An overview of HTS (high-temperature superconductor) transmission cable projects in Korea is introduced, and three selected topics on cryogenic research for the cable system are briefly presented. The Korean government has supported the development of HTS cables for 15 years, and a consortium of KEPCO (Korea Electric Power Corporation) and LS Cable successfully installed and demonstrated a 1 km AC cable at 154 kV transmission grid in March, 2016. Along the development, cryogenic research has been performed at Hong Ik University, and three recent topics are selected for this seminar: (1) design of Brayton refrigerator, (2) plate-fin heat exchangers for sub-cooled liquid nitrogen, and (3) proposed cryogenic design for long-length cables.
The first topic is a thermodynamic study for 10 kW Brayton refrigerator under domestic development in Korea. The key issues are the comparison of helium and neon as refrigerant and the determination of cycle parameters. The current status of prototype construction is also reported shortly. The second topic is an experimental study to verify that the risk of freeze-out of liquid nitrogen can be reduced by arranging the heat exchanger as cross-flow. It is explained how this anti-freezing scheme is applied to the cable system in practice. The last topic is a new concept of cryogenic design to make a breakthrough on the difficulty of heavy liquid nitrogen flow in longer (over 1 km) cables. We propose and investigate modified Claude cycles that will integrate the refrigerator and the circulation of liquid nitrogen. The feasible thermodynamic structures are designed for near-future application.
