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No flashy product launch, no app, just "we quietly replaced a 1960s failure point before it failed."

I'm shocked it only took five years and only cost 4 month's worth of bomalian budget.

Great job whoever was in charge.

It’s not just a tunnel, it’s a game-changing lifeline

Anyone have any idea why the cables are arranged like this? https://8400e186.delivery.rocketcdn.me/articles/wp-content/u...

What's the zig-zag pattern for, seems like a fair bit of extra conductor.

This 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/l...

A thousand words but 200 of them are bullshit, and they didn't even have to use Photoshop.

That’s just slack. You’re seeing a very long distance with extreme foreshortening in this image.

Great photo from an artistic POV, completely useless to get a sense of the main subject of the tunnel: the cables carrying electricity.

Do you mean the catenary [0]?

[0] https://en.wikipedia.org/wiki/Catenary

It's the lens distorting the view.

First guess (may be wrong) is to manage thermal expansion/contraction constantly on a micro-scale.

I would also add that there some slack for repairs.

My understanding is that it's mostly mechanical and thermal, not electrical cleverness

Maybe to reduce electromagnetic coupling? Seems they're offset a bit.

> Anyone have any idea why the cables are arranged like this?

I think that's just cables sagging, which is a requirement to accommodate thermal and seismic displacements.

Is that a tandem bicycle? Cute.

Yes. First time I see a tandem in such tunnel. Until know I just saw and used normal bicycles in such kind of tunnels.

Tandem bike or a new SCP variant.

There are three reasons:

* Cable thermal expansion under current load: 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)

It looks like AI slop to be honest. My second best guess is that it could be arrayed transformers.

I don't think a utility company in their right mind would allow workers to bicycle inside a tunnel powering the grid.

I'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.

It’s easy to find on https://openinframap.org

If 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.

Impressive 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.

"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.

> Or if one really cares about the loss, use direct current

I thought direct current had higher transmission losses vs AC

AC has higher losses over a transmission wire because of the changing magnetic field that it induces which creates losses.

There'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

You can feel it yourself if you have a piece of metal, like a bike.

Tesla vs. Edison is back! :)

Not if it's really high direct current, like https://en.wikipedia.org/wiki/High-voltage_direct_current

Problem is they need these https://en.wikipedia.org/wiki/HVDC_converter , for these 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.

From Gridlock to Grid Power: The Promise of Superconducting Cables

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.

The tunnels are just for ease of maintenance.

https://en.wikipedia.org/wiki/London_Power_Tunnels

The way the regulator regulates capital returns incentivises overspending on lavish infrastructure works as a way to return more profits back to the shareholders.

> 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.

London 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.

And unmapped (and changing, inadvertently diverted) rivers

There’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.

I think tunnels like this are more about future-proofing access than betting on a specific technology

> 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.

That sounds like an excellent use for narrow boring company tunnels.

Cables 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?

Overhead 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.

Modern 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=332f...

Yeah, 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.

Cost, 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.)

Overhead 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.

Overhead lines need big ceramic stacks because the air is the insulation. In tunnels, the insulation is in the cable itself, and the tunnel just provides structure, cooling, and controlled geometry

The tunnel is too small to use air as an insulator so they use cable assemblies with multiple layers of insulation.

Here’s some high-voltage cable spec sheets that show a cross-section of the assembly for voltages above 69kV: https://www.southwire.com/wire-cable/high-voltage-undergroun...

Anyone 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

Some 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.

My 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.

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.

Things like this are useful when for example you want to charge a fleet of electric busses overnight.

I'm looking forward to the next Amendment to the 18th Edition's conduit-fill factors.

essentialy 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

So tunneling isn't just an engineering choice, it's a planning survival strategy

So Everywhere else in Britain it is 'too expensive' to put cables underground. Just goes to show how London centric this country is.

Yes.

And I wish people would understand how costs work.

Pylons need space right, they also need maintenance corridors and access. Every ~360m you need a space to put a pylon[1]. Can you imagine the cost of buying 400m2 every 360 in zone 1?

what about the scaffolding when you need to re-string the cables? can you imagine how expensive that would be? what about if a lorry smacks into it? Its just not practical.

I grew up in norfolk, next to a bunch of HV pylons. No-one commented on them, because they were always there. THey are going to put some more in, and suddenly "its a blot on the land scape" and its "ecological damaging" Then its proposed that the cables are buried. apparently a 200 meter clearing 30km long is more ecologically friendly than pylons ever n hundred meters.

but thats an aside.

[1]https://www.quora.com/What-is-the-distance-between-electrici...

I wish that people understood how costs work? Does that count as polite conversation in London? It is about typical of how Londoners sneer at the rest of the UK.

London is the place that costs don't work. It is full of things that don't need to be there, driving up the real estate prices. The port closed decades ago, so let's move the insurance and FX markets somewhere cheaper? Let's move out the government departments too.

Modern London is all about MPs who are physically tethered to Westminster by in person voting, being surrounded by the kind of people who want direct access to MPs...

All of the companies who specialise in creaming money off real companies gravitate towards that pig trough. Today they need data centres as close as possible, so they can cream money off faster. And we now have to feed those parasites with extra power lines.

Don't lecture me on costs, while London continues to try so hard to inflate the price of the tidal mud it resides on, by sucking in the rest of the UKs wealth.

> Does that count as polite conversation in London?

no, because this is mostly a logical fallacy.

> It is full of things that don't need to be there

Like what specifically? Most heavy industry moved out in the 70/80s, the port moved to essex in the 80s. The fish and meat veg moved out to canary wharf, and are going to move further out soon. what else should be taken away?

> Today they need data centres as close as possible,

This is a cable replacement, but yeah, lets go with new datacentres in london (as we know planning is quick and simple, so they are popping up weekly....) However the key issue is that population density is now back to somewhere like it was in the 40s (https://trustforlondon.org.uk/data/population-over-time/)

So whilst power demand is largely flat, infra doesn't last for ever, so even power cables need to be replaced.

> Modern London is all about MPs who are physically tethered to Westminster by in person voting, being surrounded by the kind of people who want direct access to MPs...

Yup, all 8.9 million people that live there are entirely there to do lobbying. I to am a lobbyist.

> Don't lecture me on costs, while London continues to try so hard to inflate the price of the tidal mud it resides on, by sucking in the rest of the UKs wealth.

Well, as you've neatly avoided any mention of costs of tunnel vs pylons, its not really a lecture is it. I hope you come to peace with the general concept of london.

FX trading has been completely online for about 20 years.

You would think so, wouldn't you? Then why is the FX department at my bank based in London? As a mid market client they occasionally used to send one of them out to see me. They told me all about their office and team in London...sat in front of screens. Their system aggregated the banks position onto the screen of the master trader for each currency, sat at a screen in the next office. What utter waste

London and the south east is the UK in economic terms. Its the only those 2 regions which are net contributor to taxes

https://www.ons.gov.uk/economy/governmentpublicsectorandtaxe...

That's because all the wealth of the UK is leached towards London and the SE.

Then a small bit of what is leached is paid back in taxes and you pretend that means the leeches are subsidising the actual workers.

It would be nice to have a similar study that corrected for

1) the amount of wealth claimed to be generated in London, that was actually just financial services sucking in money from the rest of the UK

2) The cost of all the pensioners that left London when they retired, claiming their pension and health care in a different part of the country

This region is by far the most heavily subsidised in the UK in reality, which is confirmed by the number of expensive infrastructure projects there such as this one.

London is effectively kept going by these infrastructure projects and so many UK government agencies and businesses being headquartered there. Even the monarchy plays a role, as a massive gravy train mostly based there. All that money keeps other businesses in London going. Every time someone pays UK taxes in any form they are supporting jobs and physical facilities based there. The BBC is another one. People throughout the UK are forced to pay a licence fee that is mostly used to produce content in and about London.

This is part of a repeating pattern. London took massive amounts of resources such as coal, metals and manufactured goods from other parts of the UK which are now in poverty. The North Sea Oil boom of the 1980s, was used to prop up the London stock market, and only a fraction of that money stayed within Scotland which was suffering industrial decline at the time. (Aberdeen has surprisingly little to show for the oil boom and is now a city in heavy decline.)

Well they are put underground sometimes when there is a sound reason to do so. But mostly there is not a good reason to do so across hundreds of miles of agricultural land.

Sounds 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.

It 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

>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.

Manchester is burgeoning, still someways behind London.

It’d be super, smashing, great! for the cities to be far better connected together across the Pennines.

What 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.

I 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.

You're lucky to have us mate. London is the only thing going for this country. We should be betting /more/ on London.

On the flip side, that's mostly because London takes all their wealth and crowds out wealth generation

People move to where the jobs are. That's how most English towns came to exist in the first place in the industrial revolution.

We're ~30 years into a new information/digital revolution and London is a world centre of it. There's plenty of wealth generation happening. People are welcome to sit and wait for it to come to them if they want.

Can you give me some examples of wealth generation from London?. You can exclude the massive amount of Financial Services that they shout about so much, that is just a way of skimming wealth of real businesses.

The UK is run as a city state for London's behalf.

The odd thing is that it makes fun of all those coal mining and oil producing areas whose wealth it has been only too happy to steal. A sort of internal colonialism.

"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.

"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.

The 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?

Let 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.

You’re only explaining potential reasons why London is generating higher value.

Which is still implicitly accepting the fact that London does create more value that then goes to the rest of the UK rather than the reverse.