4 ms·

Am I naive in assuming that many grid stability issues could be fixed by mandating all electric heaters automatically cut off at, say below 49.9Hz? It is my un

by cjdell 6y ago

Am I naive in assuming that many grid stability issues could be fixed by mandating all electric heaters automatically cut off at, say below 49.9Hz? It is my understanding that modern home EV chargers have the capability to do this to some extent, but I'm not sure if it's actually utilised?

johncessna 6y ago
It seems like a better solution would be batteries and/or the allowance of dirtier power generation (in emergencies). I can't even wrap my head around the regulatory nightmare of shutting off everyone's heat at night in January.
- corty 6y ago
  Batteries maybe. Allowing "dirtier" non-50Hz power would make things worse, power plant turbines are optimized for 50Hz, different frequencies get inefficient quite fast. So your generation will shrink the lower you go. At the same time generators running at different frequencies will work against each other. At the same time machines will pull the frequency down even further, landing you in a vicious circle that forces the frequency toward 0Hz. No choice but to cut power before you damage too much of the grid and equipment.
- cjdell 6y ago
  Perhaps I don't understand the grid properly. I thought the average frequency was always maintained at 50Hz over a 24 hour period. Having the frequency dip below 49.9Hz would normally be exceptionally rare. I mean, if the alternative is a blackout, having heating turned off for a few minutes over a 24 period would be preferable to a nationwide blackout? It's not as if people would suddenly freeze to death anyway. Just curious if someone who understood this better had a good explanation for why this might be a bad idea.
- formerly_proven 6y ago
  Dirtier power generation doesn't work because physics. Frequency gets too high (a few Hz or so), turbogenerators/turbines blow up. Frequency gets too low, resonances destroy them. Frequency shifts quickly, massive torque and current spikes ensue. Load is dumped, frequency ramps up quickly and voltage rises very quickly. There are a number of control and monitoring systems in a power plant which ought to prevent these from happening, but in the bigger picture this means that grid power needs to be balanced continuously in order to keep nominal frequency. This becomes challenging when an interconnect fails, because this leads to very fast load changes. The reason for 50 Hz +- 0.2 Hz isn't so much about consumers; it's about being able to run the grid. In Europe there is a long-term control loop that makes it a quite accurate 50 Hz, so synchronous motor clocks work, but that has essentially nothing to do with the normal frequency control.
  - johnymnemonic 6y ago
    "Dirtier power generation doesn't work because physics. Frequency gets too high (a few Hz or so), turbogenerators/turbines blow up. Frequency gets too low, resonances destroy them." You very obviously have no idea what you are talking about. Turbines blowing up because they spin a few Hz faster? Mine never did. Turbine destroyed because of "resonances" when freq too low? Mine never did that either. Not the 1100MW one at my old job, nor the two 500MW ones at the job before that and also not the 12MW one at my current job.
    - dang 6y ago
      Hey, could you please review https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and stick to the rules when posting here? It's not ok to attack another user like that on this site, regardless of how wrong someone is or you feel they are. It sounds like you know a lot about this topic, which is great, but please omit personal swipes—that will make it much easier for people to learn from your posts.
- avianlyric 6y ago
  It’s all about speed. A power grid must be perfectly balanced at all times, there no natural storage in a power grid. If large power supplier disconnects without warning, that impact propagates at the speed of light. Other suppliers will respond by reducing their frequencies to keep voltage up, this is caused by generators physically spinning slower and converting their physical momentum into electrical energy. As you can imagine the momentum of a generator is large, but the stored energy is small compared to the rate of consumption. So you need systems that can respond within milliseconds to restore some stability. Batteries are actually one of the few technologies that can do that, but mostly your looking at shedding load. Disconnecting a consumer can happen in milliseconds, after all you just need to flip a switch (admittedly they’re very large switches). Once you shed load, then you have the time you need to spin up you “dirty” power supplies. But even the fastest response suppliers take minutes (think Hydro), not milliseconds to respond. So they’re not viable for dealing with the initial shock to the grid.
- tgsovlerkhgsel 6y ago
  It depends on how long you shut the heat off for. If you do it for 5 minutes while the gas plants spool up, few will notice and fewer will care.
monocasa 6y ago
I'm not sure that cutting off people's heat in the middle of winter is the most politically viable option.
- avianlyric 6y ago
  It’s tends to be very viable. Most places can afford for heat to be shut off for 10-15mins without issue (think water heaters and whole building heaters). That then gives the grid some time to spool up reserves. After all having your hear turn off for 10mins is better than having everything turn off for an hour, which could happen if the grid needs to shed load involuntarily.
avianlyric 6y ago
Most grids have a rapid response system like this. They’ll have contracts with very large power consumers (think big hydro pumps, metal smelters etc) that can afford to have their equipment power down without notice in exchange for energy rebates. Then when the frequency drops these consumers will automatically turn off their equipment to reduce power draw. The seeing such a huge drop like this is extremely unusual, no doubt many systems immediately started load shedding (both voluntary and involuntary) to compensate
- calaphos 6y ago
  Apparently first threshold for cutting of hydro storage pumps below 49.85 Hz was undercut very briefly. Immediately afterwards the frequency reaches that threshold again, so I assume those measurements were working as planned. Below 49Hz larger consumers would be cut off in steps of ~10% of the network load. AFAIK this includes large industrial consumers who are legally required to have the equipment in place to allow for that.
  - avianlyric 6y ago
    Industrial consumers will have a contract to be part of first tier load shedding, rather than a legal mandate. If the grid really needs to shed load, it doesn’t ask, switchgear will just be programmed to physically disconnected consumers at certain grid frequencies. As a consumer you should have equipment that can survive that if it’s important to you, the consumer can then normally get rebates for loss of service later. Special locations like hospitals are normally the last to be load shed, and the surrounding grid will shed everyone else first, before disconnecting them.
q3k 6y ago
There already are load shedding measures [1] put in place for situations like these. [1] - https://www.netzfrequenzmessung.de/abschaltung.htm https://www.netzfrequenzmessung.de/abschaltung.htm
PragmaticPulp 6y ago
This needs central coordination to really work. You also need customer incentives to get buy in. Power companies do something similar with air conditioning units in hot areas. Customers can opt-in to have a control module installed that modulates their A/C on and off at peak loads to control demand. Customers get some nominal discount on their bill for participating. Worked better when people weren’t working from home and it didn’t matter if your house was a bit warmer than normal for an hour or two mid-day. Controlling this on end devices introduces a lot of distributed systems problems, like stampeding herd when all of the devices switch back on. You could try jittered back off and such, but cold customers would just unplug and replug until it worked.
epistasis 6y ago
The term in the industry for this is "demand response," and usually it's voluntary and customers should get paid for participating. Typically it's just larger customers that can reduce demand on a very large scale. In the US there are a few startups that are aggravating residential customers into larger groups, so that each of thousands of households cuts consumption by a few hundred watts, so that the aggregate drop is big enough for the utility to care about. Utilities, at least in the US, have extremely poor capabilities for innovation and for customer relations, so that is why a startup is an intermediary. Typically, the signal for this is not the grid frequency, however! Better to plan ahead by a bit before the frequency drops, and allow people to opt out as necessary.
- avianlyric 6y ago
  For rapid response systems grid frequency is the signal! You always need something that can respond quickly to unexpected events to maintain grid stability. The best signal for that is grid frequency, as it’s a very direct measure of grid health. Many of those large consumers you speak off will be contracted to respond directly to grid frequency, either shedding load or adding supply, to make sure the grid doesn’t completely collapse if a shock event happens. That buys grid maintainers the time they need to recover the grid in a more controlled way.
bzb6 6y ago
That would be such a gross government overreach.

by cjdell 6y ago

johncessna 6y ago

It seems like a better solution would be batteries and/or the allowance of dirtier power generation (in emergencies). I can't even wrap my head around the regulatory nightmare of shutting off everyone's heat at night in January.

corty 6y ago
Batteries maybe. Allowing "dirtier" non-50Hz power would make things worse, power plant turbines are optimized for 50Hz, different frequencies get inefficient quite fast. So your generation will shrink the lower you go. At the same time generators running at different frequencies will work against each other. At the same time machines will pull the frequency down even further, landing you in a vicious circle that forces the frequency toward 0Hz. No choice but to cut power before you damage too much of the grid and equipment.
cjdell 6y ago
Perhaps I don't understand the grid properly. I thought the average frequency was always maintained at 50Hz over a 24 hour period. Having the frequency dip below 49.9Hz would normally be exceptionally rare. I mean, if the alternative is a blackout, having heating turned off for a few minutes over a 24 period would be preferable to a nationwide blackout? It's not as if people would suddenly freeze to death anyway. Just curious if someone who understood this better had a good explanation for why this might be a bad idea.
formerly_proven 6y ago
Dirtier power generation doesn't work because physics. Frequency gets too high (a few Hz or so), turbogenerators/turbines blow up. Frequency gets too low, resonances destroy them. Frequency shifts quickly, massive torque and current spikes ensue. Load is dumped, frequency ramps up quickly and voltage rises very quickly. There are a number of control and monitoring systems in a power plant which ought to prevent these from happening, but in the bigger picture this means that grid power needs to be balanced continuously in order to keep nominal frequency. This becomes challenging when an interconnect fails, because this leads to very fast load changes. The reason for 50 Hz +- 0.2 Hz isn't so much about consumers; it's about being able to run the grid. In Europe there is a long-term control loop that makes it a quite accurate 50 Hz, so synchronous motor clocks work, but that has essentially nothing to do with the normal frequency control.
- johnymnemonic 6y ago
  "Dirtier power generation doesn't work because physics. Frequency gets too high (a few Hz or so), turbogenerators/turbines blow up. Frequency gets too low, resonances destroy them." You very obviously have no idea what you are talking about. Turbines blowing up because they spin a few Hz faster? Mine never did. Turbine destroyed because of "resonances" when freq too low? Mine never did that either. Not the 1100MW one at my old job, nor the two 500MW ones at the job before that and also not the 12MW one at my current job.
  - dang 6y ago
    Hey, could you please review https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and stick to the rules when posting here? It's not ok to attack another user like that on this site, regardless of how wrong someone is or you feel they are. It sounds like you know a lot about this topic, which is great, but please omit personal swipes—that will make it much easier for people to learn from your posts.
avianlyric 6y ago
It’s all about speed. A power grid must be perfectly balanced at all times, there no natural storage in a power grid. If large power supplier disconnects without warning, that impact propagates at the speed of light. Other suppliers will respond by reducing their frequencies to keep voltage up, this is caused by generators physically spinning slower and converting their physical momentum into electrical energy. As you can imagine the momentum of a generator is large, but the stored energy is small compared to the rate of consumption. So you need systems that can respond within milliseconds to restore some stability. Batteries are actually one of the few technologies that can do that, but mostly your looking at shedding load. Disconnecting a consumer can happen in milliseconds, after all you just need to flip a switch (admittedly they’re very large switches). Once you shed load, then you have the time you need to spin up you “dirty” power supplies. But even the fastest response suppliers take minutes (think Hydro), not milliseconds to respond. So they’re not viable for dealing with the initial shock to the grid.
tgsovlerkhgsel 6y ago
It depends on how long you shut the heat off for. If you do it for 5 minutes while the gas plants spool up, few will notice and fewer will care.

monocasa 6y ago

I'm not sure that cutting off people's heat in the middle of winter is the most politically viable option.

avianlyric 6y ago
It’s tends to be very viable. Most places can afford for heat to be shut off for 10-15mins without issue (think water heaters and whole building heaters). That then gives the grid some time to spool up reserves. After all having your hear turn off for 10mins is better than having everything turn off for an hour, which could happen if the grid needs to shed load involuntarily.

avianlyric 6y ago

Most grids have a rapid response system like this. They’ll have contracts with very large power consumers (think big hydro pumps, metal smelters etc) that can afford to have their equipment power down without notice in exchange for energy rebates. Then when the frequency drops these consumers will automatically turn off their equipment to reduce power draw. The seeing such a huge drop like this is extremely unusual, no doubt many systems immediately started load shedding (both voluntary and involuntary) to compensate

calaphos 6y ago
Apparently first threshold for cutting of hydro storage pumps below 49.85 Hz was undercut very briefly. Immediately afterwards the frequency reaches that threshold again, so I assume those measurements were working as planned. Below 49Hz larger consumers would be cut off in steps of ~10% of the network load. AFAIK this includes large industrial consumers who are legally required to have the equipment in place to allow for that.
- avianlyric 6y ago
  Industrial consumers will have a contract to be part of first tier load shedding, rather than a legal mandate. If the grid really needs to shed load, it doesn’t ask, switchgear will just be programmed to physically disconnected consumers at certain grid frequencies. As a consumer you should have equipment that can survive that if it’s important to you, the consumer can then normally get rebates for loss of service later. Special locations like hospitals are normally the last to be load shed, and the surrounding grid will shed everyone else first, before disconnecting them.

q3k 6y ago

There already are load shedding measures [1] put in place for situations like these. [1] - https://www.netzfrequenzmessung.de/abschaltung.htm https://www.netzfrequenzmessung.de/abschaltung.htm

PragmaticPulp 6y ago

This needs central coordination to really work. You also need customer incentives to get buy in. Power companies do something similar with air conditioning units in hot areas. Customers can opt-in to have a control module installed that modulates their A/C on and off at peak loads to control demand. Customers get some nominal discount on their bill for participating. Worked better when people weren’t working from home and it didn’t matter if your house was a bit warmer than normal for an hour or two mid-day. Controlling this on end devices introduces a lot of distributed systems problems, like stampeding herd when all of the devices switch back on. You could try jittered back off and such, but cold customers would just unplug and replug until it worked.

epistasis 6y ago

The term in the industry for this is "demand response," and usually it's voluntary and customers should get paid for participating. Typically it's just larger customers that can reduce demand on a very large scale. In the US there are a few startups that are aggravating residential customers into larger groups, so that each of thousands of households cuts consumption by a few hundred watts, so that the aggregate drop is big enough for the utility to care about. Utilities, at least in the US, have extremely poor capabilities for innovation and for customer relations, so that is why a startup is an intermediary. Typically, the signal for this is not the grid frequency, however! Better to plan ahead by a bit before the frequency drops, and allow people to opt out as necessary.

avianlyric 6y ago
For rapid response systems grid frequency is the signal! You always need something that can respond quickly to unexpected events to maintain grid stability. The best signal for that is grid frequency, as it’s a very direct measure of grid health. Many of those large consumers you speak off will be contracted to respond directly to grid frequency, either shedding load or adding supply, to make sure the grid doesn’t completely collapse if a shock event happens. That buys grid maintainers the time they need to recover the grid in a more controlled way.

bzb6 6y ago

That would be such a gross government overreach.