Types Of Turbine

* Compounding

* Impulse

* Reheat

Compounding

Compounding is the splitting up, into two or more stages, of the steam pressure or velocity change through a turbine. Pressure compounding of an impulse turbine is the use of some stages of nozzle and blade to reduce progressively the steam pressure. This results in lower or more acceptable steam flow speeds and better turbine efficiency. 

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Velocity compounding of an impulse turbine is the use of a single nozzle with an arrangement of several moving blades on a single disc. Between the moving blades are fitted guide blades connected to the turbine casing. This arrangement produces a short lightweight turbine with a poorer efficiency which would be acceptable in, for example, an astern turbine. 

The two arrangements may be combined to give what is called 'pressure-velocity compounding'. The reaction turbine due to its blade arrangement changes the steam velocity in both fixed and moving blades with consequent gradual steam pressure reduction. Its basic arrangement therefore provides compounding. The term 'cross-compound' is used to describe a steam turbine unit made up of a high-pressure and a low-pressure turbine. 

Must read: Information About Impulse Turbine

This is the usual main propulsion turbine arrangement. The alternative is a single-cylinder unit which would be usual for turbo-generator sets, although some have been fitted for main propulsion service.