Posted by zeristor 3 days ago
Great job whoever was in charge.
What's the zig-zag pattern for, seems like a fair bit of extra conductor.
https://cdn.ca.emap.com/wp-content/uploads/sites/9/2018/04/l...
I think that's just cables sagging, which is a requirement to accommodate thermal and seismic displacements.
* 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)
I don't think a utility company in their right mind would allow workers to bicycle inside a tunnel powering the grid.
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.
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.
I thought direct current had higher transmission losses vs AC
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.
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.
It's a common claim on HN that when a regulator caps profit margins, that incentivizes the entity to make-work to increase absolute revenue and thus profits. But capital markets, i.e. investors, only care about marginal returns. Unless your profit margin cap is really high relative to average returns in the global market, there's no market pressure to do this, AFAICT. Capital projects require investment, but what investors have so much money burning holes in their pockets that they're eager to invest at marginal rates lower than what they could invest elsewhere?
The only financial incentive for this would have to come internally from the company, say from executives whose compensation would increase merely by dint of larger absolute revenues. For regulated entities maybe that's plausible? But typically executive compensation is usually tied to margins and given in stock.
I only just came to this realization when reading about the effect of tariffs and a description of why they drive up prices much more than you think. If the import price on a widget is $100, a 10% tariff drives it up to $110. If the next purchaser in the supply chain was originally paying $X, you might think they would just pay $X + $10, and on down the chain, so that retail prices only rise by $10. But that's not how it works. If the importer was adding 20% (not atypical), they're going to need to sell the widget at $120 + $10 + ($10 * 20%), so $132.00. The next purchaser will need to do the same, but on their purchase price. Whereas before they were selling at $120 + ($120 * 0.20) = 144.00, now they need to sell at $132 + ($132 * 0.20) = $158.40, an $18 jump, not $10. It compounds on down the chain. Why? Your investors are expecting you to add a Y% margin. The reality is a little more complex, of course. Maybe a supplier can get by with a smaller profit margin, but the floor is going to be their cost of capital for buying supply, which may be least 5-10%.
The fact that the tunnels are 50 meter underground leads me to wonder if their main requirement comes from national security needs.
* 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.
If you wanna knock out the grid, hit the substations and power plants.
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.
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)
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.
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.
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.
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.)
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.
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...
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.
I would imagine trench and bury or mole-digging to be a much cheaper way to install it?
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).
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.
