Taking only eighteen months to construct, the newly erected hydropower plant Heidadorf in the Swiss community of Visperterminen was officially inaugurated in October 2018.

The two-stage facility with a pair of independent turbine houses ­utilises the energy potential of the nearby brook Gamsa with an impressive total head of almost 1,000 m. As a positive side effect of the CHF 16.5m project, a considerable portion of the drained water is reused to irrigate the surrounding farmland along the pipe route. The legal framework was established with the foundation of hydropower plant Heidadorf AG, in which the ­community of Brig-Glis and operator EnBAG AG each hold a 40 per cent share. A further 18-per cent share is held by the community of Visperterminen, with local energy supplier EW Riedbach holding the remaining two per cent. Both plants were equipped with powerful latest-generation technology. The two four-jet turbines for the turbine houses in Chrizji and Stundhüs were provided by Andritz Hydro, whereas Austrian generator manufacturer Hitzinger was contracted for the design and delivery of the two synchronous generators. In a normal year, the new two-stage hydropower plant in Heidadorf generates a total of around 16 GWh of clean electrical energy.

Situated at the entrance of the Visper valley in the canton of Valais, the mountain village of Visperterminen is known for its popular “Heida” variety of white wine. It is to this fact that the village owes its informal second name of “Heidadorf”. The sun-kissed rows of vines in this community with a population of around 1350 grow at an altitude of between 600 and 1200 metres above sea level. This and the ambient topography together provide ideal conditions for generating hydropower. First steps in this direction were already taken in the early 1900s with the construction of an irrigation tunnel for the dairy farms in the higher Alpine regions. It took almost 20 years to complete the 2.65 km conduit, which is still transporting the waters of the Gamsa stream through the mountainous rock. Shortly after the conduit breakthrough in 1916, hydropower plant Riedji was taken into operation. This marked the first point where the water was utilised before being drawn again and fed to the turbine of hydropower plant Ackersand further downhill.

New construction with two turbine houses
Once the operating licence for hydropower plant Riedj ran out, initial planning for a replacement of the old facility after more than 90 years of operation began in 2009. Energy provider EnBAG from Brig-Glis was entrusted with overall responsibility for the entire Heidadorf power plant project, from planning to final implementation. As for the construction of the new facility, the future owners agreed on an adapted utilisation concept consisting of a surge chamber and two independent turbine houses. The first turbine house was constructed uphill in the small village of Chrizji, the one further downhill in the valley was installed on a dedicated site in the district of Stundhüs.
EnBAG’s project manager, Jonas Kalbermatten, says the approval process was rather uncomplicated: “We were able to find satisfactory solutions for everyone affected by the project, including the landowners on whose properties the penstock will be installed. Generally speaking, the citizens and municipal government have been very supportive of the project. And since the construction also improves the irrigation along the outflow reach, the environmental agencies also waived their veto right.” Several work teams were set up to implement the project. Six construction firms provided the professional building construction and civil engineering work.

Kick-off to construction in summer 2016
Summer 2016 marked the kick-off to the construction work, starting with the complete refurbishment of the forebay in the Nanz valley. A hydraulically controlled weir baffle is used to dam up the waters of the Gamsa, with the motive water discharged through a Tyrolean weir. To ensure ecological consistency, a water bypass was installed by the weir, which provides a constant year-round discharge volume of 78 l/s. Immediately after passing through the Tyrolean weir, the water is transported to an open desilter consisting of two reservoirs, where any sediments carried along by the mountain stream are allowed to settle. Finally, the silt is returned in a steady stream to the natural watercourse through a flushing gate. Thanks to the two separate reservoirs, the power generation process is entirely unaffected by the flushing. After desilting, the water is transported straight to the non-pressure tunnel through a stretch of GRP pipework.
A surge chamber was installed behind the non-pressure tunnel to enable proper regulation of the machine unit at the Chrizji facility. Of the total design flow rate of 875 l/s, up to 225 l/s are diverted to irrigate the surrounding Nanz valley farmland. An additional self-cleaning Coanda trash rack was installed at the forebay to remove the frequently accumulating larch needles and driftwood. The forebay also marks the starting point of the 3.8 km underground penstock. Due to the challenging geological conditions along the pipe route, the power drop was implemented in the form of ductile cast-iron pipes throughout.

Reliability in the shape of machines
ANDRITZ Hydro was able to win the contract for the complete electromechanical and secondary equipment for both turbine houses. Each of them was equipped with a four-nozzle 1,000 rpm vertical Pelton turbine. The uphill Chrizji turbine house has a design flow rate of 650 l/s and a net head of 532 m that can be utilised for hydropower generation. When the full water volume is available, each of the machines can achieve a maximum bottleneck capacity of 3,110 kW. In the event that the Chrizji turbine needs to be shut down for technical reasons, a bypass system kicks in within seconds to divert the motive water. The turbine at the downhill turbine house in Stundhüs can utilise a 600l/s design flow rate with a net head of 450,2 m. Under ideal conditions, this machine has a bottleneck capacity of 2,430 kW. The jets of both machines are controlled hydraulically, with their free-standing housings ensuring optimum accessibility for maintenance purposes. In keeping with the technical state of the art, energy production at both turbine houses is fully automated.

Custom tailored generators from Linz
Where the generators are concerned, the operators’ demands were just as exacting as with the turbines. Austrian-based industry specialist Hitzinger was an obvious choice as supplier. For more than 60 years the Linz-based generator manufacturer has been providing technically refined three-phase hydropower generators that have won top ratings in the industry the world over. This is due, for the main part, to the bespoke design and the extensive know-how that goes into the construction of the machines. No Hitzinger generator leaves the production facilities in Linz without an individual customer number. This means that each and every generator is fully custom tailored to its purpose, location and individual customer requirements. As a result, the entire machine design is fine-tuned as needed, from its magnetic characteristics to the insulation system and the proper iron-to-copper ratio. One key advantage is the ability to cooperate closely with the steel conglomerate VOEST, which also happens to be headquartered in Linz. This allows Hitzinger to make use of the latest-generation high-performance steels, which ensure less attrition and greater robustness than other metals. The specific types of steel that Hitzinger uses for its generators are resistant against extremely high temperatures.
Two additional points in favour of Hitzinger generators are their outstanding ability to sustain high rotational speeds, and their extreme running smoothness, which typically keeps vibrations to an absolute minimum. This is where customers benefit from Hitzinger’s experience in ship generator engineering – a business segment where low-vibration qualities are crucial.

Highly efficient energy transformer
During the engineering stage, special care was taken to maximise the efficiency of the synchronous generators for the Heidadorf hydropower plant project. Both machines run at a rotational speed of precisely 1,000 rpm. The turbine runner was mounted directly onto the generator shaft, and each of the machines was fitted with highly stress-resistant slide bearings. The generator at the turbine house in Chrizji was designed for a rated apparent power of 3,350 kVA and has a maximum output efficiency of more than 98 per cent under full load. The generator at the Stundhüs turbine house has a rated apparent power of 2,600 kVA and achieves an output efficiency of 97.36 per cent when operated under full load. To ensure optimum operating temperatures during the intensely heat generating energy production process, both generators are cooled by a water circulation system that uses an air-to-water heat exchanger. Both generators are from the larger-sized product line that Hitzinger has been marketing with great success for many years. Around ten years ago, Hitzinger was known primarily for its generators in the lower-performance category of up to 1 MVA. Today, however, the Linz-based industry specialist also offers generators with a performance of up to 4 MVA. Still, these ‘big boys’ come with all the quality features that their smaller siblings are known for. They are likewise precision tailored to their respective operational requirements.

Electrical energy for 4,000 households
On June 20 last year the turbines of hydropower plant Heidadorf were spun up for the first time. The official inauguration was celebrated only several months later, in late October. In their official speeches at the ceremony, Rainer Studer, Visperterminen’s President of the local Council, and Renato Kronig, President of Heidadorf AG’s Board of Directors, stressed their delight with the fact that the project was completed on time and without any accidents. In his interview with zek, Project Manager Kalbermatten offered a similarly positive summary: “Despite a very dry summer in Valais, we had extensive rainfall in the autumn. That made it possible to even exceed the manufacturer’s expectations during the first six months of operation. By the beginning of December, the two turbine houses had already generated a total of around 10 GWh.” In a normal year, the power plant generates around 16 GWh of electrical energy, which is fed into the public grid. This way, hydropower plant Heidadorf covers the annual energy requirements of around 4,000 average households. In total, the Heidadorf AG invested around CHF 16.5m in the construction of the facility.