"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."
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...
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.
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.
(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.
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.
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.
"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.
> "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.
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.
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).
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).
1. Mechanical to Electrical Energy Conversion
• Wind Energy Capture: The wind pushes against the blades of the wind turbine, causing them to rotate. These blades are attached to a central hub, which turns a low-speed shaft.
• Gearbox (in many turbines): This shaft is connected to a gearbox, which increases the rotation speed. The gearbox drives a high-speed shaft connected to the generator.
• Generator: The high-speed shaft turns the rotor inside a generator. As the rotor spins inside a magnetic field, it induces a flow of electricity—typically alternating current (AC)—using electromagnetic induction.
Some turbines use direct-drive generators (no gearbox), especially in offshore installations, which reduce maintenance.
2. Power Conditioning and Grid Integration
• Variable Speed Generation: Wind speed varies, so the output frequency and voltage can fluctuate. Wind turbines typically use power electronics (converters and inverters) to stabilize the electricity before it’s sent to the grid.
• Inverter Role: Converts variable-frequency AC or DC from the generator into grid-compatible AC (usually 50 Hz or 60 Hz depending on the region).
3. Phase Angle and Synchronization
What Is Phase Angle?
• The phase angle represents the timing difference between the voltage waveform of the turbine’s output and the grid’s voltage waveform.
• For a generator to supply power effectively, it must match the phase, frequency, and voltage of the grid.
• If the phase angle is off, power cannot flow efficiently and may even cause instability or damage.
Synchronization Process
• Before a wind turbine connects to the grid, its inverter adjusts the output so that:
• Frequency = Grid frequency (e.g., 60 Hz)
• Voltage = Grid voltage
• Phase angle = Aligned with grid phase
• Once synchronized, the turbine can export power.
4. Ancillary Services Provided by Wind Turbines
Ancillary services are support functions that maintain the stability and reliability of the power grid. Modern wind turbines, especially with advanced inverters and control systems, can provide several key services:
A. Frequency Regulation
• Wind turbines can rapidly adjust output to help balance supply and demand.
• This is called primary frequency response, essential when there’s a sudden change in load or generation.
B. Reactive Power Support / Voltage Control
• Inverters can produce or absorb reactive power, which helps maintain voltage levels on the grid.
• This is important for power factor correction and avoiding voltage collapse.
C. Inertia and Synthetic Inertia
• Traditional turbines (like in coal or gas plants) provide rotational inertia, helping to resist sudden changes in frequency.
• Wind turbines, being decoupled from the grid by power electronics, don’t naturally provide inertia.
• However, some advanced systems provide synthetic inertia by rapidly adjusting power output in response to frequency changes.
D. Black Start Capability
• Some wind turbines can assist in black start procedures (restarting the grid after a blackout), but this is still limited and evolving.
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.
"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.
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.
> 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)
It's also quite common for above-ground transmission lines to be upgraded: swap the fixed supports for carrying wheels, hook up the existing conductor to a bigger or more modern one, and pull it through! An older line can get a nice 30% upgrade at very little cost this way.
> 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.
Could underground lines be placed in tunnels large enough for repair crews to reach where they need to work by going through the tunnel?
Well, I'm sure they could for runs that aren't too long, so perhaps the question should be over what distance is it economically and technically feasible to run underground lines in tunnels human accessible maintenance tunnels?
> 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”
That "impossible" line was paired with a new line that doesn't require pumped insulating oil due to better insulating materials. Then the old line was de-energized and repaired, and is kept as a spare.
This news cycle was pretty hilarious (and just as sad) to hunt through.
From what I deciphered, the actual suggested cause was "aeolian vibrations" [0], which is one of the three forms of wind-induced conductor vibrations according to this [1] IEEE article. Also known as "flutter" according to Wikipedia [2]. (I'm not in EE so can't confirm nor debunk.)
Connected to this, another seemingly made-up term that made the news cycle was "Ging-induced vibrations" (in Portuguese media). Now, I don't speak Portuguese, but all my efforts hunting down this mysterious Ging tremendously failed. However, when I plopped ging into translation models, I couldn't help but notice that "ginga" in Portuguese means "swing", as in cable swing. So I'm giving it pretty reasonable chances that "ging" (no capitalization) might be what "flutter" is in English, i.e. the industry slang for "aeolian vibrations" there. And then the rest was just a typical journo move, much in the way of "the hacker known as 4chan".
In any case, it would have been cool if anyone actually linked to where said company made their statement, so that people could independently verify what was actually being said. From what I read, they have since explicitly debunked that they were inventing any new niche atmospheric effects. It's incredibly disheartening that such basic bits of information can become this seriously distorted before going viral, even (especially?) in this day and age. Makes you wonder how trustworthy are the regular news, even biases nonwithstanding, that aren't so readily obvious to be bollocks.
Ginga is a Brasilian Portuguese word. I spent all of the day of the blackout listening to the radio (as you might guess) and not once heard the terms "ging" or "ging-induced". Also, ginga would not be swing as in cable swing, it would be swing as in swing dance (rhythmic movement specifically to music). When possible explanations were put forward in the media, they were attributed, usually either to the portuguese representative of REN (the Chinese company supplying power structure to the country) or to an analogous representative of Spain (where the fault originated). It was always pretty clear that the fault was unknown, since this was stated plainly by the aforementioned representatives and the prime minister. I respect the language barrier, but it would be good to take it into account.
I'm part of a listserve for power systems engineers (more from academia than from industry) and the consensus seems to be that a couple of trips in short succession caused wild swings in powerflows, resulting in a cascading failure - this is a pretty boring, if consequential, N-2 event, very similar to the 2005 Northeast Blackout in the US.
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
That's not how Stack Exchange works, though. You don't have to register for a new account every time you leave an answer. The replies were all from new accounts, not established ones. I don't think it has anything to do with the amount of time since the question was asked.
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.
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).
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.
>>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.)
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.
> poses a serious danger to all living things near the line
That is always the case for the various failure modes of any high voltage line (and all the related equipment).
That said, you have it exactly backwards. Above ground lines are much easier to inadvertently come into contact with. Once faulted the breaker trips within a matter of milliseconds. It's the initial contact that's deadly.
I think they might have been referring to conductor gallop, power line sag, and subsequent fault. I read synchronisation failure as downed cable. With extreme temperature variations come extreme winds. Not sure if this was the case.
Readit News
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...
That is not possible with DC.
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.
I'm short, it's this way for a reason. The complexity is nessessary.
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.
Deleted Comment
Summarizing a couple of year of very annoying electrical studies: Yes
You can't believe how much
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.
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.
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).
1. Mechanical to Electrical Energy Conversion • Wind Energy Capture: The wind pushes against the blades of the wind turbine, causing them to rotate. These blades are attached to a central hub, which turns a low-speed shaft. • Gearbox (in many turbines): This shaft is connected to a gearbox, which increases the rotation speed. The gearbox drives a high-speed shaft connected to the generator. • Generator: The high-speed shaft turns the rotor inside a generator. As the rotor spins inside a magnetic field, it induces a flow of electricity—typically alternating current (AC)—using electromagnetic induction.
Some turbines use direct-drive generators (no gearbox), especially in offshore installations, which reduce maintenance.
2. Power Conditioning and Grid Integration • Variable Speed Generation: Wind speed varies, so the output frequency and voltage can fluctuate. Wind turbines typically use power electronics (converters and inverters) to stabilize the electricity before it’s sent to the grid. • Inverter Role: Converts variable-frequency AC or DC from the generator into grid-compatible AC (usually 50 Hz or 60 Hz depending on the region).
3. Phase Angle and Synchronization
What Is Phase Angle? • The phase angle represents the timing difference between the voltage waveform of the turbine’s output and the grid’s voltage waveform. • For a generator to supply power effectively, it must match the phase, frequency, and voltage of the grid. • If the phase angle is off, power cannot flow efficiently and may even cause instability or damage.
Synchronization Process • Before a wind turbine connects to the grid, its inverter adjusts the output so that: • Frequency = Grid frequency (e.g., 60 Hz) • Voltage = Grid voltage • Phase angle = Aligned with grid phase • Once synchronized, the turbine can export power.
4. Ancillary Services Provided by Wind Turbines
Ancillary services are support functions that maintain the stability and reliability of the power grid. Modern wind turbines, especially with advanced inverters and control systems, can provide several key services:
A. Frequency Regulation • Wind turbines can rapidly adjust output to help balance supply and demand. • This is called primary frequency response, essential when there’s a sudden change in load or generation.
B. Reactive Power Support / Voltage Control • Inverters can produce or absorb reactive power, which helps maintain voltage levels on the grid. • This is important for power factor correction and avoiding voltage collapse.
C. Inertia and Synthetic Inertia • Traditional turbines (like in coal or gas plants) provide rotational inertia, helping to resist sudden changes in frequency. • Wind turbines, being decoupled from the grid by power electronics, don’t naturally provide inertia. • However, some advanced systems provide synthetic inertia by rapidly adjusting power output in response to frequency changes.
D. Black Start Capability • Some wind turbines can assist in black start procedures (restarting the grid after a blackout), but this is still limited and evolving.
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.
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)
Could underground lines be placed in tunnels large enough for repair crews to reach where they need to work by going through the tunnel?
Well, I'm sure they could for runs that aren't too long, so perhaps the question should be over what distance is it economically and technically feasible to run underground lines in tunnels human accessible maintenance tunnels?
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.
From what I deciphered, the actual suggested cause was "aeolian vibrations" [0], which is one of the three forms of wind-induced conductor vibrations according to this [1] IEEE article. Also known as "flutter" according to Wikipedia [2]. (I'm not in EE so can't confirm nor debunk.)
Connected to this, another seemingly made-up term that made the news cycle was "Ging-induced vibrations" (in Portuguese media). Now, I don't speak Portuguese, but all my efforts hunting down this mysterious Ging tremendously failed. However, when I plopped ging into translation models, I couldn't help but notice that "ginga" in Portuguese means "swing", as in cable swing. So I'm giving it pretty reasonable chances that "ging" (no capitalization) might be what "flutter" is in English, i.e. the industry slang for "aeolian vibrations" there. And then the rest was just a typical journo move, much in the way of "the hacker known as 4chan".
In any case, it would have been cool if anyone actually linked to where said company made their statement, so that people could independently verify what was actually being said. From what I read, they have since explicitly debunked that they were inventing any new niche atmospheric effects. It's incredibly disheartening that such basic bits of information can become this seriously distorted before going viral, even (especially?) in this day and age. Makes you wonder how trustworthy are the regular news, even biases nonwithstanding, that aren't so readily obvious to be bollocks.
[0] https://www.youtube.com/watch?v=j-VzxRfPHjU
[1] https://ieeexplore.ieee.org/document/4773888
[2] https://en.wikipedia.org/wiki/Stockbridge_damper#Wind-induce...
Dead Comment
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.
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
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.
That is always the case for the various failure modes of any high voltage line (and all the related equipment).
That said, you have it exactly backwards. Above ground lines are much easier to inadvertently come into contact with. Once faulted the breaker trips within a matter of milliseconds. It's the initial contact that's deadly.