PRESSURE - VELOCITY COMPOUNDING OF STEAM TURBINES

This method is a combination of pressure and velocity compounding. The total pressure drop is carried out in two stages and velocity obtained in each stage is also compounded. Steam pressure from boiler pressure to condenser pressure is dropped in stages through convergent - divergent nozzles. Velocity compounding is done by using a guide blade rings in between every two moving blade rings.

High - pressure steam expands through first ring nozzles, does work on the first row of moving blades and enters guide blades. Through the guide blades the steam comes out with a changed direction of flow. Then the steam flows through the second row of moving blades where it does work. The remaining reduction of pressure up to condenser pressure takes place in the second set of nozzles and the process of doing work on two set of moving blades and guide blade is continued. Thus, total pressure drop is obtained in stages through nozzles sets and velocity changes takes place through moving blades.

Turbine employing this method may be said to combine many of the advantages of both pressure and velocity compounding. By allowing a larger pressure drop in each stage, less number of stages are used and hence a shorter turbine will be obtained for a given pressure drop. Now- a - days , pressure - velocity compounded turbines are not very much in use because of very low efficiency.

This method is used in Curtis and Moore Turbine.

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