Detection of impulsive signals on tendons for hybrid wind turbines using acoustic emission measurements

Abstract

The power generation of a wind turbine is determined, among other things, by its hub height. In recent years, a new, effi-cient and economical design for high wind turbine towers called hybrid towers is developed consisting of two sections. The lower section consists of prefabricated concrete ring segments that are post-tensioned together and assembled at the tur-bines site, whereas the connected upper section is composed of conventional steel rings. The prestressed tendons in the lower section are located inside the tower and ensure the stability of the wind turbine. Thus, these are critical elements and any damage to them should be detected as early as possible. The tendons are often highly prestressed and exposed to high dynamic loads. Fatigue failure in the prestressing steel is a potential risk. As the tendons are covered in plastic pipes and in some sections have contact to the concrete segments the access is limited for inspections. The aim of the presented inves-tigations is the development of a monitoring approach for the immediate detection of the occurring wire breaks. Acoustic emission measurement has been proved to be a promising technique for that and thus should be assessed. For experiments tendons were prestressed in a test frame with the dimensions of 12 x 4.1 m analogous to the boundary conditions of a real wind turbine. Wire breaks as well as wire break-like signals were generated on tendons, which are recorded by piezoelectric sensors and analyzed by a measuring device. The results show that by acoustic emission measurement the wire break signals can be well recorded. The results from the large-scale experiments are transferred towards the application at real structures.

Matched Filter for Acoustic Emission Monitoring in Noisy Environments: Application to Wire Break Detection

“…Nowadays, these constructions are of comparatively young age but as the lifespan progresses, breakage of single wires within the tendons may also become a security hazard for this type of infrastructure. A very first investigation on the geometric damping of acoustic emissions in external tendons with regard to applications in wind energy turbines was conducted in [16]. However, this study as well as most of the other aforementioned articles mainly focus on the characteristics of wire break signals and their damping behaviour to provide guidance regarding sensor distances that allow for a reliable detection of wire breaks by ensuring comparatively good signal-to-noise ratios.…”