Obervermunt II plant
Underground Mining Power station construction
VIW AG built the pumped storage plant "Obervermunt II" (OVW II) between the Silvretta and Vermunt reservoirs. The pumped storage power station uses the gradient between the Silvretta and Vermunt reservoirs for pumped storage and plays a key role in increasing the efficiency of the use of hydropower by VIW AG. Two highly flexible sets of machinery with a wide regulation range were quickly installed with separate turbines (360MW = 2 x 180 MW) and pumps (2 x 160 MW).
The Obervermunt II plant was built as a parallel plant to the existing Obervermuntwerk (OVW). With the construction of the OVW II, a new headrace tunnel was constructed for the existing Obervermunt plant and the existing above-ground pressure pipeline removed as a compensatory measure. Main system components:
The approx. 3.0-km upstream pressure tunnel of the Obervermunt II plant (Silvretta tunnel) runs downhill from the Silvretta intake structure at an inclination of approx. 9% to the beginning of the armoured pressure shaft. Access to the Silvretta tunnel is provided via an access tunnel of approx. 510 metres.
Roughly 500 m before the penstock with its 48-degree angle, the 1300-m Obervermunt headrace tunnel (connection to the existing plant) branches off the shared pressure pipeline, which is in places constructed as a tubular tunnel.
60 metres after the junction to the Obervermunt pressure tunnel, a connecting tunnel to the upstream Krespa surge tank is connected to the Silvretta tunnel. The 300-m-high vertical shaft, which empties into the upper surge chamber, connects directly to this. This upper chamber was accessed via the access and ventilation tunnels (foxhole tunnels).
The feed water is routed via the distribution pipes attached to the Silvretta penstock to the two machine sets of Obervermunt II plant, located in the underground powerhouse (machine cavern and transformer cavern). Access to the powerhouse is provided via an access tunnel of approx. 810 metres. Construction of the powerhouse itself required the excavation of approx. 110,000 m³ of rock (machine cavern: L x W x H = approx. 120 x 25 x 39 m).
The underwater flow discharges through the outlet structure into the Vermunt reservoir.
All excavation work was carried out conventionally using blasting; only in the case of the surge tank was raise boring initially required to create a spoil shaft.
The intention was for the aggregates for the concrete for Obervermunt II power station (approximately 165,000 m³) to be derived as far as possible from the excavated material. For this measure, a material processing plant and a concrete mixing plant were purpose-built in the Vermunt area.
Residential camps were set up around Silvretta to accommodate the workers, and existing houses in the village of Silvretta were also used. In addition, a canteen was built at the Madlenerhaus.
In the winter months, the access road to the construction site (Silvretta High Alpine Road) was blocked. To supply the construction site, a materials cableway was built from Partenen to Vermunt, passenger transport made use of the existing Trominierbahn.