Abstract: The present invention relates to a wind turbine facility comprising a power generator operationally connected to an AC/AC converter adapted to receive variable frequency AC-power from the power generator, and adapted to generate substantially fixed frequency AC-power. The wind turbine facility further comprises a harmonic filter system, and a grid transformer comprising a primary winding being operationally connected to the AC/AC converter, and a secondary winding adapted to be operationally connected to an associated, substantially fixed frequency AC-power supply grid. The grid transformer further comprises a tertiary winding being operationally connected to the harmonic filter in order to suppress unwanted harmonics, such as selected harmonics generated by the AC/AC converter. The turn ratio between the primary and tertiary windings is selected in such a manner that a voltage of the tertiary winding is lower than a nominal voltage level of the associated AC-power supply grid voltage.