High-tech remedies

18.05.2015
Camera-equipped drones provide high-end display photos. (Photo: Batcam)
Camera-equipped drones provide high-end display photos. (Photo: Batcam)

When it comes to operation and costs, however, more trust is put into ground-supported camera systems, which are less susceptible to wind and supply photos of an equally brilliant quality. GEV Wind ­Power of England and their technology partner Cornis SAS of France, for example, have begun selling the ­Panoblade Inspection System for camera-based rotor blade inspection. First, the system takes pictures of each section of the blades of a turbine that has been brought to a halt before using algorithms to stitch them together into a full blade. Next, experts examine the results and record their findings in a planning tool for actual maintenance tasks. “We recognised the cost-effective and simple advantages of utilising the remote blade inspection ­system. With only one operator required to inspect up to five onshore turbines per day or three offshore turbines, this system will offer exceptional savings in both time and money,” says Alastair Gadney, Projects ­Director at GEV.

Specialists are essential

Because visual checks of the blades are only one side of the coin, specialists must be called in to do the actual work. Only they can determine how much ­damage there really is and whether a crack sounds hollow or has already cut far into the blade – or if the mark on the photo was simply dirt. For these interventions, GEV feeds the visual results into an enterprise resource planning tool. Such software helps plan ­demand-based, transparent repair. “The fundamental advantage is that it provides near real-time ­reporting on each maintenance job, thereby boosting efficiency and minimising errors generated during the manual processing of reports and invoices,” ­Gadney explains. Similar systems are available from ­Braendler Engineering (Aether Blade Inspection ­Service) and ­AtSite of Denmark.

A number of other tools can also be useful for deter­mining the condition of a blade, including thermo­graphic systems or ultrasound devices for detecting problems such as poor lamination and inclusions. Force Technology of Denmark is a specialist in this ­area. “We sell our systems to manufacturers who use ultrasound to inspect blade quality during production,” says Jens Erik Olsen of Force.

Force Technology’s devices automatically move over the blades, making delamination and inclusions visible with ultrasound. Variants include handheld scanners that allow service technicians to, for ­example, recognize the depth of cracks directly on the blade. “The scanner probes down to a depth of about 60 to 70 millimetres to document the damage. We train specialist inspectors to use these devices,” says Olsen.

Erosion eats away at blades

A special focus of inspections is on blades’ leading and trailing edges and tips. It is well worth checking these spots because erosion from rain poses a real threat to blade and paint manufacturers. For now, blade coatings have a large share of polyurethane. Depending on the blend, such products can have properties ranging from hard to soft or very elastic. Due to their extreme weather resistance, these chemical blends are basically the only choice. The problem is that they do not last anywhere near 20 years. “Their service lives are far less than ten years. In fact, erosion protection that lasted for six or seven years at the blade tips would already be considered exceptional. There are systems onshore that work quite well but also suffer damage because their erosion protection wears off,” says Stefan Brassel, blade expert at Deutsche Windtechnik Rotor und Turm GmbH­.

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