A great deal work has been done in WTG monitoring. Initially, work was done on condition monitoring systems (CMS) often based on vibration analysis with spectral methods like Fourier and wavelet transforms [4] and [5]. This offered various methods for detecting issues related to the WTG structure and the drive-train components. Since most of the CMS methods are needing the installation of additional sensors, methods based on the Supervisory Control and Data Acquisition (SCADA) system were also proposed [6].