Experimental damage detection on small wind turbines through vibration and acoustic analysis

Dynamical control system optimization and noise and vibration mitigation are particularly pressing issues as regards horizontal-axis small wind turbines. A peculiarity of this technology is that the generator constitutes a non-negligible fraction of the total mass and therefore the electromechanical coupling is relevant. Condition monitoring of small wind turbine generators is an overlooked topic in the literature and in the operation of these systems. This work is devoted to damage diagnosis on a permanent magnet generator of a horizontal-axis wind turbine having 3 kW of maximum power and 2 meters of rotor diameter. The experimental analysis is conducted through wind tunnel tests and on a generator test rig where a damaged and an undamaged generators have been driven at different rotational speeds. The test rig data are useful for studying the low-frequency tail of the spectrum, where the characteristic frequencies of the bearing are located. A fault in the cage of the bearing supporting the generator is diagnosed using the spectral coherence analysis.