Reliability of electrical and hydraulic pitch systems in wind turbines based on field-data analysis

The pitch system is notably one of the critical subsystems of a wind turbine, supporting its effective control towards maximising wind capture and at the same time protecting its integrity in cases of excessive loads. A pitching mechanism is also responsible for operational downtime, hence its reliability performance needs to be carefully evaluated so as to ensure operational availability. This study aims to derive failure rates of two configurations of pitch systems, namely the electrical and hydraulic, based on statistical analysis of a large population of onshore assets, followed by a classification of findings by turbine rating, effect of seasonality, and reliability performance of different manufacturers. The data sets underlying the present analysis are based on maintenance reports and comprise 1847 operational years of wind turbines with electrical and 848 operational years of turbines with hydraulic pitch system. Results of this study show high failure rates in pitch systems of both types, with hydraulic systems performing slightly better than electrical (0.54 vs. 0.56 failures per turbine per year), a significant variation between turbines of different manufacturers, and a tendency for higher failure rates for larger turbines.