Refrigeration System for Three-Phase AC High-Temperature Superconducting Cables

The long-term operational reliability of the cryogenic system for the superconducting cable was considered a central challenge for its commercial application. A refrigeration system featuring multiple redundancy designs was developed based on the high-temperature superconducting cables demonstration project in Xuhui District, Shanghai. The system was equipped with three types of cold sources—reverse Brayton refrigerators, Stirling refrigerators, and vacuum decompression systems—which were operated synergistically and allowed for online switching and maintenance. Two independent pump tanks were configured in parallel to provide redundancy for the liquid nitrogen circulation drive. System pressure stability was maintained through three independent control mechanisms: Liquid replenishment, gas replenishment, and heating-based pressure regulation. By July 2025, the system had been operated continuously for over 1200 days under demanding conditions. It was demonstrated through engineering practice that the multi-redundancy design significantly improved the long-term operational reliability of the superconducting cable cryogenic system, providing key technical support for its commercial promotion.