Reliable Fluid Power Pitch Systems: A review of state of the art for design and reliability evaluation of fluid power systems

The key objectives of wind turbine manufactures and buyers are to reduce the Total Cost of Ownership and Total Cost of Energy. Among others, low downtime of a wind turbine is important to increase the amount of energy produced during its lifetime. Historical data indicate that pitch systems accounts for a substantial part of the downtime of wind turbines. With a focus on fluid power pitch systems; this paper presents an overview of methods relevant to assessing and increasing the reliability and availability of such systems. Four major areas are identified and covered; failure analysis, reliability and availability assess- ment, condition monitoring and fault-tolerant control. Within each area a brief description of the state of the art is given. On basis of the state of the art, a discussion is given on where further work is required in order to obtain a systematic framework for designing reliable fluid power.