High-performance wind turbines are growing taller, meaning lifting times for maintenance and service logistics are getting longer. Under the Demag brand, Terex Material Handling has developed a crane and materials handling system to dramatically cut handling times

The desire for improved performance remains undiminished, especially in the offshore sector. Wind turbine installations that deliver a rated output of 6-7.5MW now reach heights of 150m. The wind turbine specialists of the European UpWind 20 research project believe that wind turbine installations delivering outputs of up to 20MW with 200m towers represent the limits of what is technically feasible.

Above all, for offshore wind turbine installations, this poses enormous challenges for spare parts logistics, since working hours in this sector are very expensive and windows of opportunity with good weather are usually very small. In addition, high-performance on-board hoist units are needed when components and systems have to be replaced or repaired. As installations grow in size, the times required for lifting and lowering material, tools and spare parts from the platform to the nacelle add up.

A heightened time saver

Building on its many years of experience in the wind turbine industry, Terex Material Handling has developed an innovative solution on the basis of its product range for the offshore wind turbine industry. As a result, the time required for lifting and lowering loads has been reduced significantly in comparison with systems used until now.

The modular system is based on the proven Demag KBK light crane system and the DS10-Wind rope winch. Specially selected materials ensure reliable operation, even under the arduous ambient conditions that occur on the open sea. The rope winch is supplied in four sizes and installed in the nacelle of the wind turbine together with the KBK installation.

This solution provides a maximum hook path of 180m and can lift spare parts, equipment and tools weighing up to 1,000kg at load-dependent lifting speeds. For loads weighing up to 500kg, the DS10 can lift at a speed of 48m a minute, and 24m a minute for heavy loads.

In the past, it took 36 minutes to replace a single component for towers measuring 140m in height. To do this, the crane had to be lowered three times: first of all to lift the tools into the nacelle, then to lower the defective part and pick up the new spare part, and finally to transport the tools back down to the platform. Each lifting operation took 12 minutes.

"The DS10-Wind rope winch now cuts the transport time by 50% compared with solutions that use chain hoists. It now only takes 18 minutes for a nacelle located at a height of 140m," explains Dr Thomas Bönker, head of the components business line at Terex Material Handling. "That saves costly hours for maintenance personnel and also helps minimise downtime."

No position missed

The DS10-Wind rope winch offers considerably better installation dimensions than conventional solutions. There is no need for the chain collector box, and compact dimensions can be achieved thanks to the multiple layers of lifting rope wound on the drum.

The electric drive also avoids any hydraulic problems for maintenance work. The rope winch travels horizontally along a KBK rail system arranged around the inside of the nacelle. This system enables service technicians to lift loads safely and easily from the platform to the roof of the nacelle, and to move them into the nacelle via a track switch without any need to detach and reattach them.

Besides the actual lifting operation, loads can also be transported horizontally to virtually any position within the nacelle. The KBK system can be freely configured as a crane and as a suspension monorail. Almost any point-to-point connection can be achieved by means of straight and curved track sections as well as track switches. This also gives the manufacturers of wind turbines the necessary flexibility to adapt the crane system to the layout of a nacelle infrastructure with further technical developments with ease.