INSPECTION TECHNOLOGY
❱❱ Acoustic emission and piezoelectric sensors are attached to the inner surface of the rotor blades at known weak spots with data regularly collected for analysis
Inspecting rotor blades using thermography and acoustics
performed by industrial climbers. But the problem with inspecting offshore installations is that access is only possible when wind and weather conditions permit. This makes it very difficult to plan inspection visits. Continuous structural health monitoring (SHM) of
W
rotor blades contributes significantly to the overall cost-efficiency of wind energy turbines. When the rotor is turning, the blade tips can reach a speed of 300 to 350 km/h – as fast as a Formula-1 racing car. Rotor blades deliver their best aerodynamic performance when the boundary layer of wind flows smoothly over the aerofoil without causing wake effects. Even the slightest surface damage can generate turbulence, resulting in lower efficiency. For a wind turbine, this means diminished output, less cost-effective operation, and a shorter service life. The extreme conditions at sea cause materials to
degrade much faster than on land. Specific stress factors include greater exposure to UV radiation, high wind speeds and salt-laden air. The industrial climbers who carry out the regular inspections check for signs of delamination and other forms of damage by tapping on the structure and examining its visual appearance. The poor accessibility of offshore wind
ind turbines have a design life of 20 years. The rotor blades must be regularly inspected at least once every four years to verify their structural integrity. This type of work is
Acoustics and thermal imaging are two techniques being piloted for use on off-shore wind turbines to help reduce inspection costs and improve efficiency
farms and the unpredictability of maritime weather conditions make it difficult to deploy maintenance teams, with a corresponding impact on operating costs. A typical example is the case in which inspection workers are repeatedly called out but then sent home again because the weather window is too short to permit high-altitude work. Wind farm operators are therefore looking for
alternative structural health monitoring methods that are equally as reliable as regular inspections by industrial climbers. “What we need are flexible methods that allow wind-turbine rotor blades to be inspected in situ in a minimum of time and without long preparation, and yet still deliver results that are as reliable and conclusive as those obtained when inspections are carried out by industrial climbers,” says Holger Huhn, director of research and development at WindMW Service, the company coordinating the project. These issues are being addressed in a concept
study by researchers from the Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Bremerhaven together with WindMW Service GmbH, the Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), and Deutsche WindGuard Engineering GmbH. In two parallel approaches, their goal is to reduce
wind turbine downtime and perform maintenance with fewer personnel. One approach involves the use of drones in combination with mobile thermography
March 2018 /// Environmental Engineering /// 41
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