Cooling steam control method for combined cycle power generation plants

A cooling steam system control method for a combined cycle plant, wherein the system includes a gas turbine load characteristics detecting device a steam temperature detecting device connected to the steam line at the exit of the high temperature components, comprising the steps of:

• driving the steam turbine by directing a steam line from the exhaust heat recovery boiler to the steam turbine;
• cooling high temperature parts of the gas turbine by branching the steam line from the exhaust heat recovery boiler;
• returning the cooled steam to the steam line;
• and
• controlling the amount of cooling steam supplied to the high temperature parts in accordance with dynamic characteristics of the exhaust heat recovery boiler when the load on the gas turbine is changing, wherein the controlling step comprises the steps of,
• setting a static characteristics value signal for the steam temperature in the high temperature parts corresponding to load via a function device when the load on the gas turbine is static, wherein the signal is introduced to a subtracting device after passing through a correcting circuit, and the cooling steam flow amount is adjusted by means of a control valve provided at the entrance or exit side of the high temperature parts on the steam line via a temperature controlling device, and
• setting a dynamic characteristics signal for the steam temperature in the high temperature parts corresponding to a changing load in the correcting circuit from the load characteristics detecting device via the function device, wherein the extent to which the control valve is open is adjusted when the load on the gas turbine is changing.