18-05-2025
Japan rail companies look to superconductor tech for labor, power efficiency
TOKYO -- Superconductivity, or power transmission with zero electrical resistance, may bring the Chuo Shinkansen maglev rail project under construction in Japan to mind. While it creates strong magnetic forces to propel maglev trains, superconductivity can also be used for power transmission, and its greater efficiency is hoped to help cut electricity waste.
The test to power trains in operation on East Japan Railway Co. (JR East)'s Chuo Line started this spring, with other rail companies keeping watch on the potential for it to be used to save power.
Solving transmission loss, voltage drops
The power transmission system is the lifeline for trains in Japan. In urban areas, many trains run on direct current (DC), with electricity flowing in one direction and relatively easy to manage. Such DC-electrified sections cover some 12,000 kilometers across the country -- about the same as Earth's diameter.
However, these traditional power lines have electrical resistance, resulting in inefficiency known as "transmission loss," which gradually reduces voltage along the line. Since this will disrupt train operations if not compensated for, substations are installed every 2 to 5 km in densely trafficked urban networks.
In recent years, staff shortages have made maintaining these aging substations increasingly difficult. Addressing power line efficiency has become a critical challenge for railway operators working toward energy conservation and stable service.
Under these circumstances, all eyes are on superconducting cable technology developed by the Railway Technical Research Institute, headquartered in Kokubunji, Tokyo. Superconductivity is a phenomenon in which metal and other materials, when cooled to extremely low temperatures, lose their electrical resistance. With zero-resistance power, it is possible to eliminate transmission losses and voltage drops while reducing the number of substations.
Cooling inside the cables using liquid nitrogen
The cable design is based on superconductivity research published in the journal Nature in 2003 by Masaru Tomita, director of the institute's Maglev Systems Technology Division. The cables use a tube-shaped superconductor containing metals such as yttrium cooled by liquid nitrogen to minus 196 degrees Celsius, and are put on existing power lines.
A project for practical use of the superconductor cable gained momentum in 2007. After verifying reliability and safety, the world's first live trial of the technology began in March 2024, transmitting power to commercially operated trains on a 102-meter stretch of Izuhakone Railway Co.'s Sunzu Line in Shizuoka Prefecture. Sixty-six representatives from railway companies across Japan visited the site in the last fiscal year to see the progress firsthand.
Since March this year, JR East began using the superconductor cable to supply power to trains over a 408-m section between Hino and Toyoda stations on the Chuo Line in Tokyo. The railway company hopes for future expansion if research confirms significant energy and investment savings. More than a dozen railway operators, including Tokyo Metro Co., are reportedly following the developments with interest.
Yet, maintaining a superconductive state requires continuous cooling of the cables' liquid nitrogen, so dedicated power is essential. Hurdles such as reducing material costs and establishing maintenance protocols remain before the technology can be put into widespread practice.
According to Tomita, once the installed cable stretches for at least a kilometer, the energy savings surpasses the electricity needed for cooling, making the system energy efficient. He also noted that installation costs are projected to be less than half those for a substation, which typically costs around 1 billion yen (about $6.85 million).
Tokyo Metro said, "Consolidating substations in central Tokyo would lead to effective uses of the former sites and improve on the shortage of labor for maintenance and management. On the other hand, there are issues unique to subways other than cost, such as securing locations and the difficulty of conducting maintenance inspections."
Tomita noted, "I want to cooperate in the gradual expansion of sections while thoroughly ensuring quality control, and contribute to offing two birds with one stone by solving labor shortages and tackling energy conservation."
