Mühletorplatz HPP Refurbishment

The Mühletorplatz hydro power plant in Feldkirch was built in 1906 and is operated by Stadtwerke Feldkirch since this time. Two of the originally four double-flow Francis turbines were replaced by horizontal axis Francis S-turbines in the early 1990's.
After almost 30 years of continuous operation of the horizontal axis turbines the first complete overhaul of the new Francis machines was launched in 2019. In the course of this refurbishment the two old double-flow Francis turbines were completely dismantled and overhauled too.
To increase efficiency and thus the annual production of the plant a new hydraulic shape for the runners profiles fitting into the machine units 1 & 2 was designed. To optimize the project revenues a sound analysis of the past power plant operation was performed and the outcome of this analysis was taken into account for the design of the new impellers.
In the course of the machinery overhaul the new runner with a modern X-blade design was mounted and proved the expected power and efficiency increase at the commissioning as calculated per numerical analysis. The overhauled machines showed a considerable power and efficiency increase compared to the worn out machinery which was tested in the course of a measurement campaign after the rehabilitation of the machine sets.
This paper describes a successful refurbishment project of old double-flow francis-turbines and the power and efficiency increase potential due to the replacement of old-style francis runners by a modern design with profiled X-shaped blades.