Aluminum-carbon nanotube (Al-CNT) wire in a power transmission and distribution cable

Abstract

Disclosed embodiments include a power transmission cable with a metal matrix composite (MMC) conductor of carbon nanotubes (CNTs) dispersed within an aluminum (Al) metal matrix, where the CNT composition is uniform throughout the MMC conductor.

Description

Background Art

[0001] An overhead power line is a structure used for power transmission and distribution that transmits electrical energy over long distances. It consists of one or more conductors (generally a multiple of 3) suspended by towers or poles. Since most of the insulation of an overhead power line is provided by air, generally speaking, it is the most cost-effective way for power distribution for a large amount of electrical energy. Aluminum overhead conductors are used as power transmission and distribution lines. All-aluminum conductors (AAC), all-aluminum alloy conductors (AAAC), steel-reinforced aluminum conductors (ACSR), steel-supported aluminum conductors (ACSS), fiber-reinforced aluminum conductors (ACFR), composite material-reinforced aluminum conductors (ACCR), and composite material core aluminum conductors (ACCC) are types of overhead conductors, power transmission conductors, and distribution conductors. Generally speaking, all-aluminum conductors are made of one or more strands of aluminum or aluminum alloy wire depending on specific applications.

[0002] One or more embodiments of this disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate like elements.

Brief Description of the Drawings

[0003]

Fig. 1A

Fig. 1B

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Embodiments for Carrying Out the Invention

[0004] When discussing some embodiments of this technology, the drawings, some components, and / or operations can be divided into different blocks or combined into a single block. In addition, this technology is susceptible to various modifications and alternative forms, but specific embodiments are shown in the drawings by way of example and will be described in detail below. However, it is not intended to limit this technology to the specific embodiments described herein. On the contrary, this technology is intended to cover any modifications, equivalents, and alternatives that fall within the scope of the technology as defined by the appended claims.

[0005] The embodiments shown below represent the information essential for those skilled in the art to implement the embodiments and illustrate the best mode for implementing the embodiments. Reading the following description in light of the accompanying drawings, those skilled in the art will understand the disclosed concepts and recognize their applications that are not specifically addressed herein. It should be understood that these concepts and applications fall within the scope of this disclosure and the accompanying claims.

[0006] The terms used herein are for the purpose of describing the embodiments only and are not intended to limit the scope of this disclosure. Where the context permits, words using the singular or plural form can also include the plural or singular form respectively.

[0007] The term When used herein, the term "about" refers to ±10% of the recited value. For example, about 10 meters refers to 10 meters ± 1 meter.

[0008] When used herein, terms such as "uniformly" or "evenly" in the context of a distribution can refer to a homogeneous distribution. Details will be explained in a later section.

[0009] When used herein, the term "wire" can refer to a single strand of a material that can be a conductive metal or an essentially non-conductive composite material.

[0010] When used herein, the term "conductive wire" can refer to an electrical conductor such as a metal wire. Wires can also be referred to as "twisted wires" due to their shape, but twisted wires are not necessarily formed from conductive materials.

[0011] When used herein, the term "cable" can refer to a plurality of twisted wires, such as a cable made of twisted aluminum or aluminum alloy conductors (such as AAAC cables) or a cable made of twisted steel wires forming a core and aluminum conductors twisted around the core (such as ACSR or ACSS cables).

[0012] When used herein, the term "work hardening" or "strain hardening" can refer to strengthening a metal or polymer by deformation. An example of work hardening is that which occurs in metalworking processes that intentionally induce deformation to force a shape change. These processes are known as cold working or cold forming processes. They are characterized by forming the workpiece at a temperature lower than its recrystallization temperature (e.g., usually ambient temperature). Cold forming can be achieved through techniques such as, but not limited to, drawing, bending, extrusion, rolling, and shearing.

[0013] When used herein, "dispersion strengthening" can refer to a process in which the strength of a material is improved due to the presence of insoluble hard particles such as carbon nanotubes (CNTs) distributed within a base material such as aluminum.

[0014] Aluminum-carbon nanotube (Al-CNT) conductor Aluminum is widely used for overhead line due to its relatively good electrical conductivity, low density, and material cost. The electrical conductivity of aluminum is about 61.2% to 61.8% compared to that of copper (based on the International Annealed Copper Standard (IACS)). The density of aluminum is 2.71 g / cm 3 and in comparison, the density of copper is about 8.92 g / cm 3This is the case. Although the prices of aluminum and copper metals are volatile, historically, the price of aluminum is far lower than half of that of copper. Aluminum wires with the same conductance as copper wires have a cross-section approximately 67% larger, but the weight is only about half due to the lower density. In addition, the price of aluminum wires with the same conductance is much lower than that of the copper wires for comparison.

[0015] The main drawback of pure aluminum wires is the limit of their mechanical strength. For example, the tensile strength of 1350 aluminum wires ranges from about 60 to 200 MPa depending on the heat treatment. For example, the extremely soft annealed 1350-O aluminum wires have a tensile strength in the range of 60 to 95 MPa, and the 1350-H19 aluminum wires have a tensile strength in the range of 160 MPa to 200 MPa depending on the wire diameter. For this reason, aluminum alloys such as 6201-T81 are used for the wires, which exhibit a tensile strength of about 315 to 330 MPa depending on the wire diameter, but at a significantly low electrical conductivity of about 52.5% IACS. Another drawback of aluminum and aluminum alloys is that their creep resistance is much lower compared to copper.

[0016] The disclosed solution includes a composite material for an aluminum-based wire that exhibits electrical conductivity similar to that of pure aluminum wire (e.g., 1350-O or 1350-H19 wire), has the strength of an aluminum alloy wire (e.g., 6201-T81 wire), and has improved creep resistance compared to aluminum-based wire. For example, the addition of a small amount (e.g., less than 2 weight percent (wt%), more preferably <1 wt%) of carbon nanotubes (CNT) to an aluminum metal base material provides an increase in tensile wire strength, higher heat resistance, and higher creep resistance compared to pure aluminum without CNT, while maintaining substantially similar electrical conductivity, elastic modulus, and coefficient of thermal expansion. The tensile strength and creep resistance of Al-CNT increase with an increase in the weight ratio of CNT in the composite material, while the electrical conductivity decreases. As such, a composition higher than 0.4 wt% CNT, more preferably 0.4 wt% to 0.6 wt% CNT, or even more preferably 0.5 wt% CNT can maintain an electrical conductivity of about 60% IACS. Specifically, an aluminum metal matrix composite (MMC) wire with 0.5 wt% CNT can exhibit a strength higher than 200 MPa and even exceeding 300 MPa, while meeting the AT4 specification of the International Electrotechnical Commission (IEC) 62004, the heat resistance standard for overhead power lines (as summarized in Table 1), and can exhibit an electrical conductivity close to that of 1350 aluminum (i.e., about 60% IACS).

[0017] The Al-CNT wire can achieve an increase in mechanical strength with processing and dispersion hardening by continuously reducing the cross-section of the extruded Al-CNT rod through cold working processes (such as, but not limited to, rolling, drawing, or a combination thereof) until a rod of the desired diameter is obtained. During the cold working process to achieve the desired diameter, the grain structure of the rod is refined and the CNTs are more evenly dispersed within the wire.

[0018] The disclosed embodiments include the application of processed and dispersion-hardened Al-CNT wires for power transmission and distribution cables, with examples using all-aluminum alloy conductors (AAAC) and steel-reinforced aluminum conductors (ACSR) power transmission cables. Thus, the Al-CNT composite material can overcome the drawbacks of conventional aluminum or aluminum alloy-based cables.

[0019] For example, by replacing an Al alloy conductor (e.g., Al 6201-T81) with an Al-CNT conductor having a tensile strength similar to that of an all-aluminum alloy conductor (AAAC) cable, a higher current-carrying capacity rating results due to the higher electrical conductivity and higher heat resistance of the Al-CNT conductor in comparison with the 6201-T81 Al alloy conductor typically used in AAAC cables.

[0020] In another example, by replacing the aluminum conductor in a steel-reinforced (ACSR) cable with an Al-CNT conductor, a higher current-carrying capacity rating results due to the similar electrical conductivity and higher heat resistance of the Al-CNT conductor in comparison with the Al-1350-H19 conductor typically used in ACSR cables. The ACSR cable still relies on the strength of the aluminum conductor and is supported in its weight, especially for larger diameter cables, only by the steel core. The higher tensile strength of the Al-CNT composite material compared to aluminum will thus improve the overall cable strength.

[0021] FIG. 1A is a schematic diagram illustrating a power transmission cable 100-1 (the "cable 100-1") including a plurality of conductive wires 102 and a related cross-section. As shown, the cable 100-1 is formed by twisting the conductive wires 102. For example, in an AAC cable, all the conductive wires are made of aluminum, while in an AAAC cable, all the conductive wires are made of an aluminum alloy such as 6201-T81. In some embodiments, all the conductive wires are made of an Al-CNT composite material, in which the CNTs are uniformly dispersed throughout each conductive wire. The number (usually 7, 19, or 37) and thickness of the conductive wires twisted together can be appropriately modified according to the purpose of use of the cable 100-1. The cross-sectional shape of the conductive wires is shown as circular, but the cross-sectional shape can also be trapezoidal, for example, as in an AAAC / TW cable. In some embodiments, it is possible to cover the outermost surface of the cable with an insulating material such as a polymer sleeve (not shown).

[0022] FIG. 1B is a schematic diagram illustrating a power transmission cable 100-2 (the “cable 100-2”) including a plurality of core wires 104 and conductor wires 102 and a related cross section. As shown, the cable 100-2 is formed by twisting the conductor wires 102 around a core formed from the twisted wires 104 that reinforce the strength of the cable 100-2. For example, the stranded conductor wires 102 can be made of aluminum, and the core can be made of twisted steel wires such as an ACSR or ACSS cable, or of a composite material such as an ACCR cable, an ACFR cable, or an ACCC cable. In some embodiments, all of the conductor wires are made of an Al-CNT composite material, in which the CNTs are uniformly dispersed throughout each conductor wire and the core is made of steel wires or composite material wires. The number (usually 1, 7, or 19) and thickness of the wires twisted together to form the core, and the number and thickness of the outer conductor wires twisted together can be appropriately modified according to the intended use of the cable 100-2. The cross-sectional shapes of the core wires and the outer conductor wires are shown as circular, but the cross-sectional shape can also be trapezoidal, for example, as in an ACSR / TW cable. In some embodiments, it is possible to cover the outermost surface of the cable with an insulating material such as a polymer sleeve (not shown).

[0023] FIG. 2 is a graph comparing the strengthening of an extruded Al-CNT rod with a diameter of 5 mm and an extruded aluminum (99.7%) rod with a diameter of 5 mm when reducing the wire size by continuously applying a cold drawing process. The strengthening in the Al-CNT material is due to work and dispersion hardening, while the strengthening of Al is due only to work hardening. The CNTs are already dispersed in the Al-CNT rod as extruded. Thus, the initial strength before drawing is 145 MPa, already greater than the initial strength of Al of 75 MPa. The initial rate of strengthening with the continuous reduction in wire size by applying cold working is similar for Al-CNT and Al 99.7%, but the rate of strengthening with the continuous reduction in wire size for Al-CNT remains constant, while for Al 99.7% it visibly decreases.

[0024] The desired ultimate tensile strength (UTS) and final diameter (D f ) of the wire for the initial extrusion diameter (D i ) of the Al-CNT rod can be calculated based on the following mathematical relationship. D i= D f × exp((UTS - A) / B) Equation 1

[0025] Here, A and B are constants that depend on the amount of CNT. For a base material consisting of Al 99.7 with 0.5 wt% CNT incorporated, A and B are approximately 145 and approximately 60, respectively.

[0026] Figure 3 is a graph showing the retention of UTS after heating Al and Al-CNT wires at various temperatures. As shown, the Al-CNT wire clears the AT4 specification of the IEC 62004 standard, while Al does not clear the AT1 / AT2 specifications of the IEC 62004 standard.

[0027] Table 1 summarizes the heating temperature and time conditions for various AT specifications of the IEC 62004 standard. To meet a specific AT specification, 90% of the initial UTS must be retained after heating under the conditions shown.

[0028]

Table 1

[0029] The current-carrying capacity of the material can be calculated according to the Neher-McGrath equation by considering the cable diameter, resistivity at the operating temperature, and ambient conditions (e.g., temperature, wind, sunlight) and using the following equation. AMP = ((QC + QR - QS) / R TC ) 1 / 2 Equation 2

[0030] In this case, QC represents heat loss due to convection, QR represents heat loss due to radiation, QS represents heat due to solar radiation, and R TC represents the resistance at the operating temperature. This method is described within the IEEE 738 specification.

[0031] Table 2 summarizes how various AT standards convert the continuous allowable operating temperature over 40 years and 400 hours.

[0032]

Table 2

[0033] Figure 4 is a flowchart of an example process for manufacturing an Al-CNT composite wire for a power transmission line cable. Process 400 can be implemented by a system including a computer that controls automated operations. For example, the manufacturing process can be controlled by a computer coupled to a manufacturing robot device, which includes an extruder and tooling for performing work hardening and dispersion hardening of the Al-CNT rod by drawing it down to a wire with a desired diameter as described above.

[0034] At 402, the initial diameter of the extruded Al-CNT rod is determined according to Equation 1. The initial diameter must be set with respect to the desired final diameter such that the Al-CNT wire can have the desired strength and dispersion of CNTs. Specifically, the initial diameter is based on the composition of CNTs within the Al-CNT material and the final diameter of the Al-CNT wire. For example, a computer controlling the configurable extruder can set the extruder to continuously extrude an Al-CNT rod having the initial diameter.

[0035] In 404, the Al-CNT rod is extruded at the initial diameter set in 402. Specifically, the extruder creates an Al-CNT rod with a fixed cross-sectional profile by extruding the Al-CNT material through a die that defines the initial diameter. The Al-CNT material fed into the extruder can be considered to contain only Al and CNTs, leaving aside the possibility of an insignificant amount of impurities. The extrusion process can be operated in batch mode to form discontinuous Al-CNT billets or rods, or preferably in continuous mode to form Al-CNT rods of any length. The continuous mode is preferred because the Al-CNT material is not limited in quantity as in the case of billets, etc. In other words, the Al-CNT rod can be formed to any length by continuous processing of the Al-CNT material without the need to form the Al-CNT material in batch processing of billets. The extrusion process provides an Al-CNT material with CNTs dispersed throughout the entire Al matrix. Although there may be small agglomerates of CNTs present, the composition of CNTs throughout the entire Al matrix is consistent and uniform at the macroscopic level.

[0036] In 406, the extruded Al-CNT rod undergoes a processing operation, and the cross-section is continuously reduced until an Al-CNT wire of the desired final diameter is obtained. This processing operation can improve the uniform dispersion of CNTs throughout the entire Al-CNT composite conductor wire. In some embodiments, the processing operation includes cold working operations such as a drawing process.

[0037] The resulting Al-CNT wire has a CNT composition that is uniformly distributed throughout the Al-CNT wire. In other words, there are no significant irregular voids or irregular empty spaces between the CNTs, the CNTs are not aggregated, and there are no areas where the CNT composition is higher or lower throughout the Al-CNT wire. In other words, the amount of CNTs in the Al matrix is essentially the same in all parts of the matrix, i.e., there are no distinct differences, i.e., parts with a difference in CNT composition of more than 20%, 10%, or preferably 5% compared to any other part in the Al-CNT composite. The resulting Al-CNT composite wire also has a non-porous uniform density. For example, the density of the Al-CNT composite is allowed to deviate by up to 2% from the density of the theoretical composite, which can be calculated based on the volume of the material, the relative amounts of Al and CNTs, and their respective densities. The uniform CNT composition of the Al-CNT composite wire specimen is consistent, such as having a uniform conductance throughout the Al-CNT wire, and provides uniform properties. The uniform distribution of CNTs in the Al-CNT wire specimen can be verified by high-resolution microscopy.

[0038] All Aluminum Alloy Cable (AAAC) In some examples, AAAC cables are used as conductors for overhead bare wires for primary and secondary power distribution. Since these types of cables do not have a high-strength core, it is possible to use high-strength alloys such as Aluminum 6201-T81 (Al-Mg-Si) as specified in ASTM standard B398 / B398M to achieve a high weight-to-strength ratio and the desired relaxation properties. Compared to 1350-H19 Al, which has a resistivity of 2.82 μΩ-cm (61.2% IACS) and a tensile strength of approximately 160 to 170 MPa at elongations of 2.3 to 1.4%, 6201-T81 Al has a tensile strength of approximately 315 to 330 MPa at 3% elongation and a higher resistivity of 3.28 μΩ-cm (52.5% IACS).

[0039] As specified in ASTM standard B399 / B399B, AAAC cables are available in a variety of standard designs with 7, 19, and 37 strand wires. The rated strength of the cable will depend on the diameter of the individual wires and the number of strands, and individual cables will have strengths between 289 and 319 MPa.

[0040] By replacing the individual Al 6201-T81 alloy conductors in the AAAC cable with processed and dispersion-hardened Al-0.5 wt% CNT conductors of equal tensile strength, an increase in current-carrying capacity results according to the lower resistivity and higher heat resistance of the Al-0.5 wt% CNT composite conductors compared to Al 6201-T81 alloy conductors. Since the Al-0.5 wt% CNT wires meet the AT4 specification of IEC 62004 standard, AAAC cables using Al-CNT conductors can be run at significantly higher temperatures of about 200 °C compared to conventional AAAC cables using Al 6201-T81 conductors (under the environmental conditions assumed in the examples described below) with a limit of about 75 °C, and a significant increase in current-carrying capacity results as long as the thermal relaxation specifications are met. An additional advantage is that connections to clamps, bolts, or splices are more reliable due to significantly lower creep compared to Al 6201-T81.

[0041] Table 3 lists standard AAAC cables containing Al 6201-T81 alloy conductors, along with information related to strand, individual conductor and cable size, cable strength, DC and AC resistivity, and current-carrying capacity ratings based on a maximum operating temperature of 75 °C. The conditions assumed for current-carrying capacity are an ambient temperature of 25 °C, cable installation at standard sea level in a north-south direction at 30 degrees latitude, a wind speed of 2 feet per second perpendicular to the cable at noon on June 10, clear sky, a cable emissivity of 0.5, and a solar absorptivity of 0.5.

[0042] Table 4 is a list of Al-CNT cables made of Al-0.5 wt% CNT instead of 6201-T81 conductors, in which individual Al-0.5 wt% CNT conductors have the same diameter and strength as the individual Al 6201-T81 alloy conductors in each of the AAAC cables listed in Table 3, but with lower DC and AC electrical resistivity due to the increased electrical conductivity of Al-0.5 wt% CNT (60% IACS) compared to 6201-T81 Al (52.5% IACS). Also listed in Table 4 are the initial extrusion diameters required for Al-0.5 wt% CNT rods drawn to the final diameter and strength of the individual conductors, similar to each of the individual Al 6201-T81 alloy conductors in each of the AAAC cables listed in Table 3 and calculated according to Equation 1. Compared to each of the AAAC cables, the Al-0.5 wt% CNT cables generally have a higher current-carrying capacity rating due to their IEC 62004 AT4 heat resistance and higher electrical conductivity, thus allowing an operating temperature of about 200 °C, as discussed in the examples below, due to lower Joule heat.

[0043]

Table 3

[0044]

Table 4

[0045] Aluminum Conductor Steel Reinforced Cable (ACSR) ACSR cables are used as conductors for overhead bare transmission lines and as conductors for primary and secondary distribution and messenger support lines. The ACSR cable contains a steel core and has outer aluminum conductors as described in ASTM standard B500 / B500M and usually the aluminum is 1350-H19 as described in ASTM standard B230 / B230M. The strength of the ACSR cable is provided by both the aluminum conductors and the steel core and is calculated according to ASTM standard B498 / B498M taking into account the strength of the aluminum conductors and the steel core at 1% elongation.

[0046] Steel has a higher strength than aluminum, so steel reinforcement in ACSR enables an increase in the mechanical tension in the cable. Steel also exhibits lower creep and a lower coefficient of thermal expansion than aluminum. Therefore, steel reinforcement in ACSR cables provides mechanical support against sag for the aluminum conductors, thereby facilitating the installation of long-span cables.

[0047] By varying the relative cross-sectional areas of the steel and aluminum strands, it is possible to make the cable stronger at the expense of its electrical conductivity. 1350-H19 aluminum has an electrical conductivity of about 61.2% IACS and a density of about 2.71 g / cm 3 whereas steel has an electrical conductivity of about 8% IACS and a density of about 7.8 g / cm 3 As a result of the steel reinforcement, a decrease in electrical conductivity and an increase in weight are incurred compared to an AAAC cable with a similar cross-section. However, the lower electrical conductivity has little effect on the current-carrying capability or current rating at the operating frequency since the current is carried within the aluminum conductors due to skin effect which substantially pushes the current to the surface of the conductor. The normal operating temperature of the ACSR cable is limited to less than 100 °C and to about 135 °C to 150 °C for short-term emergency operation. This is to avoid annealing of the aluminum conductors which would result in softening and permanent loss of strength of the aluminum conductors.

[0048] The Al-0.5wt% CNT wire exhibits an electrical conductivity of about 60% IACS, which is slightly lower than that of the 1350-H19 Al wire with an electrical conductivity of about 61.2% IACS. By replacing the 1350-H19 Al alloy wire in the ACSR transmission cable with Al-CNT, it is possible to achieve a higher current-carrying capacity.

[0049] Since the Al-0.5wt% CNT wire after processing and dispersion hardening exceeds the AT4 specification of the IEC 62004 heat resistance standard, it is possible to achieve a higher cable strength by replacing the 1350-H19 Al wire in the ACSR cable with an Al-CNT wire.

[0050] Since the Al-0.5wt% CNT wire exhibits a similar electrical conductivity, a higher tensile strength, a higher creep resistance, and a higher heat resistance compared to the Al 1350-H19 wire with a similar cross-section, therefore, it is advantageous to replace the 1350-H19 Al wire in the ACSR cable with an Al-CNT 0.5% wire of a similar cross-sectional dimension.

[0051] This raises the operating temperature of the ACSR cable during normal operation under the environmental conditions used in the examples described below from 75°C to beyond 200°C, thereby resulting in a substantial increase in the current-carrying capacity rating of the cable. Since the Al-0.5wt% CNT wire exhibits a higher strength and a higher creep resistance than the 1350-H19 Al wire, it will contribute to the overall mechanical strength in the ACSR cable.

[0052] For example, in a Drake cable with a 7-strand of Class A steel with a diameter of 0.1360 inches and a stress of 180 ksi at 1% elongation, and a 26-strand of aluminum 1350-H19 with a diameter of 0.1749 inches and a stress of 26 ksi at 1% elongation, the strength is calculated as follows. (26×(π / 4)×(0.1749) 2 ×24×0.93 + 7×(π / 4)×(0.1360) 2 ×180×0.96) lbs = 31,515 lbs Equation 3

[0053] In this case, the stress values and 93% and 96% derating factors for aluminum and steel are reproduced from Table 1 of ASTM Standard B230 / B230M, Table 2 of ASTM Standard B498 / B498M, and Table 6 of ASTM Standard B232 / B232M. Clearly, as the strength of the aluminum strands within the ACSR cable increases, the strength of the cable also increases. This allows the cable to be installed at a higher tension, which in turn results in proportionally less sag.

[0054] The operating temperature of 200 °C is similar to that of the ACSS cable; however, the ACSS cable contains an annealed extra-soft Al 1350-O conductor that provides little strength to the ACSS cable and relies entirely on the steel core for its strength. Thus, the ACSR cable with Al-CNT conductors combines the advantages of ACSR and ACSS cables and has high strength and high current-carrying capacity through the high electrical conductivity, heat resistance, and tensile strength of Al-CNT.

[0055] However, still, the maximum operating temperature for the ACSR cable with Al-CNT strands wound around it will be limited to approximately 245 °C to 250 °C where the zinc-coated sheath used on the steel core may rapidly deteriorate.

[0056] Specialized ACSR cables with heat-resistant Al alloys such as Al-Zr can be used for operation at higher temperatures. However, these types of cables have lower electrical conductivity than 1350-H19 aluminum. In comparison, Al-CNT composites provide the strength and heat resistance of Al-Zr while exhibiting electrical conductivity approximately equal to that of 1350-H19 aluminum. An additional advantage is that connections to clamps, bolts, or splices are more reliable due to significantly lower creep compared to Al 1350-H19.

[0057] Aluminum Conductor Steel Supported (ACSS) ACSS cables are used in overhead power transmission and distribution lines. ACSS cables have a visual appearance similar to ACSR cables; the steel core within the ACSS provides support against sag for the aluminum wires. The difference is that the aluminum strands within the ACSS are fully annealed aluminum 1350-O as described in ASTM standard B609 / B609M. They are 'extra soft' and thus do not provide much strength to the cable. After installation, the permanent elongation of the aluminum strands results in a much larger percentage of the conductor tension being carried by the steel core compared to standard ACSR. This also reduces synthetic thermal expansion and increases self-damping. For this reason, ACSS cables have less sag than ACSR cables. Due to the aluminum strands being 'extra soft', ACSS cables can operate continuously at temperatures exceeding 200 °C without losing strength. The maximum operating temperature is limited to approximately 245 °C to 250 °C where the zinc coating used on the steel core may rapidly deteriorate. Here again, the steel has an electrical conductivity of only 8% IACS and a density of 7.8 g / cm 3 compared to 1350-O aluminum with an electrical conductivity of 61.8% IACS and a density of 2.71 g / cm 3 . Thus, this support results in an increase in loss of electrical conductivity and an increase in weight compared to AAAC cables with a similar cross-section.

[0058] Since the ACSS cable is designed for operation at temperatures exceeding 200°C, replacing it with a fully annealed Al conductor with Al-CNT conductors may not result in any improvement in current capacity. However, the increased strength and high creep resistance of Al-CNT compared to Al 1350-O will contribute to a generally higher cable strength, making the connections to clamps, bolts, or splices more reliable.

[0059] Therefore, in the disclosed embodiments, replacing the Al conductor and strands with Al-CNT conductors and strands around a steel core combines the advantages of ACSR and ACSS, resulting in high strength, high electrical conductivity, and high current capacity.

[0060] Composite core aluminum cable Fiber Reinforced Aluminum Conductor (ACFR) cables with a carbon fiber core material, Composite Material Reinforced Aluminum Conductor (ACCR) cables with a core material of an aluminum matrix composite material, and Composite Core Aluminum Conductor (ACCC) cables are examples of the types of power transmission line cables described later. The composite core has a high strength-to-weight ratio and a lower coefficient of expansion compared to steel, providing less sag at high temperatures. ACFR can withstand up to 150°C, while ACCR can withstand up to 230°C. These emerging designs are often used with high heat-resistant Al alloys such as Al-Zr that meet only the AT3 standard for high electrical conductivity. Replacing these Al alloy conductors with Al-CNT that meet the AT4 standard would be advantageous.

[0061] The disclosed embodiments include solutions to the aforementioned problems. The following calculations of current-carrying capacity for AAAC and ACSR cables were performed using ETAP, which calculates current-carrying capacity based on the IEEE 738 standard. By replacing the Al 6201 alloy conductors in the AAAC cable with Al-CNT conductors, or the Al 1350-H19 conductors in the ACSR cable with Al-CNT conductors, it is possible to raise the operating temperature from 75°C to 200°C, resulting in a higher current-carrying capacity rating. Replacing the Al or Al alloy conductors in ACSS, ACFR, ACCR, or ACCC cables with Al-CNT conductors generally results in similar advantages but will depend on the cable design.

[0062] Example of an embodiment: AAAC-like cable with Al-0.5wt% CNT conductors Figure 5 is a graph showing the current-carrying capacity at a given wire temperature for a transmission line installed in the north-south direction at mean sea level at a latitude of 30 degrees, for an Acron AAAC cable with an emissivity of 0.5 and a solar absorptivity of 0.5. In this example, the environmental conditions include an air temperature of 25°C, wind speeds perpendicular to the transmission line of 0 and 2 feet per second at noon on June 10, and clear skies. Wind perpendicular to the wire cools the wire, resulting in a higher allowable current-carrying capacity. The current-carrying capacity for the AAAC Acron cable at a wind speed of 2 feet per second is 107 amperes for temperatures not exceeding 75°C, which is consistent with the published specifications table.

[0063] Replacing the Al 6201-T81 conductor in the cable with an Al-CNT conductor allows the temperature to exceed 200 °C because the strength of the Al-CNT conductor is not lost due to higher temperatures. The current-carrying capacity at a wind speed of 2 feet per second increases to 195 amperes. In particular, due to the electrical conductivity of Al-0.5 wt% CNT being approximately 8% higher compared to the Al 6201-T81 alloy, the current-carrying capacity curve for Al-CNT 0.5 wt% goes above the current-carrying capacity curve for the Al 6201-T81 alloy. The individual conductors of the Acron cable have a diameter of 0.0661 inches (1.68 mm). To obtain a rated strength of 319 MPa using Al-CNT, extrusion is started at an initial diameter of 1.2011 inches (30.51 mm) according to Equation 1.

[0064] Figure 6 is a graph showing the current-carrying capacity at a given wire temperature for a transmission line installed in the north-south direction at mean sea level at a latitude of 30 degrees, for a Butte AAAC cable with an emissivity of 0.5 and a solar absorptivity of 0.5. In this example, the environmental conditions include an air temperature of 25 °C, a wind speed perpendicular to the transmission line of 0 and 2 feet per second at noon on June 10, and clear sky. Wind perpendicular to the wire cools the wire, resulting in a higher allowable current-carrying capacity. The current-carrying capacity for the AAAC Butte cable at a wind speed of 2 feet per second is 460 amperes for temperatures not exceeding 75 °C, which is consistent with the published specifications table.

[0065] Replacing the Al 6201-T81 conductor in the cable with an Al-CNT conductor allows the temperature to exceed 200 °C because the strength of the Al-CNT conductor is not lost due to higher temperatures. The current-carrying capacity at a wind speed of 2 feet / second increases to 883 amperes. In particular, due to the electrical conductivity of Al-0.5 wt% CNT being approximately 8% higher compared to the Al 6201-T81 alloy, the current-carrying capacity curve for Al-0.5 wt% CNT goes above the current-carrying capacity curve for the Al 6201-T81 alloy. The individual conductors of the Butte cable have a diameter of 0.1283 inches (3.26 mm). To obtain a rated strength of 295 MPa using Al-CNT, extrusion is started at an initial diameter of 1.5596 inches (39.61 mm) according to Equation 1.

[0066] ACSR-like cable with Al-0.5 wt% CNT conductors Figure 7 is a graph showing the current-carrying capacity at a given wire temperature for a transmission line installed in the north-south direction at standard sea level at a latitude of 30 degrees, for a Turkish ACSR cable with an emissivity of 0.5 and a solar absorptivity of 0.5. In this example, the environmental conditions include an air temperature of 25 °C, a wind speed perpendicular to the transmission line of 0 and 2 feet / second at noon on June 10, and clear skies. Wind perpendicular to the wire cools the wire, resulting in a higher allowable current-carrying capacity. The current-carrying capacity for the ACSR Turkish cable at a wind speed of 2 feet / second is 103 amperes for temperatures not exceeding 75 °C, which is consistent with the published specification sheet.

[0067] Replacing the Al 1350-H19 conductor in the cable with an Al-CNT conductor results in the cable being able to exceed 200 °C without the strength of the Al-CNT conductor being lost due to higher temperatures. The current-carrying capacity at a wind speed of 2 feet per second increases to 166 amperes. The strength of the ACSR cable is provided by the steel core and the Al conductor. Replacing the Al 1350-H19 conductor with a high-strength Al-CNT conductor will improve the overall strength of the cable according to Equation 3. The individual Al conductors of the Turkish cable have a diameter of 0.0661 inches (1.68 mm) and are rated at 28.5 ksi (196.5 MPa) at 1% elongation. When they are replaced by Al-0.5 wt% CNT conductors with a strength of 35 ksi (241.3 MPa) at 1% elongation, the cable strength increases from 1190 lbs to 1317 lbs, or by approximately 10.6%. The correspondingly increased cable tension reduces the sag by approximately 10%. To obtain a rated strength of 241.3 MPa using Al-CNT, extrusion is started at an initial diameter of 0.3290 inches (8.36 mm) according to Equation 1.

[0068] Figure 8 is a graph showing the current-carrying capacity at a given wire temperature for a transmission line installed in a north-south direction at a standard sea level height at a latitude of 30 degrees, for a Drake ACSR cable with an emissivity of 0.5 and a solar absorptivity of 0.5. In this example, the environmental conditions include an air temperature of 25 °C and wind speeds of 0 and 2 feet per second perpendicular to the transmission line at noon on June 10th. Wind perpendicular to the wire cools the wire, resulting in a higher allowable current-carrying capacity. The current-carrying capacity for the ACSR Drake cable at a wind speed of 2 feet per second is 908 amperes for temperatures not exceeding 75 °C, which is consistent with the published specifications table.

[0069] Replacing the Al 1350-H19 conductor in the cable with an Al-CNT conductor allows the temperature to exceed 200 °C because the strength of the Al-CNT conductor is not lost due to higher temperatures. The current-carrying capacity at a wind speed of 2 feet / second increases up to 1651 amperes. The strength of the ACSR cable is provided by the steel core and the Al conductor. Replacing the Al 1350-H19 conductor with a high-strength Al-CNT conductor will improve the overall strength of the cable according to Equation 3. The individual Al conductors of the Drake have a diameter of 0.1749 inches (4.44 mm) and are rated at 24 ksi (165.5 MPa) at 1% elongation. When they are replaced by Al-0.5 wt% CNT conductors with a strength of 35 ksi (241.3 MPa) at 1% elongation, the cable strength increases from 31,500 lbs to 37,900 lbs, or by about 20.3%. The correspondingly increased cable tension reduces the sag by about 17%. To obtain a rated strength of 241.3 MPa using Al-CNT, extrusion is started at an initial diameter of 0.8706 inches (22.11 mm) according to Equation 1.

[0070] As used herein, references to "one embodiment" or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase "in one embodiment" in the specification are not necessarily all referring to the same embodiment, nor is it necessary that separate or alternative embodiments be mutually exclusive of other embodiments. In addition, various features are described that may or may not be presented by some embodiments. Similarly, various requirements are described that may or may not be requirements for some embodiments.

[0071] This disclosure includes a variety of non-limiting examples that refer to specific materials or other details, which are well known to those skilled in the art and are therefore omitted here for the sake of brevity. Additional details are readily available online or elsewhere. For example, details related to the aluminum materials referred to in the disclosed examples can be found as follows.

[0072] From the above, specific embodiments of the present invention have been described here for illustrative purposes, but it will be recognized that various modifications can be made without departing from the scope of the present invention. Therefore, the present invention is not limited except as by the accompanying claims.

Claims

1. A power transmission or distribution cable, comprising: a plurality of conductors including a metal matrix composite (MMC) conductor having a porous structure including a plurality of carbon nanotubes (CNTs) uniformly dispersed within an aluminum (Al) metal base material; A power transmission or distribution cable, wherein the composition of the CNTs is uniform such that the difference does not exceed 20% throughout the entire MMC conductor.

2. The plurality of conductors are stranded wires, and each stranded wire includes an MMC including CNTs and Al, The power transmission or distribution cable according to claim 1, wherein the composition of the CNTs is uniform throughout each MMC stranded wire.

3. The plurality of conductors include a plurality of stranded core wires surrounded by a plurality of MMC conductors twisted around the plurality of stranded core wires, The power transmission or distribution cable according to claim 2, wherein any one of the plurality of stranded core wires has a greater tensile strength and a lower electrical conductivity compared to any of the plurality of twisted MMC conductors.

4. Furthermore, including a plurality of core wires, The power transmission or distribution cable according to claim 1, wherein any one of the plurality of core wires has a greater tensile strength compared to any of the plurality of MMC conductors.

5. The power transmission or distribution cable according to claim 2 or 4, wherein the MMC conductor includes CNTs in the range of 0.1 weight percent (wt%) to 2 wt%.

6. The power transmission or distribution cable according to claim 5, wherein the MMC conductor includes CNTs in the range of 0.4 wt% to 0.6 wt%.

7. The power transmission or distribution cable according to claim 6, wherein the MMC conductor includes approximately 0.5 wt% of CNTs.

8. The power transmission or distribution cable according to claim 4, wherein each of the core wires includes steel.

9. The power transmission or distribution cable according to claim 4, wherein each of the core wires includes a composite material including a carbon glass fiber composite material or an aluminum base material composite material.

10. The power transmission or distribution cable according to any one of claims 2 to 7, wherein the MMC conductor has an electrical conductivity of at least 55% International Annealed Copper Standard (IACS).

11. The power transmission or distribution cable according to claim 10, wherein the MMC conductor has an electrical conductivity of approximately 58% IACS.

12. A power transmission or distribution cable, a plurality of wires forming a stranded core, a plurality of conductive wires twisted around the stranded core, comprising wherein the plurality of conductive wires are a metal matrix composite (MMC) of aluminum (Al) and carbon nanotubes (CNT), and the MMC has a porous structure with CNT uniformly dispersed such that the composition difference does not exceed 20% throughout, a power transmission or distribution cable.

13. The power transmission or distribution cable according to claim 12, wherein the MMC comprises CNT in the range of 0.1 weight percent (wt%) to 2 wt%.

14. The power transmission or distribution cable according to claim 13, wherein the MMC comprises CNT in the range of 0.25 wt% to 1 wt%.

15. The power transmission or distribution cable according to claim 13, wherein the MMC comprises at least 0.4 wt% of CNT.

16. The power transmission or distribution cable according to claim 13, wherein the MMC comprises CNT in the range of 0.4 wt% to 0.6 wt%.

17. The power transmission or distribution cable according to claim 13, wherein the MMC comprises approximately 0.5 wt% of CNT.

18. A method for manufacturing an aluminum-carbon nanotube (Al-CNT) composite material wire for a power transmission or distribution cable, determining an initial diameter based on a final diameter, an ultimate tensile strength of the conductive wire, and the amount of CNT in the Al-CNT to be fed into an extruder for extruding a porous rod of Al-CNT, extruding the porous rod of Al-CNT with CNT uniformly dispersed such that the composition difference is 20% or less throughout, with the initial diameter, continuously reducing the cross-sectional area of the rod by a processing treatment to form a porous Al-CNT composite material conductive wire with the final diameter smaller than the initial diameter, comprising a method.

19. The method according to claim 18, wherein the processing treatment improves the uniform dispersion of CNT throughout the Al-CNT composite material conductive wire.

20. The method according to claim 18 or 19, wherein the processing treatment includes a cold working treatment.

21. The method according to claim 18 or 19, wherein the processing treatment includes at least one of a rolling treatment or a drawing treatment.

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