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BPSC AE ME 2012 Official Paper (Part 5) (Advt. No. 04/2011)

Option 3 : most of the kinetic energy of steam is absorbed as it passes over moving blades

**Concept:**

- Compounding is done to decrease the high rotational speed of simple impulse turbines to bring it down to the practical limit required for electricity generation.
- There are two ways of compounding i.e. pressure compounding and velocity compounding.
- In pressure compounded impulse turbine (or Rateau turbine), the total pressure drop is planned for more than one stage and each stage consists of a set of nozzles and moving blades, as the enthalpy drop into several stages corresponding to each to which there is a separate set of nozzles in which the partial pressure drop occurs, and
**a single set of blades connected to a common rotor to extract the kinetic energy gained by the steam in the nozzles** - In velocity compounded impulse turbine (or Curtis turbine), the total velocity drop is arranged in more than one stage and each stage consists of a set of fixed and moving blades. There is a single nozzle in which total pressure drop takes place and the high velocity obtained is converted into work in more than one stage.

- In pressure compounded impulse turbine (or Rateau turbine), the total pressure drop is planned for more than one stage and each stage consists of a set of nozzles and moving blades, as the enthalpy drop into several stages corresponding to each to which there is a separate set of nozzles in which the partial pressure drop occurs, and
- How the pressure and velocity of steams drop for a pressure compounded and a velocity compounded impulse turbine can be seen from the following figure.

ST 1: Logical reasoning

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