The Cost of Compromise: Wind Turbine Main Shaft Grease Lubrication Engineering Study Edward Worthington and Dwaine Morris Shell Product Technology Hamburg, Germany and Houston, Texas, US
Abstract Wind turbine main shaft and blade bearings have divergent lubrication requirements due to some specific application conditions and performance implications. Main shaft bearings are heavily loaded components subjected to slow rotational speeds, shock loads and variable ambient temperatures. While blade bearings are also subjected to similar conditions relative to load and temperature, they are further exposed to limited angle of rotation and are prone to fretting wear due to high frequency vibrations. To satisfy lubricating requirements, most main shaft greases tend to contain higher viscosity base oils, whereas blade bearing greases have trended toward lighter viscosity base fluids. However, there have been, and continue to be, attempts by original equipment manufacturers and turbine owners to utilize the same lubricating grease for these divergent applications. Wind turbine original equipment manufacturers are increasing base oil viscosity for blade bearing greases while simultaneously decreasing the base oil viscosities of main shaft greases. Their intents are to gain mobility and reduce low-temperature torque in the main shaft grease, while increasing the shock load resistance of the blade bearing grease and maintaining the fretting wear protection. For the OEMs and maintenance service providers, this consolidation reduces complexity. However, this consolidation compromises optimal performance in both applications. This paper examines a case study of a specific attempt where consolidating greases for main shaft and blade bearings led to excessive wear and risk of catastrophic wind turbine failure. The analytical tools and engineering calculations used in a root cause analysis in this case study can also be applied to predict the suitability of greases for main shaft bearings and other applications. Presented at the NLGI 85th Annual Meeting Coeur d’Alene, ID June 9 - 12, 2018 Background- Renewables on the Rise Wind energy is growing in significance in the US energy production market. According to the American Wind Energy Association (AWEA): • In 2012 wind energy became the number one source of new US electricity generating capacity, supplying 42% of the newly installed capacity. [1] • The turbines themselves are producing nearly 20 times more power per turbine than those installed in 1990. [2] • Together, renewables accounted for ~67% of newly installed power generation capacity in the US in 2015. [2] • In 2016, electricity generated from wind energy avoided 159 million metric tons of carbon dioxide emissions. This is the equivalent of reducing power sector CO2 emissions by 9% and avoiding the consumption of 87 billion gallons of water. [2]
- 28 VOLUME 83, NUMBER 2
