従来，我が国の大容量火力発電プラントは主として24.1MPa，538/566℃の蒸気条件が適用されてきた．三菱重工では，広範な開発を通じて高温蒸気タービンの材料及び設計を確立し，24.1MPa，593/593℃の蒸気条件を電源開発(株)松浦２号機の1000MWタービンに適用した．その後，さらに高温化を進め，世界で初めて大容量機で24.5MPa，600/600℃の高蒸気条件を採用した中国電力(株)三隅１号機の1000MWタービンを設計，製作した．本機は1997年12月に初通気し，順調な試運転，各種試験の後，1998年６月に営業運転を開始した．本報では三隅１号機の設計の特徴及び運転実績を紹介する．

Steam conditions for large-capacity fossil-fuel-burning thermal power plant in Japan have conventionally been 24.1 Mpa 538/566℃. Mitsubishi Heavy Industries. Ltd. (MHI) has, through wide-scale development programs, set techniques for steam turbine design and materials at a high steam temperature and steam conditions of 24.1 Mpa and 593/593℃ applied to large-capacity 1 000 MW turbines, the Matsuura No. 2 Unit for the Electric Power Development Co.. Ltd. Based on our high-temperature design development. MHI has developed and manufactured the 1 000 MW turbine. Misumi No. 1 Unit, for Chugoku Electric Power Co.. Inc., for the first time in the world with steam condition of 24.5 Mpa and 600℃ and a steam reheating temperature of 600℃. The first steam admission of this unit was completed in December 1997, and underwent test runs and other tests before starting commercial operation in June 1998. This paper describes the design and operating features of Misumi No. 1 Unit.