The La Coche pumped-storage hydroelectric power plant located in the Tarentaise Valley, Savoie, France, has been expanded with the commissioning of a new 240MW turbine generator unit in October 2019.

Owned and operated by state-owned Electricite de France (EDF), the existing 360MW pumped storage facility has been operational since 1976.

Preparatory earth works for the £131m (€150m) expansion of the plant was started in 2015, while the construction of the new generating unit was started in 2016.

The commissioning of the new plant, along with the upgrades to the existing pumped storage units, is expected to increase the annual generation capacity of the La Coche facility by 20% to 650GWh, which will be enough to meet the electricity needs of approximately 270,000 people in the Savoie region.

La Coche power plant expansion details

The La Coche power plant expansion involved the construction of a 240MW Pelton turbine generator unit in an outdoor power house, as well as modification to the water-intake pipeline system for the existing underground powerhouse.

The existing water intake shaft for the underground powerhouse was bifurcated with the installation of a Y-shaped connector, and a 2.6m-diameter steel penstock was installed to provide water supply to the new plant. The pipeline bifurcation work involved the digging of approximately 300m of tunnel.

Unlike the existing generating units of the pumped-storage power plant, the new unit will operate only in turbine mode without reversible pumping operations, due to the significant increase in water flow because of the melting snow upstream.

A new operation building and a 765kV transformer have also been built at the site, as part of the expansion.

Details of the 240MW Pelton turbine for the La Coche plant

A 240MW Pelton turbine generator unit supplied by ANDRITZ Hydro is installed in the new 33m-high surface power station, which is built adjacent to the existing underground power station. It is claimed to be the most powerful Pelton turbine to be used in France till date.

The 3.6m-diameter Pelton wheel weighing 15 tonnes (t) is positioned at the bottom of the powerhouse. It rotates by water jetted by five surrounding injectors at a rate of approximately 500km/h. The rotating wheel drives the main generator positioned above to generate electricity.

The main generator weighs more than 630t comprising a rotor and a stator. The stator measures 4.5m-high and 7.5m in diameter and weighs approximately 330t, while the 4.25m-high and 4.5m-diameter rotor weighs approximately 300t.

The generator components lie enclosed within an 80cm-thick reinforced cement concrete (RCC) structure.

La Coche pumped storage plant details

The pre-existing pumped-storage plant comprises four reversible Francis type turbine and pump units housed in an underground power plant. Each turbine is capable of producing up to 80MW of electricity.

Located in the Tarentaise Valley, Savoie, France, the height difference between the upper and lower reservoirs of the pumped storage facility is 900m.

The upper reservoir is the La Coche basin, which is fed by the tributaries of the Isère river, especially during the snowmelt season. Water from the upper reservoir flows into the lower reservoir at Aigueblanche dam, via the underground powerhouse.

Water from the lower reservoir is pumped to the upper reservoir for storage, during periods of low electricity demand, and when the water level in the upper reservoir decreases.

The electricity generated by the facility is evacuated to the national grid via an onsite switchyard.

Contractors involved

ANDRITZ Hydro was contracted to supply the 240MW Pelton turbine generator unit for the new plant in 2016.

Vinci Construction was engaged for the tunnelling work, while Franki Foundation, a subsidiary of Fayat Group, was responsible for laying the foundations for the new plant.

ADC, another subsidiary of Fayat Group, was contracted to provide heavy-lifting equipment during the plant construction.

Royal SMIT Transformers, a subsidiary of SGB-SMIT Group, supplied the transformer for the La Coche power plant expansion.