Run-of-River Hydroplant Gratkorn

Detailed planning and design of the turbines

In October 2024, the new Gratkorn hydropower plant was commissioned and officially opened by project partners VERBUND and Energie Steiermark. The hydropower plant was built approximately 10 kilometres north of the centre of Graz, the capital of Styria (Austria), and supplies sustainable electricity to around 15,000 households. Two Kaplan turbines operate inside the plant. These were designed for a maximum flow rate of 205 m³/s and a head of 6.62 m. At full flow, they achieve a maximum output of more than 11 megawatts.

We are delighted that Jaberg & Partner were able to support this project with the detailed planning and design of the turbines, as well as by assisting with a model test.

Hydraulic development

On behalf of the manufacturer of Kaplan turbines, we carried out CFD-based development of the turbine hydraulics. The challenge was to design an efficient and compact vertical Kaplan turbine with a comparatively high specific speed nq for highly restricted geometric conditions.

Cross-section of the power plant with an overlay of the specified structural constraints (in grey) and the final turbine design (light colours)

Completed turbine hydraulics ready for installation at the Gratkorn hydropower plant

Due to the special structural requirements, not only did the height of the spiral casing have to be reduced (from H = 6.75 m to H = 6.25 m), but also the width (from B = 12.75 m to B = 10.5 m).

Optimisation of the impeller blades and the suction pipe

The deviation from the original design leads to increased turbulence generated by the spiral casing. As a result, the inflow conditions are not ideal, resulting in comparatively high losses.

Superposition of a conventional spiral case and the new custom-designed spiral case

Velocity distribution plotted on a mid-section in the spiral case at high load operation

Any change in the blade geometry causes a change in the flow in the suction pipe, which in turn affects the overall performance of the turbine. For this reason, the optimisation of the blades was carried out in conjunction with the optimisation of the suction pipe.

During the optimisation process, a peak efficiency of 94% was achieved. To do this, the impeller design had to be optimised for operation under high loads.