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).
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)
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.
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.
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.
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).
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.
(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)