Turbines of Alpine small hydropower plants (SHPP) with a head of several hundred metres and without headwater storage are particularly affected by hydro-abrasive erosion. This increases maintenance costs and reduces electricity production. In a case study at the SHPP Susasca near Susch (GR), the sediment yield at the water intake, the partial sediment exclusion at the sand trap, the turbine abrasion, the changes in turbine efficiency, as well as the economic and energetic effects of the sediment load and optimisation measures are investigated.
The measurement of flow velocities in the sand trap chambers in summer 2019 showed that the tranquilizing rakes were not optimally designed. Therefore, the rake bars were extended. A further measurement in summer 2021 showed a significantly more homogeneous flow velocity distribution, which favours the sediment settling. Furthermore, the instrumentation for measuring the sediment levels in the sand trap chambers was improved to support flushing as needed from remote.
In the years 2019 to 2021, the concentration of sediment particles contained in the turbine water was continuously measured, as well as their size distribution (for some periods) and other sediment properties. During the winters, the extent of abrasion on the turbines was quantified and correlated with the particle load. Furthermore, the changes of the turbine efficiencies since the commissioning of the SHPP were evaluated and correlated with the abrasion. The quantified correlations can be used as a basis for forecasts.
The findings of the project will serve to improve the design of new Alpine SHPP plants and to optimise existing ones regarding energetic and economic efficiency.