ALUMINUM CARBON NANOTUBE (Al-CNT) WIRES IN TRANSMISSION OR DISTRIBUTION LINE CABLES

Abstract

To provide a composite material for aluminum-based wires with the strength of aluminum alloy wires and improved creep resistance relative to aluminum-based wires.SOLUTION: The disclosed embodiments include a transmission line cable 100-1 with conductor wires 102, specifically a metal-matrix composite (MMC) conductor of carbon nanotubes (CNT) dispersed in aluminum (Al) metal matrix, wherein the composition of CNT is uniform throughout the entirety of the MMC conductor.SELECTED DRAWING: Figure 1A

Description

[Background technology]

[0001] An overhead power line is a structure used in transmission and distribution to transmit electrical energy over long distances. It consists of one or more conductors (generally in multiples of three) suspended by towers or poles. Overhead power lines are generally the lowest cost method of power distribution for large amounts of electrical energy, since most of the insulation is provided by air. Overhead aluminum 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-reinforced aluminum conductors (ACCR), and composite-cored aluminum conductors (ACCC) are types of overhead, transmission, and distribution conductors. Generally speaking, all-aluminum conductors are made from one or more strands of aluminum or aluminum alloy wire depending on the specific application.

[0002] One or more embodiments of the present disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. [Brief description of the drawings]

[0003] [Figure 1A] 1 is a schematic diagram illustrating a power transmission cable including multiple stranded conductors, e.g., aluminum, aluminum alloy, or aluminum-carbon nanotube (Al-CNT) conductors, and associated cross sections. [Figure 1B] FIG. 1 is a schematic diagram illustrating a power transmission cable including multiple wires forming a stranded core and multiple conductors, e.g., aluminum, aluminum alloy, or aluminum-carbon nanotube (Al-CNT) conductors, wrapped or twisted around the core, and associated cross sections. [Diagram 2] 1 is a graph showing the strength increase of aluminum and Al-CNT rods with initial diameter obtained by cold drawing to a desired diameter. [Diagram 3] 1 is a graph showing the retention of ultimate tensile strength (UTS) after heating Al and Al-0.5 wt % CNT wires at various temperatures. [Figure 4] 1 is a process flow chart for manufacturing Al-CNT composite conductor for power transmission cable. [Diagram 5] 1 is a graph showing wire temperature versus ampacity for an Akron all-aluminum alloy conductor (AAAC) cable. [Figure 6] 1 is a graph showing wire temperature versus ampacity for Butte AAAC cable. [Figure 7] 1 is a graph showing wire temperature versus ampacity for a Turkish Aluminum Steel Reinforced Conductor (ACSR) cable. [Figure 8] 1 is a graph showing wire temperature versus ampacity for Drake ACSR cables. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0005] The embodiments set forth below represent the essential information necessary to enable one skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawings, one skilled in the art will understand the concepts disclosed and will recognize applications of these concepts not specifically addressed herein. It is understood that these concepts and applications are within the scope of this disclosure and the accompanying claims.

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

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

[0008] As used herein, terms such as "uniform" or "evenly" in the context of distribution can refer to a homogeneous distribution, as will be explained in more detail in later sections.

[0009] As used herein, the term "wire" may refer to a single stand of material which may be an electrically conductive metal or an essentially non-conductive composite material.

[0010] As used herein, the term "conductor" may refer to an electrical conductor, such as a metal wire. Wires may also be referred to as "stranded wires" due to their shape, although stranded wires are not necessarily formed from a conductive material.

[0011] As used herein, the term "cable" may refer to a cable made of a plurality of twisted wires, for example twisted aluminum or aluminum alloy conductors (such as an AAAC cable) or a cable made of twisted steel wires forming a core and twisted aluminum conductors around that core (such as an ACSR or ACSS cable).

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

[0013] As used herein, "dispersion hardening" 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 matrix material, such as aluminum.

[0014] Aluminum-Carbon-Nanotube (Al-CNT) Conductor Aluminum is widely used for overhead lines due to its relatively good electrical conductivity, low density, and material cost. The electrical conductivity of aluminum is about 61.2% to 61.8% of that of copper (based on the International Annealed Copper Standard (IACS)). The density of aluminum is 2.71 g / cm 3 by comparison, the density of copper is about 8.92 g / cm 3The prices of aluminum and copper metals are fluctuating, but historically, the price of aluminum has been much less than half that of copper. Aluminum wire with the same conductance as copper wire has about 67% larger cross section, but weighs only about half as much due to its lower density. In addition, the price of aluminum wire with the same conductance is much lower than the comparable copper wire.

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

[0016] The disclosed solutions include composites for aluminum-based wires that exhibit electrical conductivity similar to pure aluminum wires (e.g., 1350-O or 1350-H19 wires), but with the strength of aluminum alloy wires (e.g., 6201-T81 wires) and improved creep resistance compared to aluminum-based wires. For example, the addition of small amounts (e.g., less than 2 weight percent (wt%), more preferably <1 wt%) of carbon nanotubes (CNTs) to an aluminum metal matrix provides increased tensile wire strength, higher heat resistance, and higher creep resistance compared to pure aluminum without CNTs, while maintaining substantially similar electrical conductivity, elastic modulus, and thermal expansion coefficient. The tensile strength and creep resistance of Al-CNTs increase with increasing weight ratio of CNTs in the composite, but electrical conductivity decreases. As such, compositions 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 electrical conductivity of about 60% IACS. Specifically, aluminum metal matrix composite (MMC) wire with 0.5 wt% CNT can exhibit strengths greater than 200 MPa, and even greater than 300 MPa, while meeting the AT4 specifications of the International Electrotechnical Commission (IEC) 62004, Heat Resistance Standard for Overhead Power Lines (as summarized in Table 1), and exhibiting electrical conductivity approaching that of 1350 aluminum (i.e., about 60% IACS).

[0017] The Al-CNT wire can achieve increased mechanical strength through work and dispersion hardening by successively 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 distributed within the wire.

[0018] The disclosed embodiments include applications of processed and dispersion hardened Al-CNT wires for power transmission and distribution cables, with examples using All Aluminum Alloy Conductor (AAAC) and Aluminum Reinforced Steel Conductor (ACSR) power transmission cables. Thus, Al-CNT composites can overcome the shortcomings of traditional aluminum or aluminum alloy based cables.

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

[0020] In another example, replacing aluminum conductors in steel reinforced (ACSR) cables with Al-CNT conductors results in higher ampacity ratings due to the similar electrical conductivity and higher heat resistance of the Al-CNT conductors compared to the Al-1350-H19 conductors typically used in ACSR cables. ACSR cables still rely on the strength of the aluminum conductors, reinforced only by the steel core to support the weight of the cable, especially for larger diameter cables. The higher tensile strength of the Al-CNT composites compared to aluminum will therefore improve the overall cable strength.

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

[0022] FIG. 1B is a schematic diagram illustrating a power transmission cable 100-2 ("cable 100-2") including multiple core wires 104 and conductors 102 and associated cross sections. As shown, cable 100-2 is formed by stranding conductors 102 around a core formed of stranded wires 104 that reinforce the strength of cable 100-2. For example, stranded conductors 102 can be made of aluminum and the core can be made of stranded steel wires, such as in ACSR or ACSS cables, or a composite material, such as in ACCR, ACFR, or ACCC cables. In some embodiments, all conductors are made of Al-CNT composites, in which CNTs are uniformly distributed throughout each conductor, and the core is made of steel wires or composite wires. The number (usually 1, 7, or 19) and thickness of wires stranded to form the core, and the number and thickness of the outer conductors stranded, can be appropriately modified according to the intended use of cable 100-2. Although the cross-sectional shape of the core wire and outer conductor is shown as circular, the cross-sectional shape can also be trapezoidal, for example, as in ACSR / TW cables. 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] Figure 2 is a graph comparing the strengthening of 5 mm diameter extruded Al-CNT rods and 5 mm diameter extruded aluminum (99.7%) rods as the wire size is reduced by successively applying cold drawing processes. The strengthening in the Al-CNT material is due to processing and dispersion hardening, while the strengthening of Al is due to processing hardening only. The CNTs are already dispersed within the as-extruded Al-CNT rods. Thus, the initial strength before drawing is 145 MPa, which is already higher than the initial strength of Al, 75 MPa. The initial rate of strengthening with successive reductions in wire size by applying cold work is similar for Al-CNT and Al 99.7%, but the rate of strengthening with successive reductions in wire size for Al-CNT remains constant, whereas it visibly decreases for Al 99.7%.

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

[0025] where A and B are constants that depend on the amount of CNTs. For a matrix made of Al 99.7 with CNTs incorporated at a composition of 0.5 wt%, A and B are approximately 145 and 60, respectively.

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

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

[0028] [Table 1]

[0029] The ampacity of a material can be calculated according to the Neher-McGrath formula by taking into account the cable diameter, resistivity at operating temperature, and ambient conditions (e.g., temperature, wind, sunlight) and using the following formula: AMP = ((QC + QR - QS) / R TC ) 1 / 2 formula 2

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

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

[0032] [Table 2]

[0033] 4 is a flow chart of an example process for manufacturing Al-CNT composite wire for power transmission cables. Process 400 can be implemented by a system including a computer controlling automated operations. For example, the manufacturing process can be controlled by a computer coupled to a manufacturing robotic device including an extruder and tooling for work hardening and dispersion hardening of Al-CNT rods by drawing to wire with a desired diameter as described above.

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

[0035] At 404, an Al-CNT rod is extruded with the initial diameter set at 402. Specifically, an 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 include only Al and CNTs, apart from the possibility of some inconsequential amounts of impurities. The extrusion process can be operated in a batch mode to form discontinuous Al-CNT billets or rods, or preferably in a continuous mode to form Al-CNT rods of any length. The continuous mode is preferred since the Al-CNT material is not limited to a fixed amount, such as a billet. In other words, the Al-CNT rods can be formed to any length by continuous processing of the Al-CNT material without the need to form the Al-CNT material in a batch processing of billets. The extrusion process provides an Al-CNT material with CNTs dispersed throughout the Al matrix. Although small agglomerates of CNTs may be present, the composition of CNTs throughout the Al matrix is ​​consistent and uniform at the macroscopic level.

[0036] At 406, the extruded Al-CNT rod is subjected to processing to continuously reduce the cross section until a desired final diameter of the Al-CNT wire is obtained. This processing can improve the uniform distribution of the CNTs throughout the Al-CNT composite wire. In some embodiments, the processing includes a cold working process, 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 random voids or random empty spaces between the CNTs, no agglomeration of the CNTs, and no areas of higher or lower CNT composition 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 parts in the Al-CNT composite that have a clear difference, i.e., a difference in CNT composition from any other part that is more than 20%, 10%, or preferably 5%. The resulting Al-CNT composite wire also has a uniform density without porosity. For example, the density of the Al-CNT composite is allowed to deviate from the theoretical composite density by up to 2%, which can be calculated based on the volume of the material, the relative amounts of Al and CNT, and their respective densities. The uniform CNT composition of the sample Al-CNT composite wires provides consistent and uniform properties, such as uniform conductance throughout the Al-CNT wires. The uniform CNT distribution in the sample Al-CNT wires can be verified by high-resolution microscopy.

[0038] All Aluminum Alloy Cable (AAAC) In some instances, AAAC cables are used as conductors for overhead bare wires for primary and secondary power distribution. Because these types of cables do not have a high-strength core, high-strength alloys such as aluminum 6201-T81 (Al-Mg-Si) can be used to achieve high strength-to-weight ratios and desired sag characteristics, as specified in ASTM Standard B398 / B398M. Compared to 1350-H19 Al, which has a resistivity of 2.82 μΩ-cm (61.2% IACS) and a tensile strength of about 160-170 MPa at 2.3-1.4% elongation, respectively, 6201-T81 Al has a tensile strength of about 315-330 MPa at 3% elongation, and a higher resistivity of 3.28 μΩ-cm (52.5% IACS).

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

[0040] By replacing individual Al 6201-T81 alloy conductors in an AAAC cable with processed and dispersion hardened Al-0.5wt% 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-0.5wt% CNT composite conductors compared to the Al 6201-T81 alloy conductors. Since the Al-0.5wt% CNT wire meets the AT4 specification of the IEC 62004 standard, the AAAC cable using Al-CNT conductors can be run at a significantly higher temperature of about 200°C compared to a conventional AAAC cable using Al 6201-T81 conductors, which is limited to about 75°C (under the environmental conditions assumed in the example described below), resulting in a significant increase in current carrying capacity as long as the heat sag specification is met. An added benefit is that connections to clams, bolts, or splices will be 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 based on a maximum operating temperature of 75°C with information related to stranding, individual conductor and cable sizes, cable strength, DC and AC resistivity, and ampacity ratings. Conditions assumed for ampacity are an ambient temperature of 25°C, cable installation at standard sea level in a north-south direction at latitude 30°, wind speed perpendicular to the cable of 2 ft / sec at noon on June 10th, clear skies, cable emissivity of 0.5, and solar absorptance of 0.5.

[0042] Table 4 lists Al-CNT cables consisting of Al-0.5wt% CNT instead of 6201-T81 conductors, where the individual Al-0.5wt% CNT conductors have the same diameter and strength as the individual Al 6201-T81 alloy conductors in the respective AAAC cables listed in Table 3, but with lower DC and AC electrical resistivity due to the increased electrical conductivity of Al-0.5wt% CNT (60% IACS) compared to 6201-T81 Al (52.5% IACS). Table 4 also lists the initial extrusion diameter required for the Al-0.5wt% CNT rods to be drawn to the final diameter and strength of the individual conductors, as well as each of the individual Al 6201-T81 alloy conductors in the respective AAAC cables listed in Table 3 and calculated according to Equation 1. Compared to the respective AAAC cables, the Al-0.5wt% CNT cables will generally have higher ampacity ratings due to their IEC 62004 AT4 heat resistance and higher electrical conductivity, and therefore lower Joule heating, allowing operating temperatures of about 200°C, as discussed in the examples below.

[0043] [Table 3]

[0044] [Table 4]

[0045] Aluminium-reinforced steel cable (ACSR) ACSR cables are used as conductors for overhead bare lines and as primary and secondary distribution conductors and messenger support conductors. ACSR cables contain a steel core as described in ASTM standard B500 / B500M and have an outer aluminum conductor, usually aluminum 1350-H19, as described in ASTM standard B230 / B230M. The strength of ACSR cables is given by both the aluminum conductor and the steel core and is calculated according to ASTM standard B498 / B498M by taking into account the strength of the aluminum conductor at 1% elongation and the steel core.

[0046] Steel has a higher strength than aluminum, so the steel reinforcement in ACSR allows for increased mechanical tension in the cable. Steel also exhibits lower creep and thermal expansion coefficients than aluminum. Thus, the 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 strength 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 ACSR cables have a density of 100°C. The steel reinforcement therefore results in a reduction in electrical conductivity and an increase in weight compared to AAAC cables of similar cross section. However, the lower electrical conductivity has little effect on the current carrying capability or ampacity rating at the operating frequency, since the current is carried in the aluminum conductor due to the skin, which essentially pushes the current to the surface of the conductor. The normal operating temperature of ACSR cables is limited to below 100°C, and to about 135°C to 150°C for short-term emergency operation. This is to avoid annealing of the aluminum conductor, which results in softening of the aluminum conductor and permanent loss of strength.

[0048] The Al-0.5wt% CNT conductor exhibits electrical conductivity of about 60% IACS, slightly lower than the 1350-H19 Al wire with electrical conductivity of about 61.2% IACS. Higher current carrying capacity can be achieved by replacing the 1350-H19 Al alloy conductor with Al-CNT in ACSR power transmission cables.

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

[0050] It would therefore be advantageous to replace the 1350-H19 Al conductors in ACSR cables with Al-CNT 0.5% conductors of similar cross-sectional dimensions, since the Al-0.5wt% CNT conductors exhibit similar electrical conductivity, higher tensile strength, higher creep resistance, and higher heat resistance compared to Al 1350-H19 conductors with similar cross-sections.

[0051] This increases the operating temperature of the ACSR cable from 75° C. to over 200° C. during normal operation under the environmental conditions used in the examples described below, thereby resulting in a substantial increase in the ampacity rating of the cable. The Al-0.5wt% CNT conductor exhibits higher strength and higher creep resistance than the 1350-H19 Al conductor, thus contributing to the overall mechanical strength of the ACSR cable.

[0052] For example, for a Drake cable with 7 strands of Class A steel, 0.1360 inch diameter, and 180 ksi stress at 1% elongation, and 26 strands of aluminum 1350-H19, 0.1749 inch diameter, and 26 ksi stress 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=31,515lbs Equation 3

[0053] In this, 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. Obviously, increasing the strength of the aluminum strands in an ACSR cable increases the strength of the cable. This allows the cable to be installed at a higher tension, resulting in inversely less sag.

[0054] The operating temperature of 200°C is similar to that of ACSS cables; however, CSS cables are made of annealed, very soft aluminum which offers little strength to ACSS cables. It contains 1350-O conductors and relies entirely on the steel core for its strength. Therefore, the Al-CNT ACSR cable with conductor combines the advantages of ACSR and ACSS cables and is NT has high electrical conductivity, heat resistance, tensile strength, and high strength and current carrying capacity. cormorant.

[0055] However, the maximum operating temperature for an ACSR cable wound with Al-CNT strands would still be limited to about 245°C to 250°C, where the galvanized coating used on the steel core could degrade rapidly.

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

[0057] Aluminum Conductor Cable Supported by Steel (ACSS) ACSS cables are used for overhead transmission and distribution lines. ACSS cables are similar in visual appearance to ACSR cables; the steel core in ACSS provides support against sagging for the aluminum wires. The difference is that the aluminum strands in ACSS are fully annealed aluminum 1350-O as described in ASTM standard B609 / B609M. They are "very soft" and therefore do not provide as much strength to the cable. After installation, the permanent elongation of the aluminum strands results in a much greater percentage of the conductor tension being carried by the steel core compared to standard ACSR. This also reduces the resultant thermal elongation and increases self-damping. For this reason, ACSS cables sag less than ACSR cables. Because the aluminum strands are "very soft", ACSS cables can operate continuously at temperatures above 200°C without losing strength. The maximum operating temperature is limited to about 245°C to 250°C, where the galvanized coating used on the steel core can rapidly deteriorate. Again, the steel has an electrical conductivity of 61.8% IACS and a strength of 2.71 g / cm 3 With a density of 7.8 g / cm3 and electrical conductivity of only 8% IACS, compared to 1350-O aluminum 3 This support therefore results in increased losses of electrical conductivity and increased weight compared to AAAC cables of similar cross section.

[0058] Since ACSS cables are designed for operation at temperatures above 200° C., substituting fully annealed Al conductors with Al-CNT conductors may not result in any improvement in ampacity. However, the increased strength and high creep resistance of Al-CNT compared to Al 1350-O will contribute to an overall higher cable strength, making connections to clamps, bolts, or splices more reliable.

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

[0060] Composite Core Aluminum Cable Fiber-reinforced aluminum conductor (ACFR) cables with carbon fiber cores, composite-reinforced aluminum conductor (ACCR) cables with aluminum matrix composite cores, and composite-core aluminum conductor (ACCC) cables are examples of the following types of power line cables. Composite cores have 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-temperature resistant Al alloys such as Al-Zr, whose high electrical conductivity only meets the AT3 standard. It would be advantageous to replace these Al alloy conductors with Al-CNT, which meets the AT4 standard.

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

[0062] Example of embodiment: AAAC-like cable with Al-0.5wt% CNT conductors Figure 5 is a graph showing ampacity at a given conductor temperature for an Akron AAAC cable with an emissivity of 0.5 and an insolation of 0.5 for a conductor installed at 30 degrees latitude and at standard sea level in a north-south orientation. In this example, the environmental conditions include an air temperature of 25°C, wind speeds of 0 and 2 feet per second perpendicular to the conductor at noon on June 10th, and clear skies. The wind perpendicular to the conductor cools the conductor, resulting in a higher ampacity. The ampacity for the AAAC Akron cable at a wind speed of 2 feet per second is 107 amps for temperatures not exceeding 75°C, which is consistent with published specification tables.

[0063] Replacing the Al 6201-T81 conductors in the cable with Al-CNT conductors allows temperatures to exceed 200°C, without the higher temperatures resulting in loss of strength for the Al-CNT conductors. The ampacity at 2 ft / sec wind increases to 195 amps. Notably, the ampacity curve for Al-CNT 0.5 wt% goes above that for Al 6201-T81 alloy, due to the electrical conductivity of Al-0.5 wt% CNT, which is about 8% higher compared to the Al 6201-T81 alloy. The individual conductors in the Akron cable are 0.0661 in. (1.68 mm) in diameter. To obtain a rated strength of 319 MPa using Al-CNT, extrusion is started at an initial diameter of 1.2011 in. (30.51 mm) according to Equation 1.

[0064] Figure 6 is a graph showing ampacity at a given conductor temperature for a conductor installed at standard sea level in a north-south orientation at 30 degrees latitude for a Butte AAAC cable with an emissivity of 0.5 and an insolation of 0.5. In this example, the environmental conditions include an air temperature of 25°C, wind speeds of 0 and 2 feet per second perpendicular to the conductor at noon on June 10th, and clear skies. The wind perpendicular to the conductor cools the conductor, resulting in a higher ampacity. The ampacity for the AAAC Butte cable at a wind speed of 2 feet per second is 460 amps for temperatures not exceeding 75°C, which is consistent with published specification tables.

[0065] Replacing the Al 6201-T81 conductors in the cable with Al-CNT conductors allows temperatures to exceed 200°C, as the higher temperatures do not result in the Al-CNT conductor losing strength. The ampacity at 2 ft / sec wind increases to 883 amps. Notably, the ampacity curve for Al-0.5wt% CNT goes above the ampacity curve for Al 6201-T81 alloy, due to the electrical conductivity of Al-0.5wt% CNT, which is about 8% higher compared to the Al 6201-T81 alloy. The individual conductors in the Butte cable are 0.1283 in. (3.26 mm) in diameter. To obtain a rated strength of 295 MPa using Al-CNT, extrusion is started at an initial diameter of 1.5596 in. (39.61 mm) according to Equation 1.

[0066] ACSR-like cable with Al-0.5wt% CNT conductor Figure 7 shows the ampacity at a given conductor temperature for a conductor installed at 30 degrees latitude and at standard sea level in a north-south direction for a Turkish ACSR cable with an emissivity of 0.5 and an insolation of 0.5. In this example, the environmental conditions include an air temperature of 25°C, wind speeds of 0 and 2 feet / second perpendicular to the conductor at noon on June 10th, and clear skies. The wind perpendicular to the conductor cools the conductor, resulting in a higher ampacity. The ampacity for the ACSR Turkey cable at a wind speed of 2 feet / second is 103 amps for temperatures not exceeding 75°C, which is consistent with published specification tables.

[0067] Replacing the Al 1350-H19 conductors in the cable with Al-CNT conductors allows temperatures to exceed 200°C without the higher temperatures resulting in loss of strength for the Al-CNT conductors. The current carrying capacity at 2 ft / sec wind speed increases to 166 amps. The strength of the ACSR cable is provided by the steel core and Al conductors. Replacing the Al 1350-H19 conductors with the higher strength Al-CNT conductors will improve the overall strength of the cable according to Equation 3. The individual Al conductors in the Turk cable have a diameter of 0.0661 in (1.68 mm) and are rated at 28.5 ksi (196.5 MPa) at 1% elongation. If 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 about 10.6%. The corresponding increase in cable tension reduces sag by about 10%. To obtain a rated strength of 241.3 MPa using Al-CNT, extrusions are started at an initial diameter of 0.3290 inches (8.36 mm) according to Equation 1.

[0068] Figure 8 is a graph showing ampacity at a given conductor temperature for a conductor installed at standard sea level in a north-south orientation at 30 degrees latitude for a Drake ACSR cable with an emissivity of 0.5 and an insolation coefficient 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 conductor at noon on June 10th. The wind perpendicular to the conductor cools the conductor, resulting in a higher ampacity. The ampacity for the ACSR Drake cable at a wind speed of 2 feet per second is 908 amps for temperatures not exceeding 75°C, which is consistent with published specification tables.

[0069] Replacing the Al 1350-H19 conductors in the cable with Al-CNT conductors allows temperatures to exceed 200°C without the higher temperatures resulting in loss of strength for the Al-CNT conductors. The ampacity at 2 ft / sec wind speed increases to 1651 amps. The strength of the ACSR cable is provided by the steel core and Al conductors. Replacing the Al 1350-H19 conductors with the higher strength Al-CNT conductors will improve the overall strength of the cable according to Equation 3. Drake's individual Al conductors have a diameter of 0.1749 in (4.44 mm) and are rated at 24 ksi (165.5 MPa) at 1% elongation. If 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 about 20.3%. The corresponding increase in cable tension reduces sag by about 17%. To obtain a rated strength of 241.3 MPa using Al-CNT, extrusions are started at an initial diameter of 0.8706 inches (22.11 mm) according to Equation 1.

[0070] In this specification, references such as "one embodiment" or "one example" mean that a particular feature, structure, or characteristic described with respect to an embodiment is included in at least one embodiment of the disclosure. The phrase "in one embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment or that separate or alternative embodiments are mutually exclusive of other embodiments. In addition, various features are described, but may be exhibited by some embodiments and not by others. Similarly, various requirements are described, but may be requirements for some embodiments and not for other embodiments.

[0071] This disclosure includes various non-limiting examples that refer to specific materials or other details that are well known to those of ordinary skill in the art and are therefore omitted here for brevity. Additional details are readily available online or elsewhere. For example, details relating to the aluminum material referenced in the disclosed examples can be found as follows:

[0072] From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications can be made without departing from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. A cable used for transmitting or distributing electric power, a plurality of conductive wires, each of the conductive wires comprising a metal matrix composite (MMC) of aluminum (Al) and carbon nanotubes (CNT); the CNTs are uniformly dispersed throughout the MMC; A cable, wherein the MMC has a density deviation of within 2% from the theoretical value calculated based on the amount and density of aluminum and CNT.

2. Each of the conductors has an average diameter between 0.218 mm and 5 mm. The cable of claim 1 .

3. The concentration of CNTs contained in the MMC is between 0.5 weight percent (wt%) and 2 wt%. The cable of claim 1 .

4. Each of the conductive wires has a tensile strength greater than that of an aluminum conductive wire that does not contain CNTs. The cable of claim 1 .

5. Each of the conductors has an electrical conductivity of about 60% International Annealed Copper Standard (IACS). The cable of claim 1 .

6. The cable is used for overhead transmission applications. The cable of claim 1 .

7. A cable used for transmitting or distributing electric power, comprising: a plurality of conductive wires, each of the conductive wires being formed from a metal matrix composite (MMC) consisting essentially of aluminum (Al) and carbon nanotubes (CNTs); the CNTs are uniformly dispersed throughout the MMC; the CNT concentration is uniform across the length and cross section of each of the conductors; The cable is non-porous and has a uniform density.

8. Each of the conductors has a density that deviates within 2% from a theoretical density calculated based on the ratio and density of Al and CNT in the MMC conductor.

8. The cable of claim 7.

9. Each MMC conductor has an electrical conductivity of about 60% International Annealed Copper Standard (IACS).

8. The cable of claim 7.

10. The concentration of CNT contained in the MMC is between 0.4 wt% and 0.6 wt%.

8. The cable of claim 7.

11. The cable of claim 7, further comprising a core consisting of one or more core conductors, each core conductor comprising a material selected from steel, carbon-glass fiber composite, or aluminum matrix composite.

12. The cable of claim 7, wherein each of the conductors exhibits a tensile strength of at least 200 MPa.

13. The cable of claim 7, further comprising an outermost insulating polymer sleeve covering the cable exterior.

14. A method for producing aluminum-carbon nanotube (Al-CNT) composite wire for cables used in the transmission or distribution of electric power, comprising: continuously extruding a non-porous rod of Al-CNT material having an initial diameter; processing the rod through a plurality of cold working steps selected from drawing or rolling to successively reduce the cross-sectional area of ​​the rod to form a non-porous Al—CNT composite wire having a final diameter smaller than the initial diameter; It encompasses The method wherein the multiple cold working steps improve the uniform dispersion of CNTs within the non-porous Al-CNT composite.

15. The method of claim 14, wherein the cold working is performed below the recrystallization temperature without intermediate annealing or heat treatment.

16. The method of claim 14, wherein the cold working reduction rate and pass schedule are selected so that the final Al-CNT composite conductor exhibits an electrical conductivity of about 60% IACS and an ultimate tensile strength of at least 240 MPa.

17. A method for producing aluminum-carbon nanotube (Al-CNT) composite wire for a cable used in the transmission or distribution of electrical power, comprising: extruding an Al-CNT rod having an initial diameter determined according to a target tensile strength and CNT concentration; reducing the cross-sectional area of ​​the rod by at least one processing step to obtain a wire of non-porous Al-CNT composite having a diameter smaller than the initial diameter; It encompasses The method wherein the density of the Al-CNT composite wire is within 2% deviation from the theoretical density calculated based on the concentrations and densities of the Al and CNTs.

18. The method of claim 17, wherein the extrusion includes continuous extrusion, allowing for the formation of composite rods of any length.

19. The method of claim 17, wherein the Al-CNT material fed to the extruder that performs the extrusion consists essentially of aluminum and carbon nanotubes.

20. The method of claim 17, wherein the processing comprises sequential cold working steps, each step further refining the grain structure and promoting uniform dispersion of CNTs throughout the aluminum matrix.

21. The method of claim 17, wherein the CNT concentration in the Al-CNT composite is selected within the range of 0.4 wt% to 0.6 wt% to achieve a balance between electrical conductivity of at least 58% IACS and high tensile strength.

22. A method for producing aluminum-carbon nanotube (Al-CNT) composite wire for a cable used in the transmission or distribution of electric power, comprising: extruding a rod of a mixture of Al and CNTs; mechanically processing the rod at a temperature below the recrystallization point of aluminum to obtain a diameter-collected non-porous Al-CNT composite wire; It encompasses The method wherein the resulting conductor is characterized by a uniform distribution of CNTs and a void-free microstructure.

23. The method described in claim 22, wherein the dispersion of the CNTs is controlled during at least one of the extrusion or mechanical processing so that the CNT concentration within the conductor does not vary by more than 20%.

24. The method of claim 22, wherein the mechanical processing is selected from the group consisting of wire drawing and rolling, each performed at a temperature below the recrystallization point of aluminum.

25. The method of claim 22, wherein process parameters including initial rod diameter, CNT concentration, and processing area reduction schedule are selected such that the final Al-CNT composite wire achieves a tensile strength of at least 200 MPa and an electrical conductivity of at least 58% IACS.

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