Social media abuzz with news of recent voltage fluctuations observed (early October 2025) on Spanish Grid

Frequent readers will note that we’re trying to follow (from afar) the ongoing investigations into the April 2025 power outage on the Iberian Peninsula … and will recall

1)  that the ENTSO- ‘Factual Report’ was released a week ago as the next steps in the investigations.

2)  with that report noting voltage fluctuations were noticed preceding the power outage – including (p9/264):

‘From approximately 09:00, the variability of the voltage in Spain started increasing, albeit without significant variations until shortly after 10:30, when the voltage in a part of the 400kV transmission network briefly approached – but did not exceed – 435kV.

The voltages in the 400 kV network remained below 435kV during the period before the incident. No significant oscillations with amplitudes above 20mHz could be detected until 12:03.

During the half hour preceding the blackout, two main periods of oscillations – power, voltage, and frequency swings – were observed in the Continental Europe Synchronous Area (CE SA), the first of which took place from 12:03 to 12:08. The analysis indicates that this oscillation had a local character primarily affecting Spanish and Portuguese power systems with a dominant frequency of 0.63Hz. The second oscillation occurred between 12:19 and 12:22 as an inter-area oscillation, with a dominant frequency of 0.21Hz, corresponding to the East-Centre-West continental mode. In order to damp these oscillations, the operators in the control rooms of the relevant TSOs took several mitigating measures, such as reducing the export from Spain to France, coupling of internal power lines in the South of Spain, or changing the operation mode of the HVDC link between France and Spain. While these measures mitigated the oscillations, their nature led to an increase of voltage in the Iberian power system.

At 12:32:00 – the starting point of incident as considered for the purpose of this report – the voltage of Iberian power system at the 400 kV level was below 420 kV and no notable oscillation with amplitude higher than 20mHz could have been observed. The evolution of the system and market conditions until this point of time is explained in further detail in Chapter 2.’

etc…

So it was no surprise that social media lit up with reports of voltage fluctuations having been detected more recently on the Spanish Grid, and with Red Eléctrica (the TSO) having applied for more capability to manage such fluctuations.

Various notes on social media

Readers should note this big caveat at this point:

1)  Adages such as ‘on the internet, nobody knows you’re a dog’ very much sum up the challenge of trying to ascertain the credibility of any particular voice; and

2)  This is also affected by:

(a)  The fact that I’m half the world away; and

(b)  My lack of Spanish language ability; and

(c)  My mechanical engineering background is strained to understand the interaction of various electrical engineering phenomenon

etc…

So with that caveat in mind, the following might be useful references for readers here to follow and explore in detail:

1)  Ruben Santamarta noted about ‘spooky season’ on LinkedIn a couple days ago:

… with that update pointing through to the article ‘This spooky season…The Voltage Oscillations Return’, which seems worth reading.

2)  Dr Dizar Al Kez is someone I’ve been following for a while, and who noted this on LinkedIn a couple days ago:

3)  Michael Caravaggio (from EPRI) noted this update on LinkedIn a couple of days ago:

Hopefully the links above will provide readers a useful starting point.

(Brief) Response by Red Eléctrica

At this point (and noting I’m very hampered by lack of Spanish language skills) all I could see was this response by Red Eléctrica on Twitter on Thursday 9th October 2025: