Large steam-turbine plants have two forms: condensing plants, electric power plants.
The great masses of hot steam, having accomplished the mechanics work in the turbines of condensing steam-turbine plants, are condensed - i.e. are cooled down and turned back into distilled water, and returned to the boiler for production of steam to activate the turbine.
Condensation of steam takes place in condensers where the hot steam is cooled when it comes in contact with tubes through which cooling water, supplied from a water reservoir (river or lake), is circulated. This cooling water, after it takes the heat from the spent steam, is returned to the water source carrying along with it the unutilized heat energy. This water is called the circulating water. The importance of the distilled water for feeding steam boilers is extremely great since chemical clean water decreases the formation of scale in the boiler tubes, and thus, makes their service life longer.
Condensing plants of large generating capacity are built close in sources of fuel, in order not to transport large quantities of fuel over considerable distances.
The electric power generated in such plants is transmitted over long distances for the supply of large industrial regions. So these plants are called regional thermal power plants.
Heat and electric power plants, in addition to electric power generation, also supply heat to closely located consumers (within of radius of 50 km) i.e. serve as district heat plants. To such heat consumers belong all kinds of industrial enterprises that require heat for production purposes, and also municipal consumers such as baths, laundries and the heating systems of dwelling houses and other buildings. The electric power developed by the generators is fed to the switchboard of the plant, whence it is delivered by overhead transmission and cable lines to the consumers.