Centrali Idroelettriche
In a generalized manner one is constituted from a captazione work of waters, works of transport of waters, machinery that transforms the hydraulic energy in mechanical energy and this last one in elettrica.Il first hydroelectric system was constructed in 1880, in the Northumberland. The revaluation of the hydraulic energy coincided with the development of the generating electrical worker coupled to the hydraulic turbine and with the crescent asks of electricity that it characterized the beginning of XX the century. The hydraulic energy represents approximately 1/4 of the energy total produced in the world and in the last years it is considerable increasing of importance; in many countries, which as an example Norway, Republic democratic of the Congo and Brasi them, represent the dominant source for the electric power production. The Itaipu system on the River Paranà, between Brasi them and Paraguay, officially inaugurated in 1982, has worst to the world (12,600 megawatt to full regimen). In some countries they have been constructed to hydroelectric systems of small dimensions, with ability comprised between a kilowatt and a megawatt. In many districts of China, as an example, small center them of this type constitute the principal source of energy. The technology of the greater part of the great systems is remained the same one for all the century. The systems are use from a great river basin of reservoir, to mount of a dam, where the flow of the water can be controlled in order to maintain a level almost constant. From the lead forced, the water enters in it upsets some through valves that control the amount of the flow second the energy question and exits passing through the drainage channel. The generators are mount to you directly over upset some to them, on vertical trees. The type of turbine depends on the jump and the water capacity: for high it knows to you are used upsets of it Pelton, for means knows to you are used upsets of it Francis, for relatively low unevennesses and with great capacities they are used upsets of it Kaplan.Negli modern hydroelectric systems come employed generally it upsets of it Kaplan until 60 m. and upsets of it 600 Francis until m. the system that has the greater unevenness (approximately 1770 m.) it is found to Reisseck, in Austria, and uses a Pelton turbine, while single units of remarkable dimensions are installed in the system of Itaipu, in Brasi them: draft of 18 upsets of it Francis from 700 megawatt ciascuna, for one total ability to 12.600 megawatt. Many of the hydroelectric systems to low unevenness realize to you before the 1930 have been abandon because of elevated expenses to you of maintenance and labor. However the crescent cost of fossil fuel has brought back the interest also on the systems of small dimentioni.