Is it time to seriously consider burying power lines? 2

[Mbrooke]

I'm starting to get the epiphany that it is no longer cost practical to keep power lines above ground. Case in point- storm rolled through the North East during the night. Eversource Connecticut alone had 85,000+ without power and currently about 61,000. 26,000 for Central Hudson and Gas. 10s of thousands in National Grid territory. School buses driving over power lines, people trapped in homes, outages expected to last 3 days.

https://outagemap.eversource.com/external/default.html

https://outagemap.ny.nationalgridus.com/

https://outagemap.ma.nationalgridus.com/

https://stormcentral.cenhud.com/

Even Con Ed has them in their over head network but not to the extent its neighbors do:

https://apps.coned.com/stormcenter/external/default.html

Oh, the school kids:

https://www.wfsb.com/news/school-bu...cle_3b973ac4-fc9b-11e9-97bb-47a18a7356d4.html

Normally I wouldn't blink. But this is now happening every month it seems. Just two weeks ago the same thing happened across the north east. Prior to that micro bursts. Every winter an ice storm. Random Tornadoes. When I was younger it was just a few thousand customers and few hours until power restored. Now its 100,000 and close to a week without power.

Then look at PG&E. Texas. Middle America. I keep seeing a trend where distribution infrastructure is destroyed on a multi state level in just a few hours.

There is also the safety aspect of people driving over live wires, becoming tangled in them, people handling them during storm cleanup (no one takes the warnings seriously around here), attacking line crews and even folks taking the copper primary for scrap because people (and even police) assume them to be line workers in their T-shirts and white pickup trucks. Stores throwing out tens of thousands in food. Lost business. Fights at the gas pump. CO poisonings are another biggy- to this day people still think running a generator in doors with a window cracked is perfectly safe.

 

[bacon4life]

mbrooke- The reduced cable capacity and the inability to easily connect to underground cables prevents the system you described in a suburban setting. In the first photo you showed a 3 phase backbone with a single phase transformer. When this is converted to underground it would become two separate systems. The backbone will be large cables using 600A type connectors, all protected by a circuit breaker/recloser. Every couple of blocks, there will be a vault with a piece of padmounted switchgear with fuses that connects the 600A backbone to a fused 200A system. Individual transformers are then connected to the 200A system.
Also keep in mind that the thermal capacity of a 15 kV underground cable drops is about half of the capacity of an overhead wire the same size. Taking these two impacts together, an underground system requires two to four times as much conductor as an overhead system.

 

[Mbrooke]

I don't see any verizon on that Manhattan pole however.

 

[Mbrooke]

@Bacon4life: All valid.

But what is to stop me from just tapping off the main backbone up to pad mounted units, and then feed through for any future pad mounts? I mean Con Ed somewhat does this where a 13.8 or 27.6 kv feeder cable will directly feed two dozen network transformers.

Not ideal, but- I think with some out of the box thinking we can make it happen.

I view it like residential fire sprinklers. I've had people tell me you need a tap before the water meter, ball valve, check valve, flapper, pressure gauge, flow meter, singling system, drain valve, heat trace, possibly a booster pump, separate 2 1/2 inch piping with GPM and head pressure calcs routed with special consideration and if the capacity is not enough a separate water tank in the attic. You can skip the simease but in the end you may have to install it anyways. Even the brochures and leading books on residential sprinkler show a quixotic Rube Goldberg pipe dream which I think borders on criminal. Nothing more than propaganda designed to present sprinklers as financially insurmountable.

I'm like bro- just take some 1/2 inch pex or copper tap it off the nearest cold water pipe and run it to a few concealed heads lol. 2.5 gallons a minute in any room even at 15 psi is enough to save countless lives. The 10-15 feet of stagnant potable water will present as much health risk as any spigot or tap that never gets used on countless building water supply systems. The price will be minimal as 92% of the piping is already in place for sinks, showers and toilets.



Its the idea that a system must be built a certain way with existing parts, practices, procedures and design that stifles descent and perpetuates the myth that any human progress is grossly impractical not worth being considered or entertained.

I'm highly optimistic something, anything can be done.

 

[Mbrooke]

mbrooke- The reduced cable capacity and the inability to easily connect to underground cables prevents the system you described in a suburban setting. In the first photo you showed a 3 phase backbone with a single phase transformer. When this is converted to underground it would become two separate systems. The backbone will be large cables using 600A type connectors, all protected by a circuit breaker/recloser. Every couple of blocks, there will be a vault with a piece of padmounted switchgear with fuses that connects the 600A backbone to a fused 200A system. Individual transformers are then connected to the 200A system.
Also keep in mind that the thermal capacity of a 15 kV underground cable drops is about half of the capacity of an overhead wire the same size. Taking these two impacts together, an underground system requires two to four times as much conductor as an overhead system.

@Bacon4Life: This is what I came up with:

https://files.engineering.com/getfi...8f85-71243d015c13&file=autodraw_12_7_2019.jpg

I'm thinking of not having a 400/600 amp backbone with PME/FPE gear. Just 200 amp fused feeders from the intermediate substation looping through padmount units. Load breaks and fuses at the supply stations to curb cost.

 

[jraef]

I live in neighborhood with underground utilities, installed in the late 1960s, early 70s. The 12kV lines under my sidewalk had an insulation failure about 15 years ago, blew a 5ft long section out of the concrete in front of my house. The underground transformer for the neighborhood is on my property and at the time, I had a home office. So since I was shut down, I entertained myself by watching the process of repairing it. That alone convinced me that underground lines are not the panacea that people want to think they are. When lines went down in areas I have live in with overhead distribution, repairs were fast and relatively simple. We were down for 3 days to fix and test one underground blowout. The underground transformer has also failed and been replaced twice in the 22 years I have lived here. When it rains, that transformer is totally under water for days.

Turned out by the way that ALL of the 12kV lines in this neighborhood have failing insulation, starting just 10 years after installation. PG&E was sold on a program to try to extend its life by injecting a “gel” substance under high pressure into the jacket at the transformer connections. Cost them millions of dollars in the 1980s. Turned out that the gel never made it more than about 10ft along the cable from the injection fittings. This failure was about 15ft away.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[bacon4life]

I don't quite understand the picture versus your comments. There seems to be 500 kcmil AL feeding from the 11 kV substation out to PME gear. This is the portion I usually think of as the backbone.

We have some feeders limited to about 200A at 12 kV, and a typical commercial building is 50A. Since only a few buildings fit on each baby feeder, adding just one large building can require either an entirely new feeder, or moving several loads to different feeders to keep them all feeders below thermal limits.

Interesting thoughts about removing field fuses and changing from substation breakers to fuses. If the system is entirely underground, the fast restoration ability of breakers would be used less often than a system with mixed overhead/underground. Since fuses have to be replaced after a fault, one would have to examine the impact on restoration times for having to replace substation fuses after every fault. In addition to the crew that isolates/repairs a fault, you would also need an additional crew at the substation replacing the fuses in order to provide fast restoration. There seems to be lots of buzz about flisr, and add moving from breakers to fuses seems like the opposite direction.

 

[cuky2000]

Mbrooke,

All my sympathize is with your insistence to see more UG projects and I wish to be wrong in my early assessment of conversion OH to UG. Unfortunately, the current financial reality to approve capital cost does not favor our desire to see more undergrounding projects.

I strongly suggest taking a little pause of the technical subject and search how utilities operate went investing large capitals and to whom they justify the investment not only with regulatory State/Federal Agencies such as the Board of Public Utilities(BPU)/PUC /FERC/NERC etc regarding Cost-Benefit and Reliability Analysis but also how utilities presenting themself to the financial community (Banks, Moody, Standard and Poor's) regarding potential concerns to be placed on credit downgraded and their share value credit ratings. Utility engineers are usually off the bonus program almost exclusively reserved for CEO, CFO & upper management.

I have been working that last few years in a multi-billion dollar program to upgrade utility electrical system primarily on the technical side. Our experience indicates how difficult will be to justify an underground project if there is an OH cost-effective option.

This issue is more dramatic went the project is Distribution than transmission since the return on the investment (ROI)rules for distribution projects are less attractive than the transmission project. That's why we see less "D" investment than "T" money.

That's why I believe that [highlight #FCE94F]"Conversion of OH to underground will be slow and justifiable on a case-by-case basis only if there is not a suitable overhead option".[/highlight]

 

[Mbrooke]

I don't quite understand the picture versus your comments. There seems to be 500 kcmil AL feeding from the 11 kV substation out to PME gear. This is the portion I usually think of as the backbone.

Correct, in a typical system there is / would be a backbone.

We have some feeders limited to about 200A at 12 kV, and a typical commercial building is 50A. Since only a few buildings fit on each baby feeder, adding just one large building can require either an entirely new feeder, or moving several loads to different feeders to keep them all feeders below thermal limits.

Correct, but in existing installations that would be planned in advance.

Interesting thoughts about removing field fuses and changing from substation breakers to fuses. If the system is entirely underground, the fast restoration ability of breakers would be used less often than a system with mixed overhead/underground. Since fuses have to be replaced after a fault, one would have to examine the impact on restoration times for having to replace substation fuses after every fault. In addition to the crew that isolates/repairs a fault, you would also need an additional crew at the substation replacing the fuses in order to provide fast restoration. There seems to be lots of buzz about flisr, and add moving from breakers to fuses seems like the opposite direction.

The way I see it is cost. Fuses are cheaper as whole, especially when you have an intermediate substation.

I am torn between this approach and just running 34.5kv to everything. The issue is that 34.5kv has far more reactance.

 

[Mbrooke]

@Cuky: I agree with you, I do my friend

However, with storms bringing down overhead lines more and more often en mass I think the gap between overhead and underground will grow closer.

Also, I want to find a way to lower the cost of underground distribution. There has to be a way. Even if it means running 500MCM underground and taping lateral #2 unfused spurs off it. Lets say I'm a bit desperate

 

[waross]

Horizontal directional drilling is probably a lot cheaper than excavating and back filling.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

Noted- had not considered that.