A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in 1884.
Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 90 % of all electricity generation in the United States (1996) is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process.
An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine. No steam turbine is truly isentropic, however, with typical isentropic efficiencies ranging from 20-90 % based on the application of the turbine. The interior of a turbine comprises several sets of blades or buckets. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.
Steam turbines are used to transfer energy to drive a machine. They are used to create electricity from various energy sources that produce the raw material steam. These energy sources include fossil fuel, nuclear energy, geothermal energy and even solar power. Steam turbines have also been used to power locomotives and ships. Steam turbines convert heat energy into kinetic energy and from there can create electric energy via a generator.
The steam turbine system is used to create over 80 percent of the world’s electricity supply. In order for the turbines to work, steam must first be created from an energy source.