Poschiavino – Villa di Tirano Power Plant

Hydroelectric power station localized on the right bank of the Adda River near the Poschiavino tributary in the Municipality of Villa di Tirano in the Province of Sondrio. It taps the waters of the stream of the same name, which come from the restitution channel of the Enel Green Power station.

The water intake, a modest amount and completely underground, is comprised of a funnel connector able to convey the waters of the surge channel into the penstock. The latter, also underground, was constructed with boxlike prefabricated elements made of reinforced concrete, 2500 x 2500 mm in size, covered internally with liners; it extends in a crimp embankment to the Poschiavino stream at 1,092 m with a constant drop of 0.638% and a maximum drawing capacity of 9500 l/s.

The main building is partially underground with the relative surge channel. However, particular care was given to the architectonical aspect of the outer parts of the building, developed in two main volumes: one by the semicircular form where the transformers and the command rooms housed and the other a squared base, which houses the machine room and the electromechanical parts.

The generator group is comprised of a Kaplan turbine with a vertical axis, bump-mounted, which produces on average 4 Mw annually, with a nominal drop of 12.62 m.

The distinctive trait of this plant is the presence of a piezometric tower, in adherence with the main building, functioning as an “expansion tank”. This structure, constructed completely in exposed reinforced concrete, has a base dimension of 6.20 m x 5.05 m and has a total exterior height of 9.75m.

Particular attention was given both in the planning phase as well as in the positioning of the penstock, particularly in correspondence with the railway station (Sondrio–Tirano line), which required building an onsite product and the use of a pipe jacking technique in order to place the conduit under the railway line.

Particular attention was also requested for the implementation of the restitution channel of the turbine feedwater; in fact, it was necessary to erect a section of the provisional embankment as work was being performed near the Adda River and at a lower level than the streambed.

Another distinctive trait of the plant is the covering of the main building, constructed in metal woodworking and completely removable in order to mount and eventually remove all the mechanical equipment.