Feasibility Study of a Simulation Driven Approach for Estimating Reliability of Wind Turbine Fluid Power Pitch Systems

Recent field data indicates that pitch systems account for a substantial part of a wind turbines down time. Reducing downtime means increasing the total amount of energy produced during its lifetime. Both electrical and fluid power pitch systems are employed with a roughly 50/50 distribution. Fluid power pitch systems generally show higher reliability and have been favored on larger offshore wind turbines. Still general issues such as leakage, contamination and electrical faults make current systems work sub-optimal. Current field data for wind turbines present overall pitch system reliability and the reliability of component groups (valves, accumulators, pumps etc.). However, the failure modes of the components and more importantly the root causes are not evident. The root causes and failure mode probabilities are central for changing current pitch system designs and operational concepts to increase reliability. This paper presents a feasibility study of estimating pitch system reliability based on a failure rate prediction method for generic fluid power components. Special attention is given to the use of computer simulations for assessing working conditions such as flow, pressure, work cycle, fluid contamination concentration etc. The fluid power pitch system is co-simulated with the 5MW NREL wind turbine implemented in the FAST software. The estimated failure rates is compared to field data and comments are given to the correlation and discrepancies based on the uncertainties of the simulated conditions.