Περίληψη:
This thesis will investigate the reliability issues associated with one of the most critical parts of a wind turbine, the gearbox. The transmission or gearbox converts the low rotor blades rotational speed to high generator-required rotational speed. This vital part of a wind turbine is very expensive to manufacture and to replace it in case of failure. In order to extend the life-span of a gearbox, regular maintenance is needed, which adds to the overall cost. This complex piece of engineering is very heavy, which puts extra stress to the tower. Usually wind turbines with gearboxes need stronger and deeper foundation. In addition gearbox reduces the efficiency of a wind turbine due to inertia; it is vulnerable to wind gusts and the most likely part of a wind turbine to fail.
One way to improve the efficiency of a wind turbine and make it more fault-tolerant is to avoid using gearboxes and use direct-drive systems instead. At gearless or direct-drive wind turbines, the rotor is the only moving part that transfers the energy from the blades to the electric generator via a low speed shaft. Those wind turbines eliminate gearboxes by replacing them with variable speed electric generators and solid-state electronic converters. The downside is that a wind turbine with direct drive generators, which operates at lower rotational speeds, can cost up to 30% more than other turbines.
In this thesis we investigate several issues arising from the use of transmissions or gearboxes. The analysis addresses Mechanical as well as Electrical issues. At the first part, static structure analysis will be presented. At the second part, an electrical analysis will be given, pointing out ways to convert the low frequency and low voltage AC signal to grid-required AC signal. Finally, ways to improve even further the electrical part of the wind turbine will be suggested with the use of advance power electronics [1].