Air injection system for cooling rotor in gas turbine engine and method of cooling such rotor

An air injection system for use in a gas turbine engine includes at least one outlet port (42) through which air is extracted from the engine only during less than full load operation, at least one rotor cooling pipe (46A-D), which is used to inject the air extracted from the outlet port(s) (42) into a rotor chamber (Rc), a piping system (44) that provides fluid communication between the one outlet port(s) and the rotor cooling pipe(s), a blower system (50) for extracting air from the engine through the outlet port(s) and for conveying the extracted air through the piping system (44) and the rotor cooling pipe(s) (46A-D) into the rotor chamber (Rc), and a valve system (48A,B). The valve system is closed during full load engine operation to prevent air from passing through the piping system (44), and open during less than full load engine operation to allow air to pass through the piping system.