1. Introduction:
Human use of copper dates back to 10,000 years ago. An 8,700-year-old artifact, a copper ear plug, has been discovered in northern Iraq. China had bronze pieces more than 4,000 years ago, during the Xia Yu era.
The application of copper as a conductor has a history of more than 200 years, since its discovery and application in the late 18th century with electricity.
Aluminum, being a young metal, was called “silver gold” in the mid-19th century, even more precious than gold.
It was not until 1886 that the American scientist Hall independently researched and developed the electrolytic method for producing aluminum, which made industrialization possible.
Aluminum began to be used as a conductor in 1896, when British scientist Colly erected the first suspended aluminum braided wire in Bolton.
In 1910, the American Aluminum Association invented stranded aluminum wire with a steel core and erected it above Niagara Falls.
Since then, overhead high-voltage transmission lines have been gradually replaced by steel-core aluminum stranded wires. Furthermore, developed industrial countries in Europe and America began using aluminum conductors to replace copper conductors as distribution lines in 1910.
Today, around 14% of the aluminum produced in the world is used as electrical material. The United States has the highest percentage of aluminum used in wires, reaching around 35%.
In China, the amount of aluminum used by the electrical industry represents about a third of the country's total aluminum consumption, mainly for high voltage transmission.
However, the proportion of aluminum conductors used in power distribution is less than 5%. The choice between copper and aluminum conductors is influenced by historical factors, national conditions, resource situations and other factors.
In the 1950s, the price of copper rose rapidly and the global wire and cable industry proposed replacing copper with aluminum.
To achieve the same electrical performance, the cross-sectional area of aluminum conductors needed to be two steps larger than that of copper conductors or increased by 50%.
The same proposal was made in the 1960s and 1970s for the same reasons. Since 2005, the proposal to replace copper with aluminum has been raised again.
With the advancement of technology, this time the replacement of copper with aluminum is mainly done with aluminum alloy instead of pure aluminum.
What is the prospect of replacing copper with aluminum? We need to have a better understanding of the properties of aluminum, copper and aluminum alloys.
2. Comparison of copper and aluminum
2.1 Performance comparison between aluminum and copper (20℃)
| aluminum | Aluminum | Copper | |||||
| Annealed | Difficult (H8) | Annealed | Hard | ||||
| Atomic weight density/kgm -3 resistivity/n Ω mconductivity/% IACS | 26.98 2700 |
63.54 8890 |
|||||
| 27.8 62 |
28.3 61 |
17.24 100 |
17.77 97 |
||||
| Temperature coefficient of resistance/(n Ω · m) · K-1 | 0.1 | 0.1 | 0.09825 | 0.09525 | |||
| Tensile strength/MPa | 80-110 | 150-200 | 200~270 | 350470 | |||
| Positive modulus of elasticity/MPa | 63 | 63 | 120 | 120 | |||
| Linear expansion coefficient/ × 10 -6 K -1 | 23 | 23 | 17 | 17 | |||
| Specific thermal capacity | /J（kgK） -1 /J（℃.cm3） -1 | 900 2.38 |
392 3.42 |
||||
| Thermal conductivity/W · (m · K) – 1 | 231 | 436 | |||||
| Thermal resistance/K · W -1 | 0.491 | 0.259 | |||||
| Calomel electrode potential/V | -0.75 | -0.22 | |||||
| Brinell hardness | about 25 | about 45 | about 60 | about 120 | |||
| Melting point /℃ | 600 | 1083 | |||||
| Heat of fusion/ × 10 5 Jkg -1 | 3,906 | 2,142 | |||||
Note: Data is from “Aluminum Alloy and Its Processing Handbook” 2nd Edition.
2.2 Application of Copper and Aluminum Conductors in Power Cables
In terms of cable production standards, all power cable manufacturing follows GB12706.1-2008 “Extruded insulated power cables and accessories rated voltage 1kV (Um=1.2kV) to 35kV (Um=40.5kV ): Part 1: Cables with voltage rating of 1kV (Um=1.2kV) and 3kV (Um=3.6kV)”, where the cable conductors are produced in accordance with GB/T3956-2008.
GB/T3956-2008 “Conductors for Cables” has clear provisions that can use the first or second type of annealed copper conductor with or without a layer of gold-plated metal, or aluminum or aluminum alloy conductor.
Tensile Strength and Conductivity of Electrical Aluminum
| state | σb /MPa | Resistivity (max.) /(Ωmm2)m -1 |
Conductivity (min) /% IACS |
| 1350-O | 58.3~98 | 0.027899 | 61.8 |
| 1350-H12 or H22 | 82.3~117.6 | 0.028035 | 61.5 |
| 1350-H14 or 24 | 102.9~137.2 | 0.028080 | 61.4 |
| 1350-H16 or 26 | 117.6~150.9 | 0.028126 | 61.3 |
| 1350-H19 | 161.7~198.9 | 0.028172 | 61.2 |
Note: Data is from “Aluminum Alloy and Its Processing Handbook” 2nd Edition.
2.3 Problems with Aluminum Conductors in Power Cable Applications
In the 1960s and 1970s, copper prices soared globally. Due to political factors, copper was considered a strategic material and subject to commercial control.
As a result, aluminum was widely used as the main conductor material for transmission cables, and “replacing copper with aluminum” became a common technical policy in the electrical industry.
Approval was required to choose copper conductor cables.
Therefore, pure aluminum cables were used for the main lines and branches of civil buildings.
The disadvantages of pure aluminum conductors (AA1350) are mainly reflected in the following aspects:
(1) Poor mechanical strength, easy to break.
(2) Susceptible to deformation, screws need to be tightened regularly.
(3) Easy to overload and generate heat, causing safety hazards.
(4) There is no good solution to the copper-aluminum transition connection problem.
These problems are not only faced by China, but also by the global cable industry. With the improvement of the international situation and the implementation of China's reform and opening-up policies, we can easily import a large amount of copper resources from abroad, and the price difference between copper and aluminum is not significant.
Thus, replacing copper with aluminum gradually became less popular in China. At the same time, foreign countries actively developed new aluminum alloy conductors and solved the connection problems between alloy conductors and terminals.
Eventually, the United States and Europe extensively applied aluminum alloy conductors in distribution lines. In the United States National Electrical Code (5) NEC330.14, it is stipulated that: “Solid conductors with cross-sectional areas of 8, 10, 12AWG (equivalent to 8.37 mm2, 5.26 mm2, 3.332 mm2 in China) shall be manufactured from AA8000 series electrical grade aluminum alloy materials.
Stranded conductors from 8AWG (equivalent to 8.37 mm2 in China) to 1000kcmil (equivalent to 506.7 mm2 in China) are marked Type RHH, RHW, XHHW, THW, THHW, THWN, THHN, Service Entry Type SE Style U and SE Style R shall be made of AA-8000 series electrical grade aluminum alloy conductive materials.”
3. Aluminum alloy conductors
3.1 Development of Aluminum Alloy Conductors
Aluminum alloys used as conductors experienced rapid development in the 1960s and 1970s due to rising copper prices.
In the International Aluminum Industry Association's list of aluminum alloys, the main aluminum alloys used as conductors are AA1000 series (pure aluminum), AA6000 series (Al-Mg-Si alloy) and AA8000 series (Al -Mg-Cu- Fe alloy) conductors. AA1000 series conductors are mainly used in high voltage overhead lines; AA6000 series Al-Mg-Si conductors are mainly used in high voltage overhead lines and aluminum busbars.
Both types of conductors exist in a hard state and welding is the primary method for joint connections. AA8000 series Al-Mg-Cu-Fe is a soft aluminum alloy which is actually used in distribution line.
The AA8000 series aluminum alloy obtained a series of patents in the 1960s and 1970s.
aluminum alloy
| League name | US patent number | |
| ANSI-H35.1 | UN | |
| 8017 | A98017 | |
| 8030 | A98030 | 3711339 |
| 8076 | A98076 | 3697260 |
| 8130 | A98130 | |
| 8176 | A98176 | RE28419 |
| 8176 | A98176 | RE30465 |
| 8177 | A98177 | |
3.2 The main chemical composition of AA8000 series conductors is as follows:
| aluminum alloy | Percentage of chemical composition based on quality | |||||||||
| ANSI | UN | Aluminum | Silicon | Iron | Copper | Magnesium | Zinc | Boron | Others (total) | Others (total) |
| 8017 8030 8076 8130 8176 8177 |
A98017 A98030 A98076 A98130 A98176 A98177 |
Residual Residual Residual Residual Residual | 0.10 0.10 0.10 0.15B 0.03-0.15 0.10 |
0.55-0.8 0.30-0.8 0.6-0.9 0.40-1.0B 0.40-1.0 0.25-0.45 |
0.10-0.20 0.15-0.30 0.04 0.05-0.15 …… 0.04 |
0.01-0.05 0.05 0.08-0.22 … … 0.04-0.12 |
0.05 0.05 0.05 0.10 0.10 0.05 |
0.04 0.001-0.04 0.04 … …0.04 |
0.03 A 0.03 0.03 0.03 0.05C 0.03 |
0.10 0.10 0.10 0.10 0.15 0.10 |
- A: The maximum lithium content is 0.03.
- B: The maximum silicon and iron content is 1.0.
- C: The maximum gallium content is 0.03.
Note: Data from the Aluminum Electrical Conductor Manual, Third Edition.
3.3 Comparison between AA8000 series conductors and pure aluminum conductors (AA1350).
Due to the addition of copper/iron/magnesium elements, these elements play a very critical role in the alloy:
Copper: Increases the stability of the alloy's electrical resistance at high temperatures.
Iron: Anti-creep and compression resistance are increased by 280%, avoiding relaxation problems caused by creep.
Magnesium: Can increase contact points and has higher tensile strength under the same interface pressure.
Performance of Aluminum Alloy for Soft Wire
| Item | σb /MPa | σ 0.2 /MPa | σ/% | Conductivity /% IACS |
| 1350 | 74.5 | 27.5 | 32 | 63.5 |
| Triple E | 95 | 67.7 | 33 | 62.5 |
| Super-T | 95 | 67.6 | 33 | 62.5 |
| X8076 | 108.8 | 60.8 | 22 | 61.5 |
| Estabiloy | 113.8 | 53.9 | 20 | 61.8 |
| NiCo | 108.8 | 67.7 | 26 | 61.3 |
| X8130 | 102.0 | 60.8 | 21 | 62.1 |
Note: Data from Aluminum Alloys and its Processing Manual, Second Edition.
(1) Mechanical strength: From the table, it can be seen that, compared with AA1350 pure aluminum conductors, the tensile strength of AA8000 series conductors is about 150% of that of pure aluminum, and the yield strength is about 200% of pure aluminum.
(2) Anti-creep performance: In the 500-hour creep test, it can be seen that compared with AA1350 pure aluminum conductors, the anti-creep performance of AA8000 series alloys is about 280% of aluminum pure, reaching basically the same level as copper conductors.
3.4 Comparison between aluminum alloy and copper conductors.
| Driver characteristics | Density (g/ m3 ) |
Fusion point (℃) |
Linear expansion coefficient | Resistivity (Ω* mm2 /m) |
Conductivity %IACS |
Tensile strength (MPa) |
Yield strength (MPa) |
Elongation Rate (%) |
| Electrical copper (Cu) | 8.89 | 1083 | 17*10 -6 | 0.017241 | 100 | 220-270 | 60-80 | 30-45 |
| AA8000 Aluminum Alloy | 2.7 | 660 | 23*10 -6 | 0.0279 | 61.8 | 113.8 | 53.9 | 30 |
Compared with copper conductors, it is found that due to different resistivities, the IACS of AA8000 aluminum alloy conductors is 61.8% copper.
When we increase the cross-sectional area of aluminum alloy conductors by two levels or increase it to 150% of the cross-sectional area of copper conductors, their electrical performance is consistent.
The tensile strength of aluminum alloy conductors is only half that of copper conductors (113.8:220MPa).
Due to the density of AA8000 aluminum alloy being only 30.4% of that of copper conductors, even if the cross-sectional area of aluminum alloy conductors is increased to 150% of the cross-sectional area of copper conductors, the weight of aluminum alloy conductors is only 45% copper conductors.
This makes the tensile strength of aluminum alloy conductors relatively advantageous compared to copper conductors.
The yield strength of AA8000 aluminum alloy conductors is close to that of copper conductors, making the creep performance of aluminum alloy conductors close to that of copper conductors.
In terms of elongation at break, aluminum alloy conductor is basically the same as copper conductor.
Due to the different expansion coefficients of aluminum alloy and copper conductors, it is not suitable to directly connect copper and aluminum alloy conductors. We guarantee connection reliability through the following method.
3.5 Connection reliability
The GB14315-2008 standard for crimp-type copper and aluminum terminals and connectors for power cable conductors has been officially implemented.
In this standard, the copper-aluminum transition terminal has also been officially included in the standard, providing a theoretical basis for connecting alloy cables and copper bars or electrical equipment made of copper.
Currently, there are basically three ways to use copper-aluminum transitions:
(1) Alloy cable + copper-aluminum transition terminal (the terminal is directly connected to the copper bar).
(2) Alloy cable + aluminum terminal (when the aluminum terminal is connected to the tinned copper busbar, the screw is tightened according to the torque value provided by the national standard, and a disc-shaped washer is added to ensure an effective connection between copper and aluminum metals during thermal expansion and contraction).
(3) Alloy cable + aluminum terminal + bimetallic washer (the aluminum part of the washer is connected to the aluminum terminal, and the copper part is connected to the copper bus).
All of these connection methods require 1,000 thermal cycling test cycles in accordance with IEC61238-2008 or GB9327-2008, simulating 30 years of use to ensure the reliability of the cable connections.
Thermal cycle tests conducted by Georgia Power Company and Shanghai Cable Research Institute have shown that the connection of alloy cables is safe and reliable, and experimental data shows that the reliability of their connection is even more stable than that of alloy conductors. copper.
4. Status of copper and aluminum resources
4.1 A global perspective on copper and aluminum resources
According to data from the US Geological Survey (USGS), the element copper represents less than 0.01% of the element content of the crust, while the element aluminum represents 7.73% of the element content of the crust.
The content of the aluminum element is more than 1000 times greater than that of the copper element in the crust. Based on the current consumption rate, global copper resources can support an additional 32 years of use at a growth rate of 3% per year.
As for aluminum resources, based on the current scale of mining (about 140 million tons per year), existing bauxite reserves have been sufficient to meet the needs of the global aluminum industry for almost 180 years.
4.2 Situation of national copper and aluminum resources
Since 2004, China has exported around 10% of its annual aluminum demand, resulting in serious overcapacity.
At the same time, according to statistics from the National Development and Reform Commission, from 2004 to 2006, China's annual copper gap exceeded 1.3 million tons.
According to data from the 2008 China Statistical Yearbook, in 2007, China imported 4.52 million tons of copper ore and refined copper, and the value of imports of copper and copper products was 27.1 billion dollars.
China's metallic copper market relies heavily on imports and China's insatiable demand for copper materials has led to a continuous increase in international copper prices.
Chinese companies also went abroad with unprecedented enthusiasm, acquiring foreign mining companies and exploring non-Chinese mines, paying a price that is still remembered by the Chinese people.
Since the beginning of 2004, copper prices have increased more than 200%, while aluminum prices have not fluctuated as dramatically as copper prices.
Changing the serious dependence on copper materials is essential to changing the international supply and demand relationship, saving foreign exchange, making full use of domestic resources and ensuring the sustainable development of the energy industry.
5. Conclusion
Due to the excellent electrical conductivity and mechanical properties of aluminum alloy conductors, the disadvantages of unreliable connection, low mechanical strength and easy creep of aluminum conductors have been improved.
Its mechanical performance is comparable to that of copper conductors. Electrical performance can be achieved by increasing the cross-sectional area, which has the same conductivity as copper conductors.
Therefore, aluminum alloy conductors are widely used in low voltage distribution systems.
The promotion and application of aluminum alloy conductors in the domestic market will save a large amount of copper resources, reduce the country's dependence on foreign copper resources, save a lot of foreign exchange, and allow users to save money.
It also makes it easier for installers to install them. With many advantages, we have reason to believe that the application of aluminum alloy conductors in low voltage power cables will become more popular and the trend of replacing copper with aluminum will cause a revolution in the cable industry.
