Analysis of Pitch Gear Deterioration using Indicators

This work concerns a case study in the context of risk-based operation and maintenance of offshore wind turbines. For turbines with electrical pitch systems, deterioration can generally be observed at the pitch gear teeth; especially at the point the blades are located during normal production. This deterioration is expected to cause larger loads, because increased play causes dynamic loads. At some point, the increased loads can be expected to cause a failure somewhere in the pitch system. If the loads increase with the size of the damage, the loads can be used as indicators of the size of the damage. This hypothesis was supported by results from a measurement campaign where measurements were available both before and after maintenance was performed. The loads dramatically decreased after the maintenance. However, after a few more months of measurements, and by including data from the SCADA system, it became obvious that seasonal changes in the temperature were the primary cause of the decrease. A model was established to remove the effect of the explained variation, and see if deterioration can be detected in the peak torque.