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Conductor and loss of cable

Release time:2022-09-09 09:01     Views:

The conductors used for cables are copper and aluminum. Aluminum alloy and copper clad aluminum are derived from aluminum. Previously, wires and cables were made of copper conductors because of their excellent conductivity and mechanical properties. The DC resistivity at 20 ℃ is 1.72 × ten ˉ 6 Ω ˙ cm。

Since the 1950s, China was embargoed by capitalist countries because copper was an important strategic material due to the Korean War. Chinese people still remember the patriotic enthusiasm of responding to the call to donate their bronze wares to the country. At the same time, "replacing copper with aluminum" has spread all aspects of life, and the use of aluminum wires and cables is implemented as a technical policy. 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 have paid attention to safety, can only make do. Because aluminum is inferior to copper in both electrical and mechanical properties. The DC resistivity at 20 ℃ is 2.82 × ten ˉ 6 Ω ˙ Cm, about 1.64 times that of copper. Its brittleness makes the joint easy to break, and the reliability of the joint is reduced due to the creep characteristics. Creep is the thermoplastic deformation that increases with time under higher temperature (such as 70 ℃) and greater pressure (such as bolt compression). It is the main reason that the reliability of wire and cable joints is reduced, or even damaged. After a long time of exploration, we also found some solutions, such as strengthening inspection tour, regularly strengthening and screwing bolts.

Of course, there are always two sides of things. Aluminum conductor wires and cables are popular because of their low price and light weight, which greatly reduces the labor intensity of construction.

In the period of reform and opening up, the economy has developed rapidly, people's requirements for quality have been improved, and they have got rid of some constraints. As a result, they have turned from one extreme to the other. In the southeast coast, they have given up "replacing copper with aluminum", and almost all wires and cables use copper conductors, with unprecedented depth and breadth. The depth -- the proportion of copper and aluminum conductors has exceeded that of developed countries, and the breadth -- has gradually expanded from the southeast coast to the mainland.

The development of things has gone to the opposite. Because of the soaring copper price, the price of wires and cables has doubled. People have to rethink. At the same time, two small whirlwinds blew up. One was the emergence of copper clad aluminum cable, and the other was the introduction of aluminum alloy conductor cable technology from North America. Aluminum alloy cable came into being in China.

Copper clad aluminum cable is said to be able to replace copper cable. But in fact, it is only applicable to small cross-section and high-frequency devices. Due to the skin effect of high-frequency current, copper clad aluminum wire can play its advantages. Relevant standards at home and abroad are also limited to electronic devices. Copper clad aluminum wire cannot be used to make power cables. On the one hand, it is only applicable to single strand wire, and it is meaningless to use multi strand wire. On the other hand, joint technology cannot solve this problem, so this whirlwind soon becomes low pressure.

Aluminum alloy conductor is the electrical aluminum added with trace elements such as silicon, copper, zinc, iron and boron. Mechanical properties have been greatly improved, such as flexibility optimization and creep resistance. Where the annealing process is excellent, its conductivity can be very close to electrical aluminum. The national standard "Conductor of cable" GB/T3956-2008 takes the resistance of aluminum and aluminum alloy conductor as the same value.

One of the key technologies of aluminum alloy cable is connector. The joint material and process are important factors affecting the quality. Cable manufacturers with imported technology provide technical services in addition to selling cables. If the joint is to be reliable, the supplier must appoint professionals to guide the construction. Therefore, its price is much higher than that of aluminum cable. Because of the large profit margin, the number of manufacturers has suddenly increased from two to more than one hundred, and the small whirlwind is expanding. At present, all enterprises produce according to their own enterprise standards, which seems to be the same, but in fact, the quality varies greatly.