Detection of Gear Tooth Crack in a Wind Turbine Planetary Gearbox

Abstract

A planetary gearbox of a horizontal axis wind turbine drive train is modelled as a vibratory system and vibration response is investigated for detecting a typical gear tooth flaw. A detailed dynamic model involving two translational and one rotational degree of freedom for each component of the planetary stage is formulated. The gearbox stage considered in the study is a low speed planetary gear stage (three identical planets with spur teeth, sun and fixed ring gear) as the typical arrangement commonly used in wind turbine industry. The effect of gravity is incorporated in the mathematical formulation as the mass of the drivetrain components is considerable in such application. The vibration response of the elements is influenced by the gear mesh stiffness variations. The presence of a tooth crack shifts the localized mean value of gear mesh stiffness to a lower value. The localized change in turn influences the vibration response of all the components. In order to extract fault-induced vibration features, a difference signal is generated from the synchronous time domain vibration signals for the healthy and cracked tooth. The time domain and frequency domain data of the proposed difference signal are studied. They reveal useful information for the purpose of detection of gear tooth crack. The spectral characteristics can be used for condition monitoring and early detection of gear tooth crack for a wind turbine gearbox.