Abstract: This combined cycle gas turbine plant has a gas turbine (104) and a steam turbine (106) mounted on the same shaft. A control system is configured for switching the plant from a rated mode of operation, in which the plant is operated on gas turbine output and steam turbine output, to a reduced load mode of operation, in which the plant is operated on gas turbine output alone. The switch from the rated mode of operation to the reduced load mode of operation occurs if plant demand decreases below a predetermined threshold. The steam turbine is run under full speed no load conditions in the reduced load mode of operation, and is heated using controlled steam admission, to maintain the steam turbine in a heated ‘stand-by’ state.

Abstract: In an operation method of a multi-shaft combined cycle plant, a low-load mode in which an output of the multi-shaft combined cycle plant is adjusted by adjustment of only an output of a gas turbine and a high-load mode in which the output of the multi-shaft combined cycle plant is adjustable by adjustment of the output of the gas turbine and adjustment of an output of a steam turbine are switched according to a demanded load. In the low-load mode, steam at a standby flow rate at which the steam turbine is capable of maintaining a predetermined initial load is supplied to the steam turbine, and the initial load is applied to the steam turbine.