[Aluminium] In terms of conductivity alone, silver is higher, gold is second, copper is third, and aluminum is fourth, but gold and silver are precious metals, which are expensive and will not be in other sectors of industry and the national economy. Use them as conductor materials, of course, in some special cases, such as contact alloys. So the usual conductive material is only copper and aluminum. The resistivity of soft aluminum and copper are 27.8 and 17.24nΩ∙m, respectively, and the resistivity of hard aluminum and copper are 283 and 17.77nΩ∙m respectively. That is, the resistivity of aluminum is about 61.3% larger than that of copper. In other words, if the conductivity of copper is 1, and 100% IACS (International Annealed Copper Standard), the conductivity of aluminum is approximately 61.5% IACS.
However, keep in mind that the density of aluminum is only 2700kg/m3, while copper is as large as 8890kg/m3, only 30.37% of copper, that is, the density of copper is 3.29 times that of aluminum. In other words, the electrical conductivity per unit mass is 208% of that of copper. When the electrical conductivity is the same, the quality of the aluminum conductor or aluminum wire is only 1/2 that of copper. This facilitates the erection of the high-voltage transmission lines and facilitates the handling. Significantly increase the distance between lines. If copper wires are not used for general purpose aluminum lines, it will be at least three times more difficult to erect large HVDC transmission lines across the Yangtze River. Two towers with a height of 180m must be built in the Yangtze River to deliver the strong currents from the Three Gorges to the north and south of the river. There are thousands of factories, mines and millions of households inside and outside Wuling. If aluminum wires are used instead of copper wires to transport high voltage power, then the distance between the wires is not 100-250m today, but it must be shortened to 30-50m. This will not only increase the cost of erection lines, but also increase the occupancy of land by two or three times.
The price of aluminum is much lower than that of copper. In May 2012, the price of aluminum on the Shanghai Futures Exchange was about 15,900 yuan/ton, while the number of 1# copper was about 5,450 yuan/ton, and the copper price was 3.43 times that of aluminum; copper was a With scarce metal resources, the reserves of copper in the world are only 365 million tons, and aluminum is the more abundant metal element on the earth and moon, accounting for more than 8% of the solid part of the earth's surface, and sea water also contains 0.5ppm aluminum. Inexhaustible, inexhaustible.
Aluminum has a very high corrosion resistance to sulphide, but copper is not, which is another advantage of aluminum as a conductor because most insulating materials contain sulphide. Therefore, the tinning process before the insulation treatment can be omitted, and copper must be tin-plated. The aluminum wire will not form stearate with the oil in the insulating material during the process of insulating paint, and has good compatibility with insulating paint.
The ability of aluminum to dissipate current heat is much greater than that of copper. When the conductivities of aluminum and copper conductors are equal, although the mass of the former is only 1/2 that of the latter, the thermal conductivity of aluminum (231 w/m∙k) is higher than that of copper. The (436w/m∙k) is low, but since the surface area of ​​the aluminum conductor is much larger than that of copper, the aluminum wire has a stronger heat dissipation capability.
Today's high-voltage transmission lines are all ACSR, which can greatly increase the strength of the strands, making it an irreplaceable high-voltage transmission line, and it also has the advantages of small surface potential gradients and small stippling characteristics. .
Although aluminum as an electrical material has a series of advantages as described above, it also has some disadvantages such as: a low degree of creep is slightly low, and an aluminum wire in use occasionally suddenly breaks for no reason at the time of use, because the creep gradually reduces the cross section. Caused. Therefore, when calculating the load (including additional load, such as condensed ice) of the wire during operation, it should not be calculated based on the tensile strength, but also the creep strength. The creep strength of the hard aluminum wire is 12N/mm2, and the creep strength of the aluminum-magnesium-silicon alloy wire containing 0.51% Mg and 0.49% Si is 26,012N/mm2.
As the wind is constantly scraping, the overhead line is always in a vibrating state, so that the wire is subjected to complex stress effects such as tensile stress and bending stress. Under the long-term effect of these stresses, defective parts or places where the stress is concentrated (such as in the fixed connection, near the clamp, etc.) will be broken due to fatigue. The room temperature fatigue strength of the hard aluminum wire is 70N/mm2, which is lower than its yield strength. When the temperature is increased to 1500C, the fatigue strength is greatly reduced. Aluminium also has some copper notch sensitivity, and its coefficient of linear expansion is also 35.5% larger than that of copper. These are disadvantages of aluminum as an electrical material.
From the above description, it can be clearly seen that aluminum is a cost-effective electrician material and is a large amount of electrician metal used today. In 2011, the amount of aluminum used for electric wire and cable in the world was the amount of aluminum used as electric conductor. Roughly, about 16.60 kt of total consumption, or about 6860 kt, is consumed in recycled aluminum, which is lower in developed countries, while the share of developing countries is higher, because their electricity construction is in a period of rapid development.
Aluminum is mainly used in power, telecommunications, transportation, aluminum electrolyzers and other sectors in the form of wire rods, tubes, bus bars, conductive tracks, and foils. The use of aluminum as a conductor began in 1876, when Britishman Wle Carley erected the world's leading aluminium overhead conductor in Bolton. In 1910, Alcoa's technician W. Hoopes invented the ACSR and set it up over Niagara Falls. Since then, overhead high-voltage transmission lines have gradually replaced ACSR, and the United States, Britain, and Germany have tried to use aluminum as distribution lines since 1910, but the larger-scale use was after 1955.
Since 1960, the power conductors in the world are almost all aluminum, but the amount of indoor aluminum conductors is still small, mainly copper. The global aluminum wire aluminization rate (aluminization rate = [2Al/(Cu+2Al)]) is higher in the United States and reached 36.6% in 2011.
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