The invention relates to wind turbines, particularly to controlling reactive power exchange between a power grid and a wind power plant. The wind power plant has a plurality of wind turbine generators each having a corresponding power converter with a converter controller. Further, the wind power plant has a power plant transformer with an on load tap changer coupled between the wind power plant and the power grid. The power plant controller is regulating the on load tap changer and is generating reactive component setpoints for the wind turbine generators, when determining a need for production of short-term reactive power due to a sudden change in reactive power measured at the point of common coupling.