Advantages of copper cables

Feb 12,2020
 For the wire and cable industry, the most obvious material replacement is to use aluminum conductor instead of copper conductor. In the relative cost of copper and aluminum conductors, we need to consider the price, specific gravity, conductivity and other factors, in order to get the real answer whether using aluminum conductors can save costs. Copper is heavier than aluminum. The specific gravity of copper is 8.9g.cm3, and the specific gravity of aluminum is 2.7g/cm3. That is to say, under the same conductor specification, the weight of copper conductor is 3.3 times that of aluminum conductor. However, the conductivity of aluminum is only 61% of that of copper, that is to say, the cross section of aluminum conductor is 61% larger than that of copper conductor under the same transmission current. Therefore, in terms of conductor weight, to make the two conductors have the same carrying capacity, the weight of copper conductor is about twice that of aluminum conductor. In addition, the price ratio of copper to aluminum is about 3.5, so the cost of equivalent copper conductor is seven times that of aluminum conductor.
Of course, the simple cost comparison mentioned above does not explain the whole problem. Because the cable product is limited by the standard conductor specification, it is impossible to buy the aluminum core cable with the same conductivity as the copper core cable. Therefore, if the cable is made of aluminum conductor, the aluminum conductor with larger cross section must be used. Experience shows that under the condition of equal carrying capacity, the conductor section of aluminum core cable should be twice that of copper core cable. Since the cross-section of the aluminum conductor is twice that of the copper conductor, the subsequent increase in the insulation, sheath and armor materials of the aluminum conductor weakens the price advantage of using the aluminum conductor. That is to say, the price advantage of aluminum and copper is not great, because the conductor is only a small part of the cost of the whole cable after all.
Taking 70mm2 copper core cable as an example, the cost of copper conductor accounts for about 65% of the cost of the whole cable, while the cost of 120mm2 aluminum core cable with equal current carrying capacity can be saved by 23.5%. If the cost of copper conductor accounts for 80% of the cost of the whole cable, the cost savings of aluminum core cable with equal current carrying capacity can reach 46%. Only when the cost of copper conductor in the cable drops below 50% of the cost of the whole cable, the aluminum core cable will lose its cost advantage. At present, the cost of most copper core low-voltage cables and many medium voltage cable conductors has exceeded 50%. Therefore, compared with copper core power cables, aluminum core power cables have obvious advantages in cost saving.
Copper has always been the dominant material
After China's reform and opening up, copper cable has largely replaced aluminum cable. The first reason is that the domestic and foreign markets have achieved convergence. Although the price of copper materials is more expensive, the power sector can bear it. In exchange, it is safe and reliable, and the construction is convenient. Second, from the perspective of safety and reliability, because the key point of using aluminum core power cable is the joint technology and its reliability. Third, in some cities, especially in large cities, aluminum core power cables are not used because of the limited underground laying space.
Wire and cable
Since human beings entered the electrical age, copper has been playing a leading role in power conductors. But for a long time, the price of copper has been at a high level, which has a negative impact on its dominant position in power conductors.
Aluminum alloy cable has certain characteristics. From the economic point of view, the advantages of aluminum alloy cable are: the cost of manufacturing and transportation is not high; but the disadvantages of aluminum alloy cable are also very obvious: the current carrying capacity is small, and after adding other kinds of alloy elements into aluminum, the conductivity decreases. In addition, the volume of aluminum alloy cable is large. Although the process is strictly controlled to improve the compression coefficient and reduce the increment of aluminum alloy cable section, the outer diameter of aluminum alloy cable is still 1.2 times larger than that of copper cable.
In terms of high-temperature resistance, aluminum alloy cable has weak performance. The melting temperature of aluminum is 660 ℃, while copper can reach 1080 ℃. The fire-resistant cable used in high-temperature environment is required to be able to maintain the power on function under the action of 750 ℃ ~ 1000 ℃, but in such cable selection, aluminum alloy cable cannot be used. If the conductivity of copper is 100%, the unit volume resistivity of aluminum alloy is equivalent to that of aluminum, about 61.2%. When the cross-sectional area of aluminum alloy cable is about 1.5 times that of copper cable, its DC resistance is the same.
According to the data provided in the supervision and testing of metal materials for power grid equipment, the resistance of copper conductor is not more than 0.158 Ω / km at 20 ℃, while that of aluminum alloy conductor is 0.249 Ω / km.
Experts believe that as a distribution cable, not only the conductivity of the cable should be considered, but also the conductivity of the cable system. In other words, the conductivity of the middle connection and terminal connection of the cable must be considered, which is the key to ensure the reliability of the cable system.
According to the statistics of Beijing electric power company, 80% of power cable faults occur at the joints. In this regard, copper has the incomparable advantages of aluminum and aluminum alloy. Even if it is oxidized, the generated copper oxide is still a good conductor, which can ensure the electrical connection performance of the connector and the terminal; and even if the aluminum alloy cable has a good construction process guarantee, after the connector or the terminal is oxidized, the generated aluminum oxide is an insulator, which will lead to the deterioration of the conductivity of the connector or the terminal, Thus, the heating of the connector or terminal is increased, so that the oxidation is more serious. This vicious cycle leads to cable system failure.
In addition, at present, the corrosion resistance of aluminum alloy cable is not as good as that of pure aluminum, which is quite different from that of copper. In terms of the electrical conductivity of the cable, whether it is the conductor DC resistance of the cable with the same cross-section specification, or the electrical conductivity of the cable connector and terminal in the long-term operation process, aluminum alloy cable is obviously inferior to copper cable, and the larger the nominal cross-section, the more prominent the disadvantage of aluminum alloy cable.
Views on "saving copper with aluminum"
Compared with copper cable, the main technical performance of aluminum alloy cable is not dominant. The cable industry proposes "saving copper with aluminum", the key is economic factors. Therefore, the cable industry "can not only carry out the copper saving", but what scale should be made, not what people can control, but the market has the final say.
First, we should adhere to a strict scientific attitude. Although the application technology of aluminum alloy cable has made a significant breakthrough, but restricted by the technical performance, in the urban power supply main line, large power plant, heavy pollution environment, and the environment that is not easy to maintain, from the perspective of use safety, copper cable should be used.
Second, we should regulate market order and stop blind development. At present, the intensive degree of China's wire and cable industry is not high, the level of technology and management among enterprises is uneven, and the disordered competition is prominent. Due to the high quality management requirements in the production process of aluminum alloy cable, the matching requirements for connectors are not low. If many enterprises, regardless of their own conditions, do not have technical support, rush to produce aluminum alloy cables, it will inevitably cause market disorder, product quality can not be guaranteed, once there is a safety accident, it will seriously affect the credibility of the cable industry.
Third, we should rely on scientific and technological innovation to improve the technology. At present, the production and application experience of aluminum alloy cable at home and abroad is very limited, and many deep-seated technical problems need further study. At the same time, the product standard of aluminum alloy cable has not yet been issued by the state, and the supporting standard is even less, and the product manufacturing technology and application technology are not fully mature. In this case, the cable user should strictly carry out scheme demonstration and strictly control the cable product quality and construction quality.
To succeed in development, innovation is essential, but without inheritance, innovation will become a water without source and a tree without roots. In this way, it is difficult to succeed. Only when we not only know how to develop our own characteristics, have the courage to innovate, but also be good at inheriting the traditions of our predecessors, can we succeed more easily. We can get inspiration from the front wheel of history, keep innovating, keep improving in the process of manufacturing wires and cables, keep pace with the development of society and science and technology, and push the cable industry to a new stage and field.