Increasing the safety of Limberg III: Numerical investigation of emergengy shut-off valves

Stefan Holler, Helmut Benigni*, Helmut Jaberg, Pascal Dörig, Gerhard Penninger, David Gieffing

*Corresponding author for this work

Research output: Contribution to conferencePaperpeer-review


At the hydro power plant site "Kaprun", the power plant capacity will be upgraded with the construction of the Limberg III pumped storage power plant (see Figure 1). In the course of this upgrade, a new headrace system (headrace tunnel, surge tank and penstock) will be constructed between the Moserboden lake (headwater reservoir) and the Wasserfallboden lake (tailwater reservoir), including an all new cavern powerhouse. Furthermore a new valve chamber (SK Drossen), hosting a DN4900 tandem butterfly valve arrangement, is to be installed serving as a shut-off and safety device. By applying a combined 3D-CFD and transient 1D-CFD study, the shut-off behaviour of the butterfly valve arrangement in a catastrophic pipe burst event had to be determined. If such a disaster occurs, the butterfly valve is the only remaining possibility to prevent the entire water content of the headwater reservoir from flooding the valley below. In the present case, a one-dimensional transient CFD calculation (water-hammer calculation or pressure surge investigation) is used to determine the dynamic shut-off behaviour of the emergency valve in the system in case of a pipe burst. In order to obtain the hydraulic characteristics of the valve required for a reliable transient analysis, extensive 3D CFD simulations were necessary. By applying CFD, the hydraulic properties of the tandem valve design as well as the mechanical loads during the emergency shut-off could be determined.
In the course of the water-hammer analysis, a torque equilibrium was then determined for the butterfly valves, considering all occurring forces (servo pressures, friction, forces on the valve plates, etc.). The calculation finally provides the shut-off behaviour, the closing time of the valve resulting from the actual flow conditions and all safety-relevant data such as the maximum loads on the components or the amount of water leaking into the environment in
course of a pipe burst event. First results of the 3D CFD-study already showed, that cavitation has to be expected in case of an emergency shut-off of the valves required due to a pipe burst event. Hence, a ventilation downstream of the valves was found to become mandatory to protect the headrace tunnel against inadmissible pressure below vapour pressure. For this purpose, the 3D-CFD-simulations had to be carried out as multi-phase simulations in order to determine the required air volume on the one hand and its effect on the hydraulic properties and the loads on the other hand. Modern techniques in numerical simulation methods provide the only feasible possibility to accurately calculate the occurring loads during an emergency closure of such valves. Commercial software-packages for water-hammer simulations usually do not provide numerical models for a realistic calculation of complex components like surge tanks, hydraulic turbines or emergency closing valves in a high head hydro power plant. But especially these components need to be modelled correctly in order to get a significant and reliable solution. A validation of the numerical models by means of onsite measurements at the existing hydro power plant yields additional confidence for a safe operation after the finalization of the power plant upgrade. The present paper shows the successful application of custom-designed numerical models for emergency closing valves in the course of water-hammer analysis at the Limberg III power plant.
Original languageEnglish
Number of pages12
Publication statusPublished - 9 Nov 2022
Event21st International Seminar on Hydropower Plants: ViennaHydro 2022 - Wien, Austria
Duration: 9 Nov 202211 Nov 2022


Conference21st International Seminar on Hydropower Plants
Abbreviated titleViennaHydro 2022
Internet address

ASJC Scopus subject areas

  • Engineering(all)

Fields of Expertise

  • Sustainable Systems

Treatment code (Nähere Zuordnung)

  • Application


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