Hydropower – tried and tested for thousands of years; more modern than ever before

Emission-free, controllable, base load capable and reliable: hydropower electricity generation is your ideal companion alongside the volatile feed-in from wind and solar energy.

The power supply must be reliably accessible 24/7. *1 Hydroelectric power makes a vital contribution to this. While wind and sun are subject to strong fluctuations as energy suppliers, electricity from hydropower is always available.

This means that the required amounts of electricity can be fed into the grid within seconds to compensate for the gaps from the volatile feed-in of wind and solar energy.
With the expansion of wind and solar energy, providing this primary control energy is becoming more important every day in order to ensure the normal frequency of 50 Hz in the power grid. The Uniper Company operates 22 run-of-river power plants on the Lech River, a tributary of the Danube River, as well as the Rosshaupten storage power plant on the lake Forggensee.
With an overall expansion capacity of around 260 megawatts, around 1.1 billion kilowatt hours of electricity are generated per year.*2 This can theoretically supply around 366 000 households with electricity. At the same time, around 634 000 tons of CO2 are saved, compared to generating energy from fossil fuels.

To ensure that safe and sustainable energy will continue to be generated on the Lech in the future, Uniper is continuously investing in the maintenance and efficiency of the plants. As part of this work, plans were made to overhaul three generators at the Epfach and Finsterau hydroelectric power stations built between 1947 and 1950. Corresponding tenders were sent out by Uniper at the beginning of February 2022 to various companies specializing in such challenges.

Map section of Germany with the region of Landsberg am Lech and surroundings
Locations of the run-of-river power plants Epfach and Finsterau*5

Lech barrage 10 - Epfach*3
Built: 1947 – 1950
Power generated: 8.3 MW at 8.5 m drop height
Energy generation: 6 straflo turbines und generators
Expansion flow rate: 120 m³/s
Control work capacity: 40726 MWh/year

Lech barrage 7 - Finsterau*4
Built: 1947 – 1950
Power generated: 7.7 MW at 8.0 m drop height
Energy generation: 6 straflo turbines und generators
Expansion flow rate: 120 m³/s
Control work capacity: 37079 MWh/year

The 256 km long Lech river has its source in Vorarlberg, Austria and flows into the Danube river in southern Bavaria.*9 There is a height difference of 1 500 meters*10 between its source and the mouth, which is used by 23 barrages to generate natural electricity from hydropower. Its turquoise to jade green water is magically fascinating. The Lech owes this colour to the high mineral content that the river dissolves from its stones, as well as to the low water temperature.

Reliable and flexible partner

The BENNING Electrical Machines Division (BeM) has been repairing generators and motors since the 1930s. This division therefore has decades of experience and references in the construction, reproduction and repair of e-machines for a wide variety of industries. These include the steel and aluminium processing industry, mining, oil, gas and petrochemicals, railways and power generation.

In the past, BENNING has already repaired several hydroelectric generators on behalf of Uniper. In particular, the high flexibility in the implementation phase, without making compromises in occupational safety and quality, convinced the client. As a result, BENNING was also asked to submit an offer in February.

BENNING’s planning know-how and the cost-effectiveness of the submitted offer convinced Uniper. After inspecting the systems and creating an assembly concept, the order was placed for the renovation of three hydroelectric power generators from two different power plants.

In order to minimise downtime and the resulting power generation losses, the three generators were going to be modernised between March and August. It was planned in such a way because in these months the level of the Lech falls, and with it the generation of energy.
The order stipulated that towards the end of the summer the generators would be put back into operation so that the capacity of the two power plants could be fully utilised again when the river levels rose in the autumn.

The BeM project team began reassembling the newly wound generator stator and rotor poles on July 11, 2022, so that the generators were able to start operating again as planned in August.

Insertion of coils in the BENNING repair workshop in Bocholt, Germany

The team manufactured three new stator laminations from modern, low-loss dynamo laminations in the repair shop in Bocholt beforehand. Each package consists of approx. 8 000 sheet metal segments manufactured using the laser cutting process.

Using modern equipment, the BeM team produced 1 500 new high-voltage coils in a short time and inserted them into the grooves of the generator stator, which have an internal diameter of more than 3 metres. Technical expertise, craftsmanship and the use of state-of-the-art materials and insulating materials now ensure an increase in efficiency, high operational reliability and a long service life for the machines.

The reconditioned segments before being transported back to the Lech River
The reconditioned segments before being transported back to the Lech River

“Since occupational health and safety are of the highest priority for both us and our customer, a rescue exercise was carried out at the Finsterau hydroelectric power plant before dismantling began. This involved simulating the rescue of an unconscious employee, who had to be transported safely and as quickly as possible to the power station gate from the power station basement using recovery equipment.”

Matthias Loerwink,
BENNING, Electrical Machines Division

Challenges during disassembly and reassembly

The power plants each have six Straflo turbines.*6/*7 In this construction, the rotor of the generator and the rotor of the turbine form a complete unit.*8
A separate shaft is not planned. The excitation winding is located in the rotating ring that the turbine blades carry. Therefore, this type of generator does not have a classic flywheel. The stator winding is built into the turbine housing.

Due to the Straflo concept, there were special requirements for the disassembly and later reassembly processes of the generator.
Since the rotor had to remain in the power plant due to the design, the BENNING technicians dismantled the rotor poles on site. Beforehand, the generator stators had to be split into their two shells in the power plant and the lower half swung out under the rotor. The stator shells and the dismantled rotor poles were then transported to the Bocholt plant for refurbishment.

During the reassembly, the BENNING Service Team first reinstalled the refurbished rotor poles in order to then swivel in the lower-lying generator shell under the rotor. Due to their design, the stator halves had to be assembled on site so that the last coils of the 6 kV stator windings could only be installed and electrically connected during reassembly. For this purpose, the BeM team has special mobile equipment, since both the insertion of the last coils and the later curing of the resin posed a special challenge for the technicians on site.
The reinstalled generators showed optimal values in the acceptance measurements and confirmed the success of the generator repairs. The tests carried out included not only the measurement of electrical parameters and load characteristics, but also the determination of the thermal limit values as well as the noise and vibration values.

This means that the full feed-in capacity is again available at the Epfach and Finsterau run-of-river power plants, so that the sustainably generated electricity will continue to make an important contribution to the energy transition in the future.

Further Information

author/contact: Matthias Loerwink
telephone: +49 2871 93 318

*1 Source: https://www.uniper.energy/sites/default/files/2022-04/broschure_kraftwerksgruppe_lech.pdf
*2 Source: https://www.uniper.energy/de/deutschland/kraftwerke-deutschland/kraftwerksgruppe-lech
*3 Source: https://dewiki.de/Lexikon/Lechstaustufe_10_–_Epfach
*4 Source: https://de.wikipedia.org/wiki/Lechstaustufe_7_–_Finsterau
*5 Source: https://www.uniper.energy/sites/default/files/2022-04/broschure_kraftwerksgruppe_lech.pdf
*6 Source: https://de.wikipedia.org/wiki/Lechstaustufe_10_–_Epfach
*7 Source: https://de.wikipedia.org/wiki/Lechstaustufe_7_–_Finsterau
*8 Source: https://de.wikipedia.org/wiki/Kaplan-Turbine#Straflo-Turbine
*9 Source: https://de.wikipedia.org/wiki/Lech
*10 Source: https://www.wasserqualität-trinkwasserqualität.de/wasser-qualitaet/fluesse/lech

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