Combined cycle power plant and cooling steam supply method for gas turbine therein

A combined cycle power plant comprising:

• a gas turbine plant having a high temperature portion, said gas turbine plant including a gas turbine, an air compressor driven by said gas turbine, and a combustor for burning fuel and compressed air from said air compressor;
• a waste heat recovery boiler for generating steam by using exhaust heat from said gas turbine plant as a heat source, said waste heat recovery boiler including a high pressure steam generating portion;
• a steam turbine plant including a high pressure turbine communicating with said high pressure steam generating portion of said waste heat recovery boiler so as to receive high pressure steam from said high pressure steam generating portion;
• and
• a cooling steam supply passage communicating with said gas turbine plant and with said steam turbine plant so as to supply cooling steam into said high temperature portion of said gas turbine plant, wherein said cooling steam supply passage is adapted to receive and mix only an exhaust steam from said high pressure turbine and a cooling water spray such that a temperature of the cooling steam is adjusted to a temperature appropriate for cooling said high temperature portion of said gas turbine plant.