The 355-tonne rotor was successfully lifted into Limberg 3

The complete rotor is the heaviest machine part that had to be moved on the Limberg 3 construction site. Due to its enormous dimensions and weight, it had to be manufactured inside the cavern. The cavern’s height of 17 metres was therefore optimised to the required tilting and lifting procedures.

It’s a length process requiring a lot of patience. It took almost a year to complete production of the rotor inside the mountain. This makes it all the more important that the interaction between crane driver and banksman is 100% coordinated. Using the indoor cranes, the gigantic steel colossus was lifted onto the stator with only 4-5 millimetres of leeway. It is critical here that the personnel have a sensitive touch, strong nerves and good coordination. Just a tiny mistake or excess movements could seriously damage the stator. The entire project team was all the more delighted that the most difficult and challenging lift of the entire project went off without a hitch after three hours.

Limberg 3 is considered to be the most modern pumped storage power plant in Austria. From 2025, the two machine sets will deliver an impressive output of 480 megawatts, which is equivalent to the energy generated by around 60 large wind turbines.

Rotor: Facts & Figures

• Mass of ribbed shaft: approx. 90 t
• Mass of laminated core: approx. 185 t
• Mass of rotor to be lifted in: 372 t
• Nominal power 240 MW

The rotor 

The rotary motion of the rotor turns hydropower into electrical power – with a capacity of 240 megawatts (MW). The rotor first has to be laminated, after which it has a mass of 355 tonnes, making it the heaviest single lift on the entire construction site. The shaft needs a suitably rugged design to be able to withstand these gigantic loads. With a breathtaking 450-550 revolutions per minute, the machine is faster than any racing car. And it needs to be because the pumped storage power plant should not only store excess electricity for the winter, but also be able to intervene in a matter of minutes to even out any voltage fluctuations.

The base construction of the rotor is the so-called ribbed shaft. This ten metre-long forged shaft with steel ribs welded onto it had already been transported to the construction site inside the mountain on a special transporter and then reversed uphill into the power plant cavern. This involved passing through an impressive 5.5 kilometres of tunnels. After that, the generator shaft was erected with millimetre precision using a specially designed and manufactured tilting and lifting device with the help of two overhead cranes and positioned at the rotor assembly site.

The so-called laminated core is layered and overlapped on this ribbed shaft using countless 0.5 mm-thick electrical sheets. After multiple intermediate pressing steps and continuous quality control, the laminated core is then heated to 150 °C to achieve pre-ageing/setting. After the final pressing together with end plates on both ends, the finished laminated core is shrunk onto the ribbed shaft. The sheet metal package is heated to up to 180 °C, which expands it radially, and fixed to the ribbed shaft via shrink discs. After this process, the winding bars are installed in the rotor slots and hard-soldered together. Finally, the two outer cap rings, which support the two axial ends of the rotor winding, are mounted and shrunk in place. After a thorough electrical inspection, the rotor is ready to be lifted into place.