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... it wasn’t the network part of National Grid that failed. It was the system operator / balancing function that collapsed as a result of the generators tripping. So NG’s Response and Reserve contracts with third parties weren’t adequate.
This coming week should be interesting.
Out of curiosity, how does LFDD work? Are, for example, National Rail and Forgemasters required to trip a big relay and stop consuming electricity completely or is it more subtle - stop running the trains and furnaces but you can keep the signals and office laptop running?
Some of you on here may have the expertise to answer this: The Scottish Hydro was all installed many years ago. would refitting the generators with modern ones increase output significantly or would it make little difference?
I thought there had been a few upgrades since the initial installations TJ.
I don't know Scotroutes. Just wondering if modern generators would be more efficient.
As somebody said above we as a country have got used to 100% availability of power, but i can remember living next to a large steelworks that had a huge power demand for 4 electric arc furnaces, and other power hungry plant, even with their own power station, there where still power cuts of many hours, we had to boil water on the coal fire, quite often, especially in winter.
Four candles anyone
Only power cuts I remember was in the winter of discontent when strikes shut down capacity
TJ, most hydro would benefit from modern turbines if they arent already fitted.
How much improvement? 10%? 100%? Just you seem to know about this stuff. I shall have a look see if I can find any info on when they were upgraded
Water turbines are already highly efficient. The design was pretty much perfected 100+ years ago. Mechanical effeciency is better than 90% for most designs. It's doubtful you could get a measurable increase in power generation by modernising turbines in hydro plants
Water turbines are already highly efficient. The design was pretty much perfected 100+ years ago. Mechanical effeciency is better than 90% for most designs. It’s doubtful you could get a measurable increase in power generation by modernising turbines in hydro plants
Not true, there are modern designs that are more efficient than previous generations.
TJ, I'll have a look at my books when I get home*, can't remember the numbers but I do remember it making an appreciable difference once the numbers are scaled up.
*I'll try and remember, I know I'm really bad for not doing this
Ta dude. The better informed we are the better we can debate. 😉
Not just the turbines but the generators.
Out of curiosity, how does LFDD work?
The previous step in the process Demand Control is managed by the DNO Control engineers triggering auto tap changes on the transformers at the Primary substations...a two stage process able to drop volts in ~3% increments (and delivering a MWs drop as a consequence).
The Low Frequency Demand Disconnection event on Friday I believe was triggered automatically at the main substations given that we hit 48.9Hz* I am waiting for news but I don’t think the Control Room guys were involved at all. Frequency cliff-edged, so RoCoF was off the charts and as a result the network self-protected (relays at S/S). Removing hundreds of MWs of Demand in order to arrest the Frequency dropping further (which would have potentially blacked out the entire country).
*Normal Operating parameters are in the range 49.8Hz to 50.2Hz; statutory obligation to keep it in the safe zone of 49.5Hz to 50.5Hz. So 48.9Hz is extraordinary.
Interesting @grtdkad. So in this scenario, is there any prioritising of who gets disconnected? I (like many 'normal' consumers) was fine. But hospital, airport and rail were interrupted? I would have thought telephony/hospitals/key transport would be the last to be turned off?
Notice the CEO put a post up on Linkedin...
https://www.linkedin.com/pulse/never-good-time-power-cut-john-pettigrew
Interesting background reading.
'interesting' comments
Thank you for that explanation.
From what I've been reading the local operators are required to shed 60% (in England) of peak load but how they do it isn't a National Grid decision. I guess it's easier to disconnect a few big substations and not worry about who's downstream than lots of little ones.
What I still don't know is if someone like National Rail is effectively their own power operator and therefore responsible for their own chaos or if they depend on all the local operators that they pass through (seems unlikely that they plug 25kV into a local substation).
However you look at it, The Telegraph's headlines blaming National Grid seem over simplified.
@ajaj- are you suggesting that the right wing press are trying to make ‘black and white’ a ‘shade of grey’ issue to wind up the hard of thinking?
I will be writing a sternly worded letter to the editor, after clearing the cornflakes up of course.
TJ - I've consulted the book (Renewable Energy - Power for a Sustainable Future, Boyle, 2nd Edition) and from what it says depending on the plant you could see gains of 30%+ after refurbishment, that was the figure given for two of the 100MW turbines at Cruachan. Now I imagine not all of that will be down to the turbine itself as flow optimisation via fluid mechanics has come a long way and the penstocks probably have years worth of erosion or buildup in them messing with the flow but that's the net outcome.
I'd link a PDF but that would be verboten however the book itself is on fleabay for £3.50 as is Energy Systems and Sustainability by the same author, I'd really recommend picking them up as they provide a very balanced view of the technologies on offer. Another book which is worth a look is Sustainable Energy – without the hot air availabple as a pdf here: https://www.withouthotair.com/
Ta.
That including modern generators or is that much of a muchness?
Probably not, it's more refurbing old 50's/60's tech.
MOre delays at hinkley. Now at least 7 years late with 6 years of construction still to run.
From what I’ve been reading the local operators are required to shed 60% (in England) of peak load but how they do it isn’t a National Grid decision.
Potentially substations showing the highest power factor at the time?
You'd think this is a practical use of smart meters - in the event of the network approaching its absolute maximum capacity it should shed the highest loads. If you've got the washing machine, dryer, hot tub, oven, grill, microwave, halogen lighting etc on at peak time I think you'd be fair game for a 10-20 minute disconnection in these one-off circumstances.
Chief Exec on the radio this morning. Get the impression National Grid is trying to be diplomatic and not point fingers at either the Generators (who's plant fell off the network in the first place) or DNOs (who had some strange prioritisation of who they switched off when Grid requested 5% demand to be shed). However, comes across to joe-public as being vague.
...Generators (who’s plant fell off the network in the first place)
I heard the interview and got the distinct impression that the interviewer (Eddie Mair?) thought that 'generators falling off' was some metal whizzy things coming loose and dropping to the floor. Also, he seemed to be alluding to there being some sort of personal safety implications (unrelated to the power loss aspect) of the frequency dropping below the "legal minimum" of 49.5 Hz.
The one line summary of the interview in the headlines at 08:00 did not bear much relationship to the actual conversation!
On a another question:
I assume that domestic and small scale wind/solar installations are connected to the grid via some sort of inverter. I presume that these are frequency / phase locked to the grid somehow (local sensing?). Do they just follow frequency changes on the grid? Or are they biased somehow to try and maintain 50Hz (so assisting with frequency stability)? Do these automatically disconnect if the frequency is outside a certain tolerance? If so, is there any 'randomness' built into their response, or will they all respond in the same way at the same time?
Ta.
Can someone help me understand why this was a frequency drop not a voltage drop? Why not a "brownout"?
Do they just follow frequency changes on the grid?
Correct. The 50Hz is essentially mechanically driven by the various generators on the network. The frequency rising or falling is literally these generators changing speed in response to load.
Whoa there. When a generator is synchronised there should never be a change in speed. The generators adjust to demand by putting more power in. Think of driving or cycling at a set rpm along the flat and then the additional effort required to maintain that same speed up a hill.
Now obviously speed does fluctuate but only ever very slightly, if a generator starts to diverge then it should automatically disconnect at a certain threshold.
This is why wind turbines are utterly useless at black start, since their speed is so prone to fluctuations it would be extremely difficult to synchronise them and keep them at a sensible load. You need something with a regulated output and at the moment only steam can do that at the required scale (the Cruachan question is interesting, I'm not sure it works independently but rather acts as a generator to bring Peterhead online).
"You’d think this is a practical use of smart meters "
You don't need smart meters to do that, just something that looks at mains frequency. Which is a trivial piece of electronics that could easily be incorporated into appliances. Smart meters don't help because they're at the supply entry to the house so don't have enough discrimination (i.e. they can't turn off the tumble dryer without turning off the lights too).
"Why not a “brownout”?"
If the very informative post above is correct then there will have been a voltage drop first.
So we’re still in the realms of providing data to NG on asset performance (that was triggered based on the frequency drop) due for noon Wednesday but then brought forward to Tuesday evening with more urgency to allow them to prep their report to ofgem (due on Friday).
Why no brown out on Friday?
We’ve looked at the one-second metering data (which logs GB system frequency and our response), it looks like the effect of the two main generators tripping off over 1500MWs resulted in a cliff-edge Rate of Change of Frequency (RoCoF) that (a) triggered all of the Frequency Response assets which appear to have responded successfully within a range of 1s to 30s (start up time depending on their contract); but (b) I have been told of a number of smaller providers e.g. a 40MW CHP and a (tbc)MW solar farm that also tripped-off to self protect from the main event which will have added to the RoCoF issue. I imagine that if there were two there will actually have been many more but they’re not rushing forward to confess.
And with less thermal spinning generation on the bars on Friday (it was a sunny and windy day so renewables % was very high) the Frequency Response contracts held by Grid appear to have been inadequate to arrest the Frequency drop accelerating through 49.5Hz (which should have triggered a Grid Engineer instructing the DNO to drop voltage) and instead it recovered momentarily before again dropping rapidly down as far as 48.79Hz which resulted in the automatic relays enacting the Demand Disconnection “event” at the DNO substations.
The Demand Disconnection ultimately did its job and brought the generation and Demand (and therefore system frequency) back in to balance.
As a result of Friday, Grid as System Operator will need to look at their Response and Reserve contracts to make sure they have adequate capacity (they are driven by Ofgem to contain costs for the consumer) - currently spend over £1bn pa on balancing the system. Perhaps it needs to be more?
They’re currently saying everything worked to plan, I’m not convinced that that statement is entirely complete or sincere, as it lacks context.
The DNOs will need to review the blunt instrument of Substation Demand Disconnection - which critical consumers are at the end of the wire?
Critical risk consumers need to think about their own resilience. Is the UPS working? is the emergency diesel generator fully synch’d and performing well? I see loads of consumer owned kit which is decades old and not fit for purpose (with diesel in tanks not used from one year to the next). Hopeless some of them!
I see loads of consumer owned kit which is decades old and not fit for purpose
I used to work in a factory that depended on electricity and had its own diesel backup generator (Rolls Royce, none the less). This was religiously started and run up every month to prove it "worked". It was an illuminating event when our insurance assessors decided that we needed to do a load test - The radiator burst, the exhaust fell to pieces and all the paint fell off the underside of the roof!
“Load test”, yup that experience is not unusual!
The analogy that is often referenced for back up kit is car ownership. If you use your car daily, you are pretty confident that it will start when you need it and it will be reliable. Compared to having a car, just in case you need to travel but parking it up on the drive until you’re big annual trip. Are you sure it’s going to start?
...Battery? Fuel contamination? Seals and gaskets? Oil pressure?
Much, much better to use the kit on load regularly (...and ideally get paid by Grid for one of their services ^^^).
Ref
change in speed. The generators adjust to demand by putting more power in
Think of conventional power generation operating at a standard 3000rpm
As well as pure kWs of power, the large conventional stations also have to provide ‘Mandatory Frequency Response’
GB norm is 50Hz, which is satisfied at 3000rpm where 3000 / 60 (seconds) = 50 (Hz)
So if GB demand increases beyond current plant output, system Frequency would drop momentarily below 50Hz, so the gens would run harder for a period, increasing output to equalise demand / generation again at 50Hz.
...and visa, versa: Demand drops, Frequency will spike up, generator output needs to be pulled back.
Happens continuously all day every day.
But with much less conventional thermal generation in the summer fuel mix (on high renewable days like Friday), there’s not as much available to provide Frequency Response or their natural inertia.
So we have seen new solutions developed to fill that service gap. With new Frequency markets and new technologies bidding in and satisfyingly the requirements. Hence the rapid development of commercial scale battery storage schemes in the last few years - up to 50MW assets; but as Grid (and the consumer) have benefited from lower Frequency market prices, a good number of battery developers have got cold feet and put projects on hold.
Electricity trilemma:
Cheap. Reliable. Green.
Choose two...
The Railway gets its feed from DNO “grid sites”. We star feed off these, with strategic gaps on our HV network to separate grid sites. This stops us running them in parallel unless we are doing switching when we have to check for synchronicity and sometimes get permission to close our gap. We then move our gap to another HV breaker on our network keeping parallel time to a minimum. The Grid sites sync is important as if we get it wrong huge currents can flow causing all manner of tripping/outages and interviews without tea and biscuits.
Sitting at each of our subs stations on our HV network (33kv/22kv/11kv) are auxiliary transformers that supply signalling equipment, normally one on each side of the sub station HV feeders and some sites also have an area board feed as well as an emergency back up.
The problem occurs when we loose the grid site and all the signalling kit tries to switch to the local DNO and if that’s fed from the same grid site.......
The other problem we had was that the loss of the OHL 25Kv upset some off the new trains and a tech with a laptop had to go to each one to reset them! Quite why this caused the above issue I don’t know
( I work in a third rail D.C. control , which has both an HV AC network and a D.C. network)
https://hornseaprojectone.co.uk/News/2019/08/Update-on-Hornsea-One
“During a rare and unusual set of circumstances affecting the grid, Hornsea One experienced a technical fault which meant the power station rapidly de-loaded – that is it stopped producing electricity. Normally the grid would be able to cope with a loss of this volume (0.8GW). If National Grid had any concerns about the operation of Hornsea One we would not be allowed to generate. The relevant part of the system has been reconfigured and we are fully confident should this extremely rare situation arise again, Hornsea One would respond as required.”
I have been told of a number of smaller providers e.g. a 40MW CHP and a (tbc)MW solar farm that also tripped-off to self protect from the main event which will have added to the RoCoF issue. I imagine that if there were two there will actually have been many more but they’re not rushing forward to confess.
won't they be listed automatically on bmreports? I had a look on the day it happened but only to look for the gas station and hornsea, I have a feeling there were other unscheduled events too but can't remember what.
grtdkad, any idea how long the process was from dynamic f response through to demand disconnection was on Friday?
Ah, actually I've spotted the info in the "interesting background reading" comments.
BJ ref listed on bmreports. Not as far as I’m aware, as while these were relatively large, they examples I am aware of are behind the meter (sub 50MW) and therefore non-BM.
I assume that domestic and small scale wind/solar installations are connected to the grid via some sort of inverter. I presume that these are frequency / phase locked to the grid somehow (local sensing?). Do they just follow frequency changes on the grid? Or are they biased somehow to try and maintain 50Hz (so assisting with frequency stability)? Do these automatically disconnect if the frequency is outside a certain tolerance? If so, is there any ‘randomness’ built into their response, or will they all respond in the same way at the same time?
My domestic PV installation will apparently disconnect if it can't sync properly. I'm not aware that it ever has (except on total loss of supply) and I don't know what parameters it uses. My guess is that each inverter manufacturer will set their own limits. I'm assuming the inverter controls frequency against an electronic standard, so it won't respond to demand in the same way as a rotating alternator.
Interim report seems to imply that the regulations are not fit for purpose for days when there is low system inertia, as a result this must mean that the BM for frequency response will be opened up, especially in summer? Would this then imply that when you deploy renewable you need triple the capacity in reserve to balance the system, ie matched capacity of traditional generation for when its still and dark, and short term matched capacity in the form of batteries or self disconnection for when the system is running on low inertia, i.e windy summers days?
I tend to agree DJ, NG are correct in stating that everything worked as it should but it begs the question whether holding adequate Frequency Response contracts to cover the largest single loss is “adequate” when we have seen the domino effect.
Now much clearer in terms of sequence of events post lightning strike: and now including ~500MW of small distribution-connected generation that went first, then Hornsea, then RWE’s Little Barford which went in three ~200MW stages (steam turbine then the gas turbines).
^deleted