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 not particularly cheap or effective. From the article:
> 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.
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…
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.
HVDC converter stations are expensive though. And you would need to have one every time you have a substation to directly replace an AC cable. It makes sense for longer distances.
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 advantages pertain irrespective of environment.
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).
These cables can run much hotter and so have better capacity. BUT there is a big downside. Because they run so hot (you can grill a burger on them with ease), there will be a lot more resistance resulting in net losses.
Also fun, because they can run so hot when rain hits it literally sizzles and cooks resulting in extra noise.
"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!
Something that everyone is going to need to get used to is that with carbon-free, cost-free primary inputs the emphasis on efficiency that we have historically known is going to disappear. It fundamentally does not matter if something that we need to make the system work loses a few percent of the energy.
That's not new at all - we already accept ICE's losing a ton of energy as heat, we accepted incandescent light bulbs losing a ton of energy as heat, etc.
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.
It does when the grid is running on batteries for extended periods of time. I guess it just comes down to what is cheaper between x% more batteries and y% larger conductors.
Colocating batteries with panels should be more cost effective as they can avoid the DC-AC-DC conversion while using half as many inverters as 2 separate installations.
I was hoping Ultraconductors[1,1a] would make it out of the lab, and into general use... but the crash of 2008 apparently killed them off. (OR... it was a scam all along. The patent they reference [2] is for a polymer about as conductive as the nichrome wires you use in your toaster)
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.
There is also a parallel technology that does a better job of understanding line conditions with regards to heat, humidity, etc. and enables higher utilization as well (versus having to rate the lines to the worst 20 year scenario).
You may be referring to either 1) the real-time line ratings (directionally required by FERC order 881, or 2) technology like the "SmartValve" from Smart Wires which dynamically adjusts impedance to keep conductors within their operating envelope.
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.
The article doesn't say much about it but I am sure there is significant work being done at the transmission substations as well to support the extra capacity.
As the new conductors will have lower impedance, some breakers may need to be replaced to interrupt higher fault current. Otherwise, it's likely the only substation equipment needing to upgrade would be series compensation stations which may have lower normal and emergency ratings than the upgraded conductors.
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?
I only know the western US. And my experience is consistant with your own -- specialized applications.
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.
Fair enough. I had a conversation with one utility that was fine with transformers popping (even if preventable) because a popped transformer becomes a capitalizable expense.
Spot on. David Roberts (Volts) also asked about that in one of his interviews.
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).
Strange not to mention wire weight which I gather is an extremely important factor. If these are also heavier, they may sag more for strictly physical reasons and that would cause problems. I guess the modeling behind this article probably takes that into account.
> "Chojkiewicz and her colleagues at Berkeley’s Energy and Resources Group and Goldman School of Public Policy studied the use of advanced conductors that wrap more aluminum around a smaller, stronger composite core. These Aluminum Conductor Composite Cores (ACCCs) are more conductive and can operate at higher temperatures, resulting in roughly a doubling of capacity for an equivalent diameter wire."
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.
Skin effect works at all frequencies besides DC. At 60 Hz it’s 8.5mm. So, solid conductors thicker than 17mm have some skin loss. You can mitigate this by winding multi strand wire in a particular way, though.
Increased weight makes reconductoring much more difficult as the structures are designed to carry specific weight. Increased size can also impact structure loading from ice or wind. So, generally, reconductoring does not materially increase weight.
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.
Anywhere that icing is possible during the winter, the static weight of the conductors is not generally the dominant design constraint; it is the diameter of the cable and the resulting additional load when icing occurs. Weight really only increases sag, which constrains attachment height, but wind gusts with increased wind resistance increase horizontal load. In areas that don't get ice, diameter drives wind loading, again making wind gusts the dominant failure mode for pole lines. This comes about as most poles and/or other support structures for overhead conductors have far greater strength vertically than horizontally.
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...
Good explainer, thanks for posting.
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 not particularly cheap or effective. From the article:
> 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.
Wouldn’t increasing the voltage require new towers in most cases? The towers are sized to give sufficient isolation.
Maybe. But it wouldn't require new land.
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.
> They ignored simply increasing the voltage
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…
HVDC is not a silver bullet.
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.
HVDC converter stations are expensive though. And you would need to have one every time you have a substation to directly replace an AC cable. It makes sense for longer distances.
I thought the advantage of HVDC was mostly for subterranean and undersea cables. Why would it be better above ground?
Two major reasons:
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 advantages pertain irrespective of environment.
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).
These cables can run much hotter and so have better capacity. BUT there is a big downside. Because they run so hot (you can grill a burger on them with ease), there will be a lot more resistance resulting in net losses. Also fun, because they can run so hot when rain hits it literally sizzles and cooks resulting in extra noise.
Wow! A random datasheet[0] says:
"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...
Something that everyone is going to need to get used to is that with carbon-free, cost-free primary inputs the emphasis on efficiency that we have historically known is going to disappear. It fundamentally does not matter if something that we need to make the system work loses a few percent of the energy.
That's not new at all - we already accept ICE's losing a ton of energy as heat, we accepted incandescent light bulbs losing a ton of energy as heat, etc.
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.
It does when the grid is running on batteries for extended periods of time. I guess it just comes down to what is cheaper between x% more batteries and y% larger conductors.
If the solar is remote and the batteries are near the load though you don’t need any more batteries in this situation, just more panels.
Colocating batteries with panels should be more cost effective as they can avoid the DC-AC-DC conversion while using half as many inverters as 2 separate installations.
That doesn't sound free.
Isn't that going to be a fire hazard as well?
They already need to be kept away from vegetation to prevent faults.
I was hoping Ultraconductors[1,1a] would make it out of the lab, and into general use... but the crash of 2008 apparently killed them off. (OR... it was a scam all along. The patent they reference [2] is for a polymer about as conductive as the nichrome wires you use in your toaster)
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...
[2] https://patents.google.com/patent/US5777292A/en
[3] https://patents.google.com/patent/US6552883/en
There is also a parallel technology that does a better job of understanding line conditions with regards to heat, humidity, etc. and enables higher utilization as well (versus having to rate the lines to the worst 20 year scenario).
You may be referring to either 1) the real-time line ratings (directionally required by FERC order 881, or 2) technology like the "SmartValve" from Smart Wires which dynamically adjusts impedance to keep conductors within their operating envelope.
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.
The article doesn't say much about it but I am sure there is significant work being done at the transmission substations as well to support the extra capacity.
As the new conductors will have lower impedance, some breakers may need to be replaced to interrupt higher fault current. Otherwise, it's likely the only substation equipment needing to upgrade would be series compensation stations which may have lower normal and emergency ratings than the upgraded conductors.
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.
Good points.
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?
I only know the western US. And my experience is consistant with your own -- specialized applications.
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.
Fair enough. I had a conversation with one utility that was fine with transformers popping (even if preventable) because a popped transformer becomes a capitalizable expense.
If substations are being upgraded, they should also be installing batteries and inverters at the substations at the same time.
This sounds like moving the goal and a much more difficult problem than just upgrading the substation.
Spot on. David Roberts (Volts) also asked about that in one of his interviews.
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).
previously https://news.ycombinator.com/item?id=39485940
Strange not to mention wire weight which I gather is an extremely important factor. If these are also heavier, they may sag more for strictly physical reasons and that would cause problems. I guess the modeling behind this article probably takes that into account.
> "Chojkiewicz and her colleagues at Berkeley’s Energy and Resources Group and Goldman School of Public Policy studied the use of advanced conductors that wrap more aluminum around a smaller, stronger composite core. These Aluminum Conductor Composite Cores (ACCCs) are more conductive and can operate at higher temperatures, resulting in roughly a doubling of capacity for an equivalent diameter wire."
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.
Skin effect is a high-frequency thing. From memory the down-rating tables start at 100 kHz.
Skin effect works at all frequencies besides DC. At 60 Hz it’s 8.5mm. So, solid conductors thicker than 17mm have some skin loss. You can mitigate this by winding multi strand wire in a particular way, though.
Increased weight makes reconductoring much more difficult as the structures are designed to carry specific weight. Increased size can also impact structure loading from ice or wind. So, generally, reconductoring does not materially increase weight.
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.
Anywhere that icing is possible during the winter, the static weight of the conductors is not generally the dominant design constraint; it is the diameter of the cable and the resulting additional load when icing occurs. Weight really only increases sag, which constrains attachment height, but wind gusts with increased wind resistance increase horizontal load. In areas that don't get ice, diameter drives wind loading, again making wind gusts the dominant failure mode for pole lines. This comes about as most poles and/or other support structures for overhead conductors have far greater strength vertically than horizontally.
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....
Composite-core cables are lighter. The core is carbon and fiberglas fiber, rather than steel.[1]
[1] https://compow.com/blog/midal-accc
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