Knocking sounds in the wind turbine gearbox during slowing down—case study

Abstract

In the gearbox of a wind turbine under investigation, a knocking sound was noticed during coasting down of the machine. The noise was present in one of several gearboxes of the same type and the search for the source of the sound was undertaken. Gearbox manufacturer specialists after an inspection were pointing out sources outside the gearbox—runner unbalance or generator, but the machine owner ordered an additional research comprising vibration measurement and further analyses. The analysis of the vibration signal was carried out with the use of advanced signal analysis tools and the knocking vibration frequency was found to be the same as the frequency of the intermediate shaft. A machine inspection which was carried out pointed at a few potential sources of the sound, but did not specifically determined its source.