Screw jacks play pivotal role in transporting giant wind turbines20 January 2017

Adwen has designed and built an transport frame Adwen has designed and built an enormous transport frame

Offshore wind turbines are providing an ever-larger percentage of the world’s electrical power. As a result, there is an increasing need to get the giant nacelles that house all the machinery from factory to dockside for shipment out to the wind farm safely and efficiently.

High capacity screw jacks manufactured by Grob Antriebstechnik and available in the UK through Drive Lines Technologies Ltd play a vital role in this difficult task.

There are over 300,000 commercial wind turbines operating around the world and the number is growing on an almost daily basis. The world’s largest offshore wind farm, Hornsea II, is under construction and will see 300 turbines erected off Yorkshire’s North Sea coast. Once on-stream they will generate 1.8GW of energy, enough to power 1.6 million homes.

All the machinery associated with wind turbines is housed in the giant nacelle at the top of the tower. Up close it is apparent that the nacelle of a typical offshore wind turbine is the size of a house and its interior is filled with a huge gearbox, a drive shaft, a gear ring that allows the turbine to turn into the wind and the generator, plus ancillary equipment. They weigh in at over 200 tonnes, or the equivalent of six fully loaded articulated lorries.

One of the leading manufacturers of turbine nacelles is Adwen in Bremerhaven, in north-west Germany. Manufacturing each nacelle is an engineering achievement of considerable note, but there is also a question to be answered. How do you transport the nacelle from the factory to the harbour so that it can be loaded onto a barge and taken out to the wind farm?

The answer is that every time a nacelle is finished, it must be tested and then lifted onto a special heavy duty vehicle, which transports the nacelle to the home harbour of the offshore wind farm. However, such gigantic masses cannot be moved with normal hoists; instead, a special solution is required.

Adwen has designed and built an enormous transport frame that is raised by four Grob screw jacks. Once completely fitted out the nacelle sits on the frame and is set down on the floor of the production building, where the final inspection takes place. After the inspectors’ sign-off, the transport frame is raised to the height of the loading surface of the heavy haulage vehicle and transferred onto it. So that the transport frame with its nacelle is raised or lowered evenly and without jolts, a very slow stroke speed is used: the actual driving time for a full stroke is around 17 minutes.

The four powerful screw jacks are Grob’s MC150 units, which are configured to ensure that this enormous weight is moved very easily. Each drive is based on a simple and therefore reliable worm mechanism driven by its own electric motor and can accept a static load of up to 150 tonnes.

In use the four lifting spindles are constantly monitored by a load cell that measures the actual load, while a rotary encoder detects the precise position of the lifting spindle and constantly feeds exact positional information back to the single PLC (programmable logic controller) that controls the entire operations.

Grob is recognised the world over for the excellence of its linear actuation technologies. For over 70 years it has applied technical innovations to solve problems in linear lifting, moving and conveying. Its MC series of screw jacks is available in 14 sizes in both travelling nut version and translating screw versions and the largest units have a static load capacity of up to 200 tonnes.

For higher duty cycles the high-performance HMC series screw jacks are tailored for particularly demanding duties where standard linear drives are not suitable. Special features include a main housing formed with integral cooling fins for maximum heat dissipation so that an optimised duty cycle can be achieved and an oil bath that keeps the worm gear constantly lubricated. This means the HMC units can lift greater loads or alternatively run at higher speeds than more conventional designs.

During the nacelle lift all measured signals are displayed on the control panel and processed within the powerful state of the art PLC. This ensures absolutely synchronous running of the four linear drives in the system and prevents incorrectly loading or overloading of the spindles. Handling real time data, the PLC can instantly compensate for differences in the geometry of the transport frame.

Once on the road vehicle, the nacelle can be slowly and carefully transported to the docks, where a floating crane takes over and lifts the nacelle onto it transport barge ready for the voyage out to its working station on the wind farm.

Mark Venables

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