Subcooled liquid nitrogen refrigerator for HTS power systems Original Research Article

Subcooled liquid nitrogen is a good cooling medium of high temperature superconducting (HTS) electric power systems such as an electric power line and a power transformer. To produce subcooled liquid nitrogen, a cryocooler is used and a circulation pump is installed in the system. Several subcooled liquid nitrogen circulation systems were constructed and tested. Those are used as a refrigerator for HTS power systems. The pressure of subcooled liquid nitrogen is maintained at atmospheric pressure (0.108 MPa) and the working temperature is 68 K. One system of HTS power transformer was tested in distribution power line. In each case, the temperature of the cold head of the cryocooler is kept at 64 K little above nitrogen freezing temperature. For the stable operation, the system must work even in the case of shaking condition by earthquake, the pressure must be stable and be kept at atmospheric pressure.