Surely this would be a DC line, right? AC induces resistance in superconductors because it necessarily induces a changing magnetic field, iirc (or maybe that's only particular types of superconductors).

Edit: Found this, which isn't specific but refers to it as a three-phase transmission cable which implies it is indeed AC http://www.jicable.org/2007/Actes/Session_A3/JIC07_A34.pdf