Study on field suppression unit in DC excitation system for saturated iron-core superconducting fault current limiter

Saturated Iron-core Superconducting Fault Current Limiter (SISFCL) has superior properties as a fault current limiting device. DC excitation system plays a key role during the operation of SISFCL. Besides its basic function, outputting DC excitation current to keep Iron-core saturated, its field suppression unit absorbs magnetic energy stored in superconducting coil and suppresses the reverse voltage applied to superconducting coil, high speed switch IGBT, and DC excitation circuit elements to a safe level instantly when a fault happens. In this paper, SISFCL device and its dc excitation system will be briefly introduced, then the field suppression unit will be analyzed, calculated and discussed in detail based on the researching of 220 kV / 300 MVA SISFCL, which has been developed and run in power grid in China.