Condition monitoring of a wind turbine DFIG by current or power analysis

As wind energy assumes greater importance in remote and offshore locations, effective and reliable condition monitoring techniques are required. This paper proposes a method analysing electrical signals from the stator terminals of the wound rotor induction generators commonly used in wind turbines. Analytical equations have been derived for the frequency content of line current and total instantaneous power for healthy and faulty wound rotor induction generators and these have been used to analyse signals from test rigs in the steady state. Analysis at constant speed yields a set of equation constants which describe the frequencies of most interest as observed from the test rig environments. Having discovered a consistent group of fault frequencies the data is then demonstrated at variable speed to show the variability of those fault frequencies with speed. It is concluded that tracking these speed dependent fault frequencies will be an effective way to monitor the health of a wound rotor induction generator in a wind turbine.