Qualitative diagnostics of wind-turbine blades inspection using active thermography

Abstract

Paper presents production-ready system designed for non-destructive inspection of wind-turbine blades. System is based on active thermography method with pulsed excitation. Designed and implemented by author’s solution, software and image processing techniques allow implementing the system as an end line manufacturing quality control. Authors present new approach to calibrate geometrical distortion of thermal cameras with using Peltier unit matrix. Results of assessments carried out on a portion of a wind turbine blade are presented in the last part of this article. The application and production of composite materials in industry is rapidly growing. Most manufacturing stages are not automated and require partial, or full manual handiwork. This includes the resin impregnation and wet lay-up. Described production process may introduce variety of structural defects, such as delamination’s, voids, problems associated with wet lay-up, cracks, non-uniform layer composition. These defects can become a source of future exploitation problems. Wind energy is undergoing expansion and it is bound to grow to a commercial/consumer level in the decades to come. This growth has materialized in the form of large-scale wind farms, wind energy cooperatives, wind turbines owned by individual investors, and multinational exploration of remote sites and offshore locations. Condition monitoring and diagnostics has always been an important factor in wind energy in order to increase reliability and safety. A reliable, accurate and nondestructive damage detection method is a key element in successful monitoring of wind energy structures. A number of different damage detection methods have been developed and tested over the years including: visual inspection, passive and active approaches based on ultrasonic signals, liquid penetrant testing, eddy current based methods, radiographic methods and thermographic methods [1][2][3]. The size increase in wind power systems over the past decades lead to a greater focus on vibration problems of the structure, in particular the rotor-blades system which size and flexibility leads to high amplitude vibrations. The good balance of the rotor is important to ensure a safe, as well as an economic operation of the turbine and a good structural health preventing from early fatigue of the components, all the more so as loads are transmitted directly from the rotor to the drivetrain and generator, and can thus damage other functional subsystems. One of the rotor imbalances type is a mass imbalance. It is the result of an inhomogeneous mass distribution across the blades caused by the manufacturing inaccuracies. This involves a greater risk of the formation of defects in the structure of the blades, which require new rapid and reliable diagnostic methods for maintaining the safety of the exploitation of wind turbines. The monitoring and diagnostics of the blades is a complex problem, and raises several questions as on how it