Towards lifetime lubrication of wind turbine gearboxes: Technical and physical investigations on used oils

Modern geared wind turbines rely on the adequate performance of their lubricant to ensure optimum operation of their main gearboxes. Potential oil ageing mechanisms, such as oxidation or additive depletion, can degrade oil performance over time. An oil that performs satisfactorily throughout the entire life of the turbine can reduce the downtime, resources, and costs associated with oil changes or repairs. Therefore, the purpose of this study is to investigate the ageing of field oil through oil analysis and artificial ageing. In addition, the possibility of oil service life extension by top-treating used oils with additives was investigated. For the field oil evaluation, oil samples were taken from operating wind turbines with lifespans up to 16 years. The deterioration of their copper corrosion, foaming, and wear performance was assessed using standard tests and its influence on gearbox operation was identified. Although these properties had degraded to some extent, most oils continued to perform satisfactorily. To counteract oil ageing, top-treating (adding additives to the field oils) was performed to restore the corresponding properties of oils. Subsequent standard tests confirmed that this approach is generally effective, but there are still some potential problems. To further investigate the oils’ lifespan limits, field oils were subjected to artificial ageing. This process involved oil heating and the artificial, accelerated consumption of anti-wear additives. Experimental results indicated that artificial ageing has only a minor influence on wear despite a significant reduction in additive concentration. In conclusion, proper monitoring of oils and timely top-treat have the potential to achieve lifelong wind turbine gearbox lubrication.