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Japan takes superconducting power transmission leap

TOKYO — Superconducting power transmission technology, which promises to deliver electricity while leaking almost none along the way, has entered the practical stage in Japan, offering a potentially less costly way to operate trains and a possible countermeasure to global warming.

A Japan Railway-affiliated research institute has laid a 1.5-km superconducting transmission line — the world’s longest practical-use cable — at a facility in Miyazaki Prefecture, where it is holding demonstration tests.

The production of the line was outsourced to Mitsui Mining & Smelting, and several railroad companies are showing interest in adopting the technology, the institute said.

Transmission loss is mainly caused when electricity turns into heat due to the electrical resistance of electric wires. When a transmission line is cooled to minus 269 C with liquid helium and put into a superconducting state, however, the electrical resistance becomes zero, and power loss can be all but eliminated.

The technology’s cost had been a major hurdle to its spread. But thanks to the development of materials that can be superconducting at minus 196 C, liquid nitrogen can be used as a coolant, which is 10% cheaper than the standard liquid helium.

The Railway Technical Research Institute, based in Tokyo, has taken this less expensive coolant, innovated with it and discovered a way to coat transmission lines with it.

The test cable can carry the railway-required 1,500 volts and several hundred amperes.

Although cooling adds costs to normal power transmission, “if we can make the distance of one power line more than 1 km, we can reduce the cost by utilizing existing power transmission facilities, and the advantage of eliminating power transmission losses outweighs the additional cooling cost, ” the Railway Technical Research Institute says.

Superconducting power transmission also has the advantage of reducing the number of substations needed to maintain voltage. Substations are located every 3 km, and the annual maintenance cost is estimated to be 20 million yen ($173,000) per substation. The Railway Technical Research Institute is already working on the development of a power transmission line longer than 1.5 km. If realized, the cost benefits of superconducting power transmission would be further enhanced.

According to the Institute of Energy Economics, Japan, the country loses 4% of its electricity as it is being delivered. The country’s railways use about 17 billion kilowatt-hours a year, and 4% of that is about 700 million kilowatt-hours, equivalent to what 160,000 ordinary households require.

Transmission loss is a serious issue in many countries. Lines in India leak about 17% of the electricity they carry.

Japan is not alone in making advances in superconducting power transmission technology. China’s state-owned transmission company in November installed a 1.2-km superconducting line in Shanghai. In Germany, the Ministry of Economy and Energy leads a project that in 2020 began laying a 12-km superconducting transmission line under Munich.

Japan has strengths in materials for power lines, as companies like SWCC Showa Holdings manufacture power lines used for superconducting power transmission. The Linear Chuo Shinkansen, a high-speed maglev train line between Tokyo and Nagoya, that Central Japan Railway is working on also uses superconductivity, and the know-how cultivated there has become the technological foundation for the power transmission field.

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