Wind turbine plants have grown in size in recent years, making an efficient structural health monitoring of all of their structures ever more important. Wind turbine towers deform elastically under the loads applied to them by wind and inertial forces acting on the rotating rotor blades. In order to properly analyze these deformations, an earthbound system is desirable that can measure the tower’s movement in two directions from a large measurement working distance of over 150 m and a single location. To achieve this, a terrestrial laser scanner (TLS) in line-scanning mode with horizontal alignment was applied to measure the tower cross-section and to determine its axial (in the line-of-sight) and lateral (transverse to the line-of-sight) position with the help of a least-squares fit. As a result, the proposed measurement approach allowed for analyzing the tower’s deformation. The method was validated on a 3.4 MW wind turbine with a hub height of 128 m by comparing the measurement results to a reference video measurement, which recorded the nacelle movement from below and determined the nacelle movement with the help of point-tracking software. The measurements were compared in the time and frequency domain for different operating conditions, such as low/strong wind and start-up/braking of the turbine. There was a high correlation between the signals from the laser-based and the reference measurement in the time domain, and the same peak of the dominant tower oscillation was determined in the frequency domain. The proposed method was therefore an effective tool for the in-process structural health monitoring of tall wind turbine towers.

Wind turbines have grown in size in recent years, making efficient structural health monitoring of all of their structures even more important. Wind turbine blades deform elastically under the loads applied to them by wind and inertial forces acting on the rotating rotor blades. In order to properly analyze these deformations, an earthbound system is desirable that can measure the blade deformation, as well as the tower–blade tip clearance from a large measurement working distance of over 150 m and a single location. To achieve this, a terrestrial laser scanner (TLS) in line-scanning mode with vertical alignment is used to measure the distance to passing blades and the tower for different wind loads over time. In detail, the blade deformations for two different wind load categories are evaluated and compared. Additionally, the tower–blade tip clearance is calculated and analyzed with regard to the rotor speed. Using a Monte Carlo simulation, the measurement uncertainty is determined to be in the millimeter range for both the blade deformation analysis and the tower–blade tip clearance. The in-process applicable measurement methods are applied and validated on a 3.4 MW wind turbine with a hub height of 128 m. The deformation of the blade increases with higher wind speed in the wind direction, while the tower–blade tip clearance decreases with higher wind speed. Both relations are measured not only qualitatively but also quantitatively. Furthermore, no difference between the three rotor blades is observed, and each of the three blades is shown to be separately measurable. The tower–blade tip clearance is compared to a reference video measurement, which recorded the tower–blade tip clearance from the side, validating the novel measurement approach. Therefore, the proposed setup and methods are proven to be effective tools for the in-process structural health monitoring of wind turbine blades.

Zusammenfassung Die Windkraft stellt eine wichtige Energiequelle in Deutschland dar. Form und Lage der Rotorblätter von Windenergieanlagen haben dabei einen großen Einfluss auf die Effizienz und die Lebensdauer der Anlage. Geometrische Merkmale von Rotorblättern werden mit Blattschablonen, photogrammetrischen oder interferometrischen Messverfahren erfasst. Hierzu muss die Anlage jedoch gestoppt und ggf. mit Mustern bzw. Markern versehen werden. Für In-Prozess-Messungen ohne Manipulation der Windenergieanlage bietet sich das Prinzip der Laufzeitmessung an, auf dem sogenannte terrestrische Laserscanner aufbauen. Bisher unbekannt ist jedoch die erreichbare Messunsicherheit bei der Bestimmung von Pitchwinkeln. In diesem Beitrag werden die Messunsicherheiten bei der Erfassung der Rotorblattoberfläche für Distanzen > 100 m experimentell untersucht und zur Bestimmung der Unsicherheit des Pitchwinkels mittels Monte-Carlo Simulation fortgepflanzt. Für die Betrachtung der Pitchwinkelunsicherheit wird unterschieden, ob die Nenngeometrie der Rotorblätter bekannt ist und absolute Aussagen über die Pitchwinkel getroffen werden können, oder ob die Nenngeometrie unbekannt ist und nur relative Pitchwinkelunterschiede zwischen den Rotorblättern ausgewertet werden können.

Wind turbines have grown in size in recent years, making an efficient structural health monitoring of all of their structures ever more important. Wind turbine blades deform elastically under the loads applied to them by wind and inertial forces acting on the rotating rotor blades. In order to properly analyze these deformations, an earthbound system is desirable that can measure the blade deformation, as well as the tower-blade tip clearance from a large measurement working distance of over 150 m and a single location. To achieve this, a terrestrial laser scanner (TLS) in line-scanning mode with vertical alignment is used to measure the distance to passing blades and the tower for different wind loads over time. In detail, the blade deformations for two different wind load categories are evaluated and compared. Additionally, the tower-blade tip clearance is calculated and analyzed with regard to the rotor speed. Using a Monte-Carlo simulation, the measurement uncertainty is determined to be in the mm-range for both the blade deformation analysis and the tower-blade tip clearance. The in-process applicable measurement methods are applied and validated on a 3.4 MW wind turbine with a hub height of 128 m. As a result, the deformation of the blade increases with higher wind speed in wind direction, while the tower-blade tip clearance decreases with higher wind speed. Both relations are measured not only qualitatively but also quantitatively. Furthermore, no difference between the three rotor blades is observed, i.e. each of the three blades is shown to be separately measurable. The tower-blade tip clearance is compared to a reference video measurement, which recorded the tower-blade tip clearance from the side, with validated the novel measurement approach. Therefore, the proposed setup and methods are proven to be effective tools for the in-process structural health monitoring of wind turbine blades.