"Superconducting Power Transmission" Realizes Zero Resistance

Superconductivity refers to the phenomenon that the resistance becomes zero when a specific metal or compound cools to a very low temperature. The superconducting cable is a cable made by storing the wire material manufactured using this technology in an insulating tube. Insulation pipe is filled with liquid nitrogen and other refrigerants to maintain the low temperature required for superconductivity. The power loss of this transmission method is far lower than that of ordinary copper wire.

Transmission cables are the key to “superconducting transmission,” and the development of this technology has basically ended. With the use of superconducting power transmission, the power loss of transmission will drop sharply. As an energy saver, this technology will also play a role in remote electricity coordination across borders.

The total domestic electricity generation in Japan in 2011 was 857.4 billion kWh, of which the loss from the power station to the home was about 5%, which was equivalent to the one-year power output of six 1 million kilowatt-class nuclear power plants. The data showed that the wire resistance caused The loss is about half. Because of this, people are looking forward to zero resistance superconducting cables.

"Superconductivity" driving tram

The Institute of Railway Integrated Technology located in Kokubunji, Tokyo is commonly known as "Railway Research Institute." On the experimental track laid in the Institute, a genuine tram was running. Next to the track, there is a black cable about 31m long. This is the superconducting cable used for power transmission.

The superconducting cable developed by the railway research institute supports direct current transmission, and a superconducting material wire made of a rare metal tantalum is packaged in a roughly 10 cm thick pipe. During operation, liquid nitrogen at -196 degrees is circulated internally and the wire is cooled to zero the resistance.

Because superconducting power transmission requires liquid nitrogen circulation, it is generally used to set up and return two cables in parallel. However, taking into account the degree of freedom in remote use and installation, the railway research institute adopted a multi-layered heat insulation pipe and designed a structure that allows liquid nitrogen to travel back and forth in an insulated pipe.

Dr. Fujita Yu, Director of the Research and Development Department of the National Academy of Railway Research and Development, and the director of the superconducting application research department, said: "Not only is transmission loss reduced, superconducting cables are also effective for the effective use of renewable energy."

Performance testing using a 31m cable is now almost complete. The world’s first verification experiment using a superconducting cable to power a vehicle has begun in June. According to the schedule, a full validation experiment using a 310m cable will begin in the fall. Dr. Tomita expressed with confidence that "this experiment is aimed at the use of the actual railway network and will become a major breakthrough." Practicality is expected to be achieved within 5 to 10 years.

Japan took the lead in mass production of cables

Ishikari City, Hokkaido is also promoting transmission projects using superconducting cables.

The location is Shikari Bay Xingang area. According to the project's plan, the solar panel production will be delivered to the SAKURA Internet's Ishikari Data Center via DC 500m long superconducting cable. Transmission is scheduled to begin within 2 years. After 2014, the city will re-lay 2km long cables to verify the power loss and maintenance costs of remote transmission.

A large number of servers are running in the data center and they need to be cooled, so the power demand is huge. Efficient use of electrical energy helps to significantly reduce operating costs.

This time, with the effect of cold weather and DC, the power consumption of the Ishikari Data Center has been reduced to less than half of the previous. For the significance of the experiment, Dr. Yamaguchi Yamaguchi, a professor at the Chubu University Superconductivity and Sustainable Energy Research Center, which plays a central role in the project, said: "By combining superconducting power transmission, solar power can be efficiently used."

The discovery of superconductivity by humans dates back to 1911 more than 100 years ago. However, the superconductors that were discovered had to reach the superconducting state when the temperature dropped to an absolute zero (-273.15 degrees). Cooling requires the use of expensive liquid helium and is difficult to apply to power transmission.

However, as "high-temperature superconductors" that can reach the superconducting state at higher temperatures were successfully developed in 1986, the development of superconducting cables became more and more prosperous.

High-temperature superconductors include many types. For example, a superconductor using a rare metal helium reaches a superconducting state at about -160 degrees. Superconducting materials that can also achieve superconducting states at -180 degrees using rare earth antimony have also been successfully developed.

Cooling these superconductors can use a higher temperature than liquid helium, but the price is much cheaper, and it is easy to store liquid nitrogen. Because high-temperature superconductors can be used stably, the value of commercial use has gradually emerged.

Sumitomo Electric Industrial Superconducting Product Development Minister Lin Heyan said: “The cable performance has reached a practical level.” In the mass production of superconducting cable technology, Japanese companies are at the forefront of the world.

Sumitomo Electric Industries is a pioneer among Japanese companies. In 2003, the company took the lead in the world to successfully mass-produce high-temperature superconducting cable materials. We have supplied wire and cables made from helium to many domestic and foreign superconducting transmission experiments.

On the other hand, other Japanese wire companies such as Furukawa Electric Industries, Fujikura, etc. have developed Tantalum cables. According to some people's opinions, the use of silver on the silver wire of the tantalum system is small, and it is advantageous in terms of cost. However, in terms of mass production technology, the system is the most recent, and it has recently come into practical use.

Although superconducting cables help save energy, they are not universal.

The resistance of the superconducting cable is indeed zero, but maintaining the superconducting state requires constant cooling during the liquid nitrogen cycle, which requires the use of a freezer and a pump. Refrigerators and pumps consume power, so strictly speaking, transmission losses are not zero.

At present, the long-distance transmission of power loss and the transmission of power to large-scale facilities with large power consumption are estimated to be the main purpose of superconducting transmission. In the future, with the development of high-efficiency refrigerators, the scope of application will be expanded in one step.

In addition, for the examples of railways and data centers described above, HVDC transmission is a key point. Superconducting power transmission must be combined with the HVDC transmission network to achieve real value. Professor Yamaguchi said: "The loss of DC is much lower than that of AC."

The AC superconducting cable adopts a structure in which three core wires are introduced into one tube. Because the wires affect each other, there is a power loss called "AC loss." DC does not have this loss. Moreover, the DC cable requires only one core wire, the thickness can be smaller than the AC, and the cooling cost is low.

However, the existing transmission network is dominated by exchanges. DC access to the power grid requires transformer equipment.

However, in the future, DC may be promoted. The railway has now taken the lead in DC. About 70% of the electrified sections of Japan's national general railways (JR and non-government railways) have been DC-based, and new lines are also basically using DC systems.

DC power is also expected to be popular in data centres that use electricity in large quantities.

SAKURA Internet Co., Ltd. Yasuhiro Tanaka said: "The DC transmission efficiency is high, and it is expected to reduce the initial cost. In the future, we will continue to increase DC equipment."

Transmission to the other side of the earth

Superconducting DC transmission can also coordinate electricity across countries and continents. It is worth looking forward to in the application of ultra-long-distance transmission, for example, from countries with high natural energy production efficiency to countries with large electricity consumption. Or from the country where the night power is remaining, it is transported to a country where the other side of the earth is suffering from a power shortage.

Now, all regions are promoting the idea of ​​a smart grid (a new generation of transmission grid) that coordinates power across borders. The "Desertec Project" centered on Europe is one of them.

The desert project plans to install solar panels in the desert areas of Africa, set up large-scale windmills in coastal areas, and transfer the electrical energy generated by these devices to Europe and North Africa. Professor Yamaguchi said that during the process of the project, "the trend of using superconducting DC cables has also emerged."

Superconducting power transmission can contribute to energy conservation. In the future, the demand for superconducting power transmission in the world is expected to increase. Japanese companies leading the world in this field have also ushered in huge business opportunities.