Hydrostatic yaw bearing design for 500 kW horizontal axis wind turbine

Official URL: http://192.168.1.20/record=b1534383 (Table of Contents)

As wind turbines get larger, nacelle structure that is carried by yaw bearings becomes heavier. In order to bear these increasing loads, yaw bearing needs to have more than one row of rolling elements which cause increase in weight and consequently the cost of the yaw bearing in classical design [1]. As the industry trends demand larger and larger wind turbines, the slew bearing costs keep increasing. In addition to cost, slew bearings suffer other reliability problems in very large turbines. As the turbine size keeps increasing both overall nacelle weight and wind loads acting on the yaw system (radial, axial and moment loads) get very large. During operation these heavy loads act on a single/local point on the bearing for extended periods during which heavy loads oscillate with varying wind speeds/loads. Large cyclic loads acting on a specific point on bearing race cause indentation marks which is also called Brinelling failure. As turbine capacities keep growing well beyond 10 MW with offshore units, the need for a robust low cost alternative grows. Hydrostatic bearings are well known systems that are used in large and heavy load machinery. This thesis aims to investigate applicability and feasibility of alternative hydrostatic yaw bearing design for a sample horizontal axis wind turbine. Motivation of the thesis is to develop a hydrostatic bearing design for yaw system for a 500 KW wind turbine, and demonstrate advantages and disadvantages of the hydrostatic bearing yaw system in comparison to classical rolling element bearings by evaluating load capacity, rigidity, stiffness, cost and life.