【 summary 】 with aluminum and copper has been the subject of considerable debate, can replace, how to replace, we have been argued for this topic. This article from the development background of aluminum alloy cable, and from a people care about the electrical, mechanical, aluminum alloy cable connections, corrosion resistant performance and the cost compared with copper for full, and combined with aluminum alloy cable application situation at home and abroad are analyzed.

Key words: aluminum alloy cable: with aluminum and copper: creep performance: the connection performance: the corrosion resistant ability

The background,

In the early 1960 s, the world began to appear the situation of copper resources nervous, people began to seek substitute for copper, which involves the cable conductor materials. Due to the order of metal under normal temperature and electrical conductivity is silver, copper, gold, aluminum, magnesium, iron, therefore people naturally think of aluminum and copper, so the world appear to aluminum and copper boom.

As early as the 1960 s, our country also started to aluminum and copper, aluminium core cable a large number of applications, from RuHuXian high-voltage transmission lines to the residents, all adopt the aluminum core, the electric power cable design code, and specify the appropriate USES of aluminum and copper technical and economic policy. But in the practical application of long-term found that due to the mechanical strength and flexibility of pure aluminum is poor, can appear in the process of using aluminium wire crack, broken, after long-term use of aluminium wire is embrittlement, is not conducive to maintenance. Early residential household aluminium wire section is small, the power supply ability is insufficient, can't meet the needs of power growth, residents their newly bought copper wire and aluminium wire directly twist together, electrochemical action happens in humid air, cause the contact resistance, over time, the occurrence of the phenomenon such as short circuit, open circuit, coupled with the original wire and cable insulation is poor, low melting point, the probability of fire. According to the ministry of public security fire department statistics show that electrical wiring caused fires have been higher, about 15% of the total number of fire.

Not just in China, the same experience also happened in North America. In the 60 s of the development of North America AA1350 pure aluminum, pure aluminum thread residential use hard, due to poor mechanical properties, the installation process, the mechanical connection using artificial control difference is very big, can appear after fastening too loose or too tight, under the effect of pressure, the deformation will occur after a long run nonrecoverable, known as "creep". After creep produced, so the clamping force is not enough, the points of contact pressure makes the contact resistance increases rapidly, after electric current flows through the junction overheating, if not regular maintenance, the result will be a break, the fire accident. After more than two years of meticulous research and analysis, found the problem mainly appear in the conductor wire and join point.

Due to the existence of the above problem, the use of pure aluminium material as the cable conductor, especially in residential into line, frequent accidents, making pure aluminium in people's impression of a cable safety performance is low, and due to the power supply tension lowered the electrolytic aluminium production in China. At the same time, the international market copper supplies are easing, make pure aluminium cable gradually fade out the domestic field of low voltage power distribution, copper cable is widely used again.

But as to the international copper prices soared this year, combined with China's copper resources nervous, on the verge of scarce, according to Chinese nonferrous metal net, reserves of about 26 million tons of copper resources in China, and China every year around 5 million tonnes of actual amount with copper, copper cable use about 70% of China's total copper consumption. Every year China imports 70% of copper concentrate, if do not rely on imports, China's copper resources can use up to five years. China is a country with rich aluminum, according to incomplete statistics, China's reserves of about 2.7 billion tons of aluminum resources, and China is still a major aluminum producers. So in this background, have to hark back to copper aluminum generation policy.

Second, the performance comparison

Over the years, americans have been expected to develop a kind of conductor, can continue to aluminum and copper, but has not been a breakthrough from the technology, therefore has not been able to realize the historic revolution. Aiming at the existing shortcomings of pure aluminium as the cable conductor, Australia and Canada and other developed countries take the lead in this respect to do a lot of research. Established in the end of 20 century 60 developed aluminium alloy conductor, aluminum alloy conductor in North America has nearly 40 years, has developed countries such as Australia and Canada of the customers agree, in North America were 90% of residential and commercial buildings use aluminum alloy cable. Why aluminum alloy cable has such a broad market, compared with pure aluminium and copper have what features, this article will from the materials, electrical properties, mechanical properties of aluminium alloy conductor, connection performance and corrosion resistance and so on various aspects to do comprehensive analysis.

1. The conductor material

New type of aluminum alloy material in pure aluminium added on the basis of copper, iron, magnesium, silicon and rare earth elements, etc. A variety of elements, through special process synthesis and annealing treatment and other advanced technology, make up for the deficiency of the pure aluminum cable, improve the performance of the electric conductivity, bending of the cable, creep resistance and corrosion resistance, ensure even in a long time when overload and overheat cable connection thermal stability.

2. The electrical properties

Aluminum and copper are cost-effective in terms of conductive metal, as in North America in the cable transmission, high voltage overhead lines and cable transmission cables 100% aluminum conductor, medium voltage transmission 99% aluminum conductor. High voltage power transmission in China, are mainly pure aluminum.

Many people thought that the resistivity of aluminum conductors than copper conductors, aluminum is used as the conductor of the cable in the process of transmission energy loss should be bigger than copper material. In fact, this view is unwarranted. Because the energy loss in the process of transmission depends on the conductor resistance instead of resistivity. According to the national standard of GB/T3956-2008 cable conductor, at 20 ℃, the dc resistance of a copper conductor section and its corresponding big one or two specifications of the aluminum or aluminum alloy conductor dc resistance. That is to say, from the transmission energy loss in the process of consideration. A copper conductor can completely by corresponding big two specifications of the aluminum or aluminum alloy conductor cable is replaced, the aluminum or aluminum alloy cable current carrying capacity is greater than that of copper.

Because of the new type of extruded aluminum alloy conductor in the former want to undertake the processing of annealing process, conductor after recrystallization and stress recovery processing, relative to conductivity of pure aluminum, conductivity can reach 61.5% IACS, performance is more better than that of pure aluminium.

3. The mechanical properties of

(1). Flexible

Hard the elongation of 0.5 to 2.0% of pure aluminum, and aluminum alloy after annealing process treatment, cable elongation increased by 30%, compared to traditional copper has better flexibility, installation time needed to pull a lot smaller than copper.

(2). Bending performance

The bending performance is very poor, pure aluminum bending is easy to break, break, therefore often causes accidents. The minimum bend radius aluminum alloy cable for 7 times the cable diameter, far better than that of GB/T 12706 "of" minimum bending radius of cable installation of 10 to 20 times the cable diameter, thus aluminum alloy cable during the installation process is easier to bend, effectively reduce the installation cost, reduce the risk of accidents.

(3). Creep resistance

Adding iron, aluminum alloy materials after annealing treatment reinforcement effect, creep performance compared to the pure aluminium increased by 300%, and thus avoid the long-term by creep caused by the effect of mechanical force, contact resistance increases the risk of accidents.

(4). Other

Aluminum alloy cable elasticity than copper 40% less elasticity, and have no memory effect, etc., more than the copper conductor is suitable for installation.

4. The connection performance

In the accumulation of past experience and cognitive, copper aluminum connection has been the most critical problem. Copper and aluminum (or aluminum) if connected directly contact, because of the metal material is qualitative different, there is potential difference, electrochemical corrosion will happen in the damp air. In power system, increases the corrosion resistance, the fever, joint is the safe operation of the system.

In addition, copper and aluminum (or aluminum) expansion coefficient is different, if the rigid connection can cause metal fatigue, can cause joint loose after long time use, also can increase the contact resistance, this is a widespread concern.

Aluminum alloy power cable to the end of treatment, rely mainly on the following means:

First, the tin plating. Terminal of aluminium or copper platoon tin tin is feasible. With copper platoon tin and tin plating aluminum terminals to solve the problem of copper aluminum transition has been widely used in electric power industry, and was proved to be safe and reliable.

Second, using the transition of special gaskets, the gasket between copper and aluminum, effectively prevent the corrosion of copper aluminum contact problem.

Third, daub antioxidants. When the copper contact no tin of electrical equipment, and it's no use aluminum terminal plating tin, can adopt the method of daub antioxidants. Antioxidant between copper and aluminum, can effectively prevent the entry of the electrolyte, so as to avoid the electrochemical corrosion.

Using above the first and the third way connection, need to add dish washers to absorb the copper/aluminum different expansion coefficient of relaxation, with torque wrench tight, don't need to make any connection of the whole system maintenance and secondary tighten. Since joined the copper, iron, magnesium, aluminum alloy materials, rare earth and other elements, greatly improve the connection performance. Especially when annealed conductors, adding iron to produce the high strength and creep resistance, even in the heat for a long time, also can ensure stability of the connection. Copper/aluminum alloy connection testing laboratory in North America by the authority in accordance with the long running (more than 30 years) formulated by the cold head heat cycle test standard: 100 in the Shanghai electric cable research institute of China, passed in accordance with the long running (more than 30 years) formulated by the IEC1000 connection head thermal cycle test standard.

5. Corrosion resistance ability

Is divided into chemical corrosion and electrochemical corrosion, and corrosion from pure metal properties, corrosion resistant properties of aluminum is better than that of copper. Aluminum in the air soon formed a thickness of about 2 x 10-4 mm compact oxidation film, prevent the internal metal was further corrosion. While copper could not form oxidation film, so the pollutants will further into the corrosion.

In cable application, the join also determines the corrosion resistant ability of the system, the join of electrochemical corrosion was caused by different electrode potential, the difference between metal resistance, electrical conductivity of the electrolyte, the contact area on the surface of the Yin and Yang (current density) and polarization properties of metal factors such as the result of joint action. Application for several years in the North America using mature terminal, remove the hidden danger existing in the terminal connections.

The potential difference, the greater the corrosion will be more serious. Aluminum alloy with rare metal, in terms of chemical properties, further improve the aluminum as the conductor of the corrosion resistant ability of metal materials, reduce the potential difference between different metals.

Third, cost analysis

Due to the density of aluminum is about 1/3 of the copper, conductive rate is 61.5% IACS, so under the same load flow, half the weight of the aluminum alloy cable lighter than copper cable. When aluminum alloy cable cross section is 1.5 times that of copper, its electrical properties is the same. Many people have this concern, worry about aluminum alloy cable cross section increases to 1.5 times that of the copper, cable diameter increases a lot, thus increase the cable insulation material, around the bag, filling, sheath material and auxiliary material cost, and also concerns would increase the cost of installation. Actually this fear is completely unnecessary. Because USES special compression technology, after compression, step by step, conductor compression coefficient is 0.95, reached world leading level. And a copper cable through compression molding, normally only compression coefficient is 0.80, so its diameter than copper wire by only 5%, thus aluminum alloy cable on the premise of increased slightly outside diameter, conductivity can completely reach the capacity of conductive copper cables, and therefore will not increase the cost of how many other materials. Same cable current carrying capacity of aluminum alloy is half the weight of copper, so use aluminum alloy cable is light weight, can avoid cost of bridge.

Four, flame retardant insulation and metal interlock armoured

Since the beginning of the aluminum alloy cable on the market for its high standards, aluminum alloy with environmental crosslinking polyethylene cable material, not only service life is greatly superior to PVC insulation, and safety performance is more outstanding, plus unique metal interlock armoured structure, meet the requirements of low smoke zero halogen flame retardant grade A, this kind of cable during combustion of high light transmittance, reached 99%, only produce trace amounts of smoke, and thus to minimize the damage to the human body, equipment and buildings, for during the fire evacuation and rescue in time.

Five, the conclusion

Through the above analysis, it can be seen as a pure aluminum aluminum alloy cable made up for hard cable conductor of many shortcomings, solved the years failed to solve technical problems, and some characteristic is better than that of copper. Aluminum alloy cable with its superior performance in North America market nearly forty years. Now in China such as Beijing, Shanghai, sichuan, chongqing, tianjin region is widely used in civil and industrial buildings, such as the Shanghai world expo, Beijing wukesong sports center, wuhan hongshan power supply companies and other large projects. Either from the perspective of the technical indexes and economic benefit of the product, or stand in the perspective of national strategic reserves of copper resources in aluminum and copper in the field of power cable is completely feasible, a large number of experimental data and application proved that the policies in favor of aluminum and copper in today must repeat, and even a large number of promotion should be, this is the trend of the development of Chinese cable.