here's what it is supposed to look like. a transposition tower rotates the relative position of the three phase wires. this is done to balance the impedance of each of the wires so that one of them doesn't hog current.pic.twitter.com/srxgskSWWG
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here's what it is supposed to look like. a transposition tower rotates the relative position of the three phase wires. this is done to balance the impedance of each of the wires so that one of them doesn't hog current.pic.twitter.com/srxgskSWWG
here's the problem. the jumper conductor (the horizontal piece that brings a conductor from one side of the tower to the other) has fallen down. you can see the insulator dangling (circled.) but why did it fall?pic.twitter.com/3E2ghZi2jV
let's look at an insulator up close. they're actually quite large; they just appear small because you're seeing them from the ground. noticed the hook that holds it in place?pic.twitter.com/BOMY5RH5yl
and this is the C hook on the dangling insulator. looks like part of it broke off, doesn't it?pic.twitter.com/HnpVEWCKM4
zooming in even closer, you can see something odd about the way the C hook broke off. inspect it with the eye of a materials engineer. what do you see?pic.twitter.com/qBopsM4Ofd
penciled over in red are wear marks. this hook has been swinging back and forth for a very, very long time -- you can see rust stains (circled in black) the blue circle shows where the hook finally snapped. oh, and this is about an inch in diameter.pic.twitter.com/vtHUDKEdrF
here is a worn but unbroken C hook, glove for scale. that is a lot of metal to wear through!pic.twitter.com/d9jFQm0M1E
the C hook hangs from this hangar bracket, and you can see signs of wear on this side, too.pic.twitter.com/MaDaPeTxXI
so when the C hook broke and the hanger fell, the steel-reinforced aluminum conductor that carries 115,000V bounced and shorted out against the metal side of the tower, spraying chunks of white-hot aluminum across the ground underneath the tower.pic.twitter.com/0iEWxChFy5
the weather was extremely hot, dry, and windy, and this immediately started a fire.pic.twitter.com/ZSanR0lkQi
the fire spread rapidly, and about 2 hours later, at 8am on November 8th, 2018, entered the nearby town of Paradise, CA.pic.twitter.com/PD3LCMRt1Q
this was the Camp fire, the most destructive in California history, and it burned most of the city to the ground, including my grandparents house.pic.twitter.com/5rwh6QbRlf
(my grandfather had passed away a couple of years before, and my grandmother had moved to a facility scant *months* before the fire)
sadly, many others were not so lucky, and some were not able to escape the fire, including computing pioneer Bill Godbout (https://en.wikipedia.org/wiki/Bill_Godbout …)
i wanted to add a little more detail on the human cost of the fire but--i just can't do it. i read through the stories and i had to stop. these are people who knew my grandparents, went to church together, participated in civic life. it's too hard.
so let's get back to the engineering talk. remember that worn C hook? how long was it rubbing against the hangar bracket?pic.twitter.com/6gtcF8opOx
the answer is that we don't know. we think it is about 97 (!) years old, but we're not sure because PG&E (the electric company that owns the lines) didn't keep records about it.pic.twitter.com/OfstxfUIbH
after the fire, many of the pieces were taken to the FBI lab's metallurgical unit at Quantico, and they determined that the C hook was made of cast iron. not all the C hooks on these 100-year old towers were made of cast iron--many were made of steel. but again: no records.pic.twitter.com/8kY4zPWPUR
PG&E knew that this was a problem because at some point they bolted on L brackets and moved the C hooks onto the new brackets, probably concerned that the old bracket hole had mostly worn through. we don't know when they did this because they kept no records.pic.twitter.com/QF4FqbLdfw
and yes, PG&E is legally required to inspect these towers periodically. we don't know exactly when, because (you guessed it) no records from before the year 2000.
the investigating team interviewed troublemen (inspectors for PG&E) to find out exactly how they did the inspections. they were done mostly from helicopters. and despite having official procedures, here's what they did
is the tower still standing?
just to pile it on a little more, here's another tower nearby. at some point, the jumper conductor broke, but to fix it, they just pulled it tight and spliced it. think: someone looked at this, with the taught conductor and the insulator pulled up sideways, and said "good enough"pic.twitter.com/LukQDGaWui
there's even documented evidence that PG&E knew about the problem with the C hooks and hangers and yet did nothing.pic.twitter.com/iseQoJGGaz
i like this used car analogy. basically, they bought a used car and ran it without oil changes until the engine seized.pic.twitter.com/Mm0pVk16e8
sadly, this is not new behavior for PG&E. it's just like the San Bruno gas explosion.pic.twitter.com/uZ0gdhrwQ8
here's my previous thread on the San Bruno gas explosion.https://twitter.com/TubeTimeUS/status/1211454598575058944 …
on June 16 of this year, PG&E pled guilty to charges of unlawfully causing a fire and 84 counts of involuntary manslaughter. their penalty? a $4 million fine.
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