Switch water on - Hydroelectric generating station

Hydroelectric generating station
What is a hydroelectric power plant? For hydroelectric power plant we mean the series of systems for the production of electric energy obtained by water masses in movement. Water is carried into one or more turbines which rotate thanks to the water push. Every turbine is connected to an alternator which turns the rotation movement into electric energy. The water speed is produced through a jump. An artificial lake is generally crested by a dam, so water is carried into a conduct which turns out to be forced in the last part.

The plant
The “Taccani” hydroelectric power plant of Trezzo upon Adda, in the province of Milan, is situated on the watercourse of the River Adda, inside the homonymous park. The building of the plant is placed on the right riverside of the Adda, a little upstream of the barrage and stands on the base of the rocky promontory, on the top of which there are the ruins of the castle built in 1370 on the relics of a previous Lombard construction. The power plant, continually on duty since 1906, was built by Benigno Crespi, who needed electrical energy for the functioning of some machinery, mainly (power) looms.
Crespi entrusted the task to plan and build the plant to the architect Gaetano Moretti so that it could perfectly integrate in the surrounding territory. A style similar to the one of the ancient castle was chosen by the builder and the typical local stone, called “ceppo”, was used as building material.
The architect decided to represent the structure in neo-Gothic style, bearing in mind the one of French cathedrals so that the inhabitants still call the plant “the cathedral on water”. There are, besides, some components, such as the iron supports, in Art Nouveau style, represented with decorations which allude to natural elements. The plant was an “energy pole”, as regards the period it was built in, as it included, besides the hydroelectric sector with ten generators, also a thermoelectric section with four steam generators, destined to supplement the hydroelectric production during the winter minimum flows of the Adda.
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The journey of energy
The drop of about 8 m between the derivation dam that blocks up the River Adda and the water return spot is exceptionally useful to the functioning of the turbines and so to the whole plant. The building of the power plant is in unison with the one of water plugs, which are preceded by a barrage consisting of a grid and a comb groom, placed level with every production group to prevent the materials, transported by the stream, from reaching the turbines. Short conduits provided with a flat interception floodgate introduce the water downstream into a tank, where, through two tunnels, it‘s returned to the river. Every turbine trails its alternator in rotation and this produces energy, which through appropriate wires is sent to the transformers. These ones raise the energy voltages from 6 kV to 15kV production, to be transferred afterwards to the primary booth of Roncello, where the voltage is further raised to 132 kV. In the power station the energy from more plants is conveyed and then it‘s distributed to the surrounding towns.
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The main components and their characteristics
The first distinctive element of the plant is the barrage, which, through the dam, serves to maintain constant the water level and create the 8-metre jump. This barrage, in the past, through a navigation basin, could be sailed by boats, especially the ones which transported coal, because at first the plant used this material. The barrage consists of ten floodgates: three flat ones and seven sectored ones. The flat ones can be completely opened or closed, whereas the sectored ones are adjustable. At the beginning their opening was regulated manually by the workers. Nowadays, on the contrary, they are moved in an oil-pressure way and they can be also controlled from the switch-board room of the plant. There are dissimilar types of turbines in the plant of Trezzo: two propeller ones and two Kaplan, which are in a position to use flows up to 30 cubic metres. There is also a cooling system able to refrigerate the different parts of the turbine to reduce its wear, the noise and the steam produced. In Taccani hydroelectric power plant there are ten alternators, of which six are on duty. These alternators consist mainly of two parts: a stator (the external fixed element) and a rotor (the internal in-motion component) to which the turbine is linked, through the shaft. Energy is produced by generators inside the alternator and then sent to the transformers. The water cycle, however, is concluded only after the restitution work. In fact, going out of the turbines, the water flows in a big tank and, through two tunnels, passing below the promontory, it‘s given back to the river stream.
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Environment safeguard
Since the construction of the plant, attention has been particularly paid to the ambient impact and to the safeguard of the landscape. The cover of the façades, in fact, had been completed in local stone (“ceppo” of Adda) for a harmonious introduction in the territory, in the same way a re-climbing escalator for fish had been created on the left riverside to safeguard the fish fauna. Also at the beginning of the 1990s, on the occasion of the renewal of the establishment, further solutions for the environment protection were studied. Moreover, it must be remembered the great importance of the River Adda, which in the past represented a considerable navigation route, such as to promote communication, whereas nowadays it constitutes an important source of “clean” energy (because the water isn‘t exposed to any chemical treatment), accompanied by the cultural and natural patrimony the river Adda offers.
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