4 ms·

Other interesting fact is how grid uses frequency to communicate the load demand. Load drops, the big spinny generators stop having so much resistance and acce

by ilyt 3y ago

Other interesting fact is how grid uses frequency to communicate the load demand. Load drops, the big spinny generators stop having so much resistance and accelerate. Load increases and the big spinny generators have more load, synchronously slowing down. So in simplest system just feeding your generator more when frequency is below nominal and less when it is above is enough

Someone 3y ago
More info at https://en.wikipedia.org/wiki/Droop_speed_control https://en.wikipedia.org/wiki/Droop_speed_control
isoprophlex 3y ago
Whoa, ever since learning about this, I randomly tell people about this. Noone ever seems to understand my fascination with this distributed grid of spinny things interacting. I'm glad there's at least two of us ;)
- HPsquared 3y ago
  Before quartz oscillators, clocks would use the grid as their time reference. It can be done mechanically via a small synchronous motor and some gears. I'm not sure if it's still the case today, but the grid frequency used to be managed through the night so those clocks were most accurate in the morning (for peoples' alarm clocks)
  - michaelt 3y ago
    > Before quartz oscillators Some systems still use grid frequency for timekeeping. If you own a mechanical rotary timeswitch, it's got a synchronous motor spinning 50 or 60 times a second, then a series of gears, gearing it down to 1 rotation per day.
    - isoprophlex 3y ago
      Yeah. Some years back there was a structural underfreq event for a couple of weeks on the European grid. My microwave phased out of time by several minutes, and then phased back. Was fun to observe. https://www.theguardian.com/world/2018/mar/08/european-clocks-lose-six-minutes-dispute-power-electricity-grid https://www.theguardian.com/world/2018/mar/08/european-clock...
      - cesarb 3y ago
        Interestingly, my country (Brazil) doesn't seem to regulate the grid frequency for use as a time reference, at least as far as I could find. So if this happened here, and if the microwave used the grid frequency for its clock, the clock would stay wrong.
    - throwaway173738 3y ago
      A switch such as would be present in an older clothes dryer or washing machine. The newer ones use electronically controlled relays but I could see the designers skipping the quartz oscillator because the time difference comes out in the wash.
      - tnorthcutt 3y ago
        comes out in the wash Very, very well done
  - bri3d 3y ago
    This isn't just a "before quartz oscillators" thing; it's still in extremely widespread use today since quartz oscillators still cost some fraction more than $0. And, it's not always mechanical, there are a lot of all-in-one timekeeping/clock chips that use AC as the reference frequency for their internal oscillator/PLL. Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference. Due to the growing complexity of power grids and in Europe, international power-grid politics and infighting, the grid frequency is becoming less stable and you see these devices fluctuate badly more often than they used to. https://hackaday.com/2018/03/09/europe-loses-six-minutes-due-to-sagging-frequency-and-international-politics/ https://hackaday.com/2018/03/09/europe-loses-six-minutes-due...
    - kensey 3y ago
      I have one of those little “binary clocks” (it technically displays in BCD, but it’s still “binary”, right?). When I first set it up, it was running really fast —- like it was gaining hours over the course of a day. Turns out it had a button combo for “switch between 50Hz and 60Hz mode” that was similar to its combo for (what I thought I was setting) “switch between 12- and 24-hour mode”. (I think the 12/24 switch was “hold the hour button down while plugging in” and the 50/60 switch was “hold both buttons down while plugging in”.)
    - bsder 3y ago
      > Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference. I find this incredibly hard to believe. Crystals are incredibly cheap and waaaaaay more accurate than anything that the grid does. If you're not an actual motor, sensing the grid is both an engineering challenge and a non-trivial expense.
      - AdamH12113 3y ago
        To my understanding, the grid is managed to have a fixed number of cycles per day, which would make it perfectly accurate. A cheap crystal can easily lose a few seconds per day. And given how hard it is to keep 60 Hz noise out of circuits, I can’t imagine the sensing would be difficult.
- jupp0r 3y ago
  There is a whole world of nerds who do this in their job every day. They are fun people.
- yannyu 3y ago
  I studied electrical engineering, but power engineering isn't a course that I took. The most enlightening quote I've heard about this was a response to a question: "What happens when I turn on an electric device in my house?" "A turbine in a power plant spins more slowly for just a moment."
pixl97 3y ago
Heh, it's easy to model when you have a few generators, especially when one is much bigger than the others on the grid. But what's fun these days is you can have an absolutely huge number of generators. Keeping things in phase just seems insane to me. Practical engineering has a great video about power black starts that give some insight into this complicated machine. https://www.youtube.com/watch?v=uOSnQM1Zu4w https://www.youtube.com/watch?v=uOSnQM1Zu4w
- HPsquared 3y ago
  It's a bit like they are all connected together by gears. All the generators are in phase. The most difficult bit for an operator is to make sure the generator is synchronized before they actually connect it. Only after it's synchronized can they start actually feeding power in. You can't just turn these things on and off at will like a regular motor. To extend the gears analogy, gears need to be synchronised before they can engage - just like synchronous AC generators.
- jnsaff2 3y ago
  It's not hard to keep it in phase. Once it's synchronized it is actually rather hard to not keep it in phase. Generator spins at 50hz Motor spins at 50hz Add load to the motor, it starts slowing down both itself and the generator. Generator governor increases input energy, frequency goes up. Both are in phase all the time. Remove load, both start spinning faster. Reduce governor to regulate it to 50hz again. It's a bit harder with inverters but the idea is similar, you follow the grid phase and if you want to send energy to the grid you will be slightly early to the grid phase and if you want to take energy from the grid your phase will slightly lag.
- binbag 3y ago
  As another commenter says, it's actually easier the more generators you have because the rotational inertia of all the spinning masses is larger. This (and the storage problem) is one of the reasons that wind and solar destabalise grids - they are interfaced to the rest of the grid by converters that create ac sources - but there's no real rotating mass there, so the inertia is tiny. The result is that as we add more renewable power to the network, it becomes less able to 'roll with the punches' of loads coming on and off line. PS One of the answers in the SO thread mentions JET in the UK. I spent a few summers there as an electrical engineering student (it's home to the MAST and JET fusion reactors). When the JET tokamak ignites a plasma, it can't sustain it for very long (we are not yet at the point of extracting enough energy to sustain the reaction). As a result they need to ignite the plasma and keep it hot. They can't do it for more than 1-10 seconds. During that time, they draw massive amounts of power - they're permitted to draw up to 1% of the UK's capacity for a short period, whilst they simultaneously dump all the energy stored in two gigantic flywheel generators housed in a nearby building. I've never been there when the flywheels are running but I've climbed around beneath them. There's nothing quite like massive engineering :)
madaxe_again 3y ago
I do this at home - I’m off-grid, but have a picogrid here as we’re distributed over a fairly large area and have a few structures separated by up to a kilometre, and we’ve multiple PV arrays, a hydro generator to be installed later this summer when the river is low, and a few wind turbines. By far and away the easiest way to control production - i.e. brake/feather turbines or dump PV, is frequency shifting, as I’ve batteries and inverters in several locations and while networking them would be possible, it’s unnecessary. It’s typically intended for grid-tie operations, but here I use it to control our tiny isolated grid. It’s a pretty small range (50.2-53hz) over which they shift, but it’s more than enough. https://www.victronenergy.com/live/ac_coupling:fronius https://www.victronenergy.com/live/ac_coupling:fronius
- ilyt 3y ago
  Huh, didn't even knew that's the feature on small inverters
- dtgriscom 3y ago
  So, no A/C-driven analog clocks, huh?
  - madaxe_again 3y ago
    Indeed. All the wallclocks I have here are old electromechanical beasties, 15 years off a single D cell type affairs with a traditional spring mechanism and a solenoid that winds it periodically. I also discovered that some cheaper LED drivers are extremely sensitive to frequency shifts, and bulbs just flat out flat out die within weeks.
    - ilyt 3y ago
      > I also discovered that some cheaper LED drivers are extremely sensitive to frequency shifts, and bulbs just flat out flat out die within weeks. Huh, that's just outright bizzare. The most adding few hz should do is change power by few %
      - 3y ago
jillesvangurp 3y ago
These days with batteries, a lot of that demand can be served very rapidly. Batteries act as buffers and increasingly replace traditional back up generation (stand by coal/gas plants). A lot of these load spikes are short lived. There are all sorts of weird spikes related to people turning on their tea kettles in the morning or turning on their stoves around 6 pm, etc. Battery production is currently shifting from hundreds of gwh per year to twh per year worth of production. They last quite long too. If you cycle 1 twh of battery every day, it would run out in about a decade (assuming 3000 cycles or so). And if you do that, that amounts to absorbing and serving about 365 twh. The worlds entire electricity production is measured in peta watt hour (pwh). About 25 phw. or 25000 twh. So, with battery production scaling int he tens of twh per year, there may soon be enough battery to absorb and produce that kind of volume. Doesn't mean it will be used exclusively for that. But it drives the point home that we are talking some very non trivial levels of standby power. That's car batteries, home batteries, grid batteries, etc. connected to the grid. Mostly neither charging or discharging most of the time. Tesla and a few others are starting to experiment with virtual energy providers. That might go from a few GW to having in the order of TW of power available on demand very shortly. There are about half a million tesla home batteries out there apparently. Even a few thousand of those already add up to quite a bit of collective power. Imagine that scaling to millions of connected batteries. They'd be the largest power supplier, by far, in most markets. That won't run the grid for hours/days obviously. But it does eliminate a lot stand by capacity that is expensive and poorly utilized. That's also the future for energy intensive industries. They'll want to generate most of their power locally (because that's cheaper) and use batteries to buffer it and fall back to the grid only when that runs out and export to the grid whenever there's a surplus locally. So, that reduces load on the grid and evens out a lot of the load spikes. And a lot of the time they'll be feeding energy into the grid. Anything energy intensive is going to compete on cost. And that means investing in local production and batteries.

by ilyt 3y ago

Someone 3y ago

More info at https://en.wikipedia.org/wiki/Droop_speed_control https://en.wikipedia.org/wiki/Droop_speed_control

isoprophlex 3y ago

Whoa, ever since learning about this, I randomly tell people about this. Noone ever seems to understand my fascination with this distributed grid of spinny things interacting. I'm glad there's at least two of us ;)

HPsquared 3y ago
Before quartz oscillators, clocks would use the grid as their time reference. It can be done mechanically via a small synchronous motor and some gears. I'm not sure if it's still the case today, but the grid frequency used to be managed through the night so those clocks were most accurate in the morning (for peoples' alarm clocks)
- michaelt 3y ago
  > Before quartz oscillators Some systems still use grid frequency for timekeeping. If you own a mechanical rotary timeswitch, it's got a synchronous motor spinning 50 or 60 times a second, then a series of gears, gearing it down to 1 rotation per day.
  - isoprophlex 3y ago
    Yeah. Some years back there was a structural underfreq event for a couple of weeks on the European grid. My microwave phased out of time by several minutes, and then phased back. Was fun to observe. https://www.theguardian.com/world/2018/mar/08/european-clocks-lose-six-minutes-dispute-power-electricity-grid https://www.theguardian.com/world/2018/mar/08/european-clock...
    - cesarb 3y ago
      Interestingly, my country (Brazil) doesn't seem to regulate the grid frequency for use as a time reference, at least as far as I could find. So if this happened here, and if the microwave used the grid frequency for its clock, the clock would stay wrong.
  - throwaway173738 3y ago
    A switch such as would be present in an older clothes dryer or washing machine. The newer ones use electronically controlled relays but I could see the designers skipping the quartz oscillator because the time difference comes out in the wash.
    - tnorthcutt 3y ago
      comes out in the wash Very, very well done
- bri3d 3y ago
  This isn't just a "before quartz oscillators" thing; it's still in extremely widespread use today since quartz oscillators still cost some fraction more than $0. And, it's not always mechanical, there are a lot of all-in-one timekeeping/clock chips that use AC as the reference frequency for their internal oscillator/PLL. Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference. Due to the growing complexity of power grids and in Europe, international power-grid politics and infighting, the grid frequency is becoming less stable and you see these devices fluctuate badly more often than they used to. https://hackaday.com/2018/03/09/europe-loses-six-minutes-due-to-sagging-frequency-and-international-politics/ https://hackaday.com/2018/03/09/europe-loses-six-minutes-due...
  - kensey 3y ago
    I have one of those little “binary clocks” (it technically displays in BCD, but it’s still “binary”, right?). When I first set it up, it was running really fast —- like it was gaining hours over the course of a day. Turns out it had a button combo for “switch between 50Hz and 60Hz mode” that was similar to its combo for (what I thought I was setting) “switch between 12- and 24-hour mode”. (I think the 12/24 switch was “hold the hour button down while plugging in” and the 50/60 switch was “hold both buttons down while plugging in”.)
  - bsder 3y ago
    > Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference. I find this incredibly hard to believe. Crystals are incredibly cheap and waaaaaay more accurate than anything that the grid does. If you're not an actual motor, sensing the grid is both an engineering challenge and a non-trivial expense.
    - AdamH12113 3y ago
      To my understanding, the grid is managed to have a fixed number of cycles per day, which would make it perfectly accurate. A cheap crystal can easily lose a few seconds per day. And given how hard it is to keep 60 Hz noise out of circuits, I can’t imagine the sensing would be difficult.
jupp0r 3y ago
There is a whole world of nerds who do this in their job every day. They are fun people.
yannyu 3y ago
I studied electrical engineering, but power engineering isn't a course that I took. The most enlightening quote I've heard about this was a response to a question: "What happens when I turn on an electric device in my house?" "A turbine in a power plant spins more slowly for just a moment."

pixl97 3y ago

Heh, it's easy to model when you have a few generators, especially when one is much bigger than the others on the grid. But what's fun these days is you can have an absolutely huge number of generators. Keeping things in phase just seems insane to me. Practical engineering has a great video about power black starts that give some insight into this complicated machine. https://www.youtube.com/watch?v=uOSnQM1Zu4w https://www.youtube.com/watch?v=uOSnQM1Zu4w

HPsquared 3y ago
It's a bit like they are all connected together by gears. All the generators are in phase. The most difficult bit for an operator is to make sure the generator is synchronized before they actually connect it. Only after it's synchronized can they start actually feeding power in. You can't just turn these things on and off at will like a regular motor. To extend the gears analogy, gears need to be synchronised before they can engage - just like synchronous AC generators.
jnsaff2 3y ago
It's not hard to keep it in phase. Once it's synchronized it is actually rather hard to not keep it in phase. Generator spins at 50hz Motor spins at 50hz Add load to the motor, it starts slowing down both itself and the generator. Generator governor increases input energy, frequency goes up. Both are in phase all the time. Remove load, both start spinning faster. Reduce governor to regulate it to 50hz again. It's a bit harder with inverters but the idea is similar, you follow the grid phase and if you want to send energy to the grid you will be slightly early to the grid phase and if you want to take energy from the grid your phase will slightly lag.
binbag 3y ago
As another commenter says, it's actually easier the more generators you have because the rotational inertia of all the spinning masses is larger. This (and the storage problem) is one of the reasons that wind and solar destabalise grids - they are interfaced to the rest of the grid by converters that create ac sources - but there's no real rotating mass there, so the inertia is tiny. The result is that as we add more renewable power to the network, it becomes less able to 'roll with the punches' of loads coming on and off line. PS One of the answers in the SO thread mentions JET in the UK. I spent a few summers there as an electrical engineering student (it's home to the MAST and JET fusion reactors). When the JET tokamak ignites a plasma, it can't sustain it for very long (we are not yet at the point of extracting enough energy to sustain the reaction). As a result they need to ignite the plasma and keep it hot. They can't do it for more than 1-10 seconds. During that time, they draw massive amounts of power - they're permitted to draw up to 1% of the UK's capacity for a short period, whilst they simultaneously dump all the energy stored in two gigantic flywheel generators housed in a nearby building. I've never been there when the flywheels are running but I've climbed around beneath them. There's nothing quite like massive engineering :)

madaxe_again 3y ago

I do this at home - I’m off-grid, but have a picogrid here as we’re distributed over a fairly large area and have a few structures separated by up to a kilometre, and we’ve multiple PV arrays, a hydro generator to be installed later this summer when the river is low, and a few wind turbines. By far and away the easiest way to control production - i.e. brake/feather turbines or dump PV, is frequency shifting, as I’ve batteries and inverters in several locations and while networking them would be possible, it’s unnecessary. It’s typically intended for grid-tie operations, but here I use it to control our tiny isolated grid. It’s a pretty small range (50.2-53hz) over which they shift, but it’s more than enough. https://www.victronenergy.com/live/ac_coupling:fronius https://www.victronenergy.com/live/ac_coupling:fronius

ilyt 3y ago
Huh, didn't even knew that's the feature on small inverters
dtgriscom 3y ago
So, no A/C-driven analog clocks, huh?
- madaxe_again 3y ago
  Indeed. All the wallclocks I have here are old electromechanical beasties, 15 years off a single D cell type affairs with a traditional spring mechanism and a solenoid that winds it periodically. I also discovered that some cheaper LED drivers are extremely sensitive to frequency shifts, and bulbs just flat out flat out die within weeks.
  - ilyt 3y ago
    > I also discovered that some cheaper LED drivers are extremely sensitive to frequency shifts, and bulbs just flat out flat out die within weeks. Huh, that's just outright bizzare. The most adding few hz should do is change power by few %
    - 3y ago

jillesvangurp 3y ago

These days with batteries, a lot of that demand can be served very rapidly. Batteries act as buffers and increasingly replace traditional back up generation (stand by coal/gas plants). A lot of these load spikes are short lived. There are all sorts of weird spikes related to people turning on their tea kettles in the morning or turning on their stoves around 6 pm, etc. Battery production is currently shifting from hundreds of gwh per year to twh per year worth of production. They last quite long too. If you cycle 1 twh of battery every day, it would run out in about a decade (assuming 3000 cycles or so). And if you do that, that amounts to absorbing and serving about 365 twh. The worlds entire electricity production is measured in peta watt hour (pwh). About 25 phw. or 25000 twh. So, with battery production scaling int he tens of twh per year, there may soon be enough battery to absorb and produce that kind of volume. Doesn't mean it will be used exclusively for that. But it drives the point home that we are talking some very non trivial levels of standby power. That's car batteries, home batteries, grid batteries, etc. connected to the grid. Mostly neither charging or discharging most of the time. Tesla and a few others are starting to experiment with virtual energy providers. That might go from a few GW to having in the order of TW of power available on demand very shortly. There are about half a million tesla home batteries out there apparently. Even a few thousand of those already add up to quite a bit of collective power. Imagine that scaling to millions of connected batteries. They'd be the largest power supplier, by far, in most markets. That won't run the grid for hours/days obviously. But it does eliminate a lot stand by capacity that is expensive and poorly utilized. That's also the future for energy intensive industries. They'll want to generate most of their power locally (because that's cheaper) and use batteries to buffer it and fall back to the grid only when that runs out and export to the grid whenever there's a surplus locally. So, that reduces load on the grid and evens out a lot of the load spikes. And a lot of the time they'll be feeding energy into the grid. Anything energy intensive is going to compete on cost. And that means investing in local production and batteries.