Limberg II – the ‘invisible’ plant

1 April 2010

Construction is well underway at Limberg II, the Euro 365M (US$467M) peak-load pumped storage project that, upon completion, will increase capacity at Kaprun from 353MW to 833MW. The project is located in the southern part of the federal province of Salzburg, north of the Glockner Group in the Kaprun Valley, near the junction of the three regions of Salzburg, East Tyrol and Carinthia. It will operate on the existing Mooserboden and Wasserfallboden reservoirs in the lower Kaprun valley. The reservoirs have a live storage of 81.2 and 84.9Mm3 respectively, and a mean level difference of 366m for pumped storage. The power conduit between Mooserboden and Wasserfallboden will have a maximum flow of 140cm/sec The project includes 7.5km of road tunnel and escape tunnel; a cavern measuring 62m x 25m x 44m; a 4km-long, 7m-diameter headrace tunnel; a 750m-long, 5.5m-diameter inclined shaft; a 600m-long, 8m-diameter tailrace tunnel; two valve chambers; and a surge tank.

The underground extension to Kaprun is being developed by Verbund subsidiary, Austrian Hydro Power (AHP), with the scheme playing a key role in Verbund’s drive to cut power imports and market clean hydro supplies in Germany and other EU markets.

Construction work

AHP’s supervisory board approved construction of Limberg II at the 50-year-old site in February 2004, and initial work got underway five months later. Preparatory measures for the construction of the power plant commenced on 8 March 2006. This phase included opening up of the gate for the new Lärchwand tunnel (800m long), initiation of first building measures for the construction of the new Schrahnbach tunnels (3.5km long) as well as cross-section enlargement of the existing Lärchwand funicular (1.2km) to allow all plant to access the cavern site at Limberg.

By the end of 2008, construction work wass well ahead of schedule. Following the completion of the structural framework, work started on the interior fittings.

‘We are slightly ahead of our schedule. If everything continues in this way, we can reckon with completion of the new power plant as early as the end of 2011,’ said Dr. Herbert Schröfelbauer, chairman of the board of AHP. Completion was originally scheduled for 2012. "The structural framework is in place, we are now working on the interior fittings of the pumped storage power station," explained Limberg II project manager Erich Wagner.

Top performances in tunnelling

A tunnel system measuring a total of 5.8km was erected during the initial opening up of the construction site – with work completed in record time and top tunnelling performances of up to 24m per day. The transformer cavern (61m long, 15m wide, 16m high) and the machine cavern, which is as large as the nave of St. Stephen’s cathedral, were completely broken through in July and December 2007, respectively. Once work has been completed on the machine cavern, two reversible Francis turbines with a nominal capacity totalling 480MW will be installed. The units will be commissioned in 2011 and full operation should start in March 2012, with 1.3GWh annual average production from pumped storage mode – the current plant averages 670MkWh/yr. The fully automated plant will be monitored from Kaprun’s main control room.

In February 2008 it was possible to complete work on the pressure tunnel, which is 750m long and angled at 45 degrees. At the end of March, the 900-ton, 240m long drill of the headrace tunnel reached its goal after 3.5km.

In May, excavation was accomplished on the approx. 20 x 30m service chamber in the Höhenburg section, which stands at an altitude of 2000m. It is here that the pipe assembly for the plating of the inclined chute is now being temporarily housed. Manufacture of the piping began in July. The plating of the inclined chute should be finished at the end of May 2009.

By the end of November 2008, ahead of the first heavy snow fall, it was also possible to complete the preparatory measures for winter in the area of the Höhenburg construction site at an altitude of 2000m. The large amounts of snow that fall in the project site in the winter, and the associated risk of avalanche, make an access to this building section impossible from the beginning of December until the end of April. It was an enormous logistical challenge confronting the project’s construction experts. As a result more than 20,000 tons of concrete aggregate such as sand and gravel, 9,000 tons of binding material such as cement and flue ash, and 3,500 tons of sheet steel, among others, which are required for the manufacture of the pressure tunnel plating in the service chamber’s temporary pipe manufacture, were transported up the mountain.

Rapid progress is also being made on the concreting of the engine shaft, which began in mid January 2008. The suction line, which has a diameter of more than four meters, has already been installed. After commissioning of the power plant, this will be used for drainage of the water that has already been employed in energy generation. Work is in progress on the lower generator floor. Preparatory measures for concreting of both the intake and discharge structures in the Limberg dam and Mooserboden reservoir sections have also begin.

The preliminary works for the construction of the transmission line, which will run from the engine shaft down to the Tauern transformer station at the start of the Caprun valley, have also begun. The necessary access routes are being constructed, many of which will be used temporarily while others should remain as forest paths. 250 specialists are currently employed at the Limberg II construction site.

Invisible plant

During construction of the scheme, AHP took great care to avoid negative impacts on the environment and landscape. Only the access buildings and storage areas for tunnel excavation material will be above ground. ‘The special feature of this power plant is the fact that it blends in almost entirely with the existing landscape – i.e. it is completely subterranean in caverns,’ says AHP chairman Herbert Schröfelbauer. ‘After completion, only an access gate to the machinery caverns will be visible from the outside.’

AHP has cooperated on all environmental aspects of the project with the Salzburg Institute of Ecology. In particular the firm is using techniques for rapid soil regeneration and replanting developed at the institute. Blocks of turf and other vegetation will be removed from site prior to excavation, put into storage and returned once work is completed. Environmental experts from SIE will also be involved with the project on a day-to-day basis until completion. As a result, AHP’s so-called ‘invisible plant’ faces none of the protests often triggered by such major projects

Key figures

Capacity: 2 x 240MW
Maximum flow rate: 2 x 72m3/sec
Mean cross head: 365m
Turbines: 2 Francis pump turbines
Total investment: Euro 365M
Start of construction: 2006
Commissioning: 2012

Key players

Hinteregger & Sohne: Technical Overhead
Voith Siemens Hydro Power Generation GmbH & Co KG (St. Polten)
Andritz VA Tech Hydro (Graz)
VAM GmbH & Co Anlagentechnik und Montagen (Wels),
Poyry Energy GmbH (Wien/Salzburg)
Arge Poyry Infra GmbH/Intergeo ZT GmbH (Salzburg)
Hans Kunz GmbH (Vorarlberg)
Alstom (France)
Litostroj (Slovenija)

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