Technology for Wood and Natural Fiber-Based Materials

Research project

Non-destructive inspection of mounted rotor blades

Destroyed rotor blades from wind turbines, lying in fields, can be the result of manufacturing defects or unrecognized signs of fatigue. In order to prevent this, we have developed, together with partners from the industry, a system which enables the non-destructive inspection of the mounted rotor blades. Dismantling of the blades is thereby unnecessary.

© Fraunhofer WKI | Peter Meinlschmidt
Installation of the work platform with the measuring system on the wind turbine

A further development of the active online thermography is hereby applied. This measurement technology has been specifically adapted for this purpose and, integrated into a work platform, can be deployed directly on the suspended rotor blade. The focus is placed upon irregularities in the load-dissipating GRP belts of the blades. Delamination, undulations and water ingress can be detected quickly and reliably.

The basic principle of detection technology is that an infrared emitter is located at the lower end of the work platform, which introduces a short thermal impulse into the blade. At the upper end of the platform is a robust, industrial thermographic camera which focusses sharply on the areas of the belt which are to be inspected. Through a constant downward movement of the platform, the rotor blade is examined regarding damage. The emitter and the camera are hereby held at a constant distance from the blade by means of a specially-developed device. The measurement of a belt of a conventional onshore wind turbine takes less than ten minutes. In addition to this are the set-up times for the work platform, which account for the majority of the time required. Under good conditions, up to three wind turbines per day can be inspected.

The results of the measurements are thermographic images which can also be merged together to create a film. The scale and the distance from the flange (radius) are engraved into the images. A specially-developed software makes damage hidden in the rotor blade visible and displays the results in high contrast on the monitor. This program additionally makes it possible to view the thermographic images live during the inspection of the blade and, if necessary, to mark conspicuous points directly on the blade.

The conspicuous points can be ground open, documented and, if necessary, repaired directly after the measurement. Alternatively, this can be carried out later, as the defect locations can be easily found again thanks to the radius engraved in the thermographic image. The system is used by industry partners for specific types of turbine. A transfer to other types of turbine is possible within the framework of a research collaboration. We look forward to your inquiry!

© Fraunhofer WKI | Peter Meinlschmidt
The first evaluation of the thermographic images during the measurement
© Fraunhofer WKI | Peter Meinlschmidt
The camera and laptop with live thermographic image
© Otto Lutz
Causal research using thermography on a rotor blade which has fallen from the turbine

Funding

Industry