Wind Turbine Generator Reliability: An Exploration of the Root Causes of Generator Bearing Failures

Abstract

Increasing the availability of multi-megawatt wind turbines (WT) is necessary if the cost of energy generated by wind is to be reduced. Reliability surveys have shown that WT generator bearings have a relatively high failure rate, with failures happening too early to be due to classical rolling contact fatigue.

It has been the purpose of the present work to demonstrate the value of models which may help to explain some of the failure modes of wind turbine generators (and their root causes). The work has considered two potential root causes of wind turbine generator failure. Firstly, gearbox-generator misalignment caused by deflection of the compliant drivetrain under loading. Secondly, electrical discharge machining (EDM) of the generator bearings due to the common-mode voltage caused by pulse width modulation (PWM) of the power electronics.

Numerical simulations have been used to investigate these potential failure modes and to show how they bring about premature failure. It has been
shown that there exists a mechanism by which gearbox-generator misalignment can exacerbate EDM. This demonstrates the importance of holistic analyses
of WTs, which are complex electromechanical systems with non-trivial interactions between sub-assemblies. The need for further research has been shown.