Design and Experimental Investigations on the Helium Circulating Cooling System Operating at Around 20 K for a 300-kvar Class HTS Dynamic Synchronous Condenser

A project to develop a 10-Mvar high temperature-superconducting (HTS) dynamic synchronous condenser (DSC) is carried out by China Southern Power Grid Corporation. In order to cool the magnets to 20–30 K, a set of cryogenic system using circulating helium as the working fluid was developed, and it has been coupled and tested with the 300-kvar class dynamic synchronous condenser. Three cryogenic coolers are used as the cold source to provide more than 120 W@20 K cooling power. Cryogenic helium pump is employed to overcome a pressure drop of about 2.5 kPa induced by the helium gas circulating in the transfer tubes and heat exchangers. In the static tests coupled with the 300-kvar class dynamic synchronous condenser, the entire magnet was cooled to approximately 26.2 K by about 5 days. Once the rotor speeds up and reaches the design value of operation, the temperature rises slightly to about 26.6 K. Nowadays, the cooling system is upgrading and it will be served for the developed 10-Mvar DSC in the next year.