During recent years, condition monitoring (CM) systems are
being developed based on the collection and analysis of relevant
information from the main wind turbine components to reduce
maintenance costs and to increase production rates.
Some of these systems use anomaly detection techniques based
on an analysis of the data provided by the integrated supervisory
control and data acquisition (SCADA) system . Other
approaches are focused on specific signals measured at high frequency
rates used for dynamic testing or health monitoring. In
this sense, the best-known technology is based on vibration measurements
and their analysis in the frequency domain.
For variable-speed machines, care must be taken to ensure that
vibrations are not amplified due to the proximity of the natural frequencies
of the tower–nacelle system or of the blade to the rotor
rotational frequency or any of its multiples. For instance, several
investigations have shown that high noise amplitude levels
are generated at the blade passing frequency. Such tower
dam excitation is caused by the short-term collapse of the aerodynamic
forces at the blade when it approaches the tower once per
revolution. Moreover, the occurrence of these vibrations
results in significant fatigue loading on the tower, and they have a
negative impact on the turbine performance.