Windmill AC phase
- Thread starter Softus
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T
toasty
Interesting,
I had always assumed (which could be a dangerous thing) that the relative internal impedance of the grid (presumably pretty low) vs the internal impedance of the AC windmill (presumably relatively high) meant that once they were in phase, the grid would keep it locked as to move out of phase would effectively require massive currents given the low impedance of the grid as a whole.
regarding wind speed, and therefore rotor speed and therefore output voltage, I don't think it works quite like that, the frequency would actually be proportional to the rotor speed, the voltage is surely controlled by the electromagnetic field in the alternators field windings which the control circuits would alter to keep a steady output voltage.
Regarding how you get them in phase in the first place, I guess you just start the alternator going, and then gradually increase the field winding current and they'll automagically sync up?
Anyway, I've just realised that all of the above is just assumption, so fairly useless, but good question anyway, I'll be interested to see how far off the mark I am
I had always assumed (which could be a dangerous thing) that the relative internal impedance of the grid (presumably pretty low) vs the internal impedance of the AC windmill (presumably relatively high) meant that once they were in phase, the grid would keep it locked as to move out of phase would effectively require massive currents given the low impedance of the grid as a whole.
regarding wind speed, and therefore rotor speed and therefore output voltage, I don't think it works quite like that, the frequency would actually be proportional to the rotor speed, the voltage is surely controlled by the electromagnetic field in the alternators field windings which the control circuits would alter to keep a steady output voltage.
Regarding how you get them in phase in the first place, I guess you just start the alternator going, and then gradually increase the field winding current and they'll automagically sync up?
Anyway, I've just realised that all of the above is just assumption, so fairly useless, but good question anyway, I'll be interested to see how far off the mark I am
having the generator in a wind turbine locked to grid frequency would be a very bad thing. When the wind was low it would act as a fan consuming electricity to move air.
for most smaller wind generation you will go through conversion electronics which convert from the weired AC (varying in frequency and voltate) at the wind turbine to grid syncronised AC at the appropriate voltage and frequency..
for larger wind turbines I belive there are some tricks involving applying variable frequency AC to the field coils of the generator to get the desired frequency out.
convential generation is locked to grid frequency though and afaict the system for getting in sync is just to adjust the power into the turbine until they are in sync and then throw the switch. Once hooked up things tend to stay in sync because to go out of sync would require such massive energy. The frequency of the grid is kept under control by adjusting the ammount of power going into the generators.
for most smaller wind generation you will go through conversion electronics which convert from the weired AC (varying in frequency and voltate) at the wind turbine to grid syncronised AC at the appropriate voltage and frequency..
for larger wind turbines I belive there are some tricks involving applying variable frequency AC to the field coils of the generator to get the desired frequency out.
convential generation is locked to grid frequency though and afaict the system for getting in sync is just to adjust the power into the turbine until they are in sync and then throw the switch. Once hooked up things tend to stay in sync because to go out of sync would require such massive energy. The frequency of the grid is kept under control by adjusting the ammount of power going into the generators.
getting in synch used to be done with three light bulbs, when they went out the generator was synchronised to the grid
I think the bulbs went across each phase of the grid to each phase of the generator but I may have this wrong.
Once locked. no generator can go faster (it would be trying to speed up all the others) or slower (the others would drive it)
the frequency of the grid actually speeds up and slows dow a tiny bit depending on what actual load is a bit less or a bit more than planned. If you have a sufficiently accurate clock you can measure the variation in frequency. I used to know a website that showed actual frequency as it varied second by second. It stops being interesting fairly quickly.
the is a story in the industry of a generator that was connected to the grid without being synchronised. They say the gen ripped out its mountings, jumped in the air, and rolled across the hall.
No-one seems to know where this story came from though.
I think the bulbs went across each phase of the grid to each phase of the generator but I may have this wrong.
Once locked. no generator can go faster (it would be trying to speed up all the others) or slower (the others would drive it)
the frequency of the grid actually speeds up and slows dow a tiny bit depending on what actual load is a bit less or a bit more than planned. If you have a sufficiently accurate clock you can measure the variation in frequency. I used to know a website that showed actual frequency as it varied second by second. It stops being interesting fairly quickly.
the is a story in the industry of a generator that was connected to the grid without being synchronised. They say the gen ripped out its mountings, jumped in the air, and rolled across the hall.
No-one seems to know where this story came from though.
I've heard a slightly different version of the same... Three backup generator sets installed for a big company. First two ran up and synchronised fine. The third set had two phases reversed
you're quite right, there's a windfarm like that near me. Whenever they're turning they make it windy, and the faster they go, the windier it gets.
saw something like that on "how do they do that" or a similar program..
it was about a hydroelectric place and there was a frequency display on the wall..
they were "monitoring" one of the England matches and were on standby for when it ended to boost the power to the grid for all those kettles going on and slowing the frequency down..
the hydroelectric could be put into use with as little as 30 seconds notice or something daft..
the frequency started to drop and once it got to 49.4 Hz, the head guy gave the word and 30 seconds later the frequency started climbing back up to 50Hz..
it was about a hydroelectric place and there was a frequency display on the wall..
they were "monitoring" one of the England matches and were on standby for when it ended to boost the power to the grid for all those kettles going on and slowing the frequency down..
the hydroelectric could be put into use with as little as 30 seconds notice or something daft..
the frequency started to drop and once it got to 49.4 Hz, the head guy gave the word and 30 seconds later the frequency started climbing back up to 50Hz..
When working for the DNO, they spent many thousands on generators that sync'd on and off the NETWORK, but they proved very unreliable and very hard to use effectively.......Hence they are now all lined up unused for many years at the main depot. we once had a 180 kva genny out of sync on a housing estate, the trailer it was mounted on was bouncing nicely 
...........think it took a few appliances out in the houses too!!!
...........think it took a few appliances out in the houses too!!!That would seem sensible. If they are in sync there will be no voltage between the phase terminals on the generator and the corresponding phase terminals on the grid so the bulbs will go out.
So don't be tempted to isolate your tubine when the wind gets up!!
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