It's an interesting take to be sure. I suspect that the lack of flexibility is going to be the real killer.
You'd probably have to build offshore platforms on either side to bring the cables up and terminate them and now that's a nightmare, saltwater/salty air and electronics don't mix well.
Or you're going to have to trench very deeply for the first few miles.
Either way you're stuck with something that really doesn't want to be bent.
I think the "glass is great insulation" is a good insight and perhaps a composite glass fiber/polymer sheath would really increase the V/m without the brittleness.
a material that stretches 1% to failure (like steel/aluminum) can ballpark bend to a radius 100 times the thickness. so a 1 meter cable could bend 100m radius before cracking. assuming 10x margin that would be 1 km radius. large but not crazy. A tube that size can easily span 1 km trenches in water. you could also add a few meters of foam around it to make it neutrally buoyant and just barely press on the ocean floor.
I swoop in on something like this looking for the first obvious error in units/arithmetic/materials that renders the whole thing ludicrous, but the author has a spreadsheet and it looks like the units are about right. It's an absurdly cheap cable in terms of materials to transmit 10 GW across an ocean. The main things that render it dubious as a practical matter:
- I don't know if operating at 14 million volts is achievable in terms of converter stations. Today's highest voltage HVDC projects operate at 1.1 megavolts and it took years of development to get there from 0.6 megavolts.
- The mechanical practicality of thousands of kilometers of silica clad aluminum. There's a big mismatch in coefficients of thermal expansion and silica is brittle.
Still, this appears to be facially valid in scientific terms if not in engineering terms. That's impressive! It's a really thin intercontinental cable carrying a lot of power.
The whole thing reminded me of this discussion here from 3 years ago:
It has rough numbers for a globe-spanning HVDC cable on the order of a meter in diameter (assumes voltages more like present day commercial HVDC, much thicker conductor to compensate).
14MV would be capable of sustaining an arc 1400 feet long in normal atmosphere. I struggle to imagine how you'd build such a thing. You could maybe have a high volume sf6 pump system that would cool and quench the arc on breaker trip with a constantly replenished sf6 supply.
Isn't sf6 on the way out due to it being an extremely potent GHG?
Not sure what the alternative would be for really high voltages? Vacuum insulated switchgear seems to be a hot topic at the moment, but not sure how it'd work with such extreme voltages?
Even 1.1GV systems use semiconductor breakers. Basically, stacks and stacks of transistors. The actual physical breakers are only operated when the voltage is safely off.
I considered that. Considering the cheap cost of the cable, the best solution appears to simply be 'dont have a breaker'. In either over current or over voltage conditions, simply sacrifice the cable.
Obviously you engineer the convertor stations to minimize the chances of that happening - stopping the convertors automatically if anything looks abnormal. The cable has sufficient capacitance that you have multiple milliseconds to respond, so automated systems should have no difficulty.
> There's a big mismatch in coefficients of thermal expansion and silica is brittle.
The way these are manufactured together means the silica with the lower CTE solidifies first - giving a tube filled with molten aluminium. Next the aluminium solidifies. Then the whole thing cools down and the aluminium probably delaminated from the walls of the tube, leaving a gap of a few hundred micrometers. The aluminium also ends up stretching slightly (one time).
During use, the inner core will heat up and cool down, fairly substantially (perhaps by 100C), using that gap that formed as the cable was manufactured.
> The cable, if snagged by a ship anchor, would catastrophically fail. Not only would it snap, but the internal stresses would propagate the crack along the entire length.
I can’t this writeup seriously with comments like this. There is no mention of any attempt to calculate the allowable bend radius. Also, quenching a glass tube in a continuous process? Does that work?
The bend radius doesn't actually matter - one can fairly trivially adjust the factory ship to make bends at specific places if desired. Including, if necessary, to fit the contour of the seafloor.
The critical thing is the length of the longest unsupported span - and that's 64 meters, but surface hardening could possibly dramatically extend this, but it seems beyond available literature.
That seems wrong. If you have a cable with a literally infinite bend radius and lay it on a perfectly smooth sea floor, it will be supported in the middle and nowhere else, because the Earth is round. If you lay it on a real sea floor, the length of the longest unsupported span will depend on the shape that the installed cable takes, and whether the cable breaks in that shape will depend on the bend radius it tolerates.
Couldn't find the "downvote"-button, so I clicked "reply" instead.
Nearly every argument you made is covered and explained in the article. Your points would get more traction if you would refer to the existing arguments made.
Not quite true. Glass optical fibre is reasonably flexible. More so than many coaxial cables. Just don't go below its minimum bend radius, as it is brittle and will snap.
Glass insulated power cables might work, provided the glass layer is thin enough and its band radius isn't exceeded. One can imagine a cable insulated with many thin layers/strips of glass, which have some movement relative to each other. Multiple layers of insulation is normal practise with plastic insulation, as the failure mode is typically pinholes in the insulation and multiple layers reduced the probability of pin holes going all the way through.
Biggest problem might be a conductor with decent diameter will put a lot of stress on the interior and exterior of a bend. Some ides:
* A multi-standed conductor with each individual conductor insulated. Maybe have high voltage in the interior stands and have a radial voltage gradient (to zero) across the outer strands so no one thin layer of glass is taking the full electric field?
* Could a conductor be insulated with a woven/stranded insulating layer? One can imagine many layers of extremely fine glass fibre finished off with an enclosing layer of something else to keep everything in place. Sort of like a glass insulated coaxial cable.
Fiber optic strands are glass rods (solid interior) instead of tubes (hollow cylinder). The two shapes have different strength properties per unit mass [1, 2].
Current implementations break from simple vibrations such as a bus driving down the road and shaking the ducts the fibre is in. Lots of work required still. Crazy expensive and crazy fragile.
An insulator made of multiple materials will have the breakdown voltage of the weakest material. So, glass fibers in some sort of resin will break down at the resin's voltage, not the glass's.
Continuous melted silica coating is fine, but how does one account for all the movement, bends and vagaries of the high seas, especially for something that is so brittle?
1. The technical solution relies heavily on fantasy.
2. It is not needed. We have no significant power transmission across the low lying fruit of continental America or Eurasia, and those lines are built! Why bother crossing an ocean?
3. Why not cross Greenland and the North Sea and its islands? Under sea cables are expensive.
In Peace and Harmony Land™ I could see the value of shipping excess power from sunny/windy locations to those that are without, but I don't think the present world is ready to collaborate at that level.
There was a big solar project proposed in Australia's outback to supply Singapore but never got off the ground perhaps advances in glass / dc infrastructure could change the calculations. Same story for Sahara solar supply to Eu.
I wonder if the glass sheath could be replaced with bundled glass fibers in a dielectric gel? Would that cross section allow for a much greater distance for current to trace through the gel? Seems like maybe it would give a 2x advantage, or maybe glass ribbons could be made instead for a micro braided insulation?
I watched a video recently that talked about how China is really the only country to have developed and built UHVDC power transmission. Some look at this and say how it's a failure of everyone else. My immediate thought was: "this solves aproblem only China has" and that turned out to be correct.
China produces most of its power in the west of the country between solar farms, the Three Gorges Dam and so on. Most of the population is 2000 miles away in the east of the country. For over a billion people, the cost of more efficient long-distance transmission make economic sense.
Someone asked "could Australia do this to transmit solar power from the West coast to the east coast in peak hours?". Technically? Yes. Practically? No. Why? It's obviously expensive with far fewer people but also all that space in between is uninhabited. So if you ever need to maintain it (which you will) you have to send people out into the wilderness to do it. China doesn't have that problem because it's not really unpopulated anywhere, at least not to the scale Australia is.
My point here is that you should always ask for something like this "what problem does it solve?" And the answer for more efficient long-distance power transmission is "almost nobody".
I think power grids are going to go in the other direction and become increasingly localized rather than nationalized.
Yes. The US wind belt is from the Texas panhandle north to Canada.[1] But there's no good connectivity to anywhere with a load. Some east-west EHV lines from that area would be a big win. There's opposition from oil interests. Just trying to connect East Texas to Mississippi has been stalled for over a decade.[2]
Don't need anything as exotic as the 14MV the original poster proposes. 1MV at 1000 amps, which is a gigawatt, has been done many times in China. One right of way can have several such lines. It would be best to have at least two distant rights of way, for redundancy. California's total load is around 13GW, so the number of 1GW lines needed is not large.
Undergrounding high powered lines is a huge headache, but possible. Here's an overview.[3]
HVDC cables are kind of an often overlooked solution to net zero. Moving power over long distances, across timezones is kind of a super power. The main obstacle to scaling this from a few GW to tens/hundreds of GW is cost. Just by laying more cables can you increase capacity between regions and their ability to share excess power to each other. But each cable is a multi billion dollar project. Which means that there is only a little bit of capacity to move power around but not a lot. For example Europe can import a few GW of African solar in the middle of the winter. But it could probably need hundreds when it is dark and not windy there.
Likewise cross Atlantic cables have been talked about but so far don't exist. Same with getting power from the East coast US to the West coast and vice versa. The east coast goes dark while the west coast is still producing lots of solar. And in the morning on the west coast, it's afternoon on the east coast. There is a bit of import/export between California (solar) and Canada (wind / hydro). But it could be much more.
Cables have another important function: they can be used to charge batteries. Batteries allow you to timeshift demand: e.g. charge when the sun is out, discharge when people get home in the evening. And off peak, the cables aren't at full capacity anyway meaning that any excess power can easily be moved around to charge batteries locally or remotely. Renewables, cables and batteries largely remove the need for things like nuclear plants.
Yes it gets dark and cloudy sometimes but those are local effects and they are somewhat predictable. And if the wind is not blowing that just means it is blowing elsewhere. Wind flows from high pressure to low pressure areas. Globally, there always are high and low pressure areas. If anything, global warming is causing there to be more wind, not less. So, global wind energy production will always maintain a high average even if it drops to next to nothing locally. Likewise, global solar production moves around with the sun rise and sun set and seasons but never drops to zero everywhere. If it's night where you are, it isn't on the other side of the planet. If it's winter where you are, it isn't at -1 * your latitude.
If long distance cables get cheap and plentiful, that's a really big deal because this allows for moving around hundreds of gwh of power. HVDC allows doing that over thousands of kilometers across oceans, timezones, and continents. Cheaper HVDC lowers the cost of that power.
It does have to be thin. You need to fit as much as possible on a boat and volume increases quadratically with thickness- so if glass is 500 MV/m and XLPE is 150 MV/m you would need to carry 11x more of it. Refilling means hundreds of miles back to shore.
The importance of repairability is underestimated here. All new infrastructure must be built under assumption that there will be multiple attempts at sabotaging it by actors of various level, and multi-megavolt unrepairable cables that can be fully disabled by one smallish unmanned sub don’t win here at all.
The original version of this post did have a repair plan.
Basically, every few kilometres you turn off the surface hardening of the cable for a yard or two. That spot won't propagate cracks - which means that if someone destroys part of the cable, the rest will be fine.
Those spots of cable have no tensile strength, so you wrap just those spots in a post tensioned steel sheath.
Then, you also make a few spare kilometers of cable that you lay in the ocean floor. When an incident happens, tow a new cable into position and connect it up. Underwater glass forming is a silly idea - but you can simply crack away the glass at the ends, reconnect the aluminium, then encase the whole thing in a couple of yards of epoxy.
The above plan I considered probably was of similar cost to simply laying a new cable across the entire ocean ahead of time in preparation though.
It’s interesting. I think the real way to do this is gradually scale up. Crossing the ocean is hard mode. Instead start by something much shorter and land based. Then you at least have a stable platform to work on and can focus on the other hard problems
In 1st world countries, land based cables often cost more because you have thousands of people along the route who all don't want a power line through their small village.
Everything looks nice but something very important was not considered in all of this.
High voltage and high current means Z-pinch - the conductor itself is going to compress itself, thus resulting in basically delaminating from the glass sheathing. This is why we have rubber/petroleum-based flexible sticky insulators on cabling like that, it can somewhat flex/shrink with the conductor and is more likely to stay attached and less likely to get damaged.
Just transmit laser power down fiber optics at that point. Either way you're going to need semiconductor switching (it's IGBTs all the way down baby!) nothing electromechanical is going to handle that kind of load.
> Just transmit laser power down fiber optics at that point.
How does that work? You can only get the glass so clear, so you're going to lose all the energy. There's no equivalent to cranking the voltage to increase range.
This page doesn't say how much light was lost over the 5 miles. So I'll put it this way: If you lose just 1% every 5 miles, then by the time you go 2000 miles across an ocean you've lost 98% of your power.
High voltage does not induce pinch, only current. High voltage is used to create bursts of high current in can-crushing demonstrations. The cable is solid and the current is not concentrated in a thin cylindrical shell. The pinch is negligible, certainly in comparison to eg thermal expansion from changing load conditions.
This is the kind of transmission line design I've seen proposed for use on the Moon - where hydrocarbons are basically nonexistent, but aluminium and silicon are abundant.
Glass insulated cable sounds like a tech that should be prototyped on smaller scales - and could be somewhat useful on those smaller scales.
When you're on the moon, why bother with glass? You're surrounded by vacuum and dry rock.
I mean, sure, you can't go over 1022 kV or you get positron-electron pair production from free electrons, but that's still true on your outer surface even with insulation.
Would coaxial HVDC let you go further, because there's no external voltage gradient? I assume so, but mega-scale high-voltage engineering in space combines three hard engineering challenges, so I wouldn't want to speak with confidence.
That said, vacuum is also a fantastic thermal insulator, so perhaps you could do superconducting cables more easily.
I've heard of ballistic conductors*, I wonder if that would scale up… basically the same as the current flowing around a magnetosphere at that scale? https://en.wikipedia.org/wiki/Ring_current
On the other hand, you'd have to make the magnetosphere on the moon first, and "let's use the sky as a wire" sounds like the kind of nonsense you get in the "[Nicola] Tesla: The Lost Inventions" booklet that my mum liked, and therefore I want to discount it preemptively even if I can't say why exactly.
"Just burying your wires in lunar regolith" is another proposed option for long range transmission lines, yes!
We don't know how well that would work in practice though, because there's still a few unknowns about how properties of lunar regolith change across distance.
Some wire applications do require isolation though. For example, motor wiring and other coils.
It would be extremely challenging to make usable coils out of glass coated magnet wire - but it's not like there's oil on the Moon waiting to be made into polymer coatings.
PCB-based transformers exist, and so do ceramic substrate PCBs. If you combine the two, and find a process to weld the ceramic/glass substrate plates together instead of gluing them together, it could work as a transformer.
The glass in a lamp is not for electrical isolation, it's intended to prevent the cable from literally burning up by keeping oxygen out and protective gas in.
Yes, but it's just an inch - and we need a continuous extruded wire at least a dozen meters long. Even on the scale of an inch, thermal expansion coefficient mismatch problems exist - this was a notorious issue with manufacturability of early vacuum tubes.
Turns out it's rather tricky to make glass bond to metal well enough.
A stack of optically powered 15kV mosfets, to get to 14MV, sounds absurdly awesome. 933+ mosfets that you're trying to drive in series, egads. But neat weird idea.
> A 15 kV SiC MOSFET gate drive with power over fiber based isolated power supply and comprehensive protection functions
I distantly remember reading about someone stress testing a submarine drone tether at higher than rated voltages, seeing what practical voltage they could get out of it. I distantly recall there being a lot of concern about like corona arching or something with the sea water? That was a fun paper. I don't ever if it was only because they exceeded the insulation value, but I feel like there were some notable challenges to running high voltages in salt water that I'm not quite remembering.
The Moore-like fall of solar+battery costs took away solar satellites, solar convection plants, submarine power cables and (widely deployed though) sun tracking hardware. Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
> Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
Even more than that: I was recently at GITEX Europe, and one of the startups* was pitching "they're so cheap, we should lay them flat for cheaper installation and maintenance".
* Their name was something like "slant solar" or "tilt solar", as they had initially thought of doing exactly what you say, but I can't exactly recall the name.
The quenching is done on the boat with presumably purified water. That's a pretty small amount of heat to manage, so its not like you will run out of water.
The blog is suggesting 10 GW, which is well short of "the entire thing", and they also suggest a lot of redundancy.
If you were to use a single cable for everything, that would be silly because no redundancy, e.g. "A volcano? On the mid-Atlantic ridge? Who could have foreseen this?"
But at the same time, a cable big enough to carry the world's power is pretty big. I've done similar ballpark calculations, and to get the electrical resistance all the way around the planet and back down to 1Ω, you'd need almost exactly one square meter cross section of aluminium (so any anchor cable breaks first), and that would have so much current flowing through it that spinning metal cutting tools can't operate nearby thanks to eddy currents from the magnetic field.
141 comments
[ 4.0 ms ] story [ 155 ms ] threadYou'd probably have to build offshore platforms on either side to bring the cables up and terminate them and now that's a nightmare, saltwater/salty air and electronics don't mix well.
Or you're going to have to trench very deeply for the first few miles.
Either way you're stuck with something that really doesn't want to be bent.
I think the "glass is great insulation" is a good insight and perhaps a composite glass fiber/polymer sheath would really increase the V/m without the brittleness.
I think that's being generous.
In the deep ocean (typically 4km deep), foam collapses and doesn't float...
- I don't know if operating at 14 million volts is achievable in terms of converter stations. Today's highest voltage HVDC projects operate at 1.1 megavolts and it took years of development to get there from 0.6 megavolts.
- The mechanical practicality of thousands of kilometers of silica clad aluminum. There's a big mismatch in coefficients of thermal expansion and silica is brittle.
Still, this appears to be facially valid in scientific terms if not in engineering terms. That's impressive! It's a really thin intercontinental cable carrying a lot of power.
The whole thing reminded me of this discussion here from 3 years ago:
https://news.ycombinator.com/item?id=31971039
It has rough numbers for a globe-spanning HVDC cable on the order of a meter in diameter (assumes voltages more like present day commercial HVDC, much thicker conductor to compensate).
Not sure what the alternative would be for really high voltages? Vacuum insulated switchgear seems to be a hot topic at the moment, but not sure how it'd work with such extreme voltages?
Obviously you engineer the convertor stations to minimize the chances of that happening - stopping the convertors automatically if anything looks abnormal. The cable has sufficient capacitance that you have multiple milliseconds to respond, so automated systems should have no difficulty.
How is that different from a fuse?
If it's cost effective then go for it. But the specific thing they're skeptical about is whether a 14MV 750A fuse will be cheap enough.
Glass chemistry is still a dark arcane art on the fringes with discoveries made all the time.
I'm not suggesting either of these are better suited or even equivalent insulaters but they are more flexible than what many think of as glass:
https://cen.acs.org/materials/inorganic-chemistry/glass-isnt...
https://www.corning.com/au/en/innovation/the-glass-age/desig...
The way these are manufactured together means the silica with the lower CTE solidifies first - giving a tube filled with molten aluminium. Next the aluminium solidifies. Then the whole thing cools down and the aluminium probably delaminated from the walls of the tube, leaving a gap of a few hundred micrometers. The aluminium also ends up stretching slightly (one time).
During use, the inner core will heat up and cool down, fairly substantially (perhaps by 100C), using that gap that formed as the cable was manufactured.
I can’t this writeup seriously with comments like this. There is no mention of any attempt to calculate the allowable bend radius. Also, quenching a glass tube in a continuous process? Does that work?
The critical thing is the length of the longest unsupported span - and that's 64 meters, but surface hardening could possibly dramatically extend this, but it seems beyond available literature.
Nearly every argument you made is covered and explained in the article. Your points would get more traction if you would refer to the existing arguments made.
500 MV/m is 0.5 MV/mm, so it's 300x worse insulator than XLPE plastic per article.
Would be a bummer if we build the worldwide insulated network, only to find out it's not insulated enough ツ)_/¯
edit: datameta is right. Both units should be MV/m.
Not quite true. Glass optical fibre is reasonably flexible. More so than many coaxial cables. Just don't go below its minimum bend radius, as it is brittle and will snap.
Glass insulated power cables might work, provided the glass layer is thin enough and its band radius isn't exceeded. One can imagine a cable insulated with many thin layers/strips of glass, which have some movement relative to each other. Multiple layers of insulation is normal practise with plastic insulation, as the failure mode is typically pinholes in the insulation and multiple layers reduced the probability of pin holes going all the way through.
Biggest problem might be a conductor with decent diameter will put a lot of stress on the interior and exterior of a bend. Some ides:
* A multi-standed conductor with each individual conductor insulated. Maybe have high voltage in the interior stands and have a radial voltage gradient (to zero) across the outer strands so no one thin layer of glass is taking the full electric field?
* Could a conductor be insulated with a woven/stranded insulating layer? One can imagine many layers of extremely fine glass fibre finished off with an enclosing layer of something else to keep everything in place. Sort of like a glass insulated coaxial cable.
[1] https://physics.stackexchange.com/questions/12913/hollow-tub...
[2] https://www.mtbiker.sk/forum/download/file.php?id=207637
Hollow air core fibre does exist and seems to be touted as the next big thing though.
https://www.optcore.net/hollow-core-fiber-introduction/#h-wh...
(From vague memory, stiffness is proportional to the cube of the thickness.)
Or at least, could be. No reference to how long the cable would last (only the ship), which is kinda important.
as I understand it, nobody is doing cable laying this way - and this dream of 14MV cable is kinda hinges on that
1. The technical solution relies heavily on fantasy.
2. It is not needed. We have no significant power transmission across the low lying fruit of continental America or Eurasia, and those lines are built! Why bother crossing an ocean?
3. Why not cross Greenland and the North Sea and its islands? Under sea cables are expensive.
4. Why not cross the Bearing Strait?
(yet, I guess)
The US abandoned trade as a means to peace
They see the difference in how we treat Iraq/Libya and North Korea.
There was a big solar project proposed in Australia's outback to supply Singapore but never got off the ground perhaps advances in glass / dc infrastructure could change the calculations. Same story for Sahara solar supply to Eu.
A lack of need is not the problem here.
Solar Sahara powering Europe makes sense.
Solar Sahara powering the North East does not.
China produces most of its power in the west of the country between solar farms, the Three Gorges Dam and so on. Most of the population is 2000 miles away in the east of the country. For over a billion people, the cost of more efficient long-distance transmission make economic sense.
Someone asked "could Australia do this to transmit solar power from the West coast to the east coast in peak hours?". Technically? Yes. Practically? No. Why? It's obviously expensive with far fewer people but also all that space in between is uninhabited. So if you ever need to maintain it (which you will) you have to send people out into the wilderness to do it. China doesn't have that problem because it's not really unpopulated anywhere, at least not to the scale Australia is.
My point here is that you should always ask for something like this "what problem does it solve?" And the answer for more efficient long-distance power transmission is "almost nobody".
I think power grids are going to go in the other direction and become increasingly localized rather than nationalized.
Don't need anything as exotic as the 14MV the original poster proposes. 1MV at 1000 amps, which is a gigawatt, has been done many times in China. One right of way can have several such lines. It would be best to have at least two distant rights of way, for redundancy. California's total load is around 13GW, so the number of 1GW lines needed is not large.
Undergrounding high powered lines is a huge headache, but possible. Here's an overview.[3]
[1] https://unitedstatesmaps.org/us-wind-map/
[2] https://www.texaspolicy.com/proposed-transmission-line-in-ea...
[3] https://electrical-engineering-portal.com/res3/Undergroundin...
try a web search for Prince Rupert drop vs bullet
https://duckduckgo.com/?q=prince+rupert+drops+vs+bullet&t=lm...
The article author did not say how a cable could be wrapped in pre-stressed glass but that plain glass can be pre-stressed is encouraging.
Likewise cross Atlantic cables have been talked about but so far don't exist. Same with getting power from the East coast US to the West coast and vice versa. The east coast goes dark while the west coast is still producing lots of solar. And in the morning on the west coast, it's afternoon on the east coast. There is a bit of import/export between California (solar) and Canada (wind / hydro). But it could be much more.
Cables have another important function: they can be used to charge batteries. Batteries allow you to timeshift demand: e.g. charge when the sun is out, discharge when people get home in the evening. And off peak, the cables aren't at full capacity anyway meaning that any excess power can easily be moved around to charge batteries locally or remotely. Renewables, cables and batteries largely remove the need for things like nuclear plants.
Yes it gets dark and cloudy sometimes but those are local effects and they are somewhat predictable. And if the wind is not blowing that just means it is blowing elsewhere. Wind flows from high pressure to low pressure areas. Globally, there always are high and low pressure areas. If anything, global warming is causing there to be more wind, not less. So, global wind energy production will always maintain a high average even if it drops to next to nothing locally. Likewise, global solar production moves around with the sun rise and sun set and seasons but never drops to zero everywhere. If it's night where you are, it isn't on the other side of the planet. If it's winter where you are, it isn't at -1 * your latitude.
If long distance cables get cheap and plentiful, that's a really big deal because this allows for moving around hundreds of gwh of power. HVDC allows doing that over thousands of kilometers across oceans, timezones, and continents. Cheaper HVDC lowers the cost of that power.
Basically, every few kilometres you turn off the surface hardening of the cable for a yard or two. That spot won't propagate cracks - which means that if someone destroys part of the cable, the rest will be fine.
Those spots of cable have no tensile strength, so you wrap just those spots in a post tensioned steel sheath.
Then, you also make a few spare kilometers of cable that you lay in the ocean floor. When an incident happens, tow a new cable into position and connect it up. Underwater glass forming is a silly idea - but you can simply crack away the glass at the ends, reconnect the aluminium, then encase the whole thing in a couple of yards of epoxy.
The above plan I considered probably was of similar cost to simply laying a new cable across the entire ocean ahead of time in preparation though.
High voltage and high current means Z-pinch - the conductor itself is going to compress itself, thus resulting in basically delaminating from the glass sheathing. This is why we have rubber/petroleum-based flexible sticky insulators on cabling like that, it can somewhat flex/shrink with the conductor and is more likely to stay attached and less likely to get damaged.
Just transmit laser power down fiber optics at that point. Either way you're going to need semiconductor switching (it's IGBTs all the way down baby!) nothing electromechanical is going to handle that kind of load.
How does that work? You can only get the glass so clear, so you're going to lose all the energy. There's no equivalent to cranking the voltage to increase range.
It works like that, and I was sending 10w down fiber optics back when I worked in solar panel manufacturing.
This page doesn't say how much light was lost over the 5 miles. So I'll put it this way: If you lose just 1% every 5 miles, then by the time you go 2000 miles across an ocean you've lost 98% of your power.
Glass insulated cable sounds like a tech that should be prototyped on smaller scales - and could be somewhat useful on those smaller scales.
I mean, sure, you can't go over 1022 kV or you get positron-electron pair production from free electrons, but that's still true on your outer surface even with insulation.
Would coaxial HVDC let you go further, because there's no external voltage gradient? I assume so, but mega-scale high-voltage engineering in space combines three hard engineering challenges, so I wouldn't want to speak with confidence.
That said, vacuum is also a fantastic thermal insulator, so perhaps you could do superconducting cables more easily.
I've heard of ballistic conductors*, I wonder if that would scale up… basically the same as the current flowing around a magnetosphere at that scale? https://en.wikipedia.org/wiki/Ring_current
On the other hand, you'd have to make the magnetosphere on the moon first, and "let's use the sky as a wire" sounds like the kind of nonsense you get in the "[Nicola] Tesla: The Lost Inventions" booklet that my mum liked, and therefore I want to discount it preemptively even if I can't say why exactly.
* Not superconducting in the quantum sense, but still no resistance because there's nothing to hit: https://en.wikipedia.org/wiki/Ballistic_conduction
We don't know how well that would work in practice though, because there's still a few unknowns about how properties of lunar regolith change across distance.
Some wire applications do require isolation though. For example, motor wiring and other coils.
It would be extremely challenging to make usable coils out of glass coated magnet wire - but it's not like there's oil on the Moon waiting to be made into polymer coatings.
You make a good point about the other uses of insulation, and ISRU, on the moon.
Would ceramics work for transformers?
PCB-based transformers exist, and so do ceramic substrate PCBs. If you combine the two, and find a process to weld the ceramic/glass substrate plates together instead of gluing them together, it could work as a transformer.
Take a close look at an incandescent light bulb... There is an inch of glass insulated cable there...
Turns out it's rather tricky to make glass bond to metal well enough.
> A 15 kV SiC MOSFET gate drive with power over fiber based isolated power supply and comprehensive protection functions
https://ieeexplore.ieee.org/document/7468138
I distantly remember reading about someone stress testing a submarine drone tether at higher than rated voltages, seeing what practical voltage they could get out of it. I distantly recall there being a lot of concern about like corona arching or something with the sea water? That was a fun paper. I don't ever if it was only because they exceeded the insulation value, but I feel like there were some notable challenges to running high voltages in salt water that I'm not quite remembering.
Even more than that: I was recently at GITEX Europe, and one of the startups* was pitching "they're so cheap, we should lay them flat for cheaper installation and maintenance".
* Their name was something like "slant solar" or "tilt solar", as they had initially thought of doing exactly what you say, but I can't exactly recall the name.
https://news.ycombinator.com/item?id=42513761 ("Undersea power cable linking Finland and Estonia suffers damage", 112 comments)
It's been half a year and it still[0] hasn't been fixed yet.
How does anyone, really, imagine building planetary infrastructure where a trivial amount of asymmetric warfare can take the whole thing down?
[0] https://yle.fi/a/74-20164957 ("Fingrid said that the EstLink 2 connection should be back online on June 25, earlier than expected")
If you were to use a single cable for everything, that would be silly because no redundancy, e.g. "A volcano? On the mid-Atlantic ridge? Who could have foreseen this?"
But at the same time, a cable big enough to carry the world's power is pretty big. I've done similar ballpark calculations, and to get the electrical resistance all the way around the planet and back down to 1Ω, you'd need almost exactly one square meter cross section of aluminium (so any anchor cable breaks first), and that would have so much current flowing through it that spinning metal cutting tools can't operate nearby thanks to eddy currents from the magnetic field.