Design and development of superconducting DC cable for railway applications

We report the recent development in the national project dealing with a prototype of the next generation dc superconducting cable for railways. The main goal of the project is to upgrade the feeder of the overhead contact line system connecting the electric train with the substation. The superconducting cables are usually considered to reduce the resistive losses generated in a conventional feeding system mainly in the catenary wires. In this paper, various cable structures existing in the railway network were studied with respect of their use in the next generation of railways. The superconducting cables need to be cooled below 77 K. They consist of coaxially configured conductors and sheaths. Liquid nitrogen is forced to flow through these coaxial cables. Various designs and configurations of the cooling systems possess always some advantages and some drawbacks. Our systematic analysis showed that a 'go and return' system, where the liquid nitrogen flows through the hollow former and returns through the space between the outer layer of the HTS tapes and the cryostat wall is most effective for the railway applications; it saves both space and costs.