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Technology

All aboard the superconductivity express

TOKYO -- Japan wants to jolt its economy by exporting infrastructure and related products. Hopes are running especially high for a technology that promises to change the way we travel, transport goods and power our homes: superconductivity.

JR Tokai is leading a project to bring superconducting high-speed trains into the mainstream.

     JR Tokai, the main railway operator in central Japan, is leading a project to bring superconducting high-speed trains into the mainstream. Working with Mitsubishi Heavy Industries and other companies, JR Tokai plans to open such a train line in 2027, linking Tokyo and Nagoya. The two cities are about 286km apart; running at up to 500kph, the magnetic-levitation, or maglev, train will make the trip in 40 minutes.    

     By 2045, the line is to be extended to Osaka. Japan's government is hoping other countries will want a piece of the superconducting action.

     But how does it work, and why will the maglev train zoom past Japan's current bullet trains, which top out at 320kph?

     Under normal conditions, electricity does not flow freely through metals and alloys. It is impeded by something called, well, resistance. The greater the resistance, the smaller the flow of power. At the same time, higher resistance means more heat is generated and more electricity goes to waste.

     Typically, resistance increases as temperatures rise and decreases when they drop. Superconductivity is achieved by bringing temperatures down to a point where electrical resistance becomes zero. Electricity will flow through a wire at full capacity, when normally some of it would be lost. And no heat will be produced.

     Take an electromagnet -- a device in which a magnetic field is created by electric currents -- and cool the coils to a superconducting temperature. The result? A much more powerful magnet. This phenomenon holds the key to the maglev system. 

     Rather than rolling on wheels like normal trains, maglev trains run like their name suggests -- by levitating on magnetic energy. Magnets naturally attract or repel each other, and if you make those forces strong enough, they can lift a whole train and propel it forward at breathtaking speed.  

     In the L0 train series, which is to run on Japan's maglev line, electromagnets are positioned in the cars. Using liquid helium as a coolant, the magnets' coils are chilled until they become superconducting at minus 269 C.

     The L0 train has already clocked 500kph on JR Tokai's test line in Yamanashi Prefecture.

     As the maglev project progresses, researchers are making strides with peripheral technologies as well. The newest helium cooling equipment, developed by a company called Air Water, uses less than one-hundredth of the helium coolant the old equipment required.

Big savings

While the maglev line will not be ready for at least another 13 years, efforts are underway to make use of superconductivity's energy-saving capabilities sooner. 

     At the Railway Technical Research Institute in Kokubunji, in western Tokyo, some 300 meters of black cable has been laid alongside test tracks. Here, the Japan Railways group is conducting experiments on using superconducting cables to power trains -- the wheeled kind.

     The cable is about 10cm in diameter. Inside is a metal wire made of copper oxide, around which liquid nitrogen circulates as a coolant. At minus 196 C, the wire becomes superconducting and sends a large current of electricity to overhead cables.     

     With regular power transmission lines, around 10% of the electricity is lost to resistance. Superconducting cables do not have that problem.

     Some newer trains save power by reusing energy produced by braking friction. Superconductivity would make it possible to expand on this, allowing the use of "regenerative" energy between cars. All this energy-saving should make it possible to reduce the number of power-supplying transformer substations, which currently have to be placed at 3-5km intervals along a rail line.

     Even factoring in the power necessary for cooling, overall railway energy consumption would decline by around 5%. Japan Railways hopes to commercialize this technology within the next five to 10 years.

     Trains are not the only vehicles getting the superconductor treatment. The technology is also being applied to motors for ships and buses. It could end up in the power grid, too.     

The phenomenon of superconductivity has all sorts of potential uses. IHI developed this superconducting, energy-efficient motor for ships.

     In 2007, an industry-academia group that included heavy equipment maker IHI, cable producer Sumitomo Electric Industries and industrial gas company Taiyo Nippon Sanso developed a superconducting motor. Coils made with a bismuth-based material are cooled to minus 196 C and become superconducting electromagnets that increase rotational force. Using this motor, IHI subsequently developed a propulsion system for ships. Two motors are linked to produce an output of 800kW; fuel consumption is reportedly 25% lower compared with diesel engines of the same class. 

     That could be a big selling point at a time when tighter environmental regulations require more efficient ships. Kawasaki Heavy Industries has also developed a 3,000kW superconducting motor for midsize vessels. Used in conjunction with an engine, the motor reduces fuel consumption by 20%.

     Sumitomo Electric, meanwhile, is working on a superconducting motor that would be used in electric buses, at least at first. Might passenger cars be around the corner? It is hard to say. Since such motors have to be cooled to superlow temperatures, it would seem to make more sense to use them in vehicles like buses, which run for long periods at a time. That would maximize the energy savings.

     Tepco, the Tokyo-area power utility, and other companies are moving ahead with field tests that involve transmitting electricity to homes over superconducting cables. Japan may soon be able to offer next-generation power networks, just as emerging nations move to build up their electrical infrastructure.

(Nikkei)

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