Monday, January 5, 2009
The remaining stages of the HP turbine are a series of Rateau stages . A single Rateau stage consists of a nozzle diaphragm followed by a row of moving blades. The nozzle diaphragm separates the stages of an impulse turbine and provides support for the nozzles. The nozzles within the nozzle diaphragm serve the same purpose as the nozzles within the nozzle block. As steam passes through the nozzle, velocity is increased and pressure is decreased. After leaving the nozzle, steam then enters the moving blades where once again work is extracted from the steam. As work is extracted from the steam, its velocity will once again decrease even though its pressure will not be effected. Even though there is a velocity increase and a velocity decrease in each Rateau stage, the overall velocity from the inlet of the first Rateau stage to the exhaust of the final Rateau stage is not changed. In contrast, there is a pressure drop in each Rateau stage, resulting in an overall pressure drop from the inlet of the first Rateau stage to the exhaust of the final Rateau stage. This overall pressure drop causes the Rateau staging to be considered pressure compounded.