Design Study of LN2 Circulation in a Long SC Power Transmission Lines

AbstractIn accordance with the conventional design of superconducting power transmission (SC PT) line, HTS cable should be placed into a carefully heat-insulated cryopipe filled with cryogen (usually liquid nitrogen, LN2) in order to maintain its temperature low. Circulating LN2 removes heat penetrating through the insulation layers. The circulation rate depends on the heat load and the length of the line. Since LN2 working temperature range is restricted, it is easy to show that pressure drop, Δp, increases dramatically being almost cubic function of the cable length, L, and quadratic function of the specific heat load, q: Δp ∝ Ln+1qn, where n = 1.75..2.0. Great efforts should be made to reduce heat load on the system and hydraulic friction inside the channels. Last requirement is contrary to common practice since the entire existing test SC PT lines are constructed using corrugated cryopipes which exhibit very high Δp. Smooth cryopipes separated by short bellows inserts should be used instead. A small increase in diameter of the cryopipe also produces a large decrease in the pressure drop. The experimental results obtained at the new 200 m facility at the Chubu University confirm our approaches to the design of the long SC PT lines