[crunchlibrarian]

So bury all the cables/equipment underground? I'm sure costs are substantially higher to do so, but we could add other infrastructure along these underground lines as well if there was a shred of political will to accomplish this.

[pdkl95]

PG&E apparently[1] has a project to improve the infrastructure in some areas. They are replacing the existing 12kVA lines with insulated 15kVA lines that still carry 12kVA service. This should provide a larger margin for transient problems and protect against some types of arcing. They are also retrofitting some poles so they hold the individual cables farther apart.

However, the real problem is trees/etc growing too close to the lines, compounded by the extra dry drought conditions throughout CA. Regardless of the type of cable or other technical safety features, power lines are always going to be a fire hazard if they don't receive regular inspection and maintenance. The lesson from these fires is that the existing maintenance schedule is severely inadequate.

[1] https://www.youtube.com/watch?v=L2nWuZ8J0Go

[Mvandenbergh]

So typically burying a cable at HV or EHV is an order of magnitude more expensive than overheads. Underground cables are also prone to thermal issues (ironically) so I don't know that you'd be reducing fire risk as much as you'd think.

Much of the ignition risk comes from transformer explosions, air-insulated CB arcs, and line-to-tree arcs.

Transformer explosions are inherently harder to isolate from flammable material in the American distribution system design than they would be in a European 240v system, that's because the US system has to keep LV (110v) runs short so has extensive HV networks with pole-mounted transformers feeding a small number of properties each. 240v systems can tolerate longer LV runs and use larger pad-mounted distribution transformers with about 20x the power rating of American style pole-mount transformers.

In the Euro configuration, you therefore have many fewer transformers which have a least a fence around them with regular vegetation control within it. You can also put these transformers within enclosures. A typical UK rural/suburban arrangement has the transformer air cooled and outside within a fence with breakers and distribution boards inside a brick or GRP hut inside the fence. In urban areas the whole thing is enclosed in its own structure or in the basement of a building.

Anyway you can't do that with American transformers as there are more of them. These will therefore always be an ignition risk. Yes you can step up planned replacement of older models, be more aggressive about keeping the load per transformer down to lengthen lifetime and reduce fault risk but fundamentally they are a risk.

You can replace air insulated CBs with gas-insulated models at significant expense, that will reduce that risk.

Burying cables as I said is horrifically expensive but you could increase the size of the vegetation-cleared right of way around the overheads and step up the clearance schedule.

None of these will remove every source of ignition.

[dbcurtis]

> Transformer explosions are inherently harder to isolate from flammable material in the American distribution system design than they would be in a European 240v system, that's because the US system has to keep LV (110v) runs short so has extensive HV networks with pole-mounted transformers feeding a small number of properties each. 240v systems can tolerate longer LV runs and use larger pad-mounted distribution

Wait... In the US for household single-phase it is 240V from the pole transformer to the breaker panel, where the 120V is derived by taking one hot or the other against the neutral, and the range/drier/etc 240V circuits are simply across both hots. So there is no difference between EU or US distribution voltages until it gets inside the house. All the US does is add a neutral so that it is easy to get 120V.

[Mvandenbergh]

UK is 400v phase-phase and 230v phase-neutral. The distribution transformers are three-phase out and the LV main serving a street is 3 phase wires and a neutral, each house is fed from one of the phases and connected to the neutral.

My understanding of the standard US system is that the distribution transformer is fed with one phase, the secondary side of the transformer has a centre-tap neutral and two live phases which have 120v to neutral and 240v phase-phase.

[dbcurtis]

> UK is 400v phase-phase and 230v phase-neutral. The distribution transformers are three-phase out and the LV main serving a street is 3 phase wires and a neutral, each house is fed from one of the phases and connected to the neutral.

Good to know.

> My understanding of the standard US system is that the distribution transformer is fed with one phase, the secondary side of the transformer has a centre-tap neutral and two live phases which have 120v to neutral and 240v phase-phase.

yes

[planteen]

Three-phase power is common for service in the US for commercial, industrial, and rural areas. But it is not typical in urban or suburban residential areas.

And yes, nearly every home is served by 220 V phase-to-phase with a center tap. Am I understanding right that UK houses are only fed by single phase at 230 V with neutral?

Is the reason we have pole mounted transformers in the US really because of voltage drop though? It seems to me the reason would be they are inherently smaller due to the lower voltages, higher frequency, and only converting one phase from the distribution side. The UK has lower frequency, higher voltage, and apparently has three output phases which seems like it would require a larger transformer.

[Mvandenbergh]

>Am I understanding right that UK houses are only fed by single phase at 230 V with neutral?

That's right, typically houses along a street will alternate phases to maintain overall balance. Standard used to be 60A supply but is now 100A which I believe would be considered low in the US but we don't usually have residential air conditioners and houses are smaller and heated with gas.

I have been told that this is the reason but there are other reasons to prefer the US arrangement so it may not be the only one. US system is more resilient to secondary failure because fewer customers are fed per secondary and you have a much more extensive HV network which is more flexible.

UK distribution transformers are much, much larger. Looks like this: https://cms.esi.info/Media/productImages/Expanded_Metal_Comp... My point was that it is easier to enclose a smaller number of large assets than a large number of small ones which is relevant to fire risk.

[sgc]

There are certain areas which are known to be very high risk with population centers in the expected path of travel of a fire. It is criminally negligent to not bury lines or provide other extremely robust fire risk reduction measures in these areas. Although not exclusively, the conversation needs to focus on the smaller areas of highest risk.

[dbcurtis]

You do realize the areas of California mountains we are talking about (Paradise area) the mountains are granite?

“bury” is, as we say, “non-trival”.

[crunchlibrarian]

Super informative, thanks

[VLM]

From a safety engineering standpoint it would be much cheaper and safer not to live in a tinderbox than to try to make a tinderbox fireproof.

It seems a bad investment to try to live there.

[dsfyu404ed]

In a fight between logic and "surf and ski in the same day, brah" logic is not what wins.

[sgc]

That is a useless comment. People should not live in hurricane areas, in tornado alleys, etc. But they do. So the infrastructure needs to be designed for it. What people's pastimes are is totally irrelevant and obviously does not inform this type of decision a whit.

[dsfyu404ed]

That's not my point. My point is that people don't take long term risk of mother nature screwing them into account when they're deciding where to live, they just look at the short term benefits. They don't bother to account for there being a high chance of mother nature destroying their home within their lifetime.

"Surf and ski in the same day brah" is an example of a short term benefit.

[planteen]

I've wondered why it wasn't underground as well. I live in Colorado and have underground at my house. The EIA says underground is 5-10x more expensive.

https://www.eia.gov/todayinenergy/detail.php?id=7250

[smolder]

Or just surround electrical equipment with good old nonflammable concrete.