Community officials in the Pitztal valley in Tyrol, Austria, put their faith in hydroelectric power. Recently, the new St. Leonhard power station was completed.
In co-operation with their partners, the community in the upper Pitztal valley was able to finalise the project within 17 months. In average years, the new showcase plant will generate nearly 18 GWh of clean electricity from the region for the region. It is equipped with two cutting-edge machine sets rated at 2.4 MW each. A pleasant detail is that the 13 million Euros estimated cost was reduced by about 2 million Euros in the end.
It was about six years ago that people in the 1,500-strong community of St. Leonhard in Pitztal, Austria, first came up with plans for a new hydroelectric power station. At that time it was far from certain that the Pitze River actually has the conditions required for economical power plant operation. In 2011, civil engineers Eberl Ziviltechniker GmbH in Innsbruck were commissioned to conduct a feasibility study. “The hydrological situation at the Pitze obviously posed a central challenge. For its protection, a minimum flow similar to natural conditions had to be taken into account.”
Following the positive assessment of the study, preparations substantiated and starting in 2012, the project was pursued with some vigour. Implementation nevertheless took another three years. In March, 2015, the authorities gave the project their go-ahead. A few weeks later, local politicians broke the ground for the new power station.
EUROPE’S LARGEST COANDA SYSTEM
The St. Leonhard hydroelectric power station is a diversion plant. Its quality results from the finely tuned technical layout with regard to the difficult hydraulic conditions on the one hand and from the high material and design quality of its technical equipment on the other. The concept is classically simple: The works water is retrieved through a lateral intake and then led through a 3.8 km penstock to the power station located at an altitude 139 meters lower. There, it is processed in two identical machine sets and then led back to the Pitze’s bed.
It is a matter of course that a lot of experience and knowhow went into each part of the system and that the technical finesses are in the details. The path of the works water starts at the baffle preventing coarse debris from entering the intake. After passing the coarse screen, the water is conducted across a Coanda screen that is indeed unparalleled. 20 Grizzly Optimus modules made by Wild Metal, an industry specialist from South Tyrol, were lined up to be able to collect and filter the entire nominal discharge amounting to 4,000 litres per second. This makes that Coanda screen the largest in all of Europe. This is confirmed by Franco Schlegel from HTW Chur technical and economic university who has been dealing with the subject of optimising Coanda screens as part of his research activities. It is, however, not so much the size that matters but the system’s functionality. Coanda screens from Wild Metal are among the most well-established on the market for years. Even in difficult conditions such as sharp winter frost, they are guaranteed to effectively filter solid matter out of the water. For the new power station in St. Leonhard, the narrowest gap width was selected, a mere 0.3 millimeters, for very good reasons. The Pitze River carries traces of glacial sediment. The narrow gap width also prevents microorganisms effectively from being drawn in. The Wild Metal Coanda screen renders the use of a sand trap obsolete. This is fundamentally a low maintenance system. For cases requiring interventions, two specifically designed maintenance accesses have been installed.
HYDRAULIC STEELWORK DESIGN FACILITATES HARMONIOUS INTEGRATION
Generally, all of the hydraulic steelwork equipment of the power station was made and installed by Wild Metal. The most striking feature is the weir shutter. 16 meters wide and 2.5 meters tall, it was shipped from the factory in Ratschings, South Tyrol, Italy, in two equally-sized parts and installed using a mobile crane. The steel colossus weighing 18 tons withstanding enormous forces can be opened and closed using two laterally mounted high-performance hydraulic cylinders. The weir system was designed to withstand floods with magnitudes expected to occur only once in a century.
A significant aspect in the planning of the water catchment was the attempt to harmoniously integrate the traverse structure with the scenery of the upper Pitztal valley. “We tried to stay as close to the foundation level as possible. During construction, the construction pit at the catchment was nine metres deep, ranging down to the foundation excavation. The entire catchment structure is not protruding much at all. This is not least owed to the hydraulic steelwork equipment design. Wild Metal has been investing much energy in its continuous improvement”, says Stefan Thomaset. For planners and developer, the ecological approach of the concept was also central. This is why the catchment was situated so that another stream feeding the Pitze was not integrated. It flows into the river bed immediately downstream from the catchment, enriching the natural residual water.
COMPLEX ROUTE PLANNING
All in all, some 2,600 m3 concrete was used to build the water catchment, with an excavation volume of about 10,000 m3. From start to finish, construction work took more than 17 months. Naturally the most complex task was the installation of the penstock. Due to the uncommonly narrow valley bottom, several tributary streams, landslide zones, existing installations such as avalanche protection structures and geologically problematic areas required profound route planning for the 3.8 kilometer penstock. The developers selected FLOWTITE DN1400 GRP pipes from Amiantit. They were supplied by Amiantit’s Austrian representative, Etertec.
A power cable and fiber-optic cables were installed to run parallel to the penstock. “This will put the community of St. Leonhard in the position to supply communal buildings or infrastructures with electricity if needed. For the time being, however, all of the generated electricity is fed to the public network”, says Thomaset.
TURBINE TECHNOLOGY OUT OF TYROL
In view of the 3.8 kilometer length of the penstock, pressure shock resistance was an important consideration in the planning work. Geppert based in Hall, Austria, made and supplied the turbines. Consequently, they also performed these simulations calculating the control cycles required at the pipe break flap and at the inlet nozzles to absorb a 2.6 bar maximum pressure shock.
The experienced hydroelectric power generation specialists based in Hall won the contract to supply the entire electromechanical equipment of the power station. The operators had selected two identical vertical six-jet Pelton turbines to form the heart of the installation. The turbines have been designed for a 128 meter net head height and a nominal discharge capacity of 2 cubic meters per second each. They rotate at 500 rpm. A strong point of the 2.4 MW turbines is that they can remain on grid even in low part load operation. Each turbine can be operated to a 69 liters per second minimum. Between them, the turbines provide a 4.34 MW bottleneck performance.
TOP GENERATOR EFFICIENCY
The St. Leonhard community representatives were aware of the fact that current electricity prices caused considerable pressure on the budget. They nevertheless had no plans to compromise the equipment’s quality by cutting costs in the wrong places. As with the turbines, they shortlisted nothing but top quality when selecting the generators. They decided in favour of the tried and tested technology supplied by generator specialist Hitzinger based in Linz, Austria. Vertical synchronous generators specifically designed and dimensioned for the location’s requirements were installed. These generators are not only equipped with cutting edge water cooling but also feature auxiliary heating facilitating a fast and problem-free system start following possible standstills during the frosty months. Furthermore, the generators are equipped with generator brakes and high-grade sleeve bearings. “Hitzinger has taken our specific requirements into account in every detail. This resulted in practically fully customised machines that reach an efficiency factor of 97,8 percent under full load”, says Stefan Thomaset.
ROBUSTNESS A HALLMARK
The synchronous generators weigh 21 tons each. Their apparent power rating is 2,700 kVA. They are part of the biggest Hitzinger generator model series. For some years now, the Upper Austrian manufacturer has expanded its three-phase machine portfolio at its upper end. Hitzinger has been supplementing its tried and tested range of smaller machine types by synchronous generators with power ratings ranging all the way to 6 MVA. Hitzinger design engineers managed to transfer the numerous quality benefits of the smaller models to the more powerful series as well. These generators excel not only with their high smoothness, speed stability and efficiency but are also known to be extremely robust. Hitzinger engineers say that they were able to give the generators this property because of the many things they have learned from the extreme conditions under which marine and off-shore generators are operated. They also dimension the electromagnetic aspects of the generators very conservatively so that there is still a wide margin left to prevent Hitzinger generators from overheating. What made the two generators for the St. Leonhard power station special is a test scenario the industry leader does not often encounter. “We had the opportunity to perform alternating tests with two absolutely identical machines from our big series and from the same batch on the test bed, effectively testing them against each other. This has provided us with some very interesting insights and at the same time confirmed the quality we are committed to”, says Hitzinger’s Dr. Daniel Huber. The test results also provide convincing evidence that this Austrian generator manufacturer can now also supply top-quality vertical sleeve-bearing generators. This is new.
COMPLEX WEIR WATER SYSTEM
In order to comply with the quality objective ordinance on site, a comparatively high amount of weir water was required. From April to November, it amounts to 440 liters per second as a low water base. This is supplemented by requirements that need to be met precisely for weir water quantities of 26 to 55 percent of the arriving water flow as a dynamic weir water volume. The largest portion of the basic amount of the weir water is led through the fish pass. Another part is led through a DN300 doting duct at the entrance to the fish pass providing the attraction current for the fish. At the irrigation channel, water is constantly fed to the Pitze’s bed at 40 liters per second. This was necessary as in this area fish can swim downstream, landing soft and without injuries in a water cushion.
17 PERCENT LOWER COSTS
Following first dry tests of the turbines in July, 2016, Geppert engineers officially turned on the turbines with Pitze water three months later in mid-October. All work on the new power station was finally concluded within 17 months. The community’s representatives were particularly delighted to learn that the project’s 13 million Euros estimated costs were reduced by about 2 million Euros. Particularly in times of rock bottom electricity prices, this proves the economic responsibility of the community. “During the first years, we do not expect the installation to generate profits. I am convinced, though, that coming generations will profit and appreciate our decision”, says St. Leonhard mayor, Elmar Haid, adding “The new power station also contributes to reducing our valley’s dependency on energy imports.” All in all, the power station is expected to generate some 17.6 GWh of clean electricity in average years. This is sufficient to at least statistically make the Pitztal winter sport and hiking region energy independent for the coming decades.