Compounding of Impulse Turbine

Single row of nozzle with single row of blade is called one stage of turbine. If steam at very high pressure is allowed to expand in single stage of turbine, the blade velocity will be too high. Such a high rotational speed cannot be used properly and also there will be velocity loss at the exit of the blade due to high exit velocity of steam. Therefore, to overcome these difficulties, the turbine is compounded or staged. In compounded turbines, steam is made to expand in number of stages instead of single stage and turbine speed is reduced which secures the same enthalpy drop of steam. There are three types of compounding of impulse turbine:

1. Pressure compounding or Reteau staging.
2. Velocity compounding or Curtis staging.
3. Pressure–velocity compounding.