Trust in the solid power unit of the cavern hydropower plant

AXPO TRUSTS IN THE SOLID POWER UNIT OF THE CURNERA CAVERN HYDROPOWER PLANT

For many years, the hydraulic pres- sure in the works water conduit between the Curnera and Nalps reservoirs in Grisons in Switzerland had to be lowered via a pressure reduction regulator. The installation of a new Curnera hydroelectric unit 250 metres into the mountain now enables this hydroelectric potential to be exploited. To this end, the Vorderrhein KVR power generation group, of which Axpo has a majority holding, integrated a WWS Francis spiral turbine to drive a high-power, high-quality generator manufactured by Hitzinger in Linz. In a regular year this reliable combination of machines guarantees the production of around 10 GWh - enough to supply approximately 3.000 average housholds with green electricity.

The works water is transported through a complex 3.7-kilometre system of pipes owned by the Vorderrhein power generation group – from the upper ‘Curnera’ reservoir down to the lower ‘Nalps’ reservoir and navigating a drop of 40 – 75 metres. In 2016, KVR devised a new concept to exploit this previously untapped energy potential. The new small-scale hydropower system was installed in the vane chamber that originally also housed a pressure regulator. The Axpo project team, responsible for operation of the plant cascade, faced several tough challenges, not least those caused by the extremely cramped working conditions and restricted cavern accessibility at around 2,000 metres above sea level – and particularly the logistics of bringing in the components for the power plant infrastructure. Ultimately, a temporary cable car relay had to be set up for the purpose. An electricallypowered towing unit and a carriage wagon were installed to manoeuvre the 6-ton generator into the tunnel via the cavern opening. The extremely limited space available in the vane chamber 250 metres into the mountain made installing the individual parts of the machine very challenging. However, despite all difficulties, work was completed without any hitches. UPPER AUSTRIAN TECHNOLOGY BEATS AT THE CORE After commencement of installation in the narrow window afforded last summer, the plant went into trial operation in November 2021, and in the same year was put into regular service. The small cavern now houses a Francis spiral turbine manufactured by WWS and built for a nominal power output of 2.5 MW. As well as the turbines, the new generator at the Grisons power plant was also produced in Upper Austria. The rotor of Hitzinger’s synchronous generator is also directly connected to the turbine runner. Set up for 900 V, the generator achieves a power output of 2.5 MVA and the rotor turns at 750 rpm. In an average year, the new Upper Austrian machine group can be expected to deliver 10 GWh of green electricity to the grid.

The 2.5 MVA Hitzinger generator has been installed in the old vane chamber.

photo credits: KVR

DESIGNED FOR A LONG LIFE The operating company boasts a wealth of experience across the entire spectrum of hydropower projects, from small to large, and quality was its number one priority when choosing this machinery. After all, KVR invested around 3 million CHF in a small-scale hydropower plant that needs to be as self-sufficient and maintenance-free as possible due to its extreme inaccessibility. The choice of

The rotor is integrated in the stator.

photo credits: KVR

turbines and generator are seen as guarantees for the requisite durability and reliability. Rather than being built for years of operation, Hitzinger generators are made to serve for decades – officially, for a working life of 35 to 40 years. One of the oldest hydropower generators built by Hitzinger – and one still in operation – has been running for over 70 years. The secret of ‘a long generator life’ is a far-sighted, simple approach to the use of metal housing and magnetic set-up. Hitzinger generators remain cool, or moderately warm, when other comparable machines would be getting hot.

BACK STORY TO A SUCCESS STORY There are several other reasons for Hitzinger generators being amongst the most commonly chosen solutions for small-scale alpine hydropower plants; one key explanation being that the generators are custom-built solutions from the Austrian ‘steel city’ Linz. Every single machine is devised to meet precise customer demands in terms of design, performance and in-situ requirements. Hitzinger has been developing and refining its own software for decades. All the available parameters are integrated, before the programming, electrical and mechanical set-ups of each machine are precisiontuned. The result is a unique, tailor-made generator. In the case of the new Curnera power plant it was the ultimate location of the generator at around 2,000 metres above sea level that played the major role in the overall design of the unit. Further qualitative benefits of Hitzinger generators include the relative lack of noise production, limited emissions, high-rev reliability and, of course, their efficiency. In an age of expensive electricity, it is becoming increasingly important to improve performance behind the decimal point. Hitzinger constantly processes market feedback and observes trends to guarantee on-going development. The Curnera power plant machine is yet another reference project for the Linz manufacturer in a very competitive Swiss hydropower market.

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