Minus 196 degrees Celsius, a temperature that is difficult to reach at an earth pole, can be found underground in the center of Shanghai. On December 22, the world's first 35 kV kilometer superconducting cable demonstration project was put into operation in Shanghai, with the largest transmission capacity, the longest line and full commercial operation, why is this 1.2 km line of breakthrough significance? What technical difficulties has it overcome? What are the development and application prospects in the future? The answer to the question lies in the "heat" of innovation in China's superconducting industry.
Small channel, large capacity "high cold fan"
By cutting open a superconducting cable, you can find that its internal structure resembles a "three-color ballpoint pen". Three strands of superconducting cables insulated from each other, like three "refills". In actual operation, the "three-color ballpoint pen" will be filled with liquid nitrogen, providing a low temperature environment for the cable, so as to exert the characteristics of superconducting materials.
"Such a structural design makes the superconducting cable transmission capacity larger, the security is higher, and there is almost no electromagnetic radiation outside the cable, which is more suitable for the 'actual combat' needs of the megacity power grid." Zong Xihua, general manager of Shanghai International Superconducting Technology Co., Ltd., said.
Superconducting cable termination photographed on December 22. Photo by Xinhua News Agency reporter Ding Ting
Superconducting transmission is one of the most revolutionary frontier technologies in the power industry today. The principle is to use the superconducting properties of superconducting materials in the liquid nitrogen environment of minus 196 degrees Celsius to make the power transmission medium close to zero resistance and the power transmission loss to approach zero, so as to achieve low voltage level large-capacity transmission. "A 35 kV superconducting cable can replace 4 to 6 conventional cables of the same voltage class, saving 70% of the space in the underground pipe gallery." Xie Wei, chief engineer of State Grid Offshore Electric Power, said.
The characteristics of small channels and large capacity make the superconducting cable have significant advantages in transmission efficiency and spatial economy, and under the trend of rapid growth of electricity load in the urban center area and tight resources of underground passages, the landing application of superconducting cable is undoubtedly to solve the problem of power supply "card neck" in hot areas of load to open a new "air outlet".
The superconducting cable project put into operation is located in the Tianlin area of downtown Shanghai, which has created a number of "world records". Zong Xihua introduced that there are currently three kilometer-level superconducting cable projects in the world, China has one of them, and the other two are in South Korea and Germany, "From the perspective of various indicators, the Shanghai project can be called the world's largest transmission capacity and the longest transmission distance of the commercial operation superconducting cable project." ”
From the laboratory to the actual combat, one by one " fill in the blanks"
In order to turn the technology from blueprint to reality, the parties involved have made great efforts. Zong Xihua said that taking the insulation sleeve of the cable as an example, the temperature difference between the inside and outside of more than 200 degrees Celsius, coupled with tens of thousands of volts of high voltage and thousands of amperes of current - it is not easy to solve these problems in insulation, insulation, sealing and strength.
"In addition, our project is surrounded by hospitals, residential areas, hotels, and civil defense projects, and the complex environment means that the superconducting cable cannot go in a straight line, and the superconducting cable projects that have actually been put into operation abroad before are all short-distance experiments or straight-line point-to-point power supply, and the laying requirements of superconducting cables in complex environments and related parameter information are basically blank." Xie Wei said.
Construction drawings of a 35 kV kilometer superconducting cable project in Shanghai taken on December 22. Photo by Xinhua News Agency reporter Wang Moling
Yang Jianping, deputy director of the State Grid Offshore Electric Power Science and Technology Department, pointed to the engineering construction drawings and said: "There are many corners on the line, and there are still several meters of drops in the terrain before and after, which is not a problem for ordinary cables, but for superconducting cables with very complex structures, once the problems of bending and falling corners are not solved, it is easy to destroy the vacuum layer, so that the material loses its superconducting characteristics." The calculation of traction during the entire construction process is very demanding, and we have also carried out a lot of testing and analysis during this period. ”
It is understood that the localization rate of the core technology of the 35 kV kilometer superconducting cable project has reached 100%, and it has filled a number of international standard gaps. Focusing on the planning and design, operation and maintenance of superconducting cables, relay protection, etc., the project team has applied for more than 30 invention patents.
"Superconductivity +" draws a new blueprint for the manufacturing industry
The superconducting industry is one of the emerging industries that Shanghai focuses on cultivating, and in the past 15 years, Shanghai's science and technology and industrial departments have relayed and promoted, forming core capabilities from superconducting materials to cable integration.
"New materials are the upstream source of innovation in manufacturing. Over the years, researchers have been willing to sit on the cold bench, and enterprises have been prepared to 'money falls into the Huangpu River, and can't hear the sound for several years' before the final output. Tang Liang, chairman of Aosheng Group, said that grasping the research and development of new materials without letting go is like planting trees, and eventually achieving the effect of "one tree and one hundred acquisitions". On the 22nd, the Shanghai Superconducting Manufacturing Innovation Center was unveiled simultaneously, with the orientation of serving the country's major energy strategy and spawning emerging industries, and promoting the deep integration of superconducting technology with key areas such as power energy, large scientific devices, medical treatment, and rail transit.
For example, in the field of life and health, the current clinical diagnostic superconducting magnetic resonance products mainly have 1.5T and 3.0T specifications, with the improvement of superconducting magnet technology, 7T and higher magnetic field strength magnetic resonance superconducting magnet and imaging technology gradually matured, can provide a reliable high-definition imaging research platform for protein structural biology, pharmacy, clinical medicine and other research fields.
Zong Xihua said that the current "body value" of superconducting materials is still relatively high, with the continuous advancement of industrialization and the increasingly rich application scenarios, its cost is expected to drop significantly, so as to accelerate the realization of "samples" into "products" in more fields. (Reporters Wang Moling and Gong Wen)