Reconductoring: Boosting U.S. Grid Capacity Efficiently
spectrum.ieee.org
spectrum.ieee.org
Volts recently interviewed Emilia Chojkiewicz of UC Berkeley (quoted in article) and Jason Huang of TS Conductor.
"One easy way to boost the grid: upgrade the power lines" [Jan 31, 2024] https://www.volts.wtf/p/one-easy-way-to-boost-the-grid-upgra...
Here's a prior episode about "grid enhancing technologies" in general, including reconductoring.
"Getting more out of the grid we've already built" [Sep 13, 2023] https://www.volts.wtf/p/getting-more-out-of-the-grid-weve
Grids are a common topic on Volts. Permitting, policy, intransigent utilities, open data standards, biz models, decentralization, virtual power plants, creating a national grid, etc.
A handful of climate crisis / net-zero podcasts like Volts connect and catalyze people, resulting in new startups, legislation, and giving people hope & energy.
Highest recommendation.
Aside:
INTERGRID is my term for our future perfect grid-of-grids. Inspired by the internet, of course. One such effort is (Alphabet) X & AES' Tapestry project https://x.company/projects/tapestry/ .
It's more like we have to resist calls for everything to use the minimum amount of energy possible when the relevant thing really is minimising externalities.
"Max.allowable continuous operating temp: 175 C", and shows a current capacity plot from 55C to 175C. That's 350 F, definitely enough to grill burger.
Also, I was curious about power loss - for that one cable I found, it's 0.25816 Ω/km @ 660 amp, which comes out to 181 kilowatt of loss (150 average US homes) per mile of the line (and probably double that for second wire). That's a lot of loss!
[0] https://www.midalcable.com/storage/products/accc/accc-data-s...
> Chojkiewicz says her team’s modeling neglected those alternatives because their goal was simply to lay out the “nationwide potential,” of reconductoring.
They only compared it to buying new land and putting in completely new lines.
They ignored simply increasing the voltage, switching to HVDC and any solution other than "putting in whole new lines".
In particular, the fact that they just ignored HVDC is problematic. HVDC gets you not just cheaper transmission but lower losses so makes better use of what you have even if you don't immediately boost capacity.
And new towers with simply higher voltage on the old cables may be cheaper than these really expensive cables. And has the advantage that you can upgrade towers piecemeal as part of your maintenance cycle.
Converter stations are very expensive and also take more space. You need one every time you tap in/out of the transmission line, great for point to point links say Offshore windfarm to major IC, but general transmission gets tapped into and out of much more frequently. Even if today you plan for this link to be P2P from city A > city B today what happens tomorrow when someone builds a generation plant, or a new town, datacentre campus on that route?
The "efficiency" gain is debatable, you do lose less on transmission but you now have this cost of getting from DC>AC AC>DC which costs roughly 1.1-1.6% - in the grand scheme of things for most schemes any overall efficiency gain is marginal to nil.
Overall the most flexible thing to do is build AC at the highest voltage your towers/interconnect points support (and consider increasing that).
In the UK we are building more lines and converting more substations from 275KV to 400KV.
For good reason, you can’t do that.
Electrical distribution conductors are insulated by air (and distance). If you crank up the voltage, you could have line-to-line arc flashes if you don’t increase the conductor spacing. Increasing the conductor spacing requires new towers, so…
Capacitive losses. They're worse in water (dielectric), but they're there in air lines as well.
Compatibility and isolation of grids. If grid A is 35 degrees from grid B it's very hard to couple them. Also, cascading failures tend not cross DC boundaries.
HVDC only needs one copper conductor. HVDC has no reactive power loss. HVDC has less corona effect and self-inductance to overcome so conductors can be smaller. HVDC is not subject to grid phase problems.
In addition, since HVDC cabling can be cheaper at a given voltage, the voltage can be increased which minimizes resistive losses (Ptrans = IV while Ploss =I^2R--if you double V you halve I which reduces your losses by a factor or 4).
The other patent they reference[3]... does claim 10^11 S/cm, which is about a million times as conductive as silver.
Imagine what you could do with power cables a million times as conductive as silver.
[1] http://www.superconductors.org/ultra.htm
[1a] https://web.archive.org/web/20090201200804/http://ultracondu...
Among risks that are managed is ground faults caused by sage (as the line heats, it expands, getting closer to the ground), or 2) annealing which is a permanent expansion of the conductor due to operating too hot for too long. The advanced conductors use composite cores allowing the conductor to carry more current at a higher temperature with reduced risk for annealing.
More likely is that lower impedance on the reconductored circuit will cause increased flows on other, non-upgraded circuits, either requiring those to be reconductored, or installing phase-shifting tranformers or reactors to limit current.
Have you seen a lot of phase-shifting transformers in the U.S.? In my experience they've mostly been in Europe with a few specialized applications in the States.
I would think a utility would want to reconductor the other circuits otherwise they're leaving benefits on the table right?
They would love to reconductor the other circuits. In the US, the utilities make a guaranteed rate of return on investments in the transmission system. So, anything they regulators will let them do, they'll do -- not necessarily because it has technical benefits, but because it has economic benefits.
This is one reason why reconductoring isn't that popular with utilities -- it allows the utility to get more capacity with less spend, so less profit.
IIRC, the expert answer was: substations generally need a retrofit (eg new transformer, breakers, smarts).
Even so, reconductoring is much faster and cheaper than building new lines.
Because retro doesn't require a new permit, often reuse existing footprint, and substations can be upgraded as needed (eg only for sections pushing more power).
The primary difference between the traditional conductors and advanced conductors is temperature tolerance. Most transmission lines are aluminum conductors with a steel core for strength (ASCR). As current increases, so does temperature, causing lines to sag (or the steel anneal if too hot).
Advanced conductors use a different composition to operate at higher temperatures, or otherwise carry more current (one example: aluminum conductor, composite reinforced, or ACCR) so as to have similar weight (and profile) to the original, traditional conductor.
I've spent far too much time over the last couple of years learning pole line design using QuickPole. The other factor that keeps cropping up in my designs are grading and/or positioning issues. Putting a pole even 50cm out of line with other poles can result in it failing loading due to the added horizontal load on the pole. On a recent design I had to add downguys and anchors to 2 poles because they were out of line, a mistake during installation that nobody paid attention to. The same thing happens when a pole that is too tall is installed in an existing pole line. The wires to adjacent poles add horizontal force to the top of the pole. On one design I had a pole failing because of that, but it was fine if all the conductors were lowered 5 feet.
All I wanted to do was put fibre optic cables on poles to serve my home...
Oh, rabbit holes....
It isn't clear from the text, but the wires might not actually be any heavier, given that they replace the steel core with a composite.
Aluminum is about 2.7 g/cm^3, whereas steel is around 7.85.
I'd imagine they can switch to a slightly smaller cable size if they have to keep to the original weight and a new cable happens to be a little heavier at the same diameter.
I'm kind of surprised they don't lose the advantages of stranded cable when switching to something that looks more like a solid cable. As I understand it, for AC wiring you usually want a lot of strands because most of the current tends to travel on the surface. Maybe that's less of a thing for high voltage. Or maybe the seams between the strands are enough to cause the skin effect even if they're tight-fitting.