STORAGE POWER PLANT SAMINA RESTORED AND CONVERTED INTO PUMPED-STORAGE PLANT

Autor: Roland Gruber , 22.08.2016

Storage power plant Samina in Vaduz is the Principality of Liechtenstein’s largest and most important power station. Built in the late 1940s, the facility at that time made Liechtenstein independent of outside energy sources.

Until the 1960s, it was even possible to export excess energy generated here. Although the power station has recently been providing only 12% of the country’s required energy, it still plays an important role in sustaining the basic supply. However, time has taken its toll on power station Samina. A routine inspection in 2004 revealed several faults. Medium-term action was called for, prompting Samina’s operators, Liechtensteinische Kraftwerke, to come up with a plan for the facility’s future. After intense deliberations, it was decided that Samina should be restored and converted into a modern pumped-storage power plant.

Hydropower plant Samina near Liechtenstein’s capital Vaduz was built shortly after World War II. Back then, the project was considered a huge economic effort. The decision to go ahead with this massive project was taken not only in the hope of creating jobs, but also with a vision for future generations. After all, the Samina storage power station promised Liechtenstein’s energy independence from the Austrian town of Feldkirch. As it turned out, it was even possible to export some of the energy until the 1960.

FROM THE SAMINA TO THE RHINE VALLEY
In the Principality of Liechtenstein, suitable locations for hydropower generation are few and far between. This was also the verdict of a prestudy conducted in 1946 by a team led by Dipl.-Ing. Hans Eichberger at ETH Zurich. According to the study, the country’s only suitable source of hydropower was the Samina streamlet with its tributaries. Initially, the focus was on the Samina and Rhine valleys – an idea that was later incorporated into the power plant project. The Samina valley runs parallel to the Rhine Valley, east of the “Three Sisters”, three prominent summits of a mountain range in the Rätikon region. The bottom of the Samina valley lies 850 m in elevation above the Rhine Valley. This led to the idea of crossing the mountain ridge between the two valleys and utilising the head from the Samina to Vaduz in the Rhine Valley.

HIGH-HEAD POWER PLANT WITH WEEKLY STORAGE
Based on these considerations, hydropower plant Samina was finally designed as a high-head power plant with weekly storage. The intake and storage basins were built in the Samina Valley near Steg. The water passes through a channel and penstock system to the power house. Here three horizontal Pelton turbines are available for processing the motive water. Once fully commissioned, the facility provided a capacity of 9,600 kW with an annual output of 30.36 million kWh.

SAFETY RISK AND NEED FOR ACTION
During its many years of reliable operation, the Samina power station had been inspected regularly. In 2004, the inspection revealed serious flaws in the penstock. This implied an indirect need to act in order to defuse this immediate safety risk.

REFURBISHMENT AND RECONSTRUCTION
Additional investigations showed that the machine units also needed attention. That aside, it was necessary to ensure compliance with noise emission standards at power house site in the Schwefel region near Vaduz. In summary, the cost for the projected rehabilitation work amounted to around CHF 35m. Rebuilding the power house and expanding the facility into a pumped-storage power plant with a new underwater basin and two machine units would cost a further CHF 15m. Following extensive efficiency audits, the project team in April 2009 issued their recommendation to the Administrative Board to renovate the Samina facility and to convert it into a pumped-storage power plant. The Board agreed, and after a two-year approval process construction work began in autumn 2011.

PENSTOCK REFURBISHED
When planning the project, the team also reviewed the complicated course of the old penstock. One alternative under consideration was running a sloping conduit from the Steg reservoir straight to the power house in Vaduz. As it soon turned out, however, the original course was indeed the optimum solution. “Our predecessors were very clever in bypassing all the landslide patches and unfavourable geological spots. They really did an excellent job back then,” explains Gerald Marxner, President of the Board of Liechtensteinische Kraftwerke (LKW). To the delight of the engineering team, the hillside pipework that runs along the Samina watercourse as well as the power tunnel leading to the surge chamber were both in excellent condition – another achievement of the original engineers. As a result, all that had to be done was to replace the last section of the penstock.

MODERN POWER PLANT TECHNOLOGY
Right on schedule, the the first of two identical machine units was installed in autumn 2014. With the design flow rate increased to 2,000 l/s, it was decided to install two identical twin-jet Pelton turbines by Andritz Hydro, which provide a max. flow capacity of 1,000 l/s each. At a net head of 816 m, the units each have an output capacity of 7,300 kW. One special feature is the fact that the 1,000 rpm Pelton rotors are linked directly to the shafts of their respective generators. Providing around 9 MVA, the generators were provided by ELIN Motoren GmbH. The Styrian-based manufacturer of electrical machines also supplied the two asynchronous motors that are used for operating the pumps. Providing a capacity of 6,100 kW each, they operate at a rotational speed of 2,980 rpm and can withstand an overspeed of 4,000 rpm. It was also a challenge to implement the flywheel with an additional inertia of 400 kgm2 to withstand such high overspeed. As for the main pump, the model chosen is a horizontal multi-stage pump, which has a capacity of 500 l/s and a discharge pressure of 85 bar. In late spring in 2015, the required installation work was complete and it was time to put the units into trial operation.

READY FOR THE FUTURE
The official commissioning of Samina took place on June 25, 2015 in the presence of representatives of the national, regional and municipal governments and other guests. After three and a half years of construction and a total investment of around CHF 50m, Liechtenstein’s primary power plant was ready to be connected to the grid. With its new pumped-storage plant, Liechtenstein is well equipped for a future “smart grid” scheme, according to Liechtensteinische Kraftwerke. Thanks to the separate pump and turbine circuits, the facility can react faster and more flexibly to fluctuations than large-scale facilities of the same type.

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Storage power station Samina in Vaduz (LI) has been refurbished and converted into a pumped-storage power plant. Since summer 2015, two identical turbines by ANDRITZ HYDRO have been generating the energy at Liechtenstein’s largest power plant. When required, the water is pumped uphill to the weekly storage reservoir in a separate pump circuit.

photo credits: zek