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Grid Frequency Report 06-2026

Welcome to the 6th report this year of the data acquired with the PQopen measurement network.

News of PQopen Network

New Location in Southern-East Europe

Since June, there is a new measurement location active: ME/Podgorica. This installation in Montenegro gives additional insights in what is happening in the central European grid. Interestingly, Montenegro is additionally interconnected with Italy, a HVDC line is in operation since 2019.

Summary

In the summary, the 1s-mean value of the mains frequency is evaluated.

StatisticsValue and occurance
MIN49.8575 Hz (2026-06-14 08:00:49 CET)
1% Percentile49.9457 Hz
MEAN49.9999 Hz
99% Percentile 50.0502 Hz
MAX50.1225 Hz in AT/Graz (2026-06-28 17:01:25 CET)

Daily Mean

The daily mean can give you an overview of the „accuracy“ of the grid control and their effect on grid synchronized clocks. June was very dynamic in this case, first half was typically below 50 Hz, on 26th, the value was catched up.

Rate of Change of Frequency (ROCOF)

The ROCOF is an indicator for potential events and the steadiness of the frequency. The higher the value, the more disturbances are at work (oscillations, transients…).

ROCOF of DE/Berlin: Most of the time between +-8mHz/s with significant outlier, some of these events are plotted in the Events-Section.

Frequency Spread

I introduced the metric „Frequency Spread“ in the posting, where I analysed the dynamic of the frequency the past 15 years. From now on, I want to use this metric in this report.

Frequency spread of the previous (blue) month and June (orange). The level is still decreasing since the peak in May.

Inter-Area oscillations

The inter-area oscillations is a long-known phenomenon resulting from the wide area of interconnected countries. In Spain, two modes can be detected, the east-center-west and the east-west mode.

PSD of Frequency in ES/Pamplona. More „movement“ in the second half of month.

Oscillations in the Netherlands

Amplitude of 3.5 Hz Oscillation of different locations.

Other Abnormalities

More deviations of frequency below 49.9 Hz and over 50.1 Hz, a fall of >50% can be noticed compared to previous month:

ENTSO-E Central Europe< 49.9 Hz> 50.1 Hz
Count of threshold crossings23 (-19)21 (-9)
Number of seconds below/above449 (-600)174 (-510)
Counts of +-100 mHz threshold crossings and duration in seconds. Numbers in colons are the absolute change of value to previous month.

Events

Below, there are several graphs, each representing a detailed time series plot of cycle-by-cycle frequency as well as 10-cycle moving average, phase angle difference and voltage magnitude.

Some readers had the idea of automatically analyzing these traces and doing some sort of „triangulation“ for estimating the area of event root. I had no time in february to give it a try, but it is on my list. If someone of you is interested of trying this, please use the archived data or the API for more recent events.

List of all detected events
Timestamp (UTC)Timestamp (CET)TextCategory
2026-06-28 05:27:582026-06-28 07:27:58Short Circuit in Northern Germany;
Same Fingerprint as Event at 02:03		Transmission Outage
2026-06-28 00:03:122026-06-28 02:03:12Short Circuit in Northern Germany
TTG/380/HEIDE W-SUEDERDONN/GN		Transmission Outage
2026-06-26 11:24:492026-06-26 13:24:49Northern Germany (similar to 10:10)Frequency Swing
2026-06-26 08:10:242026-06-26 10:10:24Northern Germany, Source Unknown yetFrequency Swing
2026-06-25 08:00:042026-06-25 10:00:04(FI) Load rejection test Olkiluoto 1 B1 (890MW)Generation Outage
2026-06-23 04:54:392026-06-23 06:54:39Northern Germany IIFrequency Swing
2026-06-23 04:47:502026-06-23 06:47:50Northern GermanyFrequency Swing
2026-06-21 23:01:102026-06-22 01:01:10Neurath G (Germany) 1058 MWGeneration Outage
2026-06-21 15:50:052026-06-21 17:50:05Trip of Baltic Cable (DE<>SE)Transmission Outage
2026-06-21 13:38:142026-06-21 15:38:14Nordlink (DE<>NO) 685 MWTransmission Outage
2026-06-19 12:17:072026-06-19 14:17:07DE/BerlinFrequency Swing
2026-06-18 17:40:492026-06-18 19:40:49Äänekoski Power Station (FI)Generation Outage
2026-06-18 14:59:042026-06-18 16:59:04Northern-West EuropeLoss of load
2026-06-18 03:26:402026-06-18 05:26:40Failure in HVDC Baltic Cable DE<>SE (short circuit on German side)Transmission Outage
2026-06-16 11:26:332026-06-16 13:26:33HVDC Skagerrak 3 (440MW) DK1<>NOTransmission Outage
2026-06-16 09:51:412026-06-16 11:51:41Sourthern-East EuropeFrequency Swing
2026-06-15 11:16:322026-06-15 13:16:32Start of 3 Minute 0.65 Hz Oscillation SpainOscillation
2026-06-15 02:52:422026-06-15 04:52:42AustriaVoltage Dip
2026-06-13 03:22:022026-06-13 05:22:022.65 Hz Voltage Oscillation in SpainOscillation
2026-06-12 13:46:192026-06-12 15:46:19Event in southern-east Europe lead to a reaction staring in SwizerlandFrequency Swing
2026-06-12 12:37:212026-06-12 14:37:21Unknown Event in Nordic AreaGeneration Outage
2026-06-12 05:47:032026-06-12 07:47:03southern-east EuropeGeneration Outage
2026-06-12 03:09:512026-06-12 05:09:51Intera-Area Oscillation Spain vs. MontenegroOscillation
2026-06-11 10:08:482026-06-11 12:08:48Unknown Event in Nordic AreaTransmission Outage
2026-06-09 10:53:152026-06-09 12:53:15Switching Operation eastern GermanyFrequency Swing
2026-06-08 13:13:462026-06-08 15:13:46Failure of SwePol LinkTransmission Outage
2026-06-07 08:07:162026-06-07 10:07:16Disconnection of Kriegers Flak – Baltic 2 (Substation KFE, 400MW) after Short-CircuitTransmission Outage
2026-06-06 07:52:322026-06-06 09:52:32France: Nuclear Power Plant FLAMANVILLE 1 (1330 MW)Generation Outage
2026-06-05 09:35:442026-06-05 11:35:44Spain: Nuclear Power Plant Vandellos 1045 MWGeneration Outage
2026-06-04 15:32:392026-06-04 17:32:39Switching Operation / Transmission Restoration in FranceFrequency Swing
2026-06-04 13:51:162026-06-04 15:51:16Switching Operation / Transmission Failure in FranceFrequency Swing
2026-06-03 13:36:332026-06-03 15:36:33Unknown yetFrequency Swing
2026-06-02 14:45:012026-06-02 16:45:01Swizerland: KernKW Leibstadt 1233 MWGeneration Outage
2026-06-02 02:32:062026-06-02 04:32:06Outage in France: TRICASTIN 3 (915 MW)Generation Outage
2026-06-01 14:44:062026-06-01 16:44:06Event in NORDIC Area: Possibly Grid Disconnection of Forsmark Block 3Frequency Swing

Central Europe Area

2026-06-02 14:45:01 (UTC): Grid disconnection of Nuclear Power Plant in Swizerland (Leibstadt 1233 MW)
2026-06-04 13:51:16 (UTC): Switching Operation / Transmission Failure in France
2026-06-05 09:35:44 (UTC): Spain: Grid disconnection of Nuclear Power Plant Vandellos 1045 MW
2026-06-12 03:09:51 (UTC): Intera-Area Oscillation Spain vs. Montenegro
2026-06-12 13:46:19 (UTC): Unknown event with a surprising reaction chain: Event in Montenegro lead to first reaction in Swizerland (maybe failure in HVDC MONITA Italy<>Montenegro)
2026-06-15 11:16:32 (UTC): 3 Minutes of 0.65 Hz Oscillation Spain

Nordic Area

2026-06-01 14:44:06 (UTC): Disconnection of Forsmark Block 3
2026-06-11 10:08:48 (UTC): Short Circuit with generation disconnection in Nordic Area.
2026-06-25 08:00:04 (UTC): (FI) Load rejection test Nuclear Power Plant Olkiluoto 1 B1 (890MW)

CE & Nordic Area

2026-06-07 08:07:16 (UTC): Disconnection of Kriegers Flak – Baltic 2 (Substation KFE, 400MW) after Short-Circuit
2026-06-08 13:13:46 (UTC): Failure of SwePol Link
2026-06-16 11:26:33 (UTC): Failure of HVDC Skagerrak 3 (440MW) DK1<>NO
2026-06-18 03:26:40 (UTC): Failure in HVDC Baltic Cable DE<>SE (short circuit on German side)
2026-06-21 13:38:14 (UTC): Failure in Nordlink (DE<>NO) 685 MW
2026-06-21 15:50:05 (UTC): Trip of Baltic Cable (DE<>SE)

Yours,
Michael

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