Any thoughts/information on what happened? Was it a lack of spinning reserve?
Was it " The Portuguese operator, REN, said the outage was caused by a “rare atmospheric phenomenon”, with extreme temperature variations in Spain causing “anomalous oscillations” in very high-voltage lines."
as is written in the Guardian?
The Italien blackout from a few years ago had a definate cause in the tripping of interconnetors from Switzerland during a storm.
Frequency is crucial to any grid.
I suspect that it's not as crucial as people think. Rather it's a statement about how some parts of the electrical network were designed and configured.
Way back in the UK past we had the 3-day week caused by a miners strike which meant that the frequency was allowed to be 'way-off', apparently to the point that electric clocks could be 10 minutes away of true time (during the loaded day), and that the grid than ran fast overnight to catch up.
I do remember when working at NEI Parsons (c1979) that V/f was a concern for transformer saturation.
(I was looking at designed a digital converter to monitor the generator voltage for control purposes needing multiple readings per cycle via a 3ph->6ph transformer, a 6 phase rectifier, a voltage to frequency converter and counter per part cycle - It implicitly produced a V/f reading!, and a 1/f reading)
We have become locked in to that way of thinking, forgetting all the newer converter based transmission tech that doesn't care in the same way.
I'm glad you found it interesting
you're absolutely right, there was a loss of embedded generation, which led to the rules being changed to try to keep them spinning
Thanks for that Dave. Digging though that and its references, it does look like it was more "interesting" than previously reported.
of Hornsea 1, one report says:
3.21. We have found that the wind farm’s onshore control system operated as expected
when the system voltage dipped concurrently with the lightning strike. The offshore
wind turbine controllers, however, reacted incorrectly to voltage fluctuations on the
offshore network following the fault. This caused an instability between the onshore
control system and the individual wind turbines. The instability triggered two
modules to automatically shut down.
which seems to suggest that while the shore side did behave correctly according to the grid codes, the offshore (and/or connection) bit didn't.
There was also a loss of distributed generation:
2.4.6. The level of power loss (or increase in net demand on the electricity system)
caused the frequency of the electricity system to fall at a rate of change of
frequency (RoCoF) above 0.125Hz/s. Some distributed generators operating
under legacy Distribution Code requirements have loss of mains protection
mechanisms triggered by RoCoF set at this rate. As a result, an estimated 350-
430MW of distributed generation tripped off unnecessarily, based on
information provided by the ESO19.
- Andy.
A few points that seem to come out of this while we wait for more official information.
1) Is frequency still a useful measure of grid stability and safety with the ever increasing amount of invertor connected generation and load.?
2) What could replace frequency as a control measure?
3) Overloads and trip outs will always occur. How can the spread be better controlled? How can the recovery be improved?
4) Can the inertia and frequency control of a rotating generator be replaced by an inverter? A rotating generator with electromagnetic or fuse overload protection and transformer coupling can take significant short term overloads, maybe a factor of 3 for 10 seconds. This would require a significantly overrated and more expensive inverter system.
5) Is transient stability also a problem to be addressed by inverter connected devices. I started looking at my old uni. text book, Electric Power Systems by B.M. Weedy but decided my maths is no longer up to it.
a minor technical point, but the main reason that frequency fell in 2019 was that two large generators tripped off when they shouldn't. one was CCGT, the other offshore wind, and both were heavily penalised by the regulator Companies pay £10.5 million over 9 August power cut | Ofgem
Once the cascade starts or starts to get out of control it become like an Avalanche. Lets hope that people learn lesson from this disaster and then implement more robust and redundant systems that are capable of meeting the requirements that are now the norm rather than relying on how things were done 20 plus years ago. I do like the fact that Spain has lot of wind turbines (personally I think it still needs nuclear as well) and I hope the UK installs more but and it is a BIG BUT the Wind Turbines on mas scale change how the national grid would work/function during normal operation and under fault conditions. Frequency is crucial to any grid.
There is an interesting article on Medium https://medium.com/@IntrinsicalAI/just-a-blackout-what-public-data-reveals-about-the-iberian-grid-collapse-of-april-28th-2025-cb9acc1f783a that strongly notes that there was a major IT outage (loss of internet connectivity) across Portugal and Spain 5 minutes before the main power outage.
This appears to be the 'wrong' way around from a Power Systems first perspective. There may have been a clock synchronisation issue, but I think that would be completely unrealistic (but who knows?). Perhaps more likely the power system control had slowly been digitised and now was suffering from a loss of connectivity between control nodes, resulting in unhelpful fall backs of operating status.
Also noted was that the open source power reports showed that the Portuguese power grid started going down first. Ultimately the guy reporting the details then falls back onto the conspiracy theory that this was expressly planned as a cyber attack on the whole grid. Again I don't think this wasn't really the case.
It could easily be that there was a small cyber attack on the Portuguese internet's Border Gateway Protocol (BGP) system (or thereby) that controls how the main internet servers talk to each other, which then had unforeseen consequences that ultimately tripped the grid collapse.
At least the guy gives references. A good story to ponder.
Personally I feel that we need more battery storage attached to the Grids to help store the renewable when it’s created rather than waste it and it may also help even out the fluctuations on the Grids. Now I understand they are the size of large football stadiums and they can not AT the MOMENT create Frequency BUT they would most certainly help minimise the cascade effect that leads to the need for a Black start. It also means that Solar energy can be used at Night. (Other renewable energy sources are available)
We particularly need more grid-forming batteries that can act like spinning generators.
Most inverters will simply track the grid frequency as it falls. Until it goes out of specification, and the inverter shuts down. Which only adds to the problem.
My thoughts
Could this happen in other European countries? Yes absolutely.
Lack of information/poor information? Yes absolutely, reminds me of Ed Milliband talking about Heathrow.
Are there lessons to be learnt? Yes absolutely
- All Telecoms (mobile phone networks) need to be power independent/battery backup power for at least 24 hours to help maintain mobile coms throughout the nation
- All Data centres need to be power independent/battery backup power for at least 12 hours to help maintain Data coms throughout the nation
- Countries need to look at how much power they use and how much they buy in from abroad. It only takes 1 country interlink to go down and people will find themselves needing to wear brown trousers. In the UK I bet we have come close to that on several occasions. Picture if you will a power station going offline, then at the same time an interlink to France going down, now you are very close to the mark. Now when that cascade starts it is very difficult to stop the avalaunch.
- More COLD start sites/Black Start site need to be commissioned probably throughout the EuroGrid network
- Procedures are needed or need to be written to ensure assets can synchronise on the network especially considering the amount of renewable energy source created. Voltage and frequency errors are probably the most hidden Gremlin when adding renewable energy onto the Grid be that either NGrid or EuroGrid.
Personally I feel that we need more battery storage attached to the Grids to help store the renewable when it’s created rather than waste it and it may also help even out the fluctuations on the Grids. Now I understand they are the size of large football stadiums and they can not AT the MOMENT create Frequency BUT they would most certainly help minimise the cascade effect that leads to the need for a Black start. It also means that Solar energy can be used at Night. (Other renewable energy sources are available).
If anything solar and wind should be some of the better choices for a black start -
Agree in principle, both due to no need to look for a source of ignition, and also as an inverter type process can decouple frequency from voltage, in a way that a conventional generator can not.
But the current rules of engagement actually make that a disadvantage, as they are written for 'spinning' generators, from a time when it was safe to assume the non-inertial devices are the small part that can safely be thrown off.
It may be part of the problem that we need to get away from assuming that a falling frequency is a reliable indicator of an overload, or handling such behaviour needs to be programmed in.
On the other hand, once spinning, a real genset has much more ability to ride through inrush overloads that are inevitable as things come back on, so a more granular approach to load ramp up may be needed.
Actually at much smaller scale the inverter type variable engine speed generators don't play well when you try and sync them either.
It is really far to soon to be sure what happened here, so this is just speculative, but I think there will be some lessons to learn once it is clearer.
Mike.
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