Improvement and Adaption of Bearing Monitoring System

With the ongoing developments in the offshore wind turbine industry, weight reduction is an important aspect. With these weight reduction, manufacturers are trying to increase the effciency and size of their turbines. An example of such a technique is a single bearing drive train. These designs use a special bearing which is extra stiff due to the support of axial raceways. Manufacturers are still proving the robustness of this promising design. At the moment, some manufacturers already constructed a prototype. An example of this prototype is the XD115 of XEMC Darwind. This turbine is permanently monitored with the use of a health monitoring system. This system mainly consists of accelerometers which are located throughout the whole turbine. This monitoring system can be extended by performing spectral analysis on the measured generator current. The purpose of this thesis is to investigate if it is possible to measure mechanical vibrations in the current output of a generator with full converter. The bearing is one of the most complex elements in this single bearing drive train. There- fore, the focus is put on monitoring the bearing. In order to investigate in this topic, two types of tests are performed, lab tests and full scale tests. During the lab tests, a small set-up is made and some bearings are tested. The full scale tests are performed on the XD115 prototype. During the tests in the lab most of the characteristic bearing frequen- cies could be measured. An increase in the amplitude of these frequencies was measured after damaging the bearing. In these lab tests, an increase in friction was also measurable. The characteristic bearing frequencies could be identied much easier in the frequency spectrum of the current than in the frequency spectrum of the accelerometer. The re- sults of the tests in the full scale turbine were less promising. Neither in the frequency spectrum of the accelerometer and current, a characteristic bearing frequency could be identied. However, when the rotational speed synchronisation algorithm is used, some mechanical vibrations could be identied. The shaft speed and each time a blade passes the tower were identied in the frequency spectrum of the current. This means that a mechanical vibration was measured in the generator current.EPPElectrical Engineering, Mathematics and Computer Scienc