Apparently a local grid overload near France and a cascading failure down the Spanish network, but radio and newspapers don’t agree on root cause. Of course there is a lot of noise.
For instance, one reporter asked one of the government flunkies whether it could be a cyberattack and they turned his noncommittal “maybe, we don’t know” into “government says cyberattack may be ongoing”.
Be careful of idiot reporters out there.
Edit: I’m listening to another radio interview where they are outlining the plans to bring online Portuguese dams and thermal generators over the next few hours, progressively unplugging from the Spanish supply (fortunately we have enough of those, apparently).
It should take 3-4 hours to get everything balanced with only national supplies, and they will restore power from North to South.
Key points that started it were (you can see the chain of events in the doc):
2.4.1. At 16:52:33 on Friday 9 August 2019, a lightning strike caused a fault on the Eaton Socon – Wymondley 400kV line. This is not unusual and was rectified
within 80 milliseconds (ms)
2.4.2. The fault affected the local distribution networks and approximately 150MW of distributed generation disconnected from the networks or ‘tripped off’ due to a safety mechanism known as vector shift protection
2.4.3. The voltage control system at the Hornsea 1 offshore wind farm did not
respond to the impact of the fault on the transmission system as expected and
became unstable. Hornsea 1 rapidly reduced its power generation or ‘deloaded’
from 799MW to 62MW (a reduction of 737MW).
Curious question for someone familiar with power at grid-scale -- How granular is load shedding? And how is this measured / tracked?
In my head, I'm thinking of generators/plants, connected by some number of lines, to some amount of load, where there are limited disconnection points on the lines.
So how do grid operators know what amount of load will be cut if they disconnect point A123 (and the demand behind it) vs point B456?
Is this done sort-of-blind? Or is there continual measurement? (e.g. there's XYZ MW of load behind A123 as of 2:36pm)
I can speak for the GB case. Low Frequency Demand Disconnection (LFDD) occurs automatically and in stages when the frequency drops until it stabilises. The substations or feeders that are tripped off are not currently determined by real-time metering - instead they are pre-allocated based on their typical demand. This means that the system operator does not really know how much demand will be disconnected at any given time. If it's sunny, you could easily trip off a lot of solar generation connected on the low voltage network, causing the frequency to drop further. It is far from optimal!
> The substations or feeders that are tripped off are not currently determined by real-time metering - instead they are pre-allocated based on their typical demand. This means that the system operator does not really know how much demand will be disconnected at any given time.
This is wild. From a amateur technical perspective, it would only take a cheap hall sensor inside the transformer to have a pretty good guess of how much current has been flowing to the load.
Hell, put the hall sensor onto a board with a micro controller and a LORA transmitter and stick it to the outside of the feed line. Seems like an incredibly cheap upgrade to get real-time load data from every substation.
The nice thing about frequency based regulation is it's an inherent property of the system, so as long as you're connected to the grid you've got the info you need to decide when to turn on or off.
If you're monitoring real time power consumption you then need a whole extra infrastructure to communicate this info back and forth. Of course you then have to consider how you're going to keep that extra infra online in the event of power issues.
Frequency based regulation is only telling you that something is wrong, but not what or how to fix it.
If you find yourself in the middle of a black swan event, and 15 GW have tripped offline, you have milliseconds to dump pretty much exactly 15 GW of load, otherwise more generating capacity is going to trip offline very quickly.
If you only dump 14 GW because you used historical data (which happens to be imprecise, because today's cloud cover reduced rooftop solar output), you're still going to be in trouble. A detector scheme with sensors at every substation would allow you to do just that.
The board is not the expensive part. It's the getting reliability qualified and then having staff fit it to every substation, arrange the data links, and construct the dashboard.
I also wonder what the realtime requirement is. Data from a minute ago is fine .. except in this kind of situation, when things are changing very quickly.
Doing that at scale is tricky and requires a lot of people to participate in the mechanism, whereas the law only forces producers above a given size to participate.
The estimates we get from seasonal studies are usually close enough, especially since load shedding isn't a finesse exercise.
The situations that require load shedding usually give operators only a few minutes to react, where analyzing the issue and determining a course of action takes the lion's share. Once you're there, you want the actual action to be as simple as possible, not factor in many details.
They don't really disconnect it like that in these circumstances (as in they choose what to disconnect). As far as I know generation plants will start disconnect when grid frequency is <49Hz or >51Hz (at least in the UK) automatically as it's all starting to go very wrong. This is what causes this huge cascade effect. Roughly speak less frequency means there is more demand than supply and the other way round for higher frequencies.
This has changed a lot though, as even home batteries afaik will start discharging if they start noticing the frequency dropping to provide some support on generation. But if it's dropping too fast and too quickly it won't help.
But yes they do have very granular info on all the HV sources and how much load is on them.
Load shedding is an active measure taken when the grid operator knows that it will not be able to balance supply and demand. This is what happens in South Africa, where the operator preventively disconnects parts of the network at predetermined times to ensure network balance. As this is programmed, it is possible to rotate the areas under blackout.
In this case, we are dealing with a widespread grid incident. The various grid protection mechanisms have been triggered to prevent interconnection overload. In addition, the generators are trying to correct the grid frequency to exactly 50Hz. At 49Hz, more power must be generated; at 51Hz, less power must be generated. However, if the frequency varies too much, there are also protection mechanisms to prevent the turbines from overspeeding or amplifying frequency variations.
The grid is complex, and normally this type of incident is limited to one cell of the electricity distribution grid. A blackout is a domino effect, when a minor event triggers a chain reaction that disconnects more and more elements from the grid.
Th grid operator will have to restart or reconnect the power plants one by one, restore power to stations and sub stations. All of this must be done in a specific order before power can be restored to consumers. All of this takes time, requires resources (you need men on the ground), and the slightest error can lead to further outages.
Some consumers are prioritised, such as hospitals, transport infrastructure, telecoms and water networks.
Many critical pieces of equipment have UPS systems, but these are not always designed for such long outages or have not been tested for years. There are patients with home equipment who will struggle.
This is why rotating load shedding is preferable. The outages are not too long and vital infrastructure is not affected (or less so).
In my area, "buckets" of average load are prepared ahead of time in coordination between the transporter (who gives the order to shed), the distributer (who implements the shedding operation as close to consumers as possible), and representatives of the state (who define priority areas that can't be load-shed, or that should be load-shed last).
When yhe time comes, you just shed enough "buckets" to stabilize. Load shedding is not a precise task, when you're at that point, you'd rather load a few more megawatt and be safe, than play with the limits and be sorry.
> So how do grid operators know what amount of load will be cut if they disconnect point A123
Opening a line within the grid isn't used to shed load, as the grid is mainly redundant. It's used 1) to protect the line itself (either by letting it trip, or by opening it preventively), or 2) to force power to flow differently through the network, by modifying its impedance. Opening a line from the transport network is not a way to load shed.
In this totally random example [1], opening the line A-B increases impedance in the right part of the network, forcing power to re-route through the left part, and reduces the load on another line in the right path that was overloaded.
> Or is there continual measurement? (e.g. there's XYZ MW of load behind A123 as of 2:36pm)
The network is, indeed, monitored continually, and we do have potential network equipments failure simulations every few minutes, with contingency plans also simulated to make sure that they work in that particular case. This way, when shit hits the fan, we at least have a recently tested plan to start from.
I was going to say something similar. I live in Portugal and I've heard a lot of panic/fear mongering, mainly from the techies in the co-working space I was working on and expats.
(apologies for singling out these specific groups of people - my point is that it might be worth to put down news sources like xitter, and read AP/translated local Portuguese news)
For instance, one reporter asked one of the government flunkies whether it could be a cyberattack and they turned his noncommittal “maybe, we don’t know” into “government says cyberattack may be ongoing”.
Be careful of idiot reporters out there.
Edit: I’m listening to another radio interview where they are outlining the plans to bring online Portuguese dams and thermal generators over the next few hours, progressively unplugging from the Spanish supply (fortunately we have enough of those, apparently).
It should take 3-4 hours to get everything balanced with only national supplies, and they will restore power from North to South.