Abstract
Small horizontal-axis wind turbine (HAWT) is a technology characterized by non-trivial critical points, basically because it is targeted for domestic use and therefore cheap manufacturing and control must conjugate with good efficiency under possibly complex flow conditions (especially in urban environment). Therefore, dynamical control optimization and noise and vibration mitigation are pressing issues for this kind of technology. Despite this, it is peculiar of small HAWTs that the generator constitutes a non-negligible fraction of the total mass and therefore the electromechanical coupling is relevant, condition monitoring of small HAWT generators is an overlooked topic. The present work is a test case study of damage diagnosis on a permanent magnet generator of a HAWT having 3 kW of maximum power and 2 m 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. Vibration measurements are collected in the wind tunnel through radial accelerometers near the rear bearing of the shaft and in the test rig through uni-axial accelerometers (fixed in radial positions, in order to be aligned with front and rear bearings). The test rig data results are particularly useful for studying the low-frequency tail of the vibration spectrum, where the characteristic frequencies of the bearing are located. The experimental data are analyzed in the time and frequency domain for feature extraction: a fault in the cage of the bearing supporting the generator is diagnosed using in particular the spectral coherence analysis.
Highlights
A reliable and efficient use of small horizontal-axis wind turbine (HAWT) technology [1] poses several challenges, because, on the one hand, the market requests low price for domestic investment and, on the other hand, the flow conditions to which these devices are commonly subjected can be complex.In order to guarantee acceptable values of the power factor Cp, HAWT typically have rotational speed up to several hundreds revolutions per minute
Small horizontal-axis wind turbine (HAWT) is a technology characterized by non-trivial critical points, basically because it is targeted for domestic use and cheap manufacturing and control must conjugate with good efficiency under possibly complex flow conditions
The main issue faced in this work is the following: can it be possible to do condition monitoring of small HAWT through wind tunnel tests? In other words, was it possible, for the test case of this work, to extract from the wind tunnel measurements and the test rig measurements the same information about the damage location? The answer is positive, but it depends on the selected post-processing techniques
Summary
In order to guarantee acceptable values of the power factor Cp, HAWT typically have rotational speed up to several hundreds revolutions per minute (rpm). This implies that noise and vibration control [6,7,8] is a pressing issue. The generator can transmit powerful vibrations to the small HAWT structure, especially at high frequency. Despite this matter of fact, the literature about condition monitoring and fault diagnosis on small HAWT generators is remarkably missing
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