Vibration-based diagnostics of gearboxes under variable speed and load conditions

Maintenance represents the major cost of energy from wind turbines, once they are installed, so much research effort is currently going into reducing the costs of maintenance through improved condition monitoring. The most efficient turbines vary in speed by a ratio of up to 2:1 (+/- 33%), and so techniques developed for constant speed machines can no longer be directly applied. This paper discusses a number of recently developed techniques for compensating for the effects of variable speed on vibration signals from wind turbine gearboxes, the most critical part of typical systems. In particular it is shown how the effects of speed on gears and bearings are quite different, and require different treatment, this having been disguised for constant speed machines. Though aimed at wind turbine gearboxes, the techniques proposed in this paper are applicable to any variable speed gearboxes.