Our reporters Wang Di and Wu Xiaoying.
If the wheels of the train are removed, let it gallop along the track more than ten millimeters above, and it can still run 620 kilometers per hour, and even one day it will exceed the speed of the plane … … Is this still our usual "train"?
This is the maglev train, which has been around for many years, but still makes people feel mysterious, and it may trigger a revolution in future transportation modes.
Recently, a high-speed maglev prototype car unveiled in Chengdu, Sichuan, once again aroused people’s attention to this sci-fi vehicle.
On January 13th, the world’s first high-temperature superconducting high-speed maglev engineering prototype and test line independently developed, designed and manufactured by China was officially opened in Southwest Jiaotong University. This prototype car with all-carbon fiber and streamlined head is designed with a speed of 620 kilometers per hour, which is expected to create a new record of land traffic speed in atmospheric environment.
Compared with other magnetic levitation technologies, HTS magnetic levitation technology is especially suitable for future vacuum tube (tunnel) transportation, and the theoretically predicted speed can be higher than 1000 km/h. Considering that the flight speed of a passenger airliner is about 900 km/h, this speed can be called "flying on the ground".
"Cars, airplanes and modern ships are not original Chinese. Including the high-speed rail that we are leading the world now, it is also from the introduction, digestion, absorption and re-creation, from running to leading. But once our technology is successful, it is completely original by Chinese. It will become a subversive mode of transportation, filling the speed gap between land traffic and air traffic. " He Chuan, member of the Science and Technology Committee of the Ministry of Education and vice president of Southwest Jiaotong University, commented on the significance of this prototype and test line.
High temperature superconducting maglev train has "unique skills"
Magnetic levitation is a new technology that suspends objects completely by magnetic field. Suction (or repulsion) can not only counteract gravity and make the object suspended, but also firmly lock the object in a specific position and maintain stability.
In order to help the public understand the working principle of maglev train more intuitively, Professor Deng Zigang, deputy director of the research center of ultra-high-speed vacuum pipeline maglev transportation in Southwest Jiaotong University, made an experiment on the track of high-speed maglev prototype vehicle. He lifted a rectangular aluminum plate with both hands and threw it above the permanent magnet track. As a result, the aluminum plate did not directly hit the track: it first fell, then "floated" at a very close position to the track, and slid along the track for a short distance before landing, as light as a feather.
Deng Zigang told reporters that because the aluminum plate has resistance, the current will decay, and this aluminum plate will eventually fall on the track. If the aluminum plate is replaced by superconductor, that is, a conductor whose resistance becomes zero at a certain temperature, it can be suspended for a long time.
Maglev trains can be suspended by three principles, namely, electromagnetic levitation (EMS), electric levitation (EDS) and high temperature superconducting levitation (HTS). The electromagnetic levitation principle appeared earlier than the HTS levitation principle, which was put forward after the discovery of HTS materials in the late 1980s. Trains based on the principle of electromagnetic levitation have been commercially used in low-speed and high-speed regions, but high-temperature superconducting levitation has not yet entered the commercial market.
At home and abroad, people have used the first two principles to build a maglev prototype with a speed of 600 kilometers per hour.
In 2015, Japan’s low-temperature superconducting magnetic levitation central Shinkansen set a new world record of 603 kilometers per hour, which attracted widespread attention.
In 2019, the China 600 km/h high-speed electromagnetic levitation test prototype rolled off the assembly line in Qingdao, marking a major breakthrough in the field of high-speed magnetic levitation technology in China.
Professor Zhang Weihua, chief scientist of Southwest Jiaotong University’s research center for ultra-high-speed vacuum pipeline maglev transportation, believes that HTS levitation technology has its own unique advantages.
First, the operating cost is low. The so-called "high temperature" refers to MINUS 196 degrees Celsius, which is significantly higher than the corresponding temperature requirement of low-temperature superconductors (MINUS 269 degrees Celsius), which means that suspension can be realized in a more economical way. "Japan’s low-temperature superconducting magnetic levitation technology requires MINUS 269 degrees Celsius and needs to be cooled by liquid helium, which is a scarce resource all over the world. However, high-temperature superconducting magnetic levitation can use liquid nitrogen. 78% of the air is nitrogen, and the cost of liquid nitrogen is lower than that of mineral water. " Zhang Weihua said.
Second, the system is simpler. Similarly, taking the low-temperature superconducting maglev vehicle in Japan as a reference, it needs to be accelerated to a certain speed before it can levitate, and the high-temperature superconducting technology can realize the static levitation of the train, thus eliminating the complicated starting system.
According to the project team of Southwest Jiaotong University, HTS levitation technology has another important advantage, that is, it has completely independent intellectual property rights.
"Once our technology is successful, it is completely original by Chinese. From basic research to basic application, from practical technology to industrialization, Chinese is doing it." He Chuan said.
It is worth mentioning that no matter which technical route is adopted, compared with other modes of transportation, maglev trains have many common advantages, including low maintenance cost, high safety and less environmental pollution.
Because there is no wheel-rail contact, the train does not need wheel-rail, gearbox, bearings and other parts, so the loss of maglev train is much better than that of high-speed rail, and it will not be delayed because of rain and snow;
Because the force of the magnetic field can keep the train stable in the horizontal and vertical directions, and the maglev train adopts the structural form of "rail holding the car" or "car holding the rail", the possibility of derailment of the maglev train is greatly reduced; Without the noise of wheel and rail, the train can run more quietly.
However, under the existing technical conditions, realizing the commercialization of maglev trains still faces no small challenge, mainly due to the high construction cost and low return rate. Globally, only China, Japan and South Korea have commercial maglev trains in operation.
Due to lack of funds, progress was slow for a time.
In Deng Zigang’s view, the greatest achievement of his team in the past 20 years is to greatly improve the suspension load performance of HTS technology. Suspension load performance refers to how much suspension force can be generated per unit area.
At the end of 2000, Wang Jiasu of Southwest Jiaotong University and the research team of Wang Suyu developed the world’s first manned HTS maglev experimental vehicle "Century". At present, the suspension performance of this car has been improved by 6-7 times through optimization research.
"To improve the levitation performance, it is necessary to first study the mechanism of the vehicle-mounted high-temperature superconductor and permanent magnet orbit, which is a systematic research work. With the research conclusions as a guide, the specific implementation process is like a jigsaw puzzle. " Deng Zigang said.
The common size of superconducting bulk is very small, because the larger it is, the higher the requirements for the process are. Researchers need to choose the shape of superconducting blocks, such as round, square or regular hexagon, and then study how to arrange and place them, and strive to combine them into larger blocks with the smallest gap to maximize the performance of each superconductor.
The design of magnetic track faces similar problems. Deng Zigang revealed, "At present, the 1-meter-long track is made up of 90 sections of small magnets." They have to figure out how to arrange the magnets and realize the maximum magnetic field performance with the minimum cost.
The early orbital magnetic field was symmetrically distributed up and down, which meant that half of the magnetic field below the orbit was wasted. After continuous simulation optimization and experiments, now Deng Zigang’s team can make more than 90% of the permanent magnet magnetic field gather above the orbit and play a key role.
There are also some challenges from outside technology, such as raising R&D funds. Deng Zigang admits that because he has not won tens of millions of yuan to invest in the construction of the experimental line, "the research progress has been very slow in the past 10 years." He was very anxious to see that Brazil and other countries had built a small-capacity and short-distance test line for high-temperature superconducting magnetic levitation according to similar technologies.
In 2012, in order to support the development of the original HTS maglev technology in China, Professor Zhang Weihua, director of the State Key Laboratory of Traction Power of Southwest Jiaotong University, allocated a special fund of 1 million yuan to the HTS maglev research team, and finally built a 45-meter-long circular experimental line.
"It can be said that it has opened up a new world, brought this technology back to life, and let the outside world see the high-temperature superconducting magnetic levitation technology again." Deng Zigang said.
Realized "floating" and "moving"
The official opening of the world’s first high-temperature superconducting high-speed maglev engineering prototype car and test line on January 13th is another milestone. This project is jointly researched and developed by Southwest Jiaotong University, CRRC, China Railway and other units. It is an important step for China to promote HTS maglev technology out of the laboratory, which can verify the reliability of high-speed and long-term operation of HTS maglev trains.
Deng Zigang commented on this, "The prototype and test line with a scale of 1: 1 are necessary to study all key technologies. If there is no engineering prototype and test line, there is no way to move towards real engineering application. "
This 165-meter test line is just the beginning.
"Our current test line has achieved ‘ Float up ’ ‘ Move ’ Two goals, but to achieve ‘ Run ’ The goal is to carry out a 600-kilometer real vehicle test on a long-distance test line and complete the final verification before the HTS high-speed maglev train is put into civilian use. " Jin Zhaohui, project leader, vice president of Chengdu Southwest Jiaotong University Design and Research Institute Co., Ltd. and dean of Kunming Branch, said.
How long will it take to run?
The development speed of high-speed rail technology in China attracts worldwide attention. In just a few decades, China has never had an inch of high-speed railway, but has developed into a high-speed railway with the longest operating mileage in the world. The technology of high-speed railway, plateau, cold and heavy-haul railway in China has reached the world leading level.
Today, China is trying to achieve similar success in magnetic levitation technology. Gou Jinsong, general manager of the Maglev Engineering Division of Beijing Rail Transit Technology and Equipment Group Co., Ltd., once wrote that China, Japan, Germany, the United States and South Korea are the five countries with the most patents on maglev train technology in the world. According to the statistics he completed on November 26th, 2017, the number of patents for maglev trains in China has accounted for 27.11% of the world.
China is also one of the most active countries to promote the landing of magnetic levitation technology. Shanghai maglev train, which was opened to traffic in 2002, became the first commercial high-speed maglev train line in the world. Shanghai maglev train adopts electromagnetic levitation, and Qingdao high-speed electromagnetic levitation test prototype with a speed of 600 kilometers per hour is the result of further optimization on the basis of Shanghai maglev train technology. In 2019, the Central Committee of the Communist Party of China and the State Council issued the Outline of Building a Powerful Traffic Country, which clearly put forward the reasonable overall arrangement of research and development of technical reserves such as high-speed magnetic levitation system with a speed of 600 kilometers per hour and high-speed trains with low vacuum tubes (tunnels). In 2020, Yunnan and Zhejiang provinces announced plans to invest more than 100 billion yuan to build high-speed maglev trains.
Jin Zhaohui believes that China has the foundation for building a high-speed maglev test line and landing the industry. First of all, the civil engineering technology of HTS maglev train is very close to the existing high-speed rail technology, and the forms of bridge, tunnel and subgrade are very similar. The main change is to change the rail into a magnetic track with a linear motor in the middle. The advantage of this is that it can make the civil engineering technology have a high maturity, and it can also make use of the existing mature industrial chain. Therefore, the civil engineering technology is fully qualified for construction.
Secondly, China is rich in rare earth resources. If it is applied to HTS maglev line, it will be enough to support track construction, so the magnetic track also has the conditions for construction, production and industrial landing.
Thirdly, many domestic units can prepare HTS bulk materials, but due to the small demand, mass production has not been realized for the time being. If engineering application is realized, mass production can be realized in a short time driven by the market.
Fourthly, other technologies, such as linear motor, train control technology and safety management technology, all of which are supported by mature technology and complete industrial chain in China. Therefore, China has the foundation to build a high-speed test line and follow-up industries in the high-speed superconducting maglev train.
Jin Zhaohui believes that the technology of HTS high-speed maglev train is basically mature, and it is suitable for various environments and terrains including mountainous areas, especially for tourist tracks or intercity high-speed railways. At present, the urgent task is to build a long-distance test line in combination with application scenarios, complete the verification of system integration, and get through the last stage of commercial use.
In addition, when the construction starts, it is necessary to further reduce the construction cost. In civil engineering, the civil engineering cost will be lower than the existing high-speed rail model because of the lighter train, smaller size and uniform load. However, the new products such as linear motor and magnetic track have not been used in large-scale applications before, and the cost is still high. The R&D team also needs to work hard to reduce the construction cost and make the HTS high-speed maglev technology more competitive.
Regarding the timetable for the commercialization of HTS high-speed maglev trains, He Chuan predicted that "if the state supports the construction of long-distance test lines, it will be as short as two or three years and as long as five or six years, I am fully confident."
