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A high temperature superconducting (HTS) power cable system cooled by forced-circulation subcooled liquid nitrogen is under construction in Korea. In the system, the termination cryostat designed for normal capacity of 22.9 kV, 1.26 kA is located at each end. In order to cool the cryostat effectively, we conducted several numerical analyses. It was found that major design factors were position of inlet and outlet for the liquid nitrogen as well as mass flow rate of the liquid nitrogen in the cryostat. It was also found based on the calculation of temperature distributions in the cryostat that the mass flow rate of liquid nitrogen is needed at least 0.2 kg/s. The cryostat was designed to endure the mechanical stress induced by thermal shrinkage from room temperature to liquid nitrogen temperature. The cryostat is being installed in the 30 m length, prototype single phase HTS cable system.

Publisher Summary This chapter investigates the working of a new type of cryostat system applying boil-off calorimetry method. The power cable system consists of termination cryostats, high temperature superconducting (HTS) power cable and their cooling system. The current lead located in the termination cryostat is used to transmit the power from the room temperature power cable to the low temperature HTS power cable. Because the current lead is the major heat source of cooling load, the heat load of the current lead has influence of the liquid nitrogen consumption and the refrigeration capacity. For this reason, the design of current lead with smaller heat load is very crucial for the economic refrigeration system. One of the main characteristics of the system is to avoid gas convection cooling effect. A prototype current lead inserted in the system was made of copper. Heat loads through the copper current lead were measured for four different heat load conditions. The experimental results coincide with the numerical ones within 3% error.