Practical investigation of using passive radar for structural health monitoring of wind farms

In order to keep total life time costs of wind turbines competitive, the risk of failure has to be minimized, maintenance costs have to be reduced and energy efficiency needs to be increased. To achieve these goals, it is necessary to install efficient automated multi-sensor online monitoring and diagnose systems, so-called condition monitoring systems (CMS). The economic importance of these CMS systems has been increasingly recognized by wind farm operators, manufacturers and insurance companies. Thus, numerous CMS are already available on the market, however monitoring and fault detection is almost exclusively limited to the turbines drive train. Structural monitoring systems CMS, so called structural health monitoring systems (SHM) are currently only available to a very limited extent and are used almost exclusively in the research context. This applies especially to systems supervising wind turbines primary structural components such as the blades, tower and foundations. This paper explores the possibility of an alternative radar based monitoring technique which utilizes public broadcast transmissions to detect specific damage events remotely. Such a passive bistatic radar system (PBR) is capable of isolating and analyzing signal components of such transmissions, that have been scattered from objects within the environment such as the large scale structures from a wind turbine. This investigation aims to demonstrate that a PBR system is capable of extracting information about the wind turbines structural dynamic as a potential new class of SHM system. The presented results were obtained from measurement data taken with a prototype PBR, which is currently deployed within an on-shore wind farm.