Product use of aluminum alloy cable is analyzed.
Characteristics of aluminum alloy cable
The main components of the aluminum alloy cable are: copper, iron, silicon, magnesium, manganese, titanium, chromium, zinc and rare earth. The effect of copper increases the resistance of the conductor at high temperature.
Electrical properties of aluminium alloy cable
(1) the electric conductivity: the electric conductivity of the aluminum alloy is between the aluminum and the copper, and the ratio of the copper is slightly better than that of the copper.
(2) the cable pressing conductor characteristics: Aluminum Alloy layered compacted stranded conductor technology, compression coefficient can reach 0.93, and squeeze the coefficient of copper conductors generally only 0.80. Pressed by maximum limit, you can make up for lack of Aluminum Alloy conductor in the bulk conductivity of the stranded conductor wire core such as solid core, significantly reduces the core diameter, improving the conductive property, so the carrying capacity is the same, the outer diameter of the cable Aluminum Alloy cable replaced copper core cable after increases slightly.
Mechanical properties of two aluminum alloy cable
The elongation of hard pure aluminum is very low. It is easy to damage or break. The elongation ratio of soft state is improved, but the yield strength is only half of copper, the creep resistance is poor, and the connection is easy to loose, causing the safety running hidden trouble. The mechanical properties of the aluminum alloy conductor can be obtained by the comparison of Table 1:
(1) high extension. The elongation of the aluminum alloy conductor can reach 30%, which is close to the copper and is much higher than that of the aluminum alloy. This also shows that the aluminum alloy conductor can withstand greater force than the aluminum conductor.
(2) strong, flexible, easy to bend. In the installation, the aluminum alloy conductor has a smaller bending radius than the aluminum conductor, which is more easy to connect the terminal.
(3 creep resistance. The alloy elements in the aluminum alloy have been treated by special process, the creep resistance and the compression resistance have been greatly improved, and the stability of the connection can be ensured when the conductor meets the extreme conditions such as cold flow, overload and overheat.
Three, aluminum alloy cable corrosion resistance
Aluminum alloy conductor in addition to the rare metal, in the chemical properties, further improve the aluminum as a conductor of metal material corrosion resistance, reduce the potential difference between different metals, the smaller the potential difference, the more light corrosion. The rare earth elements in the alloy material can be filled in the surface defect, the grain size, the elimination of the role of local corrosion, but also bring the electrode potential negative shift, with the anode effect, thereby greatly improving the corrosion resistance.
Four, the economic performance of aluminum alloy cable
Compared with the copper core cable, aluminum alloy cable price advantage is obvious, the same load flow of aluminum alloy cable prices only copper core cable 60%-70%. In addition due to the lighter weight, but also indirectly reduce the cost of installation.
35kV cable conductor selection in wind farm
35kV high voltage cable used in wind farm, in order to save the project cost, the conductor first choice of aluminum core, in order to meet the voltage drop and the premise of the modified load flow, the use of economic current density to calculate the appropriate cable cross section.
With the increase in the number of wind farms and running time, the shortcomings of the aluminum core cable gradually emerged, mainly reflected in the following aspects:
One, the mechanical strength is poor, easy to break. Wind farm is located in the region of poor environment, the wind speed is larger, the cable tower after the wind load, especially the cable terminal is due to the impact of the umbrella group, the site of the wind, and therefore more prone to failure.
Two, creep resistance is poor. When the wind power cable is on the tower, when the electric current is too large, the aluminum conductor heating occurs, the cable joint is easy to loose and deformed, which leads to the line contact is not good, so that the line and equipment failure accident.
Three, high resistivity, loss of large. The wind electric field chooses the cable conductor cross section, the aluminum core cross section is much bigger than the copper core section, such as the cable section selection is too large, the cable length is far more than the cable manufacturer's biggest production disk, the cable section and the middle joint is increased, which is disadvantageous to the long running of the electric power line.
Based on the above reasons, in the past few years, the main use of the wind farm power cable copper core. All kinds of problems of copper core cable aluminum core cable can be well solved, but China's demand for copper in recent years gradually increased, prices are rising, increase the number of engineering cost of intangible, is to increase the risk of stolen cable construction site. In addition, due to the weight of the copper core cable, the requirements of the cable bracket is also higher.
Aluminum alloy cable has many advantages compared with the aluminum core and copper core cable. It can replace them in many occasions. Moreover, it can be used to increase the part of the aluminum alloy conductor in the GB/T3956-2008 "cable conductor". Therefore, it is feasible to adopt aluminum alloy cable in the wind farm.
But there are still some problems to be solved in the wind farm to promote the aluminum alloy cable:
Aluminum alloy conductor according to the added chemical composition, its model is varied, but in the domestic specification does not have to add the chemical composition of the description, therefore in the bidding and the actual supply of products is easy to exist differences.
Because the expansion coefficient of the aluminum alloy, aluminum and copper conductors are different, the different conductors are not directly connected, and the reliability of the connection between the aluminum alloy conductor and the copper and aluminum conductor can be ensured by the transition terminal.
The application of aluminum alloy cable in the wind farm is very few, and the application of the special area, such as high temperature, cold, high altitude, high salt fog, high temperature difference and so on, is used in the application.