Study on Field Suppression Unit in DC Excitation System for Saturated Iron-Core Superconducting Fault Current Limiter

As the most likely applicable fault current limiting device in the future, saturated iron-core superconducting fault current limiter (SISFCL) has many superior attributes. In a SISFCL, DC excitation system plays a key role during the operation in power grid. It not only outputs dc excitation current to make iron core saturated, but also absorbs magnetic energy stored in superconducting coil and suppresses the reverse voltage, a disaster to superconducting coil, high speed switch IGBTs and other circuit elements, to a safe level instantly when a fault happens. Field suppression unit is mainly used to achieve the second function mentioned above. This paper introduces SISFCL device and its DC excitation system briefly, then analyzes and discusses field suppression unit in detail. This work bases on research and manufacturing of 220 kV/300 MVA SISFCL, which has been developed and put into operation in power grid in China.