Korean R&D on the 6-pulse converter unit for ITER AC/DC converters

Korea is jointly responsible for the procurement package of ITER AC/DC converters shared between Korea and China. The collaborative activities among ITER Organization and Domestic Agencies under the frame of an Integrated Product Team have been underway since 2008 for the improvement and stabilization of the FDR2001 design. The Korean Domestic Agency has been being performing 2-staged converter R&D to establish the technical basis for the procurement package of ITER AC/DC converters adopting 5-inch thyristors. The first phase R&D demonstrated the basic features of ITER converter such as the proper clamping structure and current sharing of thyristors connected in parallel, and fault suppression capability (FSC) with a single-phase rectifier unit equivalent to an ITER vertical stabilization converter. The second phase R&D is intended to develop a full-scale 6-pulse ITER converter unit that realizes the full integration of all assemblies including AC bus bars and DC bus bars. The self supporting structure with aluminum material is designed to be safe from severe electromagnetic stress under high fault current. The suitable cooling design and the welding procedure have to be implemented in this structure. This paper shows the structural and thermal design. The current sharing among paralleled thyristors in each arms of the 6-pulse converter unit is improved. The design verification for FSC and the soundness over the electromagnetic stress is confirmed.