Operation of KSTAR PF Superconducting Magnet Power Supplies Under MG Power System

Poloidal field (PF) power supplies provide 20-25 kA to PF superconducting magnets to generate, maintain, and control the Korea Superconducting Tokamak Advanced Research (KSTAR) plasma. A substantial amount of grid power for PF power supplies is required. Before 2014, available grid power for PF power supplies reached only 50 MVA, which is comparably small to support the rated operation of PF magnets. To achieve high-performance and long pulse operation of KSTAR plasma, the motor generator (MG) system, whose maximum power is 200 MVA, was designed and tested up to 150 MVA with PF magnets in 2014. Frequency fluctuation of line voltage, voltage distortion, and harmonic current increases are found during the operation. The power supply control can be seriously affected by these problems because every PF power supply uses a 12-pulse thyristor converter that is sensitive to the power quality. In this paper, key features of power supply control under grid and MG power system are described, and the test results are presented.