National Grid’s Preliminary Report On Blackout
August 20, 2019
By Paul Homewood
The National Grid has just published its preliminary report into last week’s blackout:
Key points:
- Lightning was the original cause, even though such strikes are perfectly common, and do not usually result in such catastrophic blackouts
- Hornsea wind farm tripped first, contrary to original reports.
- They still don’t seem to know exactly why either Hornsea or Little Barford tripped, though it was obviously due to the lightning.
- Along with the loss of 500MW of small embedded generation (wind and solar), the total loss was about 1878MW
- National Grid has 1000MW of automatic back up power available, incl 472MW of battery storage. Clearly this was not enough.
- Following the lightning strike, the grid’s protection systems worked properly
Certain aspects don’t seem to have been highlighted:
- When Hornsea wind farm is fully operational in the next year or so, it will have capacity of 1200MW. In addition, Hornsea Project 2, due on line in 2024, will have an additional 1386MW capacity. It is not clear whether it will share the same transmission lines, but to have so much capacity at risk of tripping off is clearly far too big a risk.
- The importance of inertia, provided by heavy rotating turbines, is not discussed. If more gas and coal power had been running at the time, would the blackouts have occurred. Just as importantly, what will happen in a few years time, when gas is no longer part of the normal baseload and is simply turned on when the wind is not blowing?
- While the National Grid claim that their backup power worked properly, such measures are only useful for a short period of time, maybe an hour. The report does not mention that gas power very quickly made up the shortfall, within about half an hour.
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NOT A LOT OF PEOPLE KNOW THAT 
Reblogged this on Climate- Science.press.
Hornsea 1 & 2’s electricity to come ashore in Lincolnshire:
“The offshore Wind Farm will be located 89km off the coast of Yorkshire, with an export cable coming ashore near the village of North Cotes in Lincolnshire.”
https://www.volkerinfra.co.uk/en/projects/detail/hornsea-two-offshore-wind-farm
Hornsea 3 & 4’s electricity to come ashore in Norfolk:
“Energy firm reveals final cable route for huge wind farm in Norfolk – and cuts construction time to eight years
The energy firm behind what will be the biggest offshore wind farm in the world if built said today it had changed some its plans after feedback.
Digging a 55km long cable corridor for the Hornsea Three wind farm, from Weybourne in north Norfolk to south of Norwich, has sparked widespread concerns about the impact on the rural landscape, disruption from construction traffic and damage to wildlife.”
https://www.edp24.co.uk/news/environment/orsted-cuts-build-time-for-hornsea-three-wind-farm-to-eight-years-1-5391237
Em, but for how long will Hornsea remain operational as a creditable energy supplier? Willis Eschenbach, over at WUWT, has just had a right giggle at our loony subsidy farms following a damning report on the (in)effectiveness of U.K. and Danish wind farms. I’m sure Paul will be doing his own hatchet job on the report in due course. It’s a shocker.
Willis E refers to an old assessment – he now admits it was a 2012 paper; he claims “I can’t find any newer research” so may have missed my comment pointing out >>>>
An alternative set of opinions, by the late Prof Sir David MacKay is:
“On the Performance of Wind Farms in the United Kingdom”
Click to access windDecline.pdf
There is now actual data on older wind farms’ performances over time.
Indeed there is here:
http://energynumbers.info/uk-offshore-wind-capacity-factors
The variations are dominated by different weather conditions from one year to the next, making it hard to discern trends.
#1 I’ve always called it North Coates
but strangely Cotes is an accepted spelling as well
#2 Is Orsted still the owner ?
I thought they’d already sold it on.
The normal pattern of the biz is build it and then sell it on to another sucker
like a teachers pension fund etc.
(I might be mixing up which farm has been sold)
I read the report and my conclusion is not enough inertia in the system, along with a lack of VARS (not really mentioned in the report). I guess they will now purchase a mammoth Tesla battery to fix this, rather than abandon the drive for renewables.
In an earlier report on WUWT, linking to this page:
https://www.thisismoney.co.uk/money/news/article-7367413/Renewable-energy-blackout-risk-warns-National-Grid-outage.html
It was stated that:
“National Grid has developed a frequency ‘monitoring and control system’ to deal with issues arising from the drive to renewables.
“It should be operational by 2025 when it expects to have moved to a ‘zero carbon’ electricity system.”
Am I missing something. I thought, based on reports here and on other sites that they’d no chance of achieving this.
I’ve seen that claim too, but I don’t know where it comes from. Even the CCC accept that we will still need substantial amounts of CCGT as backup, even by 2050. (But it will have to have CCS).
The Nat Grid’s new FES also seems to agree with the CCC assessment, from first look
I can only think that said “low carbon” will only happen on occasions when the wind is blowing strong!
Thanks Paul
Normal GreenDream biz pattern
They sell you a magic green solution
..and then to fix for that ..they try and sell you another magic green solution.
The CCC is planning for 59% wind and the backup midwinter will be CCGT with CCS with much from stored hydrogen for a week or more. This apparently will cost 1-2% of GDP with hydrogen conversion from methane costing less than methane after carbon tax.
@stu green Aug 20, 2019 at 10:41 PM
TOOTSIE FRUITSIE
Someone is benefiting from this, but it isn’t the consumer.
The report didn’t say much about the voltage transient following the lightning strike(s)
Voltage control depends on the generation of reactive power and is every bit as important as active power to maintain a stable system. With a conventional generator such as coal, CCGT, and nuclear reactive power control is carried out by AVRs (automatic voltage regulators).
With wind turbines, the designs have evolved to be able to generate reactive power, however, as with battery storage systems the response time is likely to be the same as for inertia ie 0.5 S
https://www.researchgate.net/post/Can_a_doubly fed_induction_generator_produce_reactive_power
Thanks for your several pointers to useful information over the days since the event which have helped me to unravel aspects of events ahead of the media and the official report. There is some detail in the report about the reactive power presumably offered by this:
https://hornseaprojectone.co.uk/News/2018/06/Worlds-first-offshore-Reactive-Compensation-Station-installed-for-Hornsea-Project-One
I wonder whether that platform may turn out to be the guilty party for Hornsea. It does seem clear that the transmission path for Hornsea output must have been as I described, with the bulk of it routed from Keadby via Eaton Scoton, so that there was a route for a transient to travel back at the time of the lightning strike. Some questions must be asked of the onshore suppression of the transient (or rather, lack of it). Perhaps they were relying on the offshore unit?
I think there may also be questions to answer about the response of embedded generation. In the 2008 event, it contributed to the estimated peak loss of 1,993MW of generation – but allegedly only relatively late in the sequence of events. That was enough for calls to insist that protective trips be aligned with main grid generators. This time, the embedded generation is listed as falling off in the first second. I note that in the Gridwatch data, solar falls off from 3,190MW to 2,480 MW at the same time as the other trips are recorded as output. Kudos to Sheffield University for picking that up.
” I note that in the Gridwatch data, solar falls off from 3,190MW to 2,480 MW at the same time as the other trips are recorded as output. Kudos to Sheffield University for picking that up.”
Agreed. I spotted that uncharacteristic sudden drop as well (it actually started increasing after that) and it does make you wonder.
By definition the amount of embedded solar generation is estimated rather than measured. I doubt whether the loss of embedded output was only or even largely solar as there are plenty of embedded wind farms in the same area.
The important point is that the increase in the amount of embedded generation capacity requires significant modifications to the assumptions on which power system planning is based. Working on the basis that the worst potential loss is Sizewell B is not satisfactory when you can easily lose 500-1000 MW of embedded output at the same time.
Further, the frequency/voltage responses will probably not be symmetric because they are on different sides of the switching equipment – losing embedded generation is equivalent to a very sudden increase in demand.
The work that Sheffield University have done is much praised by the Grid. Forecasting solar has also been improved. Wind forecasts are much less accurate.
https://www.nationalgrideso.com/news/eso-teams-met-office-solar-forecasting-innovation-project
https://www.researchgate.net/post/Can_a_doubly-fed_induction_generator_produce_reactive_power
Paul they are being disingenuous if the say they don’t know what tripped first. All their CB changes are automatically logged to the nearest millisecond.
The possible cause of Hornslea going off is lack of low voltage ride through. It is a common problem with asynchronous generation. If Little Barford was genuinely being shutdown at the time of the trip, it could have been on governor control. The loss of Hornslea with the consequent frequency drop would have caused the machine to ramp up when it was trying to shut down. That often causes machines to trip
Little Barford was nowhere near shutdown time. Here are its half hour average outputs starting with settlement period 24 at noon:
SP……MW
24 665.62
25 664.24
26 664.02
27 661.24
28 662.02
29 661.62
30 661.64
31 662.24
32 663.44
33 663.44
34 513.54 .. average over 30 mins – operational for ~23 mins before trip at 661 MW
35 0
Then why did reports quote RWE saying at the time Little Barford was shutdown at that time ‘as arranged’
“RWE said its Little Barford gas station, which has a capacity of 730 megawatts, shut down in line with normal practice when demand hit 23,000 megawatts.”
“The plant has two gas turbines and one steam turbine. with a net capacity of 727 MW”
There may be things related to the combined cycle generation that mean output is occurring while the gas turbines are shutdown/reduced output in sequence then the steam turbine.
How many times do I have to point out that RWE Germany had no clue what was happening on the ground and gave an answer just to fob off the journalist? Wrong of them to do that, but that is what happened. The report contains more or less a blow by blow account of the trip. That is based on interviews and detailed plant records and is clearly a proper guide to what happened.
It is probably my lack of understanding, but I am puzzled at how a lighting strike can affect underground cables. From the links Joe Public added, the cables from Hornsea are either under the sea or buried under the land.
Cables carry electricity, including from lightning strikes. Transmission lines have circuit breakers that get triggered by the massive voltages and currents from a lightning strike, but they take some milliseconds to act (about 70 in this case).
I’ll repost my O/T comment from the glacier funeral thread.
“HA ha ha ha. Saw this coming a mile down the tracks.
Yep, according to Ch5 news, climate change done it!
They firmly blamed a lightning strike causing the trip, then had some sort of eco-warrior looking supposed grid expert spouting that with these sort of extreme events (a lightning strike is now extreme weather?) we will have to invest more in grid resilience or this will become a more frequent problem. Switch back to the reporter, who then said customers will have to pay an extra £10 each per station per year to make them resilient to climate change.
What can you say?”
It was notable that BBC news also truncated the explanation to 2 different headline versions.
“Due to a lightning strike” and “mostly due” (with no elaboration).
Funny how the MSM generates headlines that deliberately hide the REAL reason(s).
The climate bias is completely out of control.
I knew after this happened that a ‘likely suspect’ would be framed for this.
If you read the story the lightning angle is given first to set up the following information. In my reading though the sequence clears the lightning
There was a lightning strike on a named circuit ….which was cleared in 20sec via the protections..
It was one of many lightning strikes at the time ( Satellites now are able to report than a single front can lead to hundreds of lightning strikes – not all reach the ground though)
The biggest single generator at the moment is Sizewell B at just over 1,200MW, not 1,000MW as wrongly stated in the report (perhaps they mean that 1,000MW of backup is sufficient to handle the loss of 1,200MW without the frequency falling below the limit). I also believe that, although considered to be an incredible event, there has been at least one instance of both 1,000MW DC connectors to France simultaneously going down. As I recall, the grid was designed to cope with an instantaneous loss of 1,600MW of generation without the need for demand reduction (or blackouts).
I do not trust NG ESO to provide the truth concerning what happened.
On the day Sizewell B was operating at around 790MW, the French IFA link at 1008MW, and BritNed at 820MW (ramped up after the event to 948MW).
The 2008 event saw a total loss of 1,993MW, and also resulted in 48.8Hz trips.
I do find it odd that National Grid think it will be cheaper to constrain interconnectors to ~750MW to reduce the maximum contingency. Why build all these new ones when you can’t even use the existing ones fully, and why build them so big? That’s before considering the risks of importing a system black from the Continent which would see them all lost at once.
“Why build all these new (interconnectors) when you can’t even use the existing ones fully, and why build them so big? That’s before considering the risks of importing a system black from the Continent which would see them all lost at once.”
Because our EU masters dictate that we must.
It’s based upon *capacity* and our solar operates at <11% Capacity Factor; so 89% of solar's proportion of interconnector is money down the drain.
https://europa.eu/rapid/press-release_MEMO-15-4486_en.htm
I’m not a SME on power generation, but; Does it not cost NG more to keep a spinning reserve than it does to import power via the inter-connectors from France, et al? So to save money they reduce UK based assets and ramp up imports? And are they not building their own inter-connectors to import foreign, cheaper, generated power, rather than pay to keep our obviously needed backup? There is no altruism in the power generation business! Happy to be corrected!
The FT Nov 2016:
https://www.ft.com/content/52e957a6-b64a-11e6-ba85-95d1533d9a62
These are two different things.
If there is a problem like last week, you need fast response, which you cannot get from France.
For the longer term, when for instance the wind stops blowing for a week or two, can we rely on France to supply us, when probably the rest of Europe is in the same boat?
“It has been revealed that the National Grid regularly restricts the use of power cables from continental Europe because of fears of blackouts if they fail.
If one of the interconnectors tripped while importing at full capacity, it could cause more power cuts.
National Grid allegedly limits the use of the cables, especially at night, to reduce the size of the potential supply shock.
The National Grid plans to spend billions on laying more interconnectors to the rest of Europe. ”
Bonkers.
https://www.energy-reporters.com/transmission/major-uk-power-cut-puts-european-interconnectors-in-spotlight/
Its likely the cross channel inter connectors are to stabilize prices ( over 1/2 hour periods) rather than short term fluctuations in frequency or voltage.
To find out with certainty what tripped and when and in particular why, is going to need very particular technical expertise.
Only a few engineering geeks will understand, and this will not get into any report because what would be the point!
I keep reading statements made by so called industry experts that protection was “over sensitive” , this is false, protection is necessary to prevent danger, the grid is not as reliable as it was due to the amount of “embedded systems” .
As I have said, the consequences of more and more renewables in the grid will become apparent with no need for any action. Renewables have gotten used to the free ride that installed grid and fossil generation overcapacity has thrown after it. Now, the legacy systems are at their limits and failure is going to be an ever more frequent occurrence. And the explanations will be ever wilder. When the strain becomes too hard to bear there will be wild conspiracy theories about the wicked fossil world bringing this about. The renewable industry has become arrogant and because of the current Greta madness, they think they will own the planet. They will bring the darkness – we can only wait for the remedy to do its job.
“The importance of inertia, provided by heavy rotating turbines, is not discussed”
An April 2019 document entitled: “The Accelerated Loss of Mains Change Programme”</a by National Grid ESO and distribution network operators says on p8:
Options for Managing the Risk
Limiting the largest loss limits the rate of change
Increasing inertia by synchronising additional synchronous plant reduces the rate of change
(displaces non synchronous generation)
So they know perfectly well that keeping big machines running is an option, but that wouldn't fit in to the CO2 reduction agenda…
The interim report states:
“> To ensure that, in the event of a loss, the rate of change of frequency does not result in the disconnection of users the ESO can decide to increase the total system inertia (which would slow down changes in frequency) or reduce the size of potential generation and demand losses that could credibly occur. A smaller sized loss will result in a correspondingly smaller RoCoF in low inertia conditions.The optimal approachis to reduce the size of credible system infeed losses on generation, demand or interconnectors.This approach is more cost effective than increasing the level of inertia. <"
The power cut demonstrates that the NG have failed to accurately determine credible system infeed losses i.e. their statement = weasel words
Under ‘Power Loss’ the report says re Hornsea 1:
Hornsea One offshore wind immediately lost Hornsea modules 2 and 3, totalling 737MW. Module 1 continued to operate smoothly at 50MW throughout the event.
Curious.
It’s the South Australian storm all over again. I would be looking for a sequence of lightning induced voltage dips in the minutes preceding the final lightning strike. Did Hornsea’s protection systems detect these, and trip when the final lightning strike pushed it over the protection setting maximum count?
See previous comment. The operators of Hornsea say they have made specific technical changes as a result if this incident.
Lightning strike caused loss of load and embedded generating capacity.
The system is vulnerable, nothing can be done.
Reblogged this on Tallbloke's Talkshop and commented:
Thanks to Paul Homewood for the initial analysis. Note that module 1 of Hornsea wind farm operated normally throughout, even though modules 2 and 3 cut out.
My observation was that it affected far more than the 1.1 million customers the report identifies.
The new wind farm will need to bury the cable a long way under the Norfolk countryside they say but in a conversation with a NG engineer I was told it was too costly to do so and that is why we have overhead cables in Snowdonia. Apparently the problem is heat from the cables that needs to be dissipated. They would need to be bathed in oil underground using some form of cooling system. Presumably this takes energy so will need to be fed off the grid. I wouldn’t mind betting though that, when PP has been granted, they go back to get permission at some stage to take the cables overhead.
So, that is a lot of tosh then. Lightning. That is seriously the best they can come up with. There was none here in Milton Keynes, which is not a massive distance from Little Barford. Plus, happens quite a lot. Still no explanation as to why their spokesman said Barford was a planned shutdown. We know what happened. Hornsea destabilised the grid and had to be taken offline, but with LB gas shutting down there was suddenly too little capacity. They can’t say this though, because it points to a future without stable national power supplies. And what is being proposed to deal with that? Nada. The eco-loons are doing well with their anti-capitalist agenda. (They are aware global warming isn’t a thing; can’t believe anyone thinks it is)
My thoughts entirely – the same.
As we observe, there is a miasma of NG techie BS being put about and the real problem – they don’t want to point to it – at all.
Wind doesn’t work, witness the roll back of the insanity of ‘energiewende’ where the Germans are quietly, sneakily (as they do) binning it, turning back to COAL and dirty coal at that.
This insane drive to whirlygig ruinables: will cause massive UK blackouts, period.
We are being sold more green pups and behind our backs, how the Germans, Chinese, Indians and Japanese guffaw at ‘green’ Britain.
I expect it will fall to OFGEM and the BEIS Select Committee to probe the false stories and timings put out by the individual companies. Not something that National Grid can really comment on. I find the lie from Hornsea about when they tripped to be one of the more offensive distraction stories. The story from RWE Germany is the result of head office not knowing what happens in the outlying operations.
Reblogged this on WeatherAction News and commented:
“This assessment concludes, based on extensive evidence, that it is extremely likely that green ideology, especially the imposition of unworkable renewables and taxes, are the dominant cause of the observed hysteria since the mid-20th century. For the lunacy over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.”
“Grid instability is happening. It’s real. It’s our fault because we’re putting a lot of renewables in the system. And we are not doing a lot to stop doing that”
“Energy instability is no longer some far-off problem; it is happening here, it is happening now”
One of the slightly more obscure elements of the initial report is the table of frequency response performance. I note that the famous grid batteries only appear to have delivered about 72% of what they were supposed to. Perhaps they weren’t as charged up as they should have been.
This is the AER’s final report into the Black System Event in South Australia (SA) on 28 September 2016. –
“Resulting voltage disturbances cause shut down of several wind farms (about 456 MW)”
Click to access Black%20System%20Event%20Compliance%20Report%20-%20Investigation%20into%20the%20Pre-event%20System%20Restoration%20and%20Market%20Suspension%20aspects%20surrounding%20the%2028%20September%202016%20event.pdf
In the South Australia Sept 2016 blackout, the affected generators (all wind farms, but it could just have easily been other plants) had protection systems that tripped off if they detected 6 voltage dips within 120 seconds. They have all since increased that setting to at least 20 voltage dips within 120 seconds. The Australian Energy Regulator is now prosecuting them for failure to ride through the 6th voltage dip.
I think the constraining of continental interconnectors is perhaps being exaggerated. The 4GW often run at full blast from breakfast to bedtime. The constraining down is done at times when there would otherwise be low inertia on the system, which is most often at night, due to low demand. But I have observed that since the trip they have rarely if at all been at full blast, although it has also been rather windy during this period.
The potential biggest single trip on the system would appear to be the 2.2GW Western HVDC Scotland to England interconnector. Though I think it is currently distinctly underused, and doesn’t get near capacity very often. It has presumably been oversized to cope with continuing growth in wind, so that can change.
Energy regulator launches legal action against wind farm operators over SA statewide blackout –
I don’t see anyone predicting these are becoming more frequent!
“Weather experts described the event as a once-in-50-year storm, with 80,000 lightning strikes and tornadoes with wind speeds reaching up to 260 kilometres an hour.”
https://www.abc.net.au/news/2019-08-07/regulator-legal-action-against-energy-companies-over-sa-blackout/11390400
Ivan,
They import coal-fired from Holland and Nuclear from France, however, the DC links provide no instant reserve and would contibute to the problem of very high rates of frequency collapse.
My guess is that the system suffered a virtual voltage collapse because there were insufficient reserves of reactive power. NG won’t want to say much about it if that was, in fact, the case.
It would be interesting to see what the voltage transient looked like but that is (strangely) missing.
Whilst the report says that “The voltage performance of the National Electricity Transmission System was within SQSS and Grid Code requirements”, these are in fact very wide and a prudent system operator would aim at a much higher standard.
The cause of the Little Barford steam turbine trip could have been due to pole slipping.
https://www.eng-tips.com/viewthread.cfm?qid=111251
In the report – “The causes provided by RWE for the initiation of the trip of Little Barford steam turbine (ST1C) was the discrepancy between the three speed signals.
The standard speed sensor protection on steam turbines is three independent eddy current probes working off a toothed wheel. It is usually in the front pedestal. They have a voting arrangement, normally 2oo3. If one of these was defective, then the second one went down, it would cause an instant trip. It seems very unlikely that even a direct lightning strike on the station would affect these.So the Little Barford trip could have been just coincidental. The fact that neither of the GTs also tripped at the same time would support this.
Pole slip is unlikely to cause a speed sensor fault and would only happen if you were importing a lot of VARs. If it did occur, the generator protection would be the one taking the plant out. .
Many wind farms employ doubly-fed induction generators (mentioned above) to produce reactive power and it may now be a Grid Code requirement.
There are major technical difficulties delivering power from off-shore wind farms. It’s hard to find specific technical information for Hornsea but there is mention of the ABB Statcom system which is employed both on and offshore. Onshore it is to fulfill the Grid Code requirement to generate VARS and offshore it is to compensate for the capacitance of the HVAC cables.
In the electricity supply industry, it used to be that only proven designs were accepted and it may be the case that in the rush for renewables this has been overlooked. Hornsea is at the cutting edge and the blackout event was it’s first real-world test.
Up to then, all the performance tests will have been carried out using ‘models’. No doubt the modelers will be back at work trying to simulate the entire event.
Hornsea has its own offshore platform with a reactive compensation unit halfway to shore. I linked to its description above. I wonder what role it played.
Forget the thousands of research papers on technical aspects of Hornsea etc. These all include mathematics which is hard to follow because it’s only there for effect and is quite meaningless. (The same is true for most Climate-related papers because they also use models that have been cobbled together to give the answers the researcher wants.)
Australia is going back to – Synchronous Condensers! This is confirmation that there is really is no substitute for 100 Tons of metal spinning at 3000 RPM. (100 MW alternator)
https://www.electranet.com.au/south-australias-electricity-grid-to-be-strengthened/
ABB is now saying –
“ABB’s rotating condenser’s short-circuit power and high inertia complements the fast response time of our static VAR compensators, offering an unrivaled system solution”
https://new.abb.com/motors-generators/synchronous-condensers
PS
This is a real engineering paper from the days when the UK had an electricity supply industry which I used it to find the weight of the rotor above.
Click to access super-ac.pdf
They are doing more than that for synchronous condensers. The ones they are building for Germany will have flywheels attached because the condenser doesn’t offer enough inertia! At the conference I went to last year, Seimens said the generator only provided 15% of the inertia in a unit. Most of it would come from the big LP turbine rotors with their large diameter last stage blades.
Synchronous condensers were originally used just for VAR control – inertia wasn’t a consideration back then.
I’m still a bit confused as to what the “National Grid’s Preliminary Report On Blackout” is actually saying?
unable to cut & paste from it, but from above report they start by saying in the summary –
event 1 – the lightning strike was not a problem/they deal with this type of event all the time.
event 2&3 – immediately following this event the 2 power sources dropped out within “seconds of each other” (which went 1st & does it matter?)
then the prelim findings – snippets
2 almost …but each associated with the lightning strike…etc this appears to represent an extremely rare & unexpected event.
strikes are routinely managed
the protection systems cleared the strike.
clear as mud.
I think they are leaving it to OFGEM to dole out the blame.
Gridwatch 5 minute data that on 9th of May they lost 1GW from the NEMO interconnector link to Belgium – but there was some 20.7GW of CCGT operating at the time, so no blackout.
20th June appears to be the loss of ~750MW. It would take a lot of effort to pin down the actual station involved, but there was 14.9GW of CCGT at the time.
11th July appears to have been another big CCGT trip – 1.1GW, but out of 21.5GW of CCGT operational, illustrating the advantage of inertia in containing the problem.
If they had been operating with the levels of CCGT that we often see at a windy weekend or overnight, these trips would almost certainly have caused blackouts.