Underground transmission power lines

[dlgoff]

TL;DR Summary

For the California transmission cables

@anorlunda suggested I start a new thread about this:

See: https://www.physicsforums.com/threads/grim-day-on-the-texas-power-grid.999764/post-6521013

 

[gmax137]

Is there a source describing the proposed changes in California? What exactly is being planned? I think this thread needs something specific to discuss. I didn't see a link in the parent thread.

 

[dlgoff]

I didn't see a link in the parent thread.

It was post #149 in this thread: https://www.physicsforums.com/threads/grim-day-on-the-texas-power-grid.999764/

 

[berkeman]

It was post #149 in this thread: https://www.physicsforums.com/threads/grim-day-on-the-texas-power-grid.999764/

That's just a link to the thread. I think @gmax137 is asking for a link to information about underground TLs...

 

[berkeman]

Here are a couple links from my Google search:

https://www.usatoday.com/story/news...ldfire-blackout-fix-unlikely-work/3946935002/

https://www.npr.org/2021/07/21/1019058925/utility-bury-power-lines-wildfires-california

 

[berkeman]

https://www.npr.org/2021/07/21/1019058925/utility-bury-power-lines-wildfires-california

But it's not the really high TLs that need to get buried, right? It would be lines that are at tree-height that are the problem, I believe. @anorlunda is that right?

 

[gmax137]

But it's not the really high TLs that need to get buried, right?

I'm not so sure; the high voltage lines sag quite a bit in hot weather; when I lived in Florida, FPL would deenergize certain lines running through the everglades because the sag put the lines too close to the sawgrass.

Which brings up an issue, how do you bury lines that cross terrain like the everglades? Aside from the physical difficulty, getting an Environmental Impact Statement for work like that would be impossible in today's world.

 

[berkeman]

Which brings up an issue, how do you bury lines that cross terrain like the everglades?

Not too many everglade regions in Cali, IIRC...

Aside from the physical difficulty, getting an Environmental Impact Statement for work like that would be impossible in today's world.

Yeah, I wondered about that as well. Getting the EIR/EIS done for each mile seems like a big or sometimes impossible task. The 2nd link that I posted says PG&E buries about 70 miles of lines a year now, and wants to increase that to 1000 miles per year.

 

[anorlunda]

It was post #149 in this thread: https://www.physicsforums.com/threads/grim-day-on-the-texas-power-grid.999764/

Sorry, but the link in that post is to this thread. We could still use a link to the California proposal.

But some basics first. There's a big difference between underground transmission and underground distribution. Distribution is what goes up the street to your house. Modern housing developments have been using underground distribution for many years. The cables are underground but the transformers above ground.

I suspect that the issue in California is transmission because of the wildfire risk of overhead lines. Lacking the specifics, I can only give you some generalities.

• Underground costs much more. On the order of 7x more per mile.
• The transformers and substations remain above ground. However, a substation, including the transformers, could be enclosed in a building to help avoid the fire hazard. Fire hazard could also be reduced by putting a 1/4 mile radius concrete pad around every substation, keeping vegetation far away.
• Underground transmission lines generate an excessive amount of VARs (imaginary power). That gives the grid serious indigestion relating to voltage control. There are ways to compensate, but they are also expensive.
• HVDC underground cables avoid the VARs problem. But the AC has to be converted to DC at the source, and DC has to be converted back to AC at each substation. That too is very expensive.
• Underground transmission brings a new common mode failure possibility. I just read today about marine life kills in the PNW and British Columbia because of this summer's heat wave. Auckland, NZ suffered a 5 week long blackout in 1998 because the underground cables feeding power to the city were "cooked", destroyed by heat during exceptionally hot weather.
  
  Imagine the screams in California if so much money was spent to put stuff underground, and then substantial portions of the grid were destroyed by a hot weather event. It's enough to make some people want to move to Maine.

It would be irresponsible for me to guess at how much the proposal could increase the cost of power to consumers. But it is not a matter of a few pennies more. It could make electric power completely unaffordable to some consumers to underground the whole grid.

On the other hand, if the proposal is to underground just one or two sections of line in highly vulnerable places, the averaged cost increases would be far lower. That's why we need to see the specific proposal.

 

[dlgoff]

VARs (imaginary power)

I understand what VARs are. Thanks for the reply.

 

[dlgoff]

But it's not the really high TLs that need to get buried, right? It would be lines that are at tree-height that are the problem, I believe. @anorlunda is that right?

View attachment 286737

These pilots are heroes, IMO. Can you imagine the updrafts, etc. they must experience?

 

[gmax137]

They're all heroes, in my mind. The firefighters on the ground slog up and down steep terrain, working axes and shovels in the heat.

 

[anorlunda]

But it's not the really high TLs that need to get buried, right? It would be lines that are at tree-height that are the problem, I believe.

The biggest problem is lines that can contact branches. However, even tall lines can be toppled, or they could rain down sparks in case of a short circuit. So tall lines are less of a fire problem but still a problem.

I'm not so sure; the high voltage lines sag quite a bit in hot weather; when I lived in Florida, FPL would deenergize certain lines running through the everglades because the sag put the lines too close to the sawgrass.

Indeed, the 2003 blackout in the NE was triggered by tall lines in Ohio that sagged into trees that were not trimmed back enough. Double contingency, sagging lines and overgrown trees.


---
An inflatable Quonset hut could cover a substation. That would not protect against a major fire or explosion, but it could block sparks generated by switching operations.

 

[DaveE]

It would be lines that are at tree-height that are the problem

It's not just the height. In significant events it is more related to proper maintenance, things like failed insulators (supports) or insufficient tree trimming. There is also the question of design and construction costs. Most power lines are uninsulated wires, so if they touch a tree branch, bad stuff happens. So there are ongoing projects to convert to insulated wires.

There are options beside underground, which frankly isn't practical for such a large grid. There are many other ways to improve overhead transmission (hardening, in industry jargon). What should be done depends greatly on the local environment. Yes, overhead transmission has problems, but given the huge size of the network, the fact that fires aren't started every day, everywhere, is evidence that the current system isn't completely inappropriate. It just needs to be designed AND MAINTAINED properly.

In addition to the large cost involved, there is a big issue with how much work (i.e. time) it would take to make system wide change, this article says at the current rate of funding, it would take about 1000 years to convert all of California's grid to underground and would cost each customer $15K. Frankly any "one size fits all" solution is hopelessly naïve. What is needed is infrastructure funding to maintain, improve, or convert, the existing grid in flexible and location specific ways. The fundamental problem isn't very different than bridge or pipeline infrastructure maintenance issues; we don't spend enough to keep up what we've built over the years.

It's not conducive to social media kibitzing. But the solution is to implement what the engineers at PGE, SCE, SDGE, etc. already know should be done. Unfortunately management, political, and economic issues get in the way. The engineers aren't so good at solving those problems.

 

[Todd-in-LA]

Is there a source describing the proposed changes in California? What exactly is being planned? I think this thread needs something specific to discuss. I didn't see a link in the parent thread.

PG&E's press release is linked, below. It doesn't go into specifics, but it's all I found on their site.

PG&E Announces Major New Electric Infrastructure Safety Initiative to Protect Communities from Wildfire Threat; Undergrounding 10,000 Miles of Power Lines in Highest Fire-Threat Areas

And here is their "Wildfire Mitigation Plan."

 

[256bits]

They're all heroes, in my mind. The firefighters on the ground slog up and down steep terrain, working axes and shovels in the heat.

Conscription was the norm years back, but it is still part of the law.
https://nationalpost.com/news/canad...-forcibly-conscript-you-to-fight-forest-fires

The province’s Wildfire Act authorizes B.C.’s fire officials to “order a person who is 19 years of age or older to assist in fire control.” The person has to be “physically capable of doing so” and have skills that “can be used” to fight fires — but this technically applies to anyone who can wield a shovel or a pulaski.

The Act, passed after the record-breaking destruction of B.C.’s 2003 fire season, also allows the B.C. Wildfire Service to commandeer vehicles, equipment and even whole private businesses.

The memoirist Barry Cotton similarly recounts a 1949 wedding in Vancouver being derailed because the best man was “press-ganged into fighting a forest fire.” With the press-ganging occurring in a region without telephone contact, the best man’s fate wasn’t known for several days.

 

[Fisherman199]

My concern with PG&E's hardening attempts is that it's a stunt to attract investors instead of actually hardening the system against future fires. One can't simply just bury lines and forget about them. I'm hoping this is not the intent.

The last time I did a cost/benefit analysis for burying cable it turned out to be around 9x as expensive as overhead. Granted I had to bury in duct which greatly increases cost. They could probably get away with ~6x normal overhead costs. Still, at 10,000 miles, that's a lot of $$$. I buried 10,000 feet and costs ran into ~$2.3 million U.S. (a veritable fortune for a smaller utility).

 

[anorlunda]

The NPR article linked in #6 gives some dollar numbers. Note the part I made bold.

The daunting project announced Wednesday aims to bury about 10% of PG&E's distribution and transmission lines at a projected cost of $15 billion to as much as $30 billion, based on how much the process currently costs. The utility believes it will find ways to keep the final bill at the lower end of those estimates. Most of the costs will likely be shouldered by PG&E customers, whose electricity rates are already among the highest in the U.S.

The PG&E press release does not give a completion deadline. It says only "multi-year." Can't get much looser than that.

It also appears that PG&E's customers don't trust them any more. So no matter what they say, it won't be believed. It is a real problem with regulated monopolies. How do you fire a regulated monopoly? Utility laws are highly complex. They are not treated like normal corporations under the law. Good thing too. We need them to keep operating even if bankrupt and even if the executives are jailed.

 

[DaveE]

It also appears that PG&E's customers don't trust them any more. So no matter what they say, it won't be believed. It is a real problem with regulated monopolies. How do you fire a regulated monopoly? Utility laws are highly complex. They are not treated like normal corporations under the law. Good thing too. We need them to keep operating even if bankrupt and even if the executives are jailed.

Yup. They have proven themselves untrustworthy, IMO. PG&E in particular has a reputation of awful management. OTOH, that's no much different than any "too big to fail" publicly owned company. Their job is to make their stock price increase and/or pay dividends to their investors, delivering power is just how they achieve that goal.

That is why they are, and should be, a regulated monopoly. There is also a problem of regulatory capture, the Ca PUC doesn't have the political power or guts to really hold PG&Es shareholders accountable. The PUC isn't that accountable either. Although given the events of recent years they are getting better.

And yes, it will be the rate payers that ultimately will pay, but really, how could it be anything else? The Ca utilities are huge, and the money must come from somewhere. The PUC is walking a tightrope of not letting the shareholders completely off the hook, but also not destroying the credit rating of the utilities that would prevent raising the money they need for maintenance and upgrades. The problem with these utilities is that no matter how badly their management performs, you have to bail the company and customers out somehow; failure isn't an option.

 

[dlgoff]

That's just a link to the thread. I think @gmax137 is asking for a link to information about underground TLs...

This is the link I had in mind:

https://www.npr.org/2021/07/21/1019058925/utility-bury-power-lines-wildfires-california

Sorry for the confusion.

 

[anorlunda]

The Practical Engineering YouTube channel posted this video about the practical difficulties of underground transmission. Should Californians trust PG&E to use this technology on a large scale? At the end of the video, he mentions that modern unground is much better but it still can have difficulties.

IMO, this video is pure entertainment to any engineer. It's well worth 13 minutes to watch it.