Entergy New Orleans Transmission Tower Collapse and Resulting Blackout 6

[Mbrooke]

A major transmission tower structure appears to have collapsed into the Mississippi river blacking out all of New Orleans/Orleans Parish:

https://imgur.com/mLEWQDZ

Reports indicate this to have been a vital power path-

https://kpel965.com/major-entergy-transmission-tower-collapses-into-river/

https://www.wafb.com/2021/08/30/no-power-orleans-parish-due-catastrophic-damage/

A statement from Entergy says they lost 8 transmission lines which resulted in an energy imbalance causing local generation to trip off line:

https://www.entergynewsroom.com/sto...334907&utm_campaign=power_outages/restoration

Any more info welcome, as well as thoughts on what may have gone wrong and how to prevent this in the future.

As of right now I scouring the net for any more updates or information.

Edit: I am now hearing that possibly all generating stations on South East Louisiana have come off line. No power generation in that entire portion of the state.

 

[itsmoked]

Since this is an insanely weird tower this is going to be painful to replace.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Mbrooke]

I'm with you on that.


News reports saying that a hospital in thibodaux lost the generator supplying its ICU where patients were manually ventilated by hand while being transported to another part of the Hospital:

https://www.nola.com/news/hurricane/article_5f268aaa-0912-11ec-a8fb-d3a108e9db9f.html

 

[dpc]

There are eight major transmission sources for NOLA. All are out. This tower was part of one of them. Based on the height, perhaps a river crossing. There are design criteria for wind loading. Without knowing the actual wind at the tower, it's hard to do much analysis via sketchy reporting on the Internet. Even if adequately designed, lattice towers do require periodic inspection and maintenance. It's not unheard of for farmers to "borrow" some bits and pieces from the tower from time to time.

 

[LionelHutz]

That is 1 of 8 transmission lines, or do they consider this transmission tower to be carrying more than 1 transmission line?

If it's 1 of 8, then does anyone know how badly damaged the other 7 are? I'm thinking not because there hasn't been enough time to asses damage yet.

 

[dArsonval]

Very large tower indeed. Looks like it has two circuits on it.

 

[dpc]

It does appear to be double-circuit. That's reasonable for a long span structure like this. There may be other structure failures on the remaining lines, along with downed lines. This one is just the one getting the most media attention. The utility will be trying to figure out the fastest method of getting the least-damaged line back in service. Biggest issue for NOLA is keeping the rainwater pumps going. Their dedicated local power generation seems to be holding its own and I haven't heard of any levee failures in the immediate area. Fingers crossed.

 

[Mbrooke]

@DPC: Are there more in total? Going by some older drawing I'm docs I'm getting 9, 11 in a newer one. (Ignore the green arrows, red dashes would be the lines going into New Orleans itself)

 

[3DDave]

It makes me wonder about the advantage of building a second tower to move the wires to as a backup vs grossly overbuilding a single tower, but still running into unforeseen circumstance when the tower is so critical.

The left photo on Imgur looked like a lower segment buckled, but that might be from fastener failure, overload above the design expectation from the attached lines, some damage done in construction that left a weak spot, or loss of a footing; maybe some other factor.

I would expect an unloaded parallel tower to remain standing with no lines attached and no external loads. But is there the financial incentive and political will to have a back-up tower?

 

[dpc]

MBrooke,

No idea. The information I saw indicated 8 major incoming lines. Probably not all sources are equal. As usual, there are a lot of instant experts after the fact. The most tiresome are the people demanding that all of electrical power circuits be underground. Like any other design process, it's a series of compromises and money is always a factor.

To me a more interesting question is whether or not these systems would be designed more robustly by a publicly-owned utility as opposed to an investor-owned utility.

Dave

 

[dpc]

One more thing - even if all of the incoming transmission circuit are restored, there will still be probably hundreds of thousands without power due to the damaged distribution circuits, substations, even service drops.

 

[Eeyore11]

The fallen structure did carry two sets of phase conductors. However, it appears that the double circuit configuration was only for the river crossing, perhaps to reduce sag and maintain clearance for large ship traffic. Electrically, both are part of a single 230 kV circuit (Avondale-Harahan). You can see this if you follow the spans leading up to the structure on the opposite bank of the river (along the aptly named Powerline Drive).

Hopefully other sources into the city can be repaired more quickly than this river crossing.

 

[itsmoked]

With a tower that large and the distance of the span covered by the resulting catenary the wind loading could be enormous and wildly varying with extreme winds in different directions on the tower and the catenry at the same time. Wouldn't it make more sense to bury this thing? Toss in eye-sore (for some) and the aviation hazard.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

230 kV cable is ungodly expensive to install and will fail eventually. That said, going under just the river might have been worthy of consideration, but how many more structures are down? I think everyone is too focused on this one structure.

I don't know what wind load this line and tower were designed for, but hurricanes often spawn tornadoes and it almost certainly wasn't designed for a tornado.

 

[3DDave]

https://www.youtube.com/watch?v=3VhSxUPdgyU

Entergy Louisiana Upgrades West Bank Transmission System
Aug 21, 2019

https://twitter.com/brianemfinger/status/1432316271861841924

 

[dik]

Interesting that they were designed for a maximum 150mph winds... and with climate change, this wind speed could be a thing of the past...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Mbrooke]

@DPC: Agree, though I can understand where the under grounding folks are coming from. I mean if this becomes more common to the point people are paying for whole home standby generators, wouldn't that cost make more sense in hardening? I don't know, just a thought.


@Eeyore11: Thank you for the info! Do have, or can you post a diagram of the Amite South or New Orleans system?

 

[dpc]

I think we'll see more UG at distribution voltages, no question. Transmission line construction is mostly being driven by wind and solar these days and based on experience, they aren't going for UG transmission unless forced to.

For people who don't have much knowledge of electric power distribution, I can understand why they think everything should be UG. I think they are imagining a cost of maybe 150% over overhead. But in reality, even at 15 kV, UG will cost 5X to 8X OH for a typical distribution circuit. It's just vastly more expensive.

 

[Eeyore11]

@Eeyore11: Thank you for the info! Do have, or can you post a diagram of the Amite South or New Orleans system?

Sorry, I am not familiar with this system and such information wouldn't be mine to post.

The information in my previous post can be determined from aerial/ground level images on Bing or Google Maps, and substation names from EIA map layers.

https://maps.app.goo.gl/4FQkDQjhs5S1yhk47

https://www.eia.gov/state/maps.php

 

[bacon4life]

The wind loading of the conductor on very tall towers may be a small portion of the wind loading on the tower itself. In the case of one set of very tall lattice towers near me, wind on the conductor only contributed 30% to the total wind loading. Also the span covers a large geographic area, so it is less likely that the entire span would experience a gust at the same instant.