An overvoltage protection device for protecting a wind turbine against overvoltage is provided. The overvoltage protection device includes an electrical transformer for transforming electrical power generated by a wind turbine generator from a low-voltage region to a medium-voltage region. The electrical transformer includes at least one secondary winding electrically connected to the generator of the wind turbine, at least one primary winding electrically connected to an electrical utility grid receiving the generated electrical power, and at least one counter-winding for receiving a counter-current. A winding direction of the counter-winding is opposite to a winding direction of at least one of the primary winding and the secondary winding. Furthermore, a detection unit for detecting overvoltage at the transformer, a determination unit for determining the counter-current on the basis of the detected overvoltage, and a current driver unit for flowing the counter-current through the counter-winding are provided.