A feat of strength in Kaprun: 355-tonne rotor successfully lifted into place at Limberg III power plant

The commissioning of VERBUND’s Limberg III pumped storage power plant in Kaprun is coming ever closer.  On 9th May, the next milestone was achieved with the successful installation of the rotor of generator set 2. The 355-tonne steel element had to be lifted into the stator with millimetre accuracy using a suspension crane specifically designed for this purpose. This means the last major machine element is now in place at the site where it is to be used. The next test will be wet commissioning in mid-June, when the generator set will be tested for functionality and leaks. Maximum accuracy and zero tolerance are crucial here for VERBUND’s engineers as the rotor needs to function smoothly under extreme loads for decades to come.

Despite state-of-the-art technology, the lifting of the rotor in Austria’s most advanced pumped storage power plant is manual work. The crane operator used his joystick to steer the machine element into the stator cavity, millimetre by millimetre. The margin of just 4–5 millimetres was continuously monitored by his signallers. A strenuous and nerve-racking job. Oscillation of the 355-tonne steel giant would have fatal consequences and could severely damage the stator. So there was a palpable sense of joy and relief when the heaviest lift of the entire power plant project was successfully completed around 11:30 p.m.

It was the culmination of over a year of preparatory work and planning. Because the finished rotor would have been much too big and heavy to transport through the 5.5 kilometres of tunnels on the construction site in Kaprun, it was painstakingly assembled in situ at a site in the power plant cavern in around 12 months. Layer by layer, the sheets, which are only 0.5 mm thick, were stacked in overlapping manner until the last of a total of 80,000 rotor sheets was in place. At that point, the lamination stack reached an axial length of 3.70 metres.

The rotary motion of the rotor converts hydropower into electrical power with a maximum output of 240 megawatts. Unlike the Limberg II pumped storage power plant, the generator sets of Limberg III can be operated at variable speed, enabling an output range of between 20 and 240 MW per unit for turbine operation and between 100 and 240 MW per unit for pumping operation. This enables them to not only store excess electricity for a longer period of time, but also to step in within seconds to compensate for voltage fluctuations in the power grid.

The Limberg III pumped storage power plant will be opened in September 2025. VERBUND is investing around EUR 572 million in the project.