The cryogenic system of the 10.5kV/1.5kA high Tc superconducting fault current limiter

High-voltage insulation and filling periodically with cryogen are key problems [Mitsuii H. Review of the research and development for insulation of superconducting fault-current limiters. Cryogenics 1998;38:1159–67] for the cryogenic system of the high Tc superconducting fault current limiters (HTC-SFCLs). The nitrogen thermo-siphon cooling system has been proposed, designed and tested for the 10.5 kV/1.5 kA HTC-SFCL cooled by liquid nitrogen. The problem of the high-voltage insulation gets to be solved by this cryogenic system, and also the period of the filling with liquid nitrogen can be obviously prolonged due to the closed self-circulation, even without further extra filling. In this paper, this unique cryogenic cooling system for the 10.5 kV/1.5 kA HTC-SFCLs has been described. The saturated nitrogen steam through the high-vacuum-jacked line from the HTC-SFCLs is cooled into the liquid nitrogen which returns again to the HTC-SFCLs. Two G–M refrigerators provide the cooling capacity for the condensation in the condenser. Test results have indicated that the 5–6 L/h of the saturated nitrogen vapor condensation can meet the cooling requirement of the 10.5 kV/1.5 kA HTC-SFCLs on each phase.