Development and Operating Experience of a Two-Casing 600MW Ultra-Super-Critical Steam Turbine

600MW class steam turbines are typically manufactured in three casing configurations with two low-pressure casings. Mitsubishi Heavy Industries (MHI) has developed and manufactured a 600MW two-casing Ultra Super Critical turbine for the Hirono No.5, Tokyo Electric Power Co. in Japan, which comprises one combined high- and intermediate-pressure casing and one double-flow low-pressure casing. This unit started the commercial operation in July 2004. Two-casing design simplifies construction and maintenance requirements and saves capital cost of the plant. This compact design was realized mainly due to the development of 3000 rpm 48 inch steel low-pressure end blades, the longest steel blade in the industries for 3000 rpm machines. In addition, a highly efficient and compact design in achieving 600°C steam condition was realized by employing a combined high- and intermediate-pressure frame. This paper addresses the design features of the 600MW two-casing USC turbine, operating condition of the Hirono No.5 and the results of the verification tests performed.