Dynamic measurement of frequency and ROCOF in modern power electricity networks
Large-frequency oscillation in south-west Spain updated!
Between 18:00 and 20:00 CET (17:00-19:00 UTC) on 11 December 2025, frequency and voltage oscillations were larger than usual in Seville. The magnitude was similar to that recorded during the major blackout. A detailed analysis also revealed sub-synchronous harmonics.
Another large oscillation with similar characteristics was recorded between 20:00 and 21:00 CET (19:00–20:00 UTC) on 29 December 2025.
The updated report draws conclusions and provides in-depth analysis of the frequency spectrum of such oscillations and their most likely source. It also highlights the network's or its controls' lack of strength and its weakness towards the 15-minute market signals.
Spanish blackout
A device had already been installed in Seville when the major blackout in Spain occurred. Several weeks of data were recorded before the event, and have been continuously recorded since then.
The following document depicts two main oscillations and the blackout. The time resolution is 10 milliseconds, and both the frequency and the ROCOF were recorded at 1, 5, 10 and 50 cycle windows.
