The Steineraa power plant in the Canton of Schwyz officially commenced operations with the festive inauguration in September of last year. Behind the 12 million Swiss franc project is ebs Energie AG (ebs).
Which was not only able to realise the ambitious power plant project within the prescribed construction schedule, but also within the targeted costs framework. For the technical equipment, the operators primarily relied on the know-how of the renowned hydroelectric power specialist Troyer AG from South Tyrol, which was responsible for the entire machinery, as well as for the control and process control engineering equipment of the power plant. The power plant generates around 5 GWh in a standard year with the new 4-nozzle Pelton turbine. This makes it possible to supply 1,250 households with clean, regional power.
The vote was a clear signal: in 2009, around 97 percent of the residents of the Schwyz district spoke out in favour of awarding ebs with the concession for water usage on the Steineraa, a mountain torrent in the Schwyz district. The vote had become important to the extent that several private operators, who in some cases had already operated old plants in need of refurbishment on the body of water, had also worked on plans for hydroelectric power projects. “The district decided at that time that only a single concession would be granted. And this ultimately went to the ebs, which also belongs to the district. The private owners were then paid out, and supported by the strong vote, we then commenced with the subsequent planning for a single power plant in this segment of the body of water”, says Claus Jörg, technical manager at ebs, and at the same time project manager of the new power plant Steineraa.
FOUR-YEAR APPROVAL PROCEDURE
The Steineraa has its source in the municipality of Rothenthurm and, over its around 16 km long course, flows through the municipalities of Sattel and Steinen, to then finally flow into Lake Lauerz. The catchment area amounts to approx. 20.8 km2. A highly interesting body of water for water power utilisation. However, profound planning and intensive consultation with the authorities was required to finally receive the green light for the realisation of the project. “Especially the negotiations with the environmental groups weren’t easy. In the end, the entire approval procedure took four years before we had the approval on the table”, says Claus Jörg. Today the operators are proud of the high ecological compatibility of the new system. This is ensured on the one hand by the ecological flow of 250 l/s, which is consistently discharged at the catchment, and on the other hand by the compensating measures that provided for a fish ladder to be constructed upstream. This now guarantees the passage for fish over an existing 1.20 m high step in the headwaters of the Steineraa.
PENSTOCK TUNNEL AS A CHALLENGE
The ground-breaking ceremony took place on 19 November 2014, and construction work could commence. These ultimately took more than two and a half years before the turbine was set in motion with water from the Steineraa. As expected, the realisation of the penstock turned out to be the most difficult part of the construction work. Especially the construction of the around 200 m long penstock tunnel which starts directly at the catchment area, turned out to be a real tough nut to crack. Claus Jörg: “Following the first geological expert opinions, we expected to find relatively compact rock. However, instead we found a great deal of unstable loose rock. The construction company thus often had to change from the conventional blast heading to the more complicated loose rock heading. The securing measures were of course also much more complex. The rock was anchored with long iron rods and a 30 cm thick layer of shotcrete.”
The penstock, consisting of ductile DN800 cast iron pipes, was laid over a total length of 1,900 m. The greater part of the pipeline was laid in the neighbouring Rossbergstraße, which primarily presented construction logistics challenges. Especially in the summer months of 2015, the road had to be kept open for traffic in parallel with the construction works by means of implementing an alternating one-way routing in both directions. “The solution was that the thoroughfare was always open, especially for service vehicles, special transports, etc.”, explains Claus Jörg.
SAND TRAP CANCELLED
The new Steineraa power plant is principally a high pressure power plant that uses a natural drop step of 207 m. To this purpose, a water catchment with side water extraction was built on the municipal territory of Sattel, which, despite extensive construction measures, could be kept relatively compact. The reason for this is primarily found in the absence of a sand trap. Instead, subsequent to the extraction, a three-chamber system was implemented, with which the water is calmed and ultimately purified of sediments with a Coanda grill of the type Grizzly/Wild Metal. “In this way we saved ourselves a 40 to 50 m long sand trap. We found this solution very convincing”, says Claus Jörg.
Subsequent to this, the water finds its way to the pressure pipeline, and then encounters the turbine around 200 m deeper in the turbine hall. The machinery control centre was built in the district of Steinen, not far from the bank of the Steineraa. The turbine-propelled water is fed back into the stream bed of the mountain torrent via a short return. The generated electric energy is fed into the 15 kV-grid of ebs through a transformer station.
EFFICIENT HYDROELECTRICAL USAGE
For the electromechanical equipment of the new ebs power plant, the operators secured the services of the well-known water-to-wire specialists Troyer AG from Sterzing in South Tyrol. “We were already familiar with the Troyer company previously and knew that they deliver very good quality. We were therefore also very pleased that Troyer was able to make us an excellent price offer”, according to the project manager. In concrete terms this meant a vertical axis, 4-nozzle Pelton turbine was produced for the new power plant in the factory in Sterzing, featuring a spiral distribution piping with internal servomotors for the injector needles. The runner of high quality X4 CrNi 13/4 steel with a diameter of 995 mm was milled from a monoblock, and thus demonstrates excellent strength values as a result. The runners from Troyer AG generally score points with modern design, which guarantees highly efficient hydroelectric usage of the water.
However, not only the mechanical engineering “hardware”, but also the “software” in the form of the complete control system and the integration into the higher level control technology of ebs convinced the experienced operators from the Canton of Schwyz. User-friendly surfaces for SCADA systems have long been seen as trademarks of the software specialists from Troyer AG. The recording, representation and archiving of process variables, as well as the operation, alarm function and remote maintenance are of course optimally integrated today.
STANDSTILL IN WINTER
The turbine runner is directly coupled with a modern, brushless synchronous generator via a vertical shaft. When in operation, the rotor of the 13 ton energy converter is driven at 750 RPM. The water-cooled synchronous generator is designed for an output of 2,500 kVA.
The turbine was tailored to the prevailing hydraulic conditions. designed for a net head of 198.7 m and a rated flow of 1,250 l/s. Under full load, the machine achieves a power output of 2,017 kW. “We have now already tested the turbine several times under full load conditions and are absolutely satisfied with the performance. The guaranteed efficiency values were clearly achieved”, Claus Jörg is pleased to announce. In accordance with the technical report, the operators from ebs anticipate 47 full load days annually. Seen from the perspective of an annual average over many years, however, the experienced power plant specialists from Switzerland anticipate only approximately 178 production days. In contrast, around 140 arithmetical standstill days are anticipated. “We presume that we will often have to shut down the plant over the winter months. Luckily, the turbine demonstrates such good ranges of efficiency that we can still generate electricity with low water quantities as of approx. 100 litres and remain on the grid with the plant”, according to the Technical Manager of ebs.
POPULATION SUPPORTS THE PROJECT
On 16 September 2016, the persons responsible were able to carry out the festive inauguration of the new Steineraa power plant. An invitation was given for an open house one day later, which attracted many interested parties to the new green power plant. Today, project manager Claus Jörg can draw an all-round positive summary of a project that posed considerable structural and logistical challenges: “We had a big construction site here. This is also shown by a look at the figures: The total excavation material, for example, amounted to around 27,000 m3, while approx. 3,300 m3 of concrete in total were installed. The great thing was that we enjoyed support from the population, which completely supported the project. Luckily there were no accidents of any kind, and the project was generally very professionally carried out by the companies involved.”
POWER FOR 1,250 HOUSEHOLDS
The costs estimate for the new Steineraa power plant was initially 13.5 million CHF. That the final bill was then significantly lower was a slight surprise. “Although the construction of the pressure tunnel turned out to be much more expensive than anticipated, we were ultimately able to conclude the entire project for 12 million CHF. Not least thanks to the at that time very favourable exchange rates, we saved around 1.5 million CHF”, the project manager summarises. Thanks to the funding from the KEV (feed-in remuneration at cost), the economic efficiency of the power plant is in any case secured. ebs has relied entirely on domestic resources for years, especially on hydroelectric power. With its power plant complex, the company today has an installed total output of more than 60 MW. This means that around 220 GWh of power can be generated annually. The new Steineraa power plant contributes 5 GWh in an average year. This at least means that 1,250 households in the Schwyz district can be supplied with green energy.