Wind energy system and method for identifying low-frequency oscillations in an electrical supply network

A wind power installation or wind farm including a plurality of wind power installations configured to identify low-frequency oscillations in an electrical supply network having a line voltage associated with a nominal line frequency, the wind power installation or wind farm comprising:

• a controller configured to:
• detect at least one electrical signal of the electrical supply network as at least one test signal;
• filter and/or transform the at least one test signal into at least one check signal;
• temporally differentiate the at least one check signal or determine a difference between temporally separated values of the at least one check signal to obtain a gradient signal;
• and
• identify a presence of a low-frequency oscillation in response to the gradient signal meeting a predetermined criterion, wherein:
• transforming the at least one test signal into the at least one check signal includes transforming line voltages of the electrical supply network in three phases and current fed into the electrical supply network in three phases into a voltage signal, an active power signal and a reactive power signal as a voltage check signal, an active power check signal or a reactive power check signal,
• temporally differentiating the at least one check signal includes temporally differentiating the voltage check signal, the active power check signal and the reactive power check signal to obtain a voltage gradient signal, an active power gradient signal and a reactive power gradient signal, respectively, or determining the difference between the temporally separated values of the at least one check signal includes obtaining a difference of temporally separated values of the voltage check signal, the active power check signal and the reactive power check signal to obtain the voltage gradient signal, the active power gradient signal and the reactive power gradient signal, respectively,
• the voltage gradient signal, the active power gradient signal and the reactive power gradient signal are checked for the presence of the low-frequency oscillation, and
• the presence of the low-frequency oscillation is identified in response to the low-frequency oscillation being found at least in the voltage gradient signal and the active power gradient signal or in the voltage gradient signal and the reactive power gradient signal.