Design and Verification of Self-Sustaining Nitrogen Liquefaction System for Low Temperature Refrigeration with Magnetic Bias Superconducting Fault Current Limiter

A cryogenic liquid nitrogen refrigeration system based on GM cryocooler was designed to meet the self-sustaining requirement of magnetic bias superconducting fault current limiter. According to the operating parameters and structure size of superconducting fault current limiter (SFCL) Dewar, the flow design of self-sustaining nitrogen liquefaction system for low temperature refrigeration was carried out. The whole heat leakage of the system was analyzed and calculated, the quick insert structure of GM cryocooler and low temperature condensing heat exchanger wwa designed. The test results showed that the nitrogen liquefaction system equipped with magnetic bias SFCL has been running stably within the cryogenic Dewar for more than 2 months, during which the pressure was maintained at (negative pressure state) 85 kPa and the system temperature was 75.9 K, meeting the self-sustaining demand of low temperature Dewar. It provided the possibility of coordinated control of SFCL using small GM cryocooler as the cold source and superconducting cables, reducing the reliance on liquid nitrogen and enhancing the flexibility of the system.