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A train-sized tunnel is now carrying electricity under South London
- zeristor 10mo agoImpressive piece of work, first time I’ve heard of this. I had heard that tunnels were a good first step for rolling out super conducting cables, but that doesn’t seem to be a thing. Superconducting cables have progressed a lot. I’m assuming that setting up a cryogenic system to keep cables cool enough, in a confined space wasn’t thought to be worth it. The tunnels look tight enough, and boiling liquid nitrogen from a leak could cause asphyxiation I imagine.
- lukan 10mo ago"I had heard that tunnels were a good first step for rolling out super conducting cables, but that doesn’t seem to be a thing." Yeah tunnels underground would be better for superconducting cables, but it is indeed not really a thing as the cooling and installing and maintainance would be waaaay more expensive, than just using higher voltage. Or if one really cares about the loss, use direct current - but we are talking aber very small distances here. If superconducting would be easy, we likely just would have fusion plants everywhere with no need for transporting electricity long distances.
- ferfumarma 10mo ago> Or if one really cares about the loss, use direct current I thought direct current had higher transmission losses vs AC
- tallowen 10mo agoAC has higher losses over a transmission wire because of the changing magnetic field that it induces which creates losses.
- HPsquared 10mo agoThere's a cool effect where if you hold a fluorescent tube under a high voltage power line, capacitive coupling from the varying electric field causes it to light up. Some energy is continually leaking out via this route, the tube just reveals it. (Magnetic induction too) https://youtu.be/0D50Dcvzkr4 https://youtu.be/0D50Dcvzkr4
- afandian 10mo agoYou can feel it yourself if you have a piece of metal, like a bike.
- LargoLasskhyfv 10mo agoNot if it's really high direct current, like https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current Problem is they need these https://en.wikipedia.org/wiki/HVDC_converter https://en.wikipedia.org/wiki/HVDC_converter , for these https://en.wikipedia.org/wiki/HVDC_converter_station https://en.wikipedia.org/wiki/HVDC_converter_station which are expensive. So it depends on circumstances, how and when its economically feasible to use HVDC, or not.
- teo_zero 10mo agoTesla vs. Edison is back! :)
- mr_toad 10mo agoThe tunnels are just for ease of maintenance. https://en.wikipedia.org/wiki/London_Power_Tunnels https://en.wikipedia.org/wiki/London_Power_Tunnels
- locknitpicker 10mo ago> The tunnels are just for ease of maintenance. The fact that the tunnels are 50 meter underground leads me to wonder if their main requirement comes from national security needs.
- defrost 10mo agoLondon underground is prime real estate - to find a level and avoid * the recent new massive and extensive sewer tunnels, * the secret basement extensions of the ultra rich, multi story archival storage, vaults, etc, * the new underground tunnels (rail / subway for US readers), * old roman and other buried but still 'conserved' architecture, * crypts, graves, plague pits, * WWII UXB's etc. etc is a hell of a 3D needle to thread - there's > 2,000 years of urban layering in that small area.
- OJFord 10mo agoAnd unmapped (and changing, inadvertently diverted) rivers
- ant6n 10mo agoThere’s Probably simply too much city in the way on higher levels. If you wanna knock out the grid, hit the substations and power plants.
- deleted 10mo ago[deleted]
- everfrustrated 10mo agoThe way the regulator regulates capital returns incentivises overspending on lavish infrastructure works as a way to return more profits back to the shareholders.
- zeristor 10mo agoFrom Gridlock to Grid Power: The Promise of Superconducting Cables https://ee.eng.cam.ac.uk/index.php/2025/09/22/from-gridlock-to-grid-power-the-promise-of-superconducting-cables-in-the-uk/ https://ee.eng.cam.ac.uk/index.php/2025/09/22/from-gridlock-... An interesting article, I’ll download the IoP report and maybe read it. But it talks about doing the hard work to improve the Technological Readiness Level from 7 to 9. Although these cables need rare earths so might be problematic.
- BrtByte 10mo agoI think tunnels like this are more about future-proofing access than betting on a specific technology
- quickthrowman 10mo ago> Superconducting cables have progressed a lot. I’m assuming that setting up a cryogenic system to keep cables cool enough, in a confined space wasn’t thought to be worth it. Yeah, the cost isn’t worth it. Buying two transformers to step up the voltage on one end and step down the voltage at the other end is going to be several orders of magnitude cheaper than actively cooling cables to 20K for their entire length.
- schainks 10mo agoIndeed, the cooling infra needed for cryo makes the price per watt go up by unreasonable amounts per unit length. Also your cryo liquid should ideally be something that doesn't do the following things: 1. Leaks — shouldn't cause asphyxiation risk to humans who need to fix the leak. 2. Broken cable due to disaster – coolant doesn't turn into explosives when in contact with high voltage high current electricity. However, UHV DC electricity in tunnels could be financially attractive and safe if you can cool the tunnels properly (no superconducting cryo)
- quickthrowman 10mo ago> However, UHV DC electricity in tunnels could be financially attractive and safe if you can cool the tunnels properly (no superconducting cryo) AC transformers are so much cheaper than DC converter stations that I don’t think this will ever be true. At the distances HVDC has a distinct advantage at, you wouldn’t be building tunnels. HVDC is mostly useful for grid ties between unsynchronized grids.
- luma 10mo agoAnyone have any idea why the cables are arranged like this? https://8400e186.delivery.rocketcdn.me/articles/wp-content/uploads/sites/2/2025/12/National-Grid-London-Power-Tunnels-2_cropped.jpg https://8400e186.delivery.rocketcdn.me/articles/wp-content/u... What's the zig-zag pattern for, seems like a fair bit of extra conductor.
- probablypower 10mo agoFirst guess (may be wrong) is to manage thermal expansion/contraction constantly on a micro-scale.
- nraynaud 10mo agoI would also add that there some slack for repairs.
- jo909 10mo agoThis view is just very extreme, it is much less zig zag. It is just mounted to the wall at the high points and slack in between. Certainly there is also a reason for the exact amount of slack like thermal expansion. https://cdn.ca.emap.com/wp-content/uploads/sites/9/2018/04/londonpowertunnelsphase13to2.jpg https://cdn.ca.emap.com/wp-content/uploads/sites/9/2018/04/l...
- deleted 10mo ago[deleted]
- markdown 10mo agoA thousand words but 200 of them are bullshit, and they didn't even have to use Photoshop.
- defrost 10mo agoThere are three reasons: * Cable thermal expansion under current load: https://www.ahelek.com/news/cable-thermal-expansion-and-its-solutions/ https://www.ahelek.com/news/cable-thermal-expansion-and-its-... * The amount pictured is in excess of that required for thermal expansion. The excess is to have some spare length in case of modifications. For example if you have to replace the transformer and the terminals are not in the same location. You cannot extend a massive cable like that easily or without degrading its specs. * The sine wave pattern makes it into AC of course (/s)
- jimnotgym 10mo agoSo Everywhere else in Britain it is 'too expensive' to put cables underground. Just goes to show how London centric this country is.
- jasoncartwright 10mo agoSounds like you are trying to compare the many hundreds of miles (thousands?) of transmission cables needed to cope with the massive geographic change of generation sources to this ~20mi cable system. There are many examples of how the UK is London-centric. This isn't one of them.
- VBprogrammer 10mo agoIt sounds like sour grapes. London contributes nearly a third of the UKs tax income. It has a higher population than the whole of Scotland. Not to mention that over ground wires are manifestly better in every dimension except for aesthetics. This is a great example: https://youtu.be/z-wQnWUhX5Y?si=qdqrpJ-zS7lh2J8Z https://youtu.be/z-wQnWUhX5Y?si=qdqrpJ-zS7lh2J8Z
- jimnotgym 10mo ago>contributes nearly a third of the UKs tax income. Because it contains all of the financial services business that screw money out of all of the real businesses in the rest of the UK.
- ra 10mo agoI know what you're saying, but maybe there is a tipping point when the economics is worth it. Cool to see cycling down there - much safer than on the roads above.
- nkmnz 10mo agoWhat are the costs of an underground cable in the cities you’re considering, expressed as: 1. Cost per kWh transmitted? 2. Cost per person served? 3. Cost per pound of GDP generated? Please provide this for London and the other locations you have in mind.
- nopurpose 10mo agoCables on overhead high voltage lines are mounted using stacks of ceramic insulators, but here they seemingly just sleeved in some protection and hang on a tunnel wall. Why is that?
- jo909 10mo agoOverhead high voltage conductors are not insulated with a coating, probably for many reasons but certainly for cost and heat dissipation. That means the path through the air to some conducting materials needs a certain distance, and that even when wet or iced over or whatever can happen up there.
- VBprogrammer 10mo agoOverhead conductors use air as the insulator. Underground cables use an insulating jacket. In the past it was really difficult to build cables with voltage ranges in the 10s of thousands of volts without additional complexity like a dielectric oil being pumped through the cable. I think modern dielectrics are significantly better though.
- quickthrowman 10mo agoModern cables with XLPE insulation can handle very high voltages without active oil cooling, here’s a 345/400kV rated underground cable assembly rated for 90C: https://assets.southwire.com/adaptivemedia/rendition?id=332f49e0e9b7fa3b0f9b6d9db21f3f643366d309&prid=origin&clid=SAPDAM https://assets.southwire.com/adaptivemedia/rendition?id=332f...
- VBprogrammer 10mo agoYeah, the wires in the new London tunnels are XLPE. Despite being first used in the late 60s it took a long time to be commonly used. Though much of the infrastructure around is still very old.
- KaiserPro 10mo agoCost, mainly The cost of oil insulated cables that can do 132kv is about £900 a meter. Whilst there are HV cables that exist on the outskirts of london, they are much rarer in zones 1-3. I assume that the cost of pylons with raw cables is much much cheaper. The problem is planning permissions, physical clearance. planning permission and now one wants to live near HV cables (that they know of. There are a bunch of 33kv cables buried outside posh people's houses in zone 5, and a bunch in canals.)
- metalman 10mo agoessentialy no choice in putting infrastructure underground as the cost's and delays in putting a power corridor right of way through is unthinkable, they will almost certainly be useing old established locations for transformer substations that have the required set backs and other services, which must from time to time, come to the frenzied attention of developers, agast ,that they cant relieve someone of this "vacant" land
- BrtByte 10mo agoSo tunneling isn't just an engineering choice, it's a planning survival strategy
- nephihaha 10mo ago"In total, the £1 billion London Power Tunnels 2 (LPT2) project, which began in 2019, spans 32.5km across seven South London boroughs from Wimbledon to Hurst." In spite of devolution and the so called "levelling up" programme for other parts of the UK, London obviously continues to be heavily subsidised by the rest of the UK.
- EmbarrassedFuel 10mo ago"London obviously continues to be heavily subsidised by the rest of the UK" This is a farcical comment. Were you being sarcastic? The tax revenue from London massively subsidises the rest of the UK. The investment happens in London because you can guarantee it will make a return, and quickly.
- nephihaha 10mo agoThe real reason London is rich at all is because it was a trading depot with the continent. It made money from goods leaving England, and entering England. Later on, like Paris, it became wealthy off running an overseas empire, and when that empire vanished it turned to nearer territories. London has centuries worth of investment from everywhere else based on that. That money has stayed there, and money is spent constantly on infrastructure which helps it make more money. Contrast this with Liverpool, Cardiff or Belfast which suffered decades of decline for various reasons and a fraction of the investment. If the capital had been moved to Liverpool back at some point in the Middle Ages, then that would have remained a wealthy city instead of becoming a basket case in the eighties. The presence of the civil service and government alone would have kept Merseyside wealthy, and would have made it a huge tourist centre. Bigger than now, and even that was mostly to do with the Beatles. By the way, the state funded Wembley refit cost more than the construction of the Scottish Parliament. Guess which one got all the negative press?
- nephihaha 10mo agoLet me put this another way. If I got given a very well paid civil service job, I would end up paying a lot of tax in return. And if someone paid for my house to be renovated and build the best utility and transport connections, then the value of it would go up. And if mass media continued to promote my area continually then the value of my home would also go up. I would get given higher wages to cope with the increased cost of living there. We would get more tourists visiting my area, and firms and non-doms would set up there because of the positive image. Much like London.
- BrtByte 10mo agoNo flashy product launch, no app, just "we quietly replaced a 1960s failure point before it failed."
- zimpenfish 10mo agoI'm slightly confused by the "New Cross substation in Southwark" whilst the map immediately above clearly shows it in Lewisham[0][1]. Best I found was a page talking about vertical boreholes on Old Kent Road (opposite Commercial Way which is just inside Southwark) but nothing about a substation there on any page. [0] Estimating off the National Grid map, it's roughly vertically centred between Lewisham and Greenwich DLR stations - absolutely not in Southwark! [1] I feel like I'm going mad - the number of pages I found whilst trying to find the exact location that said the same thing under the same map is honestly discombobulating.
- fanf2 10mo agoIt’s easy to find on https://openinframap.org https://openinframap.org
- zimpenfish 10mo agoIf only the search engines had bothered to return that as a suggestion! But yeah, that's the place on OKR I mentioned - just inside the Southwark boundary, not really New Cross. Nowhere near the dot that nationalgrid have on their map either.
- sowbug 10mo agoI'm looking forward to the next Amendment to the 18th Edition's conduit-fill factors.
- blackhaj7 10mo agoAnyone know why the power cables in the image zig zag up and down? Seems like it would require more cable than a straight line so I am guessing there is a reason for it
- dmoy 10mo agohttps://news.ycombinator.com/item?id=46334725 https://news.ycombinator.com/item?id=46334725 TL;DR Camera makes it look more than it is, it's mostly just sag If you want to see electrical with significant zig zag, open up the wall of a house that was built without very detailed plans, but still hired an electrician with a lot of prior experience being told to move stuff after the fact. They just zig zag it like crazy under the drywall, so there's an incredible amount of slack to pull wire to new and exciting unplanned locations.
- blackhaj7 10mo agoVery interesting, thanks!
- 7952 10mo agoMy guess is that the droop is just due to gravity. And it is easier to affix in fewer places. But the style of photography exaggerates the effect.
- sokka_h2otribe 10mo agoSome good reasons: -gotta hang them somehow, and in a very controlled way. -thermal expansion, very important not to cause axial strain on a cable, which happens on tight bends. You might think it would be enough to just have slack "somewhere" but I think you get to have many many micro adjustments when you have it across the entire length. Why don't HV telephone lines do this? I have no idea. Maybe because they can hang and droop more easily. I hope someone more knowledgeable gives a real answer.
- matt-p 10mo agoYou are basically spot on. Thermal expansion (primarily) but you need it to be evenly spread for lots of boring reasons like as you mentioned axial force reduction, fatigue life, anchor load limits and so on. These tunnels just use forced air to cool the (XPLE) cables so they're not oil filled or anything. Tunnels are basically all thermally constrained.
- Neil44 10mo agoThings like this are useful when for example you want to charge a fleet of electric busses overnight.
- mfateev 10mo agoThat sounds like an excellent use for narrow boring company tunnels.
- londons_explore 10mo agoPretty sure they haven't yet achieved their cost/speed targets, else they would have easily won the contract for this tunnel.
- tim333 10mo agoI used to live by Brown Hart Gardens which is a modified 1902 electricity substation. There's lots of odd electricity supply stuff in London, including "the most popular modern art museum in the world", the Tate Modern. https://en.wikipedia.org/wiki/Brown_Hart_Gardens https://en.wikipedia.org/wiki/Brown_Hart_Gardens
- londons_explore 10mo agoIs it actually the most cost effective method to pay cables in such a large tunnel? I would imagine trench and bury or mole-digging to be a much cheaper way to install it?
- chrisandchris 10mo agoAFAIK, high-voltage and high-power cables are usually over-ground for two reasons: (1) less losses with air as coolant and (2) repairs are so much easier. Not having an accessible way to the cable is somethibg you don't want if you don't know exaclty where and what is broken (because you can't see it).
- londons_explore 10mo agoThat's why you usually lay them under roads - then you can dig a broken bit up with just a few hours notice. Generally you do know where things are broken - there are tools to identify the exact location of both broken conductors and broken insulation by reflecting high frequency signals down the cable.
- zeristor 10mo agoHow was it tunnelled, most tunnelling machine are large, large enough for things to have enough space to work. The conveyor belt to remove the debris, the machinery to place the concrete segments to form the wall. I guess it could be shrunk, but there wouldn’t be space for people to get through Mention is made of the North London tunnel, but in preparing for the 2012 Stratford Olympics pylons there were replaced by an Underground tunnel too, and there was a lead time of 7 years from the Stratford winning.