Patent ID: 8727705

Claim:
A steam turbine, comprising: a double-structure casing comprising an outer casing and an inner casing; a steam inlet pipe configured to feed steam into the inner casing through the outer casing; a turbine rotor operatively disposed in the inner casing; plural stages of moving blades implanted in the turbine rotor; plural stages of stationary blades circumferentially provided between a diaphragm outer ring and a diaphragm inner ring, the stages of the stationary blades being arranged alternately with the stages of the moving blades, respectively, in an axial direction of the turbine rotor; a cooling medium passage formed between the inner casing and the diaphragm outer ring, configured to flow a cooling medium; a supply pipe configured to supply the cooling medium from outside of the outer casing to the cooling medium passage; and an exhaust passage configured to guide a working fluid passed through a final stage moving blade to the outside of the outer casing, wherein the moving blade and the stationary blade constitute a stage of turbine, the inner casing comprises a plurality of protruded portions at an inner surface thereof, each of the protruded portions circumferentially protruding toward the turbine rotor correspondingly with each of the stages of the turbine, each of the protruded portions having an upstream side surface contacting with a downstream side surface of each of the diaphragm outer rings, respectively; and wherein the cooling medium passage comprises: a plurality of gap portions, each of the gap portions being formed between the inner surface of the inner casing and an outer surface of at least one of the diaphragm outer rings; and a communication hole formed in both of the diaphragm outer ring and the protruded portion, the communication hole coupling adjacent gap portions to communicate.