Home-made "double high" wires make China's high-speed rail "full power"

  83%

  With the continuous improvement of technology, my country's copper-chromium-zirconium wire can achieve a conductivity of up to 83% and a strength of 620 MPa.

my country's high-strength and high-conductivity catenary wires with independent intellectual property rights can provide strong technical support for the construction of the new high-speed rail.

  ◎Reporter Chen Xi

  With a speed of 350 kilometers per hour and an operating mileage of 36,000 kilometers, it can reach 30 provinces, autonomous regions and municipalities except Tibet... China's high-speed rail has repeatedly refreshed my country's "high-speed rail map" and records with amazing speed and breadth.

As the "heart" of high-speed trains, the power supply system provides a steady stream of power for the trains, and is also the key to ensuring the safe, high-speed, reliable and stable operation of the trains.

  The "Key Technology and Application of High-strength and High-conductivity Catenary Wires for High-speed Railways" developed by Wang Litian, chief engineer of Tianjin China Railway Electrification Design and Research Institute Co., Ltd., has realized the complete localization of my country's high-speed railway catenary wires.

After 10 years of “networking” 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 awarded 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

  As the saying goes, the train runs fast and depends on the headband.

So where does the traction power of the "front" come from?

  "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 network at the upper end of the locomotive." Wang Litian According to the introduction, once the catenary is out of power or the train's pantograph is in poor contact with the catenary, it will have an impact on the power supply of the train.

  At the same time, one of the three core technical bottlenecks restricting the speed increase of high-speed trains is also the current 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. Increase investment.

  Wang Litian explained: "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. Proportional. After the power increases, the current will increase correspondingly when the voltage remains the same. Therefore, the contact wire is required to have high conductivity."

  "While ensuring high electrical conductivity, the catenary wire also needs to ensure high strength." Wang Litian said that the pantograph and the wire cannot be separated during the high-speed train operation 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 at the same time. Therefore, the research and development of high-speed rail catenary conductors is extremely difficult. Before the implementation of Wang Litian's team project, my country's high-speed railway catenary conductors all relied 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." Wang Litian said, To achieve "China Speed", this hurdle must be crossed.

R&D and industrialization start from scratch

  As early as 2006, when my country began to build high-speed rail, Wang Litian, as a member of the expert team, began to come into contact with this field.

  "Because of 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." Wang Litian said that although Japan, France, Germany and other countries invested heavily in research and development, none of them realized engineering applications and the technology was tightly sealed.

  The foreign technology blockade made it clear to Wang Litian that in order to achieve breakthroughs in my country's high-speed rail technology, it is necessary to be self-reliant and independent, to localize copper-chromium-zirconium contact wire conductors and make China's own high-strength and high-conductivity wires.

  At that time, my country relied on imports for even copper-magnesium wires. The difficulty in developing copper-chromium-zirconium wires, which was a lot more technically difficult, was conceivable.

"It's really starting from scratch, searching for literature, there is very little content that can be used for reference." Wang Litian recalled. Fortunately, the team found Professor Meng Liang from Zhejiang University who researched high-conductivity and high-strength materials.

With the help of Professor Meng Liang’s team, it took half a year to develop a sample of copper-chromium-zirconium material wire in the laboratory, and the sample’s various parameters were excellent, with a conductivity of over 80% and strength. It reaches 620 MPa.

  But before the excitement was over, Wang Litian discovered that there is a huge difference between the research of material samples in the school laboratory and the realization of the industrialization of large-length wires. The research workload and difficulty in the laboratory only accounted for the entire The total workload and difficulty of the industrialization project is 5%-10%. The technical difficulty of realizing industrialization later is far beyond the team's imagination.

  According to Wang Litian, 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 and strengthening metal processing technology, and the fourth part is heat treatment technology.

  "The first and second parts are the most critical and the most difficult to achieve. At that time, we traveled all over the country and we couldn't find equipment that could smelt and cast copper, chromium, and zirconium wires. All the tooling and equipment must be developed by ourselves." Wang Litian Said, "It can be said that the research and development process of wire industrialization is the process of researching and developing the various equipment and processes required for manufacturing wires."

  For example, Wang Litian cited a smelting furnace. In order to avoid volatilization of chromium-zirconium alloy, the team tried a variety of process paths. Regarding the choice of furnace wall materials, the team also chose more than a dozen kinds of experiments.

  "The most difficult thing was the research and development of the smelting furnace mold. At that time, after the alloy billet was cast, the surface was very rough and cracked, there were pores in it, and the internal alloy composition was unqualified. It was useless to adjust the data." Wang Litian recalled. , Staying at the side of the smelting furnace at more than 1,000 degrees Celsius every day, repeated experiments failed, causing many researchers to start to waver.

Some people say that Japan has been researching for nearly 20 years, and the product has not been put into application. How can we research it.

  But Wang Litian did not waver, he still stood by the smelting furnace every day, and finally paid off. In an experiment, "an accident that almost caused an accident" made Wang Litian, who risked his life to stay at the smelting site, finally "pierced this layer." "Window paper" solves the most difficult technical problem in the entire research and development process.

The world's leading product performance

  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." Wang Litian proudly said, and because our product production process is simplified, the cost is much lower.

  At present, the technological level of the production of copper-chromium-zirconium wires in my country 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.

Wang Litian further explained that because my country's high-speed railways are spread all over the motherland, and some railways are located in filthy, seaside and other environments, 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.

And our copper chromium zirconium wire because of the material and process, 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, my country's copper-chromium-zirconium wire can achieve a conductivity of up to 83% and a strength of 620 MPa.

“The high-speed railway from Chongqing to Chengdu that is currently under 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.” Wang Litian is full of confidence in this, he said this time. my country's high-strength and high-conductivity catenary wires with independent intellectual property rights can provide strong technical support for the construction of the new high-speed rail.

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