On the Application of Fluid Power Transmission in Offshore Wind Turbines

Abstract

Offshore wind energy is currently characterized by the high costs associated with installation and operation. Gearboxes in particular have been singled out as a key source of the high maintenance costs of offshore wind farms. For a given wind speed, the torque of the rotor increases cubically with the diameter of its swept area. As the maximum size of wind turbines continues to increase, mass reduction and reliability are of growing importance for the system’s economy. In any industry where robust machinery is required to handle large torques, hydraulic drive systems are applied. It is therefore almost the obvious solution for wind turbines. The main components of a fluid power drive train are (1) a positive displacement pump, which transforms the mechanical power of the aerodynamic rotor into a high pressure fluid flow, and (2) a hydraulic motor, which converts the hydraulic power back into mechanical power. The research presented in this thesis is centered around the questions of whether and how the application of fluid power technology is feasible as an alternative to currently applied drive train technologies for offshore wind turbines. The approach is to define several possible configurations of the fluid power transmission system. From these, a concept using seawater hydraulics for centralized electricity production within an offshore wind farm is subjected to further analysis. Through research, modelling and experiments, the feasibility of this concept, known as the Delft Offshore Turbine is analyzed. To make offshore wind a competitive source of electricity requires more than incrementally improving and scaling-up onshore turbines. The concept for power transmission as presented in this thesis is shown to be technically feasible and will significantly reduce the complexity of offshore wind energy technology. A way to further prove the functionality and demonstrate the possible use of such a drive train is by building and testing it, preferably in a real turbine, offshore.