4 ms·

The technical term for what you're describing is under-frequency load shedding (UFLS) and it is part of most modern power systems around the world, including al

The technical term for what you're describing is under-frequency load shedding (UFLS) and it is part of most modern power systems around the world, including all of the North American grids. It is an important safeguard against system collapse, however, the goal of system operators is to avoid reaching this stage. In fact, resolving contingency events without interruption of "firm load" (that is, loads that have not previously agreed to be interrupted) is an important performance metric for any grid operator. UFLS is mostly intended to buffer transient loss of power supply (for instance, tripping of several large generators). If the grid operator knows they are facing an inadequacy of generation supply and all resources have already been called in, they will start to shed load under manual operator action to avoid UFLS activation. Before doing this they will declare an emergency which, generally speaking, requires all generators to make best efforts to supply as much energy as they can to the system. Think of it like automated emergency braking on a car vs driver braking. AEB is great, but if you can already see that you're gonna hit something, just hit the brakes right now instead of waiting for AEB. By the time UFLS kicks in, you're already in dire straits and have only moments before reaching an unrecoverable state.

namibj 6y ago
In the central european grid, there is actually a market where companies can offer frequency stabilization service to the grid, which exists in both directions. It doesn't matter if the combat a lack of power in the grid with shedding loads or spinning up another generator. This exists on a few different timescales, and the faster-responding contracts trigger at higher frequency deviations. Primary operating reserve triggers at +-200 mHz and needs to be fully available within 30 s and for up to 15 min, secondary operating reserve has to take over (and be fully available within 5 min), and the tertiary operating reserve has to be fully available within 15 min. The entso-e map: https://www.entsoe.eu/data/map/ https://www.entsoe.eu/data/map/
- mncharity 6y ago
  Curious that the map doesn't match its legend. Powerplants are drawn as substations. Ah, a PDF matches the legend.
- eigenvector 6y ago
  Yes, this function exists in some fashion in every grid (although the economic setup of how you're paid for that service differs widely). The problem in ERCOT is demand massively exceeding available supply over a period of days. You need to carry your primary operating reserve all the time, because you never know when a generator or transmission line may trip. When there's simply a lack of energy supply to meet demand on a steady state basis, you still have to preserve your primary reserves for other unexpected events and cannot call them in to meet longer term (30+ minutes) demand. So load shedding happens once available reserve dips below a certain threshold (generally around the single of the largest single contingency on the grid which may be the largest single generator or a line that feeds multiple large generators). ERCOT hasn't run out of primary reserve, but they are going to have to shed load in order to maintain adequate reserves. You always have to shed load before exhausting reserves, because one moves you closer to stability while the other moves you further away (consuming operating reserve). At this point, with power prices spiking to thousands of dollars per MWh, any plant that can run is running, including some that have come out of planned outage earlier to help out (and be paid handsomely). Even if you simply invoked some emergency order that "all generators must run until further notice", there simply isn't enough capacity due to the large number of generators on forced outage. There's no way out of that situation except temporary load shedding.
  - namibj 6y ago
    Yeah, but part of our operating reserve is in form of industrial consumers. The slow (has 15 min to get to full power) tertiary reserve is partially provided by arc furnaces in steel mills. Also, going beyond this, charging spot prices to consumers (both commercial and residential) serves to align incentives. Such as dis-incentivizing the use of resistive heating for extreme cold, as the prices are correlated with the extreme cold, making alternative heating setups for extreme weather more affordable in comparison. Or, building houses so that extreme cold can be tolerated without damage by allowing pipes to be drained and the remaining sections to be heated separately, so the house as a whole can be unheated (and the people stay with friends). Longer-term predicted loads can be billed at a fixed rate, but spiky loads, especially those correlated with ones at other customers of the utility, can't be. You'd raise the prices until demand falls below the limits, instead of needing rolling blackouts. If people can't afford to take a hot shower right now, they just wait. At least in the absence of certain diseases, the human body is fine without showering for months. And as long as your building doesn't take damage, you'd gladly be payed a few thousand $ to put on really warm clothes for half a week. And depending on the details, you'd even conclude it more economical to have to replace some pipes after water damage, than to keep that area heated.

namibj 6y ago

In the central european grid, there is actually a market where companies can offer frequency stabilization service to the grid, which exists in both directions. It doesn't matter if the combat a lack of power in the grid with shedding loads or spinning up another generator. This exists on a few different timescales, and the faster-responding contracts trigger at higher frequency deviations. Primary operating reserve triggers at +-200 mHz and needs to be fully available within 30 s and for up to 15 min, secondary operating reserve has to take over (and be fully available within 5 min), and the tertiary operating reserve has to be fully available within 15 min. The entso-e map: https://www.entsoe.eu/data/map/ https://www.entsoe.eu/data/map/

mncharity 6y ago
Curious that the map doesn't match its legend. Powerplants are drawn as substations. Ah, a PDF matches the legend.
eigenvector 6y ago
Yes, this function exists in some fashion in every grid (although the economic setup of how you're paid for that service differs widely). The problem in ERCOT is demand massively exceeding available supply over a period of days. You need to carry your primary operating reserve all the time, because you never know when a generator or transmission line may trip. When there's simply a lack of energy supply to meet demand on a steady state basis, you still have to preserve your primary reserves for other unexpected events and cannot call them in to meet longer term (30+ minutes) demand. So load shedding happens once available reserve dips below a certain threshold (generally around the single of the largest single contingency on the grid which may be the largest single generator or a line that feeds multiple large generators). ERCOT hasn't run out of primary reserve, but they are going to have to shed load in order to maintain adequate reserves. You always have to shed load before exhausting reserves, because one moves you closer to stability while the other moves you further away (consuming operating reserve). At this point, with power prices spiking to thousands of dollars per MWh, any plant that can run is running, including some that have come out of planned outage earlier to help out (and be paid handsomely). Even if you simply invoked some emergency order that "all generators must run until further notice", there simply isn't enough capacity due to the large number of generators on forced outage. There's no way out of that situation except temporary load shedding.
- namibj 6y ago
  Yeah, but part of our operating reserve is in form of industrial consumers. The slow (has 15 min to get to full power) tertiary reserve is partially provided by arc furnaces in steel mills. Also, going beyond this, charging spot prices to consumers (both commercial and residential) serves to align incentives. Such as dis-incentivizing the use of resistive heating for extreme cold, as the prices are correlated with the extreme cold, making alternative heating setups for extreme weather more affordable in comparison. Or, building houses so that extreme cold can be tolerated without damage by allowing pipes to be drained and the remaining sections to be heated separately, so the house as a whole can be unheated (and the people stay with friends). Longer-term predicted loads can be billed at a fixed rate, but spiky loads, especially those correlated with ones at other customers of the utility, can't be. You'd raise the prices until demand falls below the limits, instead of needing rolling blackouts. If people can't afford to take a hot shower right now, they just wait. At least in the absence of certain diseases, the human body is fine without showering for months. And as long as your building doesn't take damage, you'd gladly be payed a few thousand $ to put on really warm clothes for half a week. And depending on the details, you'd even conclude it more economical to have to replace some pipes after water damage, than to keep that area heated.