The invention relates to a method for producing at least one signal (oscillation signal), which indicates an oscillation in an electrical power supply system. In order to allow the oscillation behavior of an electrical power system to be detected safely and reliably at all times, an oscillation model is used which is formed from previous impedance values associated with the oscillation, or from variables dependent on these impedance values. A check is carried out to determine whether a further impedance value formed at that time or a variable which is dependent on this further impedance value differs from the oscillation model, and any occurrence of a further impedance value or of a variable dependent on this impedance value which differs from the oscillation model is assessed as the oscillation having stopped.