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.
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.
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.
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.
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.
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).
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.
[1]: https://excalidraw.com/#json=5l8OS96Wdke6l9YEClQt8,NJ-r2PtiE...
> 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.