Cooling Considerations for the Long Length HVDC Cables Cryostat within BEST PATHS Project

HVDC cables have been identified as the preferred solution for future pan-European grids for the transmission over long distances of the large power produced by renewable energy farms which are generally located far for the consumption places. The European project Best Paths has been launched to identify the remaining barriers and propose some innovative solutions to achieve such envisioned grids. As superconductivity offers very attractive and efficient solutions vision studies for long-distance superconducting power transmission lines are conducted. The superconducting technology under study is based on the MgB$_{2}$ conductor cooled with one-phase liquid hydrogen. A flexible cryostat with 15 to 25 K core cooling and with additional shield cooling using liquid nitrogen or hydrogen gas is required. For long length cables the limiting parameters are the cryostat heat load and the pressure drop. The calculation results show the interdependencies of the maximum length between neighboring cooling sections with the heat load on shield and core, mass flows and pressure drop, enthalpy change, viscosity, friction factors and cryostat geometry. The calculations are carried out for different fluid options and diameters, and the corresponding results are presented and discussed