  Wind energy is the leading non-hydro renewable technology. Increasing
reliability is a key factor in reducing the downtime of high-power wind
turbines installed in remote off-shore places, where maintenance is costly and
less reactive. Defects in the pitch system are responsible for up to $20\%$ of
a wind turbine downtime. Thus, prognosis and condition monitoring of such
defects are essential for avoiding downtime. This paper presents a generic
assessment of diagnosis capabilities in hydraulic pitch systems characterizing
high-power wind turbines. A mathematical model of the non-linear system
dynamics is presented along with a description of the most frequent faults that
can affect it. Structural analysis is employed to assess the diagnosis and
prognosis capabilities of defects in the pitch system. The structural
properties are furthermore explored to investigate possible sensor reduction
without compromising fault diagnosis capabilities.
