Possibility of DC underwater superconducting power cable cooled by long-length heat-pipe

With the progress of high Tc superconductors (HTSs), it becomes realistic to introduce them into underwater power cables. As is well known, in an underwater power transmission system any reactive power compensators cannot be installed amid the line. Therefore, DC transmission system is preferable for underwater power cables rather than AC system. Considering the situation in which superconducting technologies were introduced to DC power cables, there are several advantageous points for designing them, i.e. (1) no AC losses in superconductor, (2) no eddy current loss in either in conductor or in structural member, (3) no dielectric losses in insulators, etc.. However, in an underwater cable we have to take into consideration a difference in height level and a large additional hydraulic pressure by cryogenic liquid itself. In such a case, boiling point of the coolant increases due to the increase of the pressure. So, the authors propose a new cryogenic cooling system using long-length heat-pipes. A conceptual design of a DC superconducting underwater power cable was carried out. The fundamental idea and the conceptual design are presented.