Inter-area oscillations in Continental Europe, 2023–2026: a case-based PMU dataset

This dataset documents low-frequency inter-area oscillations in the Continental European (CE) synchronous area between 9 February 2023 and 21 October 2026, using synchronised phasor measurement unit (PMU) recordings. The dataset contains 88 cases. Each case holds frequency and voltage-angle (and, where available, voltage-magnitude) measurements from up to nine PMUs between Spain and Latvia: Málaga (ES), Winterthur (CH), Ostrhauderfehn and Ilmenau (DE), Croatia (HR), Riga, Ādaži, Daugavpils and Gulbene (LV). A Nordic PMU (Trondheim, NO) is included as an asynchronous control. The data come both on a common 10 samples/s grid and at native rate (10 or 50 samples/s). Case types 39 sustained, poorly damped East–Centre–West episodes (0.18–0.24 Hz, damping ≈ 1–3 %) in which the Iberian Peninsula oscillates in anti-phase against central Europe. 4 large East–Centre–West bursts, including the morning of 28 April 2025. The 28 April 2025 Iberian blackout sequence: 0.63 Hz forced oscillation, then 0.21 Hz inter-area oscillation, then collapse. 25 ringdowns after generation or load losses with an identified trigger, including trips of Spanish, French, German, Dutch and Polish units. 6 East–West mode (0.12–0.16 Hz) ringdowns and responses, in which Iberia and central Europe swing in phase. 11 events of the new Baltic–CE modes (0.26–0.38 Hz) after the Baltic synchronisation on 9 February 2025, including HVDC (Estlink) trips. 2 Iberian forced oscillations (0.64–0.70 Hz). Files and conventions cases_overview.html: start here. Interactive page listing all 88 cases (time, type, mode frequency, damping, amplitudes, trigger) with the frequency plots and mode shape of each case. Open it in a browser; it works offline. CE001_….zip … CE088_….zip: one archive per case, numbered chronologically and named CE<nnn>_<YYYYMMDD>_<HHMM>_<TYPE> after the peak time (UTC). Each contains: pmu_10sps.csv.gz: all available PMUs on a common 10 samples/s grid. Columns: time_utc, <station>__f_Hz, <station>__angle_deg (wrapped ±180°), <station>__vmag, and NO_NTNU__f_Hz (Nordic, asynchronous control). Empty cells mean no data. native/<station>__f_Hz.csv.gz, native/<station>__angle_deg.csv.gz: the same signals at the PMU's native rate (10 or 50 samples/s), unmodified. mode_shape.csv: per station, the time lag relative to CH_ZHAW (lag_s, positive = station late), the oscillation amplitude (amp_mHz, rms_mHz), the phase relative to CH_ZHAW (phase_deg_vs_CH_ZHAW, ±180° = anti-phase), the coherence, and the min/max frequency. case.json: case metadata (times, type, mode frequency, damping, amplitudes, phases, trigger and its external confirmation, Spain→France exchange). plot.html: interactive plot of the case at full time range. Stations: ES_Malaga (Málaga), CH_ZHAW (Winterthur, reference), DE_Ostrhauderfehn, DE_Ilmenau, HR_STER (Croatia), LV_Riga, LV_Adazi, LV_Daugavpils, LV_Gulbene, NO_NTNU (Trondheim). Times are UTC. The data are not lag-corrected; use lag_s from mode_shape.csv when comparing stations. Angles are absolute single-phase angles with site-specific offsets, so use differences between sites and their variations rather than absolute values. Damping (ζ) and frequency come from a joint NExT-ERA method on all frequency channels, 0.1–0.6 Hz, 20 min around the peak. For trip cases the mode frequency is indicative only. Main observations Between 2023 and April 2025 the East–Centre–West mode repeatedly became almost undamped for minutes to hours, mostly at midday in spring and autumn and during high Spanish exports to France. It had done so many times before its most extreme occurrence on 28 April 2025. Since the blackout this activity has decreased by about 80 % (oscillation minutes per 100 days with Iberian data, so excluding the Málaga gap from May to December 2025), but it has not disappeared. In this mode Iberia swings 3–5× more than central Europe, in anti-phase, while the Baltic states swing in phase with central Europe at a slightly larger amplitude. Limitations Iberia is represented by one distribution-level PMU, which has no data from 7 May to 17 December 2025. Some PMUs have timestamp lags of 0.3–3 s. CH_ZHAW shows a local 0.397 Hz forced oscillation from April to September 2026, caused by local power-quality issues rather than a grid mode. For the Baltic–CE mode cases of that period (0.31–0.39 Hz) it may bias the CH_ZHAW amplitude and the phases referenced to CH_ZHAW; use phase differences between the other stations instead. Mode parameters are automatic estimates. Acknowledgements The first PMU data exchange between the partner laboratories was established in the project CloudGrid (Transnational CLOUD for Interconnection of Demonstration Facilities for Smart GRID Lab Research & Development), funded by the Swiss Federal Office of Energy (SFOE, SI/501360). Frequency and PMU data were exchanged in collaboration with the GridRadar platform (Tobias Veith). The data exchange between Latvia and Switzerland is enabled by the project LACISE, funded by the Swiss State Secretariat for Economic Affairs (SECO) through the Second Swiss Contribution to reducing economic and social disparities in the EU, with co-financing from the Latvian state budget. It is carried out within the Swiss-Latvian Cooperation Programme "Partnership in Applied Research" under Grant Agreement No. LZP/LV-CH-RESEARCH/PC2, implemented in Latvia by the Ministry of Education and Science. The Croatian PMU data (HR_STER) were provided by STER (Studio Elektronike Rijeka) Ltd. from their WAMSTER synchrophasor wide-area monitoring network. This work contributes to the IEA ISGAN Smart Grids International Research Facility Network (SIRFN).