Wind at the top

25 April 2008

Aerial view of the installation project in full swing

Aerial view of the installation project in full swing

Alpine surroundings meant special challenges for Austrian transportation and lifting specialist Prangl on a high altitude wind turbine erection project. Prangl handled the complete project, comprising road transport, temporary storage, uphill transport and erection. The ten turbines were erected near the village of Ratten, in Austria's Styria province, 1,577 m above sea level. They are now supplying electricity to 10,000 homes.

The largest segments of the 60 m towers weighed 38 tonnes and the 30 m turbine blades gave an assembled rotor diameter of 62 m. The generators weighed 48 tonnes and the highest elements to be erected were the 78 tonne blade and hub assemblies.

The challenge for man and machine included the drive up to the erection site. To make the 1,000 m (in the vertical) climb the driver of the 96 tonne, eight axle Terex-Demag AC 500-2 telescopic crane had to negotiate narrow forest tracks with sharp turns and gradients up to 22%.

Another challenge was transporting the 30 turbine blades, each one forming a load 30 m long and 6.30 m high. The loads, on specially equipped five axle trailers, had a 3 m front overhang and 5 m at the rear.

Planning and organisation

Crucial to smooth completion of the project was exact planning and organization of all stages in advance. The forest tracks had to be carefully surveyed to minimise interference with the landscape. As a realistic test an aluminium dummy rotor blade was built and transported the whole distance. Bridges had to be given additional support, trees and bushes had to be cut back, and tonnes of gravel had to be brought in to improve the load-carrying capacity of the 12 km forest track that had to be kept passable in almost any weather.

The local soccer field was turned into a temporary storage site where the turbine components from Denmark were unloaded, temporarily stored and prepared for the uphill transport.

Explaining the loading, Andreas Schneider, Prangl transport manager, said, “We installed specially manufactured transport racks on our vehicles. The blades were put on them and overhung the driver's cabin”. The aim was to keep the vehicles as short as possible so that the forest track's narrow turns could be negotiated without major difficulties.

The generators were a different challenge. Although not as big as the blades, they weighed much more – 48 tons – more than a single low loader would have been able to pull up the 22% gradients, so a second tractor was linked up. Some of the turns were too tight to be taken forwards so the vehicles had to drive parts of the way backwards.

On site at the top of the hill the AC 500-2 was dismantled after completing each turbine, driven to the site of the next one and reassembled. While this was happening the transporters were on their way down to collect the next load of turbine parts and deliver them back up the hill. It took less than 24 hours to transport and erect each turbine, which, Prangl says, was a logistical and technical masterpiece in such difficult terrain.

Assembling the tower components was quite simple, certainly simpler than the assembly (helped by a second crane) of the horizontally erected hub with blades, Prangl explains. A constant obstacle was wind. “In such cases, the intuitive feeling of the crane operator is often more important than the technical capacity of the machine”, says Klaus Obertscheider, Prangl project manager.

In addition to all the above, the one stop shop approach of using one company for the complete project, contributed to completion of the project two weeks earlier than planned.

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