Lubrication mechanisms in offshore wind turbines
Date of Issue2018
Interdisciplinary Graduate School
Wind turbine technology is at the forefront of the renewable energy mix. With the subsidy scenario changing in the UK and incessant push for coal, wind turbine technology is still holding strong. The price of offshore wind in the UK, the biggest producer has gone down by one-third and US investment has gone up by 40% representing an annual investment of 13 billion dollars by 2017. Offshore wind turbine technology, thus, is the future of wind turbine investments. Wind turbines have inherent logistical challenges due to the size, and additional challenges due to the difficult offshore reach. Thus, reliability is a fundamental design requirement of all the components. The lubricant is one of the components of the drive-train based systems. Lubricant interaction with the bearing and gears has been studied extensively to improve design parameters. However, the effect of offshore parameters like salinity and water haven't been studied. The salinity and moisture interaction with the components, the tribological interactions with the bearing material and the lubricant components, and the possible onset of failures has not been studied extensively. As per the very recent advances, instead of retrofitting the onshore turbines to the offshore environment, companies are trying to take a bottom-up approach to design the wind turbine components suited precisely for the offshore environment. A fundamental study of these interactions will thus, aid such developments and design rigor. The following thesis has attempted to decipher some such possible interactions. The approach taken for this study was from the perspective of first designing lubricant compositions depending on different synthetic component chemistries. These different chemistries were then subjected to possible offshore loads. A wide range of loads was chosen to understand the possible evolution in terms of contaminants and temperature. The loads were simulated to recreate the environment the actual bearing might see. The studies were attempted at laboratory scale as well as component scale to understand the differences and similarities in mechanisms that occur with these loads. A brief understanding of wear is also presented for a subset of the studies undertaken. Viscosity is the fundamental operational and condition-monitoring parameter for assessing the health of the drive-train system. An understanding of the variation of viscosity with the offshore loads is presented in detail. One of the important contributions of this work is the understanding of the differences in process parameters based on different base oil chemistry, irrespective of the additive packages. Power efficiency, traction coefficient, and friction properties were also studied with the offshore loads and an understanding on the basis of base oils and loads are discussed in detail. Some other approaches were tried to trace the markers of degradation of the lubricant oil through aging techniques, contaminant evolution detection with FTIR and gravimetric analysis. But further investigation and use of supplementary techniques are needed to decipher the mechanisms with the qualitative techniques mentioned above. The thesis, thus, gives a tribological understanding of the behavior of the different lubricants representing different base oils in presence of offshore loads.