Conductors for cables are copper and aluminum. Aluminum alloy and copper-clad aluminum derived from aluminum, the original wire and cable are copper conductors, because its electrical conductivity and mechanical properties are ideal, 20℃ DC resistivity is 1.72×10ˉ 6Ω ˙cm.
China from the 1950s, due to the Korean War, because copper is an important strategic material and was embargoed by capitalist countries. Chinese people still remember the patriotic enthusiasm of responding to the call to donate their bronze wares to the country. At the same time, “aluminum instead of copper” throughout all aspects of life, with aluminum wire and cable as a technical policy to implement. In some places where safety and reliability are not too strict, aluminum core wires and cables are used, even in new residential buildings – places that should be concerned about safety can only be settled. Because aluminum is inferior to copper in both electrical and mechanical properties. The DC resistivity at 20℃ is 2.82×10ˉ 6Ω ˙cm, which is about 1.64 times that of copper. Its brittleness makes the joint easy to break, and because of the creep characteristic, the reliability of the joint is reduced. The so-called creep is the thermoplastic deformation that increases with time under higher temperatures (such as 70 ° C) and greater pressures (such as bolt compression). It is the main reason for the reliability reduction and even damage of wire and cable joints. After long-term exploration, some countermeasures have also been found, such as strengthening inspections and regularly strengthening tightening bolts.
Of course, things always have two sides, because the aluminum conductor wire and cable price is low, light weight, greatly reduce the construction labor intensity and is welcomed.
To the reform and opening up period, rapid economic development, people’s quality requirements to improve, get rid of some constraints, the result from one extreme to the other extreme, in the southeast coast to take the lead in giving up the “aluminum instead of copper”, wire and cable almost all use copper conductors, depth and breadth unprecedented. The depth – the ratio of copper and aluminum conductors exceeds that of developed countries, and the breadth – gradually expands from the southeast coast to the interior.
The development of things has gone in the opposite direction, as the price of copper has soared, so that the price of wire and cable has doubled, people have to rethink. At the same time, two small cyclones, one is the emergence of copper-clad aluminum cable, and the other is the introduction of aluminum alloy conductor cable technology from North America. Aluminum alloy cable came into being in China.
Copper-clad aluminum cables are claimed to replace copper cables. But in fact it is only suitable for small cross sections and for high-frequency devices, due to the skin effect of high-frequency current, copper-clad aluminum wire can play its advantages. Domestic and foreign standards are also limited to electronic devices. Copper clad aluminum wire can not be used to make power cables, on the one hand, it is only applicable to a single strand, the use of multiple strands of the lost meaning, on the other hand, the joint technology can not be solved, so the cyclone soon became a low pressure.
Aluminum alloy conductors are electrical aluminum with trace amounts of silicon, copper, zinc, iron, boron and other elements. Mechanical properties have been greatly improved, such as flexibility 靱 optimization, creep resistance has been greatly improved. Where the annealing process is exquisite, its electrical conductivity can be very close to electrical aluminum. “Conductor of cable” National standard GB/T3956-2008 takes the resistance of aluminum and aluminum alloy conductors to the same value.
One of the key technologies of aluminum alloy cable is the joint. The material and process of the joint are important factors affecting the quality, and the cable manufacturing enterprises that introduce technology provide technical services in addition to selling cables. If the joint is to be reliable, the supplier must appoint a professional to guide the construction. Therefore, its price is much higher than that of aluminum cable. Because of the large profit margins, manufacturers from the beginning of two, suddenly soared to more than 100, the small whirlwind is expanding. Because the current enterprises are produced according to their own enterprise standards, it seems to be the same, but the quality is very different.
Which is the biggest loss of copper and aluminum alloy cables? Opinions differ. Here, the data speak for itself.
The calculation formula of cable loss is:
△P=Ι2˙Rθj˙L˙NC˙NP×10ˉ³ (1)
△Q=△P˙ζ (2)
Where: △P – Power loss, kW
△Q – Energy consumption, kWh
Rθj – AC resistance per unit length of a single conductor accounting for skin and proximity effects at temperature θ, Ω/km
Ι – Calculate current,A
NC, NP – Number of conductors per loop and number of circuits
ζ – Maximum load loss hours,h/ year
L – Line length,km
Post time: Feb-28-2024