With the continuous improvement of technology, the copper-chromium-zirconium wire developed by Chinese companies can achieve a conductivity of up to 83% and a strength of 620 MPa. China's high-strength and high-conductivity catenary wires with independent intellectual property rights can provide strong technical support for the construction of high-speed rail.
With a speed of 350 kilometers per hour, an operating mileage of 36,000 kilometers, and access to 30 provinces, autonomous regions and municipalities across the country… China's high-speed rail has repeatedly refreshed China's "high-speed rail map" and records with amazing speed and breadth. As the "heart" of high-speed rail trains, an efficient power supply system provides a steady stream of power for the trains and is also the key to ensuring safe, high-speed, reliable, and stable operation of the trains.
The "Key Technology and Application of High-Strength and High-Conductivity Catenary Copper-Chromium-Zirconium Wire for High-speed Railways" developed by TJZT Electric Technology Corporation has realized the complete localization of China's high-speed railway catenary wires. After 10 years of “netting” operation on Beijing-Shanghai, Beijing-Tianjin, Beijing-Zhangjiakou, Chengyu and other high-speed railway lines of 13,000 kilometers, this result has proved that its performance leads the “world high-speed rail”. The project also won the second prize of the 2020 National Science and Technology Progress Award. At the same time, the project was granted 32 invention patents, 31 SCI papers, 6 national standards and 2 industry standards as the editor-in-chief.
Copper-magnesium wire has reached the safety limit
“When people wait for trains at high-speed railway stations, they often see transmission lines erected along the railway. These transmission lines are high-speed railway catenary networks. The electricity required for the operation of high-speed railway trains is transmitted through the catenary at the upper end of the locomotive." Once the power is cut off or the train's pantograph is in poor contact with the catenary, it will affect the train's power supply.
At the same time, one of the three core technical bottlenecks restricting the speed increase of high-speed trains is also the flow receiving capacity of the bow network. In order to ensure the stable current flow of the train at high speed, the catenary wire must have large tension and large current-carrying capacity. This requires the wire to have high strength and high conductivity at the same time, and also to ensure that the catenary is lightweight, which cannot be used in engineering. Increase investment.
When a train travels at a speed of 300 km/h or more, more than 90% of its resistance comes from wind resistance, and wind resistance is proportional to the square of the speed, and the power required by the train is proportional to the third power of the speed. After the power becomes larger, the current will increase correspondingly when the voltage remains the same. Therefore, it is necessary for the contact wire to have high conductivity. "
While ensuring high conductivity, the contact wire also needs to ensure high strength. When the train is running at high speed, the pantograph and the wire cannot be separated and must be in close contact at all times. Only when the wave propagation speed of the wire is greater than 1.4 times the train speed, can it be ensured that the pantograph and the catenary wire will not detach. To increase the wave propagation speed of the wire, the tension of the wire must be increased. When the weight of the wire remains unchanged, the strength of the wire needs to be increased so that the strength of the wire reaches the national standard safety factor of 2.0 or more. In other words, the maximum breaking force that the wire can withstand needs to be more than twice the strength of the application required to ensure safety.
It is a huge challenge to improve the strength and conductivity at the same time. As we all know, in copper alloy materials, conductivity and strength are inversely proportional, and it is very difficult to improve conductivity and strength. Therefore, the research and development of high-speed rail catenary wires is extremely difficult. Before the implementation of the TJZT project, China's high-speed rail contact wires were all dependent on imports.
“At that time, the strength of the most advanced copper-magnesium wire in the world reached the safety limit at a train speed of 350 kilometers per hour. To further increase the speed, it is necessary to develop the next generation of copper-chromium-zirconium contact wire with higher strength and higher conductivity.
R&D and industrialization start from scratch
As early as 2006, when China started the construction of high-speed rail, TJZT's CTO Dr. Wang, as a member of the expert team, began to get in touch with this field.
Due to the high activity and high volatility of chromium-zirconium alloy elements, the preparation of zero-defect ultra-long copper-chromium-zirconium wires that can meet engineering needs has become a recognized world problem, and is known as the ‘jewel in the crown’ of high-speed rail traction power supply technology. At that time, although Japan, France, Germany and other countries invested heavily in research and development, none of them realized engineering application, and the technology was tightly sealed.
The foreign technology blockade made TJZT clearly see that in order to achieve breakthroughs in China's high-speed rail technology, it must be self-reliant, independent innovation, localized copper-chromium-zirconium contact wire conductors, and made China's own high-strength and high-conductivity wires.
It took TKZT half a year, and the R&D team developed a sample of copper-chromium-zirconium wire in the laboratory. The parameters of the sample were excellent, with a conductivity of over 80% and a strength of 620 MPa.
However, the research workload and difficulty in the laboratory only accounted for 5%-10% of the total workload and difficulty of the entire industrialization project. The technical difficulty of realizing industrialization in the future far exceeded the team's imagination.
All processes in the metal smelting and processing industry are basically divided into four parts:
The first part is smelting technology
The second part is casting technology
The third part is hardening strengthened metal processing technology
The fourth part is heat treatment technology
Product performance is the world's leading
In December 2010, the pilot section of the Beijing-Shanghai high-speed rail carried out joint commissioning tests and comprehensive tests. The maximum operating speed reached the world's highest operating test speed of 486.1 kilometers per hour. Among them, the high-strength and high-conductivity copper-chromium-zirconium conductors contributed a lot.
"After testing, the conductivity of the copper-chromium-zirconium wire we independently researched and produced has reached 75%, and the strength has reached 560 MPa. The performance can be'tie' with similar products launched in Japan at the same time, while there is no similar product in Europe and the United States at this time. The product is developed." Dr. Wang proudly said, and because our product production process is simplified, the cost is much lower.
At present, TJZT's technology for producing copper-chromium-zirconium wires has achieved continuous extrusion and continuous drawing to produce two tons of copper-chromium-zirconium wires, and there are no defects in the continuous large length of the wires.
In order to ensure the safety of the wire, the wire also has high corrosion resistance, ablation resistance and good high temperature characteristics. As China's high-speed railway network is very large, and some railways are located in a corrosive environment, the requirements for the corrosion resistance of the wires are very high. At the same time, friction generates heat. When the train is running at high speed, it will rub against the catenary wire to generate heat. Generally speaking, when the temperature reaches 100 degrees Celsius, the wire strength will decrease. Because of the material and process of our copper-chromium-zirconium wire, the temperature of 100 degrees Celsius will increase the strength of the wire within a certain range. In addition, after high temperature cooling, the strength of other alloy wires will generally decrease by about 20%, while the strength of our chromium zirconium copper wire will only decrease by about 5%, which has excellent high temperature characteristics.
With the continuous improvement of technology, the copper-chromium-zirconium wire produced in China can achieve a conductivity of up to 83% and a strength of 620 MPa. "The high-speed railway from Chongqing to Chengdu, which is currently ready to start construction, can reach a speed of 400 kilometers per hour, which is a level higher than the existing 350 kilometers/hour high-speed railway for various technical requirements." The network wire can provide strong technical support for the construction of the new high-speed rail.