Worldwide power grid with glass insulated HVDC cables
135 comments
·June 12, 2025Workaccount2
hyperionplays
Jumping on this bandwagon - these days I'm working in the submarine telco cable industry.
Considering a cable from singapore <> LA direct can run up $1.4bn USD. I think author needs a lot more research.
1. route planning takes a long time, the ocean floor moves (see: Fault Lines, Underwater Volcanos, pesky fisherman) 2. The ships do move _ a lot_ even with fancy station keeping and stabilisation. 3. cables get broken - a lot. Even now there's 10-15 faults globally on submarine cables. There are companies (See: Optic Marine) who operate fleets of vessels to lay and maintain cables. I'm sure the HVDC industry has the same.
Cool idea, I have been pondering it a lot myself, I figured maybe a ground return HVDC cable might be better for inter-country power grid links.
I know Sun Cable out of Australia want to build a subsea powercable to sell energy into ASEAN.
londons_explore
> HVDC lines can have up to 10% ripple
That's exactly why one uses a high switching frequency, MOSFETs and has a tiny ripple (perhaps 0.1%). This can be obtained cheaply with multiphase convertors.
Mosfets are now cheaper than IGBT's where you are paying for power losses and plan to run at full load for more than a few days to months. That's why nearly all EV's use MOSFETs - (and will use GAN MOSFETs at MHz switching rates when the patents run out)
Remember that the cable acts like a capacitor/inductor pair to ground. Ripple currents that are lost through it are not wasted money - merely wasted capacity and resistive losses in the cable. At these currents, you can assume earth is a perfect conductor, so no losses there either.
Workaccount2
400V electric vehicles and 400,000V transmission lines play by different rules.
There are no MOSFETS anywhere in HV applications. IGBTs, but no MOSFETS. Most converters use thyristors and newer ones use IGBTs. No matter what, PN-junctions are king for HV silicon applications.
Also ripple is a function of filtering not switching. The reason higher switching frequencies generally have better ripple characteristics is because smaller capacitors can filter them and/or larger capacitors filter them better. So in a cost constrained/size constrained product you get more filtering for the same buck same size.
I also can't figure out what you are saying in your last line, apologies.
namibj
Well, SiC MOSFET do get used, but yeah. SiC JFETs are indeed better, lower lower with the same wafer technology, avalanche proof, high heat proof (the polyimide passivation hurts beyond ~220 C).
Much easier to drive when you stack them for HV.
That said, GaN is there for capacitive converters due to being able to run very efficient at >10 MHz switching frequency.
These converters in principle fit in very compact phase change coolant/insulator vessels, for example with propane. The capacitors at those frequencies get to be tiny, like, smaller than the transistor package by volume.
londons_explore
> 400V electric vehicles and 400,000V transmission lines play by different rules.
When stacked, they don't. Plenty of research on stacking both MOSFETs and entire power converters.
With stacking, the figure of merit (ie. Kilowatts per dollar, loss percentage) isn't a function of voltage (although the fact that you have to have an integer number in series and parallel could influence the design if you want to use off the shelf components)
Today's HV converter stations use IGBT's mostly because they used to be the best thing to use back in the 2010's when the design process for them started.
bilsbie
Thanks for the analysis!
I’m curious if there are any exotic materials that would be way better dielectrics?
Also are there ways to step down really high voltages? I can’t picture how the electronics would work without shorting?
Workaccount2
>I’m curious if there are any exotic materials that would be way better dielectrics?
There are, but like glass they tend to be rigid crystalline structures, and not necessarily formable into what you need. There also is the problem that the dielectric needs to be perfect, as any imperfection becomes a pressure point and once you get even a microscopic breakdown, the whole thing is junk. Any practical repair is going to be very imperfect on the molecular level, so see what I said earlier. Also gaps are imperfections, so usually layering layers of dielectric is a non-starter too (but can be done, it's just very engineering intensive). The HV will "leap" from imperfection to imperfection until it finds it's ground. Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
>Also are there ways to step down really high voltages? I can’t picture how the electronics would work without shorting
Yes, they basically use stacks of thyristors or IGBTs to actively switch the DC "phases" which get fed into a transformer to step down. Wikipedia has a surprisingly good article on it:
quickthrowman
> Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
Hell, even the difference between 600V (low voltage) THHN (thermoplastic) or XHHW (XLPE) insulation and a 2.4kV/5kV (medium voltage) cable is enormous.
anon_cow1111
Also note this image in the sibling reply's article
https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
Which is part of a transmission station bridging islands in NZ and probably one of my favorite pictures on the internet.
That's the scale of the hardware you're looking at... for a voltage 40 times lower.
Workaccount2
It's also the picture I had in mind when thinking about 14MV. The size of everything to space out the stages would need to be so vast I don't even know if it would be structurally possible.
MrBuddyCasino
Tokyo Electric Power has 1MV lines afaik.
Workaccount2
Sorry, 800kV is the highest HVDC.
philipkglass
China has one 1100 kV HVDC line completed in 2018:
https://www.nsenergybusiness.com/projects/changji-guquan-uhv...
The Changji-Guquan ultra-high-voltage direct current (UHVDC) transmission line in China is the world’s first transmission line operating at 1,100kV voltage.
philipkglass
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:
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).
londons_explore
> 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.
bob1029
Building a circuit breaker that can handle 14 megavolts of DC seems improbable to me.
londons_explore
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.
gwbas1c
> simply sacrifice the cable
How is that different from a fuse?
idiotsecant
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.
jabl
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?
defrost
There's more to glass than simple silica soda lime formulations.
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...
gsf_emergency
Not to forget Pyrex (the original formulation, not the trademark)
femto
> glass isn’t known for its ability to bend
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.
dtgriscom
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.
D13Fd
I’m no engineer, but this is a glass tube, not a glass sheet. I thing the amount of bending it does without breaking will be very small.
hcknwscommenter
fiber optic strands are glass tubes and they bend.
shrx
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].
[1] https://physics.stackexchange.com/questions/12913/hollow-tub...
[2] https://www.mtbiker.sk/forum/download/file.php?id=207637
bell-cot
Pretty much every solid material gets vastly more bendable when it's very thin.
(From vague memory, stiffness is proportional to the cube of the thickness.)
timerol
> 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 admire that the author wrote this sentence and continued with the thought experiment anyway
jauntywundrkind
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
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.
ansgri
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.
londons_explore
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.
notepad0x90
Don't forget ships and their anchors.
jillesvangurp
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.
msandford
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.
kashkhan
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.
londons_explore
> meters of foam around it to make it neutrally buoyant
In the deep ocean (typically 4km deep), foam collapses and doesn't float...
null
bluerooibos
> interesting take
I think that's being generous.
perihelions
Recent and related,
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")
ben_w
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.
ACCount36
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.
londons_explore
> Glass insulated cable sounds like a tech that should be prototyped on smaller scale
Take a close look at an incandescent light bulb... There is an inch of glass insulated cable there...
ACCount36
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.
mschuster91
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.
ben_w
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.
* Not superconducting in the quantum sense, but still no resistance because there's nothing to hit: https://en.wikipedia.org/wiki/Ballistic_conduction
ACCount36
"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.
ben_w
Bury? I was thinking just leave it exposed on the surface. Two chonky lines 2-3 meters apart, double use as a railway.
You make a good point about the other uses of insulation, and ISRU, on the moon.
Would ceramics work for transformers?
amluto
> 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?
londons_explore
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.
aitchnyu
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).
ben_w
> 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.
OK, my day job is doing HV engineering, not transmission, but high energy stuff.
The author did something kind of equivalent to:
"If we scale a GPU clock to 75 Petahertz, we can make datacenters that fit in bed rooms! Here are the FLOPS calculations to prove it!"
This whole thing is so crazy I don't know where to begin. I applaud the author for jumping into a new subject, but there is _way_ more complexity here than laid out. HV is very difficult to penetrate too because there really isn't much info available online about it.
Those initial dielectric strength numbers are definitely off (maybe they used Wikipedia, which references a value from a 1920 physics book). As from what I can find fused silica has a dielectric strength around 50-100MV/m, which is taken from the AC figure and doubled to get the DC figure (which is fairly typical). Also these numbers are extrapolated, and dielectrics often have non-linear properties. The testers used to get these figures can be a little fickle, and HV is always fickle.
On top of that, in actual HV system design, you really need to be using 25% of the actual dielectric strength for any kind of reliability. So the practical strength of fused silica would ultimately be around ~20MV/m. Which pretty much kills the whole idea right there. Never mind that a single fracture or dielectric breakdown anywhere in the whole glass sheath would require the entire thing to be replaced. Spoiler: You cannot patch HV dielectrics. Trust me, I and many others have tried.
Some other hurdles would be dealing with the insane parasitics, which the author didn't even mention, but are one of if not the most limiting factor in transmission. HVDC lines can have up to 10% ripple, which for the author would be 1.4MV of high frequency ripple. And sea water is conductive! You are basically building a massive capacitor with sea water! The losses would be enormous.
And I don't even want to think about the electronics...14MV is so insane I cannot fathom anything that would be able to reliably handle it. 1MV is already nuts. 800kV is the highest in the world, and that is kinda just a flex.