Since aluminum has good electrical conductivity, aluminum cables have been used in North America since the 1960s. At first, like high-voltage overhead lines, pure aluminum materials were used, and only later were 8000 series aluminum alloy materials widely used.
1、The origin of aluminum alloy cable material
In the period of 1965-1971, some building fire accidents occurred frequently in the United States using pure aluminum core cables. Through analysis, the main reason was that there was no special connector designed for aluminum-core cable, but directly used the connector of copper-core cable, which led to slackness, microscopic damage and arcing between the aluminum wire and the socket or switch, making the contact resistance increase to overheat and cause fire.
In order to reverse this situation, the North American cable industry from the cable products and connectors to improve several aspects, taking the following measures.
? In terms of materials; U.S. Southwire, Canada Aluminum invented 8176, 8030 and other 8000 series aluminum alloy to enhance the creep performance ;
? In the wire connection; using a variety of methods to improve the connection performance, including the use of tinned terminals, adding special gaskets between the aluminum and copper terminals, connection points coated with antioxidants, the design of special sockets, etc. ;
? In terms of standards; through the U.S. UL Corporation, and the U.S. National Fire Protection Council (NFPA) test, in 1985, the NEC electrical provisions in the 2000V below certain types of wire aluminum conductors should be used 8000 series aluminum alloy. 1988, the American Society for Testing and Materials (ASTM ) promulgated the B800 standard, the six grades of 8000 series aluminum alloy in the cable conductor standard (Note).
From the history of the development of aluminum alloy cables in the United States, there are several characteristics;
First, the problem of pure aluminum and copper connection terminals, resulting in a number of accidents;
Second, 8000 series aluminum alloy, a new model developed on the basis of pure aluminum material, the main purpose is to enhance the creep performance of the general aluminum cable, mainly to solve the problems arising from the joint terminals.
Third, in 1985, the U.S. electrical regulations stipulated that the aluminum conductors of certain types of wires below 2000V should be made of 8000 series aluminum alloy. It can be seen that in the United States, aluminum alloy cables have never entered the medium-voltage field, but only in the low-voltage part of the field applicable.
Fourth, from the promulgation of B800 standard in 1988, up to now, the history of the use of aluminum alloy cable in the United States is less than 30 years.
2、The performance of 8000 series aluminum alloy
From the above two aluminum alloy standard table, we can see that 1350 electrician pure aluminum, belongs to pure aluminum, its aluminum content is 99.50%; 8000 series aluminum alloy, belongs to other alloy series, its aluminum content is more than 98%, adding Si Cu Fe Me and other trace elements, totaling 1%-1.5%. This means that 8000 series aluminum alloy only adds a little trace element on the basis of pure aluminum, with the purpose of improving the creep performance of aluminum for the manufacture of aluminum alloy cable, and does not improve the other use performance of aluminum.
Therefore, compared with 1000 series pure aluminum, the performance of 8000 series aluminum alloy is not fundamentally improved, but only has some improvements in creep resistance.
3、The tensile strength of 8000 series aluminum alloy is worse than pure aluminum
Through the indicators of aluminum alloy product standards, it can be seen that the mechanical tensile strength of 8000 series aluminum alloy is 30% lower than pure aluminum, and more than 100% lower than copper. Therefore, from this indicator, if the cable with 8000 series aluminum alloy is not handled properly in construction, it will easily lead to breakage and cracking traces, and such breakage and cracking traces are undoubtedly a big hidden danger in the stable operation of the cable.
4, a comprehensive comparison of the performance of various materials cable
Through the product standard indicators, a comprehensive comparison of aluminum alloy cable, pure aluminum cable and copper cable performance.
In terms of electrical conductivity, copper material is the best, pure aluminum is the second, 8000 series aluminum alloy is not as good as pure aluminum.
In terms of elongation at break/flexibility, copper material is the best, 8000 series aluminum alloy is the second best, and pure aluminum is not as good as 8000 series aluminum alloy.
In terms of tensile strength, copper material is the best, pure aluminum is the second best, and aluminum alloy is 30% worse than pure aluminum.
In terms of corrosion resistance, copper material is the best, pure aluminum is the second best, and aluminum alloy is inferior to pure aluminum.
5、Conclusion
Through the performance comparison, it can be seen that the use of 8000 series aluminum alloy cable manufacturing, than pure aluminum cable manufacturing, only in creep resistance and fracture elongation has improved, other aspects of the performance not only did not improve, and even worse than pure aluminum materials. Since the price of 8000 series aluminum alloy is higher than pure aluminum, can we consider using pure aluminum instead of 8000 series aluminum alloy as the material for manufacturing cables.
Compared with copper cable, all the usage indexes of aluminum alloy cable are weaker than copper cable, so it is unrealistic for aluminum alloy cable to fully replace copper cable.
In general, the development of aluminum alloy cable provides users with a third choice outside of copper cable and pure aluminum cable. However, from the actual situation of China's power system, the higher the complexity of the system, the higher the risk, the higher the maintenance cost and the increase of spare parts. Taking these factors into account, the EU countries have adopted a more realistic policy, stipulating that the cable will be made of copper and pure aluminum materials, and not aluminum alloy materials. Is this systematic selection method of thinking worthy of our consideration?
(Note) Data source: U.S. Consumer Product Safety Commission fire investigation done in 1974 on several states and cities.
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