Refurbishment of Maroggia hydropower plant

Maroggia hydropower plant exploits water contributions of Maroggia river tributaries by means of three intake works in Valle Laresa, Val di Mezzo and Val Vignone, in the municipalities of Berbenno and Buglio in Monte (Sondrio province).

The derived flow rates are conveyed by a pipe which connects the three intakes to a forebay, built immediately downstream of Val Vignone intake.

The steel penstock, about 2.7 km long, starts from the forebay and conveys the flow rates up to the powerhouse located upstream of Ere and Ronco residential areas.

The building of the powerhouse feeds a two-jet Pelton turbine directly coupled to a synchronous generator.

Finally, water is returned to the Maroggia river through a short tailrace channel.

The plant went into operation at the end of 1998. Find out Frosio Next’s contribution to the realization of the plant!

During the first years of operation, the plant was affected by both, clogging of the intake works in Val Vignone and Val di Mezzo, related to the abundance of solid transport of medium-sized material (pebbles and gravel) due to floods, and filling and clogging of the forebay and of the mechanical parts located in the powerhouse, such that the refurbishment of the plant was unavoidable.

In order to improve the hydraulic operation conditions of the intake works in Val Vignone and Val di Mezzo, the original intake grids were replaced by new Coanda-type grids, named after the discoverer of the hydrodynamic effect on which it is based.

The screen uses the Coanda effect, a phenomenon exhibited by a fluid, whereby the flow tends to follow the surface of a solid object that is placed in its path.

The mesh wires are held horizontal and are of triangular section. The gaps among the wires are normally less than 1 mm wide.

The Coanda grid uses the surface tension properties of water capturing the liquid and moving gravel and pebbles downstream due to its steep slope.

In addition, the new Coanda grids have been protected by additional steel grids.

In 2001 Frosio Next provided the design and the construction supervision for the reconstruction of Val Vignone intake, replacing the original (inefficient) Tyrolean intake with a Coanda screen, one of the first applications in Italy. Besides the improvement of the intake efficiency, the interventions carried out on the intake structure made it possible to guarantee the release of the prescribed environmental flow, which up to that moment was hindered due to the clogging of the relative hole in the intake structure.

Subsequently, about 20 years after the first intervention, further refurbishment interventions were carried out which included, among other works, the replacement of Val Vignone and Val di Mezzo intake grids, the replacement of machine and penstock valves and turbine runner. On this occasion, Frosio Next followed the final and detailed design, work supervision and assistance during test and commissioning.

Find out more downloading our brochure!