"Real electrical systems have to deal with issues of reactance and other exciting math-heavy constructs designed to drive you into some other field of study."
They had me at this
SoftTalker 5 hours ago [-]
Wonder how much complexity using AC adds to this? With DC you would not have to worry about frequency and phase matching. But then you need to convert the DC back to AC at some point.
And only because long-distance transmission is more efficient.
mannykannot 4 hours ago [-]
I imagine AC makes things considerably more difficult. Reactance is a consequence of inductance and capacitance, which cause current and voltage changes to be out of phase with each other. While the current on a DC transmission line will vary, it will not be reversing every ~10 milliseconds, and I suppose the voltage will be very steady except during startup and shutdown.
On an AC transmission line, I suppose any corona discharge going on shuts off and restarts every time the voltage reverses. They make a characteristic buzz in humid conditions.
lazide 5 hours ago [-]
(Efficient) High voltage AC is ‘easy’ due to how well transformers work, how durable they are, and how simple they are. AC does have issues with inductive loss when buried (or near anything conductive), however. For the same reason Transformers work and are awesome.
High voltage DC is hard as it requires solid state components which are expensive to make, and prone to blowing up (aka relatively fragile). AC to DC and vice versa also adds non-trivial losses.
High voltage DC (to a first approximation) doesn’t suffer from inductive losses however, which makes it much more efficient when near conductive stuff like the ground or seawater.
It’s also ‘simpler’ (doesn’t have things like phase or frequency) which is convenient if doing things like transferring power between two power grids with dissimilar frequencies or phase.
They each have their place.
formerly_proven 3 hours ago [-]
I think the contrary is true. Frequency and phase matching is a feature, not a bug. Because AC gives you frequency, and frequency is not just easy to measure but also easy to have accurate references and very immune to noise, it is also not influenced by step-up/step-down transformers. This makes balancing an AC grid possible. Frequency below the set point? Increase power output. Frequency above? Reduce. As an added bonus, this happens to exactly match up with how synchronous generators work. So you get a fairly robust way for many distributed power plants to collectively coordinate power output without additional communication just by agreeing on the physical quantity which we can measure with the highest precision of any quantity very cheaply.
That is not possible with DC.
sam_lowry_ 1 hours ago [-]
Bingo! So many people miss this.
thenobsta 3 hours ago [-]
All of it, I guess. That phasor is always complex.
codethief 3 hours ago [-]
Ha, I was waiting to see a comment with the obvious pun to be made here. :)
That's easy enough to say but big iron power electronics are orders of magnitude more expensive than copper windings and magnetic steel laminations , both in terms of capital cost and maintenance. It's also dramatically harder to extinguish DC arcs so switching gear and substations need more expensive designs as well. The grid could not exist at present, let alone 100 years ago, if we operated it all DC. Over time more and more of it will shift to DC, particularly for long haul, but AC has enough advantages that's it's unlikely to ever go away.
I'm short, it's this way for a reason. The complexity is nessessary.
f1shy 3 hours ago [-]
DC comes with another 1000 problems. It wouldn’t be any better, really.
5 hours ago [-]
raverbashing 5 hours ago [-]
> Wonder how much complexity using AC adds to this?
Summarizing a couple of year of very annoying electrical studies: Yes
You can't believe how much
formerly_proven 3 hours ago [-]
On the other hand, having a continent-scale AC grid is not just possible but common. Europe and North Africa have one, Russia has one, China has one, the US has two or three. Meanwhile multiterminal HVDC is basically experimental stuff that's only possible with real-time digital control systems.
belter 5 hours ago [-]
Reactance is such a beautiful French word...It just reminds you of some frustrated romantic attempts in a Paris scenario. :-)
But your electrical supplier will charge you for it. Had a electrical power teacher with a past employment at a power supplier, who sadly loved to brag how he used to terrorize small farms when their own power generators had a cos φ below 0.98. I think the rule for Portugal is cos φ above 0.97 and for Spain 0.95 also known as el coseno de phi...
"With inverter-based power storage, generation, and transmission, the grid can now react incredibly quickly. This is good when they do the right thing, but can be very bad when they do the wrong thing."
I'm wondering if this will be like the 2016 South Australian blackout
"AEMO identified software settings in the wind farms that prevented repeated restarts once voltage or frequency events occurred too often. "
Grid operators are currently mostly against renewable and so they impose "blunt" disconnect rules on inverters behind renewable sources, and this comes to bite the grid when the proverbial shit hits the fan.
May be in the end this will be a good thing and grid operators will start to treat inverters and renewable as a strength and modify grid regulations as needed.
toast0 3 hours ago [-]
> "AEMO identified software settings in the wind farms that prevented repeated restarts once voltage or frequency events occurred too often. "
> Grid operators are currently mostly against renewable and so they impose "blunt" disconnect rules on inverters behind renewable sources, and this comes to bite the grid when the proverbial shit hits the fan.
As a distributed systems person, this seems like a coordination/communication problem. If a single node is having repeated events, it may likely be broken and staying offline could be a better choice. If multiple nodes are having repeated events, maybe it's better for them to stay connection and do their best.
idiotsecant 4 hours ago [-]
Grid operators are, as a rule, not opposed to renewables at all. They are 'opposed' to resources that do not provide frequency support and are non-dispatchable. Renewables need storage to be well behaved. As soon as we start factoring that into the build at scale the problems go away. Generators want to ignore all the inconvenient physics of power transmission networks and just want $$$ for MW. The system doesn't work if enough people operate like that.
guerby 2 hours ago [-]
You're completely wrong about this.
Inverters if told so can do frequency support better and cheaper than any other solutions.
No other technology can react as fast as an inverter.
See the Texas grid grid service market which is now completely dominated by GW of inverters.
"One solution is to connect inverters with “grid-forming” capabilities, which help mitigate this risk by limiting fluctuations outside of 60 Hz, increasing grid stability. Experts see utility-scale batteries as a prime opportunity to deploy grid-forming inverters to the grid, as grid-forming integration with batteries is cheaper and faster than building new transmission."
"grid-forming" inverter is just software and parameters, your el-cheapo home solar inverter can do it too. It currently is prevented from doing so by ... grid operator regulations which ask it to disconnect at the first issue.
shadowgovt 4 hours ago [-]
Funny enough, the effect of inverters on the grid may be mitigated with a relatively simple solution: add a flywheel to the inverter-based connection farms to "fake" a turbine.
The wind or solar farm drives the flywheel and if the grid-side power starts to fluctuate, it pulls on the flywheel before the inverters feel it. You lose some total efficiency in the electrical-to-mechanical-to-electrical conversion, but get enough flywheels and maybe you don't care (because they also act as a place to store peak energy production when demand is low).
reaperducer 4 hours ago [-]
Grid operators are currently mostly against renewable
As someone who moves a lot, it's always curious to me that grid operators vary so widely on this.
Some places (like where I am now), the grid operator hates renewables and especially rooftop solar.
Other places, the grid operator will actually subsidize rooftop solar because it they say it reduces the amount of generation it has to do, thus saving money on infrastructure and maintenance.
Of course, each location has wildly different climates, but the regional politics aren't that different, so I don't think it's about ideology.
shadowgovt 4 hours ago [-]
It depends heavily on their market incentives. If the local power company is also in charge of the wires, less load on the wires means less cost. In a market where distribution and generation are different operations, generation only cares about whether anyone's going to buy the electricity they want to put on the wire and you saying "No thanks, I'm full" is in direct competition to their interests (and existence as a firm).
idiotsecant 4 hours ago [-]
Huh? Transmission networks get directly financially rewarded for more power flowing in the form of wheeling charges. It's wild reading HN discussions of topics that I actually know about. It makes me wonder how much I can trust the discussions I don't know about.
pjc50 4 hours ago [-]
This is very jurisdiction-dependent, isn't it? And different for nationalized operators like the UK?
tekla 3 hours ago [-]
I know things about airplanes. The discussions here about airplanes is laughable, below wikipedia level.
goda90 6 hours ago [-]
My state, Wisconsin, has had a long political and legal battle over the construction of high voltage lines from the Madison area to Dubuque, Iowa. Opposition ranges from aesthetics to wildlife conservation to it just being a waste of money.
One line of arguments I found intriguing is that the lines should be buried instead of on towers, for a multitude of reasons. The company building it would extract profit and then long term maintenance would fall on the state. If the lines were buried, there'd be less maintenance caused by weather events, less transmission losses, and overall more efficient and resilient operation.
Obviously burying such lines has much higher up front costs and the companies looking to profit don't want to pay it.
toast0 3 hours ago [-]
> If the lines were buried, there'd be less maintenance caused by weather events, less transmission losses, and overall more efficient and resilient operation.
It's a tradeoff. When there is an issue with underground lines, it's much more expensive to locate and diagnose the fault and repair it; in both dollars and time.
In that area of the country, the ground freezes in winter, and digging becomes very difficult, which would make repairs that much more delayed and expensive.
Also, depending on requirements, it may be possible to augment capacity ny adding a second transmission line to the existing towers at a later time; that would be much less expensive than setting up the first line; but for undergrounding, such a project would most likely be as expensive as the first time, if not more. Similar with replacing the line at the end of its service life (although if the line and the towers have a similar service life, replacing them both brings costs back up similar to the initial project)
lurk2 4 hours ago [-]
> If the lines were buried, there'd be less maintenance caused by weather events, less transmission losses, and overall more efficient and resilient operation.
You may find this video by Practical Engineering to be interesting: “Repairing Underground Power Cables Is Nearly Impossible”
Noteworthy: That power line is only 10 miles long. Madison to Dubuque would be about 10X longer.
jonlandrum 5 hours ago [-]
Why were all the answers provided by new contributors? Don't see that very often.
kylehotchkiss 2 hours ago [-]
I think a lot of people here would agree that AI/LLMs got them off of stackexchange (not just stack overflow) and it's refreshing to not have to deal with the moderation's instant "did you google" / "duplicate question". These new contributors will learn and switch over to chat.com soon enough
panki27 5 hours ago [-]
Not necessarily "new to StackExchange", but at least to the physics site.
belter 5 hours ago [-]
Was posted less than 24 hours ago...
TacticalCoder 35 minutes ago [-]
[dead]
Asmod4n 6 hours ago [-]
Can this be mitigated by putting the cables under ground? Just curious, since it’s a huge debate here at times because of the massive cost of doing so.
Germany needs a connection from the coast into the south and most of it as of now will be build under ground.
Cthulhu_ 5 hours ago [-]
This article explains some issues with underground high tension cables [0]:
> Laying a 380-kV high-voltage line underground poses a number of risks. The electrical behaviour of underground cables differs from that of overhead high-voltage lines. This results in a loss of transmission capacity. To compensate for this loss, additional devices (e.g. coils) have to be installed at various points along the route.
> The combination of cables and coils creates resonance similar to a radio where multiple jammers continuously change frequency. Cables and coils can cause disruption locally, jeopardising the stability of the entire grid. In addition, it is easier for Elia to identify faults and carry out maintenance on overhead lines.
I had always heard that underground is workable for local areas but the really high voltage long-distance lines are hard to insulate undergound (on pylon towers they are not insulated at all).
masfuerte 5 hours ago [-]
High-voltage DC is frequently used for undersea transmission. This is necessarily insulated.
High voltage DC is effective above ground, too. At high enough voltage, it's actually cost effective and has fewer electrical losses than the AC equivalent. China has been doing some cool investments on high voltage DC in the past 15 years or so. We're talking 750 kV and above IIRC.
lazide 4 hours ago [-]
There are significant inductive losses with having AC under ground - dirt is conductive enough you end up with induced current (inductive losses) in it. Same with seawater.
It’s doable; but for longer distance runs when buried or under seawater, it’s usually more economic using DC which doesn’t have that issue.
schainks 2 hours ago [-]
It's vastly more expensive to put cables underground, and high voltage cables underground is in the realm of Bad Ideas because you're putting a high voltage physically near the electrical ground (the earth's crust), which adds cost, reduces reliability, and poses a serious danger to all living things near the line.
Sure, there may be exceptions that might make it worth while. However, if long distance high voltage underground wires was practical and cheap, you would see deployed much more often.
Vox_Leone 5 hours ago [-]
>>Can this be mitigated by putting the cables under ground?
Yes, it can (apparently), since these are mostly indirect effects of atmospheric vibrations (aka 'wind'). The vibration itself isn't usually the root cause of a blackout — but it sets off a chain reaction that leads to one (line contact/short circuit; conductor breakage; overcurrent & load shedding; protection system malfunction or overreaction, etc.)
lurk2 4 hours ago [-]
You may find this video by Practical Engineering to be interesting: “Repairing Underground Power Cables Is Nearly Impossible”
It's a fake term, used by the government to hide the real cause - deteriorating magnetic field, that will flip in 15-25 years, but we will start seeing a lot of issues similar to that event more often.
On an AC transmission line, I suppose any corona discharge going on shuts off and restarts every time the voltage reverses. They make a characteristic buzz in humid conditions.
High voltage DC is hard as it requires solid state components which are expensive to make, and prone to blowing up (aka relatively fragile). AC to DC and vice versa also adds non-trivial losses.
High voltage DC (to a first approximation) doesn’t suffer from inductive losses however, which makes it much more efficient when near conductive stuff like the ground or seawater.
It’s also ‘simpler’ (doesn’t have things like phase or frequency) which is convenient if doing things like transferring power between two power grids with dissimilar frequencies or phase.
They each have their place.
That is not possible with DC.
For non-physicists: https://electronics.stackexchange.com/questions/128986/why-u...
I'm short, it's this way for a reason. The complexity is nessessary.
Summarizing a couple of year of very annoying electrical studies: Yes
You can't believe how much
But your electrical supplier will charge you for it. Had a electrical power teacher with a past employment at a power supplier, who sadly loved to brag how he used to terrorize small farms when their own power generators had a cos φ below 0.98. I think the rule for Portugal is cos φ above 0.97 and for Spain 0.95 also known as el coseno de phi...
"Cos-phi compensation" - https://fortop.co.uk/knowledge/white-papers/cos-phi-compensa...
I'm wondering if this will be like the 2016 South Australian blackout
https://en.wikipedia.org/wiki/2016_South_Australian_blackout
"AEMO identified software settings in the wind farms that prevented repeated restarts once voltage or frequency events occurred too often. "
Grid operators are currently mostly against renewable and so they impose "blunt" disconnect rules on inverters behind renewable sources, and this comes to bite the grid when the proverbial shit hits the fan.
May be in the end this will be a good thing and grid operators will start to treat inverters and renewable as a strength and modify grid regulations as needed.
> Grid operators are currently mostly against renewable and so they impose "blunt" disconnect rules on inverters behind renewable sources, and this comes to bite the grid when the proverbial shit hits the fan.
As a distributed systems person, this seems like a coordination/communication problem. If a single node is having repeated events, it may likely be broken and staying offline could be a better choice. If multiple nodes are having repeated events, maybe it's better for them to stay connection and do their best.
Inverters if told so can do frequency support better and cheaper than any other solutions.
No other technology can react as fast as an inverter.
See the Texas grid grid service market which is now completely dominated by GW of inverters.
https://comptroller.texas.gov/economy/fiscal-notes/infrastru...
"One solution is to connect inverters with “grid-forming” capabilities, which help mitigate this risk by limiting fluctuations outside of 60 Hz, increasing grid stability. Experts see utility-scale batteries as a prime opportunity to deploy grid-forming inverters to the grid, as grid-forming integration with batteries is cheaper and faster than building new transmission."
"grid-forming" inverter is just software and parameters, your el-cheapo home solar inverter can do it too. It currently is prevented from doing so by ... grid operator regulations which ask it to disconnect at the first issue.
The wind or solar farm drives the flywheel and if the grid-side power starts to fluctuate, it pulls on the flywheel before the inverters feel it. You lose some total efficiency in the electrical-to-mechanical-to-electrical conversion, but get enough flywheels and maybe you don't care (because they also act as a place to store peak energy production when demand is low).
As someone who moves a lot, it's always curious to me that grid operators vary so widely on this.
Some places (like where I am now), the grid operator hates renewables and especially rooftop solar.
Other places, the grid operator will actually subsidize rooftop solar because it they say it reduces the amount of generation it has to do, thus saving money on infrastructure and maintenance.
Of course, each location has wildly different climates, but the regional politics aren't that different, so I don't think it's about ideology.
One line of arguments I found intriguing is that the lines should be buried instead of on towers, for a multitude of reasons. The company building it would extract profit and then long term maintenance would fall on the state. If the lines were buried, there'd be less maintenance caused by weather events, less transmission losses, and overall more efficient and resilient operation.
Obviously burying such lines has much higher up front costs and the companies looking to profit don't want to pay it.
It's a tradeoff. When there is an issue with underground lines, it's much more expensive to locate and diagnose the fault and repair it; in both dollars and time.
In that area of the country, the ground freezes in winter, and digging becomes very difficult, which would make repairs that much more delayed and expensive.
Also, depending on requirements, it may be possible to augment capacity ny adding a second transmission line to the existing towers at a later time; that would be much less expensive than setting up the first line; but for undergrounding, such a project would most likely be as expensive as the first time, if not more. Similar with replacing the line at the end of its service life (although if the line and the towers have a similar service life, replacing them both brings costs back up similar to the initial project)
You may find this video by Practical Engineering to be interesting: “Repairing Underground Power Cables Is Nearly Impossible”
https://www.youtube.com/watch?v=z-wQnWUhX5Y
Noteworthy: That power line is only 10 miles long. Madison to Dubuque would be about 10X longer.
Germany needs a connection from the coast into the south and most of it as of now will be build under ground.
> Laying a 380-kV high-voltage line underground poses a number of risks. The electrical behaviour of underground cables differs from that of overhead high-voltage lines. This results in a loss of transmission capacity. To compensate for this loss, additional devices (e.g. coils) have to be installed at various points along the route.
> The combination of cables and coils creates resonance similar to a radio where multiple jammers continuously change frequency. Cables and coils can cause disruption locally, jeopardising the stability of the entire grid. In addition, it is easier for Elia to identify faults and carry out maintenance on overhead lines.
[0] https://www.elia.be/en/infrastructure-and-projects/infrastru...
https://en.wikipedia.org/wiki/High-voltage_direct_current
It’s doable; but for longer distance runs when buried or under seawater, it’s usually more economic using DC which doesn’t have that issue.
Sure, there may be exceptions that might make it worth while. However, if long distance high voltage underground wires was practical and cheap, you would see deployed much more often.
Yes, it can (apparently), since these are mostly indirect effects of atmospheric vibrations (aka 'wind'). The vibration itself isn't usually the root cause of a blackout — but it sets off a chain reaction that leads to one (line contact/short circuit; conductor breakage; overcurrent & load shedding; protection system malfunction or overreaction, etc.)
https://www.youtube.com/watch?v=z-wQnWUhX5Y