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Condition monitoring -- Four case studies

Early detection of incipient faults in specific wind turbine components is being explored by a number of manufacturers and research organisations. The aim is to catch problems early before they lead to damage in other components and expensive wind turbine outages. German-Danish condition monitoring company Brüel and Kjær Vibro has recently reported results from four wind turbine case studies in a measurement program covering over 100 vibration and other sensors. The sensors are automatically monitored, including detailed analysis of the signals, and alarms warn as soon as an accepted norm is exceeded. In the first case study, a gearbox second-stage vibration level exceeded the alarm limit and an analysis of the vibration signals indicated there was a possible fault. The operator was advised to examine the gearbox, paying particular attention to the second-stage gear teeth. During the inspection, metal shavings were found in the oil filter and these originated from the damaged second stage. The second case study involved a coupling defect and the symptoms were a rapid rise in vibrations near the generator, although other measurements indicated there was no rotor imbalance or bearing fault. Inspection showed that some of the coupling links had sheared and these were then replaced. The third case study involved a bearing fault at the generator driver end. The symptoms were similar -- a rapid rise in vibration -- and inspection showed an inner race bearing fault. The fourth study revealed that one of the support pads for the gearbox had cracked, which meant the component was not anchored as firmly as it should be. The vibration level was higher than normal at moderate power, but triggered the alarm at higher power levels. In all cases, prompt action by shutting down the turbines, inspecting the suspect components and replacing them avoided more extensive damage that would potentially have caused significant outage periods.

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