GAS TURBINE COOLING SYSTEM, AND GAS TURBINE COOLING METHOD

Provided are a gas turbine cooling system and cooling method whereby it is possible to efficiently cool a gas turbine by means of steam without using the ligh-pressure steam generated at an exhaust heat recovery boiler and without reducing the generation of the high-pressure steam. This cooling system is provided with: an exhaust heat recovery boiler (2) having a gas turbine (3), a high-pressure system (6) for generating high-pressure steam by exchanging the heat with the exhaust heat from the gas turbine (3), a high-pressure drum (11) for supplying water and steam to the high-pressure system (6), a medium-pressure system (7) for generating medium-pressure steam by exchanging the heat with the exhaust heat from the gas turbine (3), and a medium-pressure drum (12) for supplying water and steam to the medium-pressure system (7); a medium-pressure steam pipe (19) for connecting the medium-pressure system (7) with the cooling system of the gas turbine (3) and for supplying medium-pressure steam from the medium-pressure system (7) to the cooling system; and a steam supply pipe (20) for connecting the high-pressure drum (11) with the medium-pressure drum (12) and for supplying the saturated steam within the high-pressure drum (11) to the medium-pressure drum (12).