Superconducting DC power transmission for subway lines that can reduce electric resistance and save energy

Electric railway systems are widely used and DC systems have been employed in a number of metropolitan areas. However, they have some problems, such as cancelled regeneration and energy loss. Introducing superconducting feeder cables into railway feeding systems offers a lot of benefits: fewer substations, equalization of load among substations, reduction of cancelled regeneration, power transmission loss. Feeding systems adopted by railways throughout the world can be classified into feeding systems through overhead trolley wires and ground third rails. These problems are especially serious in third rail system because the voltage is low and the electric current is high. By using a newly developed superconducting feeder system on a third rail system, we conducted a power transmission test. Also, the feeding of the high current and regeneration current was proved to be successful in the course of the train running test on subway line. And, we specifically analyzed the energy generated when a cable was adopted into the third rail line. As a result of adoption of a superconducting feeder cable, the voltage drop specific to railways could be reduced even with a short cable. And, if the cable is adopted in subway line, we also observe large energy-saving effect.