A method for operating a wind
turbine and / or a wind farm for feeding
electric power into an electrical supply grid, wherein an output power, in particular an active and / or reactive power, is regulated by means of at least one
power regulation module of a regulation and / or control device, wherein provision is made for a
power regulation input value to be preset and a
power regulation output value to be determined from the power regulation input value and for a power regulation output value to be output, and provision is additionally made for a
time profile of the output power of the wind energy generation to be detected over a detection time period and for a
time profile of the line
voltage of the electrical supply grid to be detected over a detection time period, wherein a check is performed over the detection time period to ascertain whether the output power and the line
voltage have an oscillation profile. In accordance with the disclosure, provision is made for an oscillation with a period and with an amplitude to be assigned to the oscillation profile and for it to be established that the oscillation continues over the detection time period and does not decrease in the process, and for a
signal to be output for signalling an oscillation buildup state.