US Patent 7392656 Steam turbine plant

A steam turbine plant includes an extraction system and a control system for controlling the steam extraction. The extraction system includes an extraction steam flowmeter and a stop valve. The control system sets a warning flow and an extracted steam stop flow for the extracted steam. When the extracted steam flow reaches the warning flow, a warning is issued and after a lapse of a predetermined time period, the stop valve is opened to restrict the extracted steam flow. When the extracted steam flow reaches the extracted steam stop flow, the stop valve is closed to stop steam extraction. A steam turbine plant can thus exercise extraction control to stably supply extracted steam while avoiding turbine trip, even if not equipped with a high-performance and expensive valve device such as an extraction steam control valve.