It used in applications and industries other than the condensing of steam turbine exhaust in power plants. The steam turbine itself is a device to convert the heat in steam to mechanical power.
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. A steam turbine is a device which 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. By Brad Buecker, Contributing Editor. Steam turbine and surface condenser performance is just as important as ever, and is intimately tied in with chemistry control on both the steam side and cooling water side.  The difference between the heat of steam per unit weight at the inlet to turbine and the heat of steam per unit weight at the outlet to turbine represents the heat given out (or heat drop) in the steam turbine which is converted to mechanical power. 650 pages on this wiki. Condenser refers here to the shell and tube heat exchanger installed at the outlet of every steam turbine in Thermal power stations of utility companies generally. 1 As the steam condenses and leaves or exhausts from the low pressure turbine, it becomes part of the condensate system. 2  The condensate system is that part of the steam cycle in which the steam condenses to water and is pumped from the main condenser toward the boiler.  Condensing turbines are most commonly found in electrical power plants. These turbines receive steam from a boiler and exhaust it to a condenser. The exhausted steam is at a pressure well below atmospheric, and is in a partially condensed state, typically of a quality near 90%. A steam turbine is a device which 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. After the steam leaves the exhaust section of the turbine, it enters a condenser, where it is cooled to its liquid state. The process of condensing the steam creates a vacuum, which then brings in more steam from the turbine. The water is returned to the boiler, reheated, and used again.  Where cooling water is in short supply, an air-cooled condenser is often used. An air-cooled condenser is however, significantly more expensive and cannot achieve as low a steam turbine exhaust pressure (and temperature) as a water-cooled surface condenser. Surface condensers are also used in applications and industries other than the condensing of steam turbine exhaust in power plants. The steam turbine itself is a device to convert the heat in steam to mechanical power. The difference between the heat of steam per unit mass at the inlet to the turbine and the heat of steam per unit mass at the outlet from the turbine represents the heat which is converted to mechanical power. Surface condensers are also used in applications and industries other than the condensing of steam turbine exhaust in power plants. The turbine shaft is connected to the shaft of the generator, where magnets spin within wire coils to produce electricity. 4. Steam turns back into water. After doing its work in the turbine, the steam is drawn into a condenser, a large chamber in the basement of the power plant. In this important step, millions of gallons of cool water from a nearby source (such as a river or lake) are pumped through a network of tubes running through the condenser. 
https://en.wikipedia.org/wiki/Steam_turbine http://www.power-eng.com/articles/print/volume-116/issue-3/features/steam-generator-chemistry-and-turbine-condenser-efficiency-not-separated-at-birth.html http://engineering.wikia.com/wiki/Condenser_%28steam_turbine%29 http://fas.org/man/dod-101/navy/docs/swos/eng/60b-102.html https://en.wikipedia.org/wiki/Steam_turbine http://www3.nd.edu/~techrev/Archive/Fall2001/a5.html https://en.wikipedia.org/wiki/Surface_condenser https://en.wikipedia.org/wiki/Surface_condenser http://www.duke-energy.com/about-energy/generating-electricity/coal-fired-how.asp
what does a steam turbine condenser do