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Wehr, Germany - A daring technological breakthrough

Since the end of 2021, the world’s most powerful horizontal air-cooled motor generator has been in commercial operation at the Wehr pumped storage plant in Germany. The successful commissioning of the new generator — allowing the plant to produce clean energy once again — marks the end of a very challenging project.

© Schluchseewerke AG

Providing about 1,000 GWh of clean and renewable energy per year, the pumped storage plant was originally built in the 1970s and has a total capacity of about 910 MVA in turbine mode and 980 MW in pump mode. With its four generating units, it is the biggest power plant in the portfolio of Schluchseewerk AG and provides crucial grid balancing services for Schluchseewerk’s owners, EnBW and RWE.

A short circuit at the B09 generator occurred in September 2019 and a new generator was needed. The owners wanted a robust machine with high availability that could withstand a high number of load changes. After a long R&D design phase and numerous recalculations and simulations, ANDRITZ presented a compelling offer for a new high-efficiency generator. The new generator design was also very daring as the cooling system had been changed from water-cooled to air-cooled, lowering costs, increasing availability and improving maintenance friendliness. The design was very challenging with a nominal voltage of 21 kV, unusual stator bar geometry and the re-use of the existing rotor. ANDRITZ deployed the considerable strengths of the Generator Competence Centers Vienna and Weiz, both in Austria, to enhance the project and they have demonstrated their impressive competence and willingness to think outside the box to deliver an exceptional technological solution. The result is a perfectly optimized product that meets all the customers’ needs and requirements.

"Unconventional thinking and the highest level of technical expertise have resulted in a unique solution – the world’s most powerful horizontal air-cooled motor generator."

A personal touch

In close cooperation with the customer, the ANDRITZ generator team installed the air-cooled motor generator of unit B09 in 2021.

© Schluchseewerke AG

Name plate of generator B09 bearing Erwin Heimhilcher’s name

© Schluchseewerke AG

A very personal touch makes this project even more appreciated. One of our project managers, who was involved in the project from the beginning and was also one of the driving forces behind this excellent technical solution, Erwin Heimhilcher, unfortunately passed away during the implementation phase of unit B09. In recognition of Erwin’s contribution and both our and the customer’s appreciation, the B09 generator now bears his name.

With this successful project ANDRITZ has set new records with the world’s most powerful horizontal air-cooled motor generator. We are thrilled to have been part of this challenging project and to have supported the customer in restoring the power plant to its full capacity. This success speaks for itself. At the beginning of 2022 a contract for a further generator unit — B10 — was also awarded to ANDRITZ.

Grid bottlenecks and black-start capabilities

Bridging grid bottlenecks and black-start capability are two of the most important features of a pumped storage power plant, supporting grid stability with rapid response to changing demand or sudden outages.
In Wehr, state-of-the-art units move huge masses of water in a closed and weather-independent cycle between the upper reservoir, the Hornberg basin of 4.4 million m3, and the lower reservoir, the Wehra basin with a capacity of 4.3 million m3. Some 630 m of elevation separate the two reservoirs. Within seconds, electricity can be generated or stored as needed depending on what the power grids demand.

With four generating units, Wehr is the biggest power plant in the portfolio of Schluchseewerk AG and provides crucial grid balancing services.

© Schluchseewerke AG

Technical Details

Total output:

980 MW / 910 MVA

Scope output:

300 MVA


21 kV 

Av. annual energy production:


1,000 GWh


Authors: Michael Fink and Marie-Antoinette Sailer

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