an epoxy-based resin, an unsaturated polyester resin, bismaleide resin, and a polyimide resin; and
a curing agent, a curing accelerator, and a releasing agent.

10. The internal strength member of claim 9, wherein the epoxy-based resin comprises diglycidyl ether bisphenol-A epoxy resin, multifunctional epoxy resin, and diglycidyl ether bisphenol-F resin.
11. The internal strength member of claim 9, wherein, with respect to 100 parts by weight of the base resin, the thermosetting resin matrix comprises:
70 to 150 parts by weight of an acid anhydride-based curing agent or 20 to 50 parts by weight of an amine-based curing agent, as the curing agent;
1 to 3 parts by weight of an imidazole-based curing accelerator or 2 to 4 parts by weight of boron triflouroethylamine-based curing accelerator, as the curing accelerator; and
1 to 5 parts by weight of the releasing agent.
12. The internal strength member of claim 8, wherein the reinforcing fiber comprises a high-strength continuous fiber having a diameter of 3 to 35 µm, and has a tensile strength of 140 kgf/mm2 or more and a coefficient of thermal expansion close to 0 or less.
13. The internal strength member of claim 12, wherein the reinforcing fiber comprises at least one fiber selected from the group consisting of carbon fiber, glass fiber, organic synthetic fiber, boron fiber, ceramic fiber, aramid fiber, alumina fiber, silicon carbide fiber, and polybenzoxazole fiber.
14. The internal strength member of claim 13, wherein the reinforcing fiber is surface-treated with a coupling agent.
15. An overhead transmission line comprising:
the internal strength member of claim 1 or 2; and
a conductor arranged around the internal strength member, the conductor being obtained by uniting a plurality of aluminum alloys or aluminum wires.

16. The overhead transmission line of claim 15, wherein a surface hardness reinforcement layer is formed on surfaces of the aluminum alloys or the aluminum wires.