Laser system surveys wind turbine vibrations from afar
Under normal operating conditions, wind turbine blades and towers perform oscillations at an amplitude of up to several metres. These oscillations induce mechanical stress to the structure which can lead to damages, in extreme cases even to the loss of the entire installation. Wind generator operators for this reason check continuously the amplitude of these oscillations. Typically they perform these checks by means of sensors integrated into the tower or rotor blade structure. The downside of this approach is that the measurements only show the strength of the vibrations at the very places where the sensors are located.
Ilja Kaufmann from Fraunhofer Institute for Optronics, System Technology and Image Processing (Fraunhofer IOSB) have developed a system that generates a comprehensive oscillation profile of the structure from a distance of several hundred metres. The instrument consists of a laser beam directed towards the generator which can scan the vibrations at any place of the structure surface. In order to enable measurement at moving parts such as the rotor blades, the laser automatically tracks these movements by means of a computer-based control system: A camera is mounted along with the laser source on the top of a tripod with pan/tilt head. The camera takes pictures of the wind generator system and feeds the images to a software that generates a virtual model of the rotors out of these data. The information generated steers the pan&tilt head in such a manner that it follows the rotating movements of the rotor. At the same time, the camera collects data about the exact position of the laser point on the rotor blade to stabilize this point on the rotor blade. This makes it possible to scan as many points on the generator surface even from a great distance. "Within s short period of time, it is possible to create much more thorough analysis than what would be possible with fixed sensors", said Kaufmann.
The system is mobile and can transported in a car. Due to the high measuring range of the system it is also possible to survey offshore wind turbines, provided the user can compensate the vessel’s movement.
At CeBIT 2014, Fraunhofer IOSB will demonstrate a prototype of the diagnosis system (hall 9, stand E4).