maggiekb at October 14th, 2013 13:27 — #1
prestonsturges at October 14th, 2013 13:34 — #2
At a local parade, a convertible with some local beauty pageant winners fired a couple big Mardi Gras style mylar streamers over our heads and onto some heavy electrical lines to the downtown area. It was like lightning right over our heads. Luckily the streamers were nowhere near the ground so it was only arcing between the wires. We turned to run, but it was all over in a flash (yes I wrote that).
mcme at October 14th, 2013 13:38 — #3
This is another example of using the Faraday cage and an excellent shot and narrated video that shows them crawling along the HV cables. They show this video in first year electrical to quiet astonishment. http://www.youtube.com/watch?v=9tzga6qAaBA
patrace at October 14th, 2013 13:54 — #4
@maggiekb The following is one of my favorite mini-docs ever, I think it deserves a place on your list.
retepslluerb at October 14th, 2013 13:55 — #5
On the East Coast of the US, electric demand is so high that utility companies can't take major transmission lines out of commission for maintenance and repair.
Doesn't sound like “high demand” too me, but more like “neglected infrastructure“. It's swell that you can do repairs on live wires, but if that is really needed (instead of being cheaper or more convenient), I shudder to think what wold happen during a large outage.
smurph at October 14th, 2013 14:14 — #6
Not sure that's specific to the East Coast - I've got pictures of the same thing being done at the end of my street here in Austin.
fallhammer at October 14th, 2013 14:56 — #7
My one and true fear, other than spiders crawling all over me is being electrocuted. I was really zapped once when I was teanager, and my flip-flop sandal caught onto an extension cord with a bare spot on it, I still have scar on the bottom of my foot. So I can't watch this video with out those sensations writhing up my back.
bzishi at October 14th, 2013 15:16 — #8
No, birds don't land on these lines. These lines are over 100 KV and the corona discharge would make enough noise to scare them away if it didn't zap them. And as far as insulators, they have found than birds will only peck on them up to a certain point before stopping because the electric field intensity eventually bothers the birds too much to continue. You have probably seen birds on low voltage lines that aren't strong enough to have a corona effect, but not ones over 100 KV, which are the ones that helicopters would inspect.
kmoser at October 14th, 2013 15:21 — #9
If the corona discharge is enough to kill them, wouldn't the area under the wires be littered with dead birds? Or do they sense the field before landing and shy away?
ravuya at October 14th, 2013 15:35 — #11
This also happens in Alberta; there are very few HV lines here (for many reasons) and a lot of them are relatively critical for feeding the US in addition to Canada, so there's a lot of this kind of stuff going on to maintain and clean them while live.
I met a few linemen who did this kind of thing; much braver than I am.
bzishi at October 14th, 2013 15:37 — #12
Here is one article on bird pecking at insulators: the authors of the article noted that when the electric field intensity gets really high the birds stop pecking at the insulators. It talks about how you want to design your system so the electric field is intense enough to irritate the birds, but not intense enough to destroy your insulator.
I also found a good photo. You can see the birds on the ground wires and in the tower latticework, but they stay off of the high voltage lines.
ryan_hoguet at October 14th, 2013 15:53 — #13
"We, in Some Strange Power's Employ, Move on a Rigorous Line" by Samuel R. Delany
mrmark at October 14th, 2013 16:42 — #14
Not a Faraday Cage. This is a demonstration of electric potential. Like the video says, as long as you don't close the circuit you can reach equilibrium with the HV lines.
mrmark at October 14th, 2013 16:43 — #15
And the helicopter pilots get to do one of the things all helicopter pilots are told to NEVER do, fly right next to power lines. Plus they have to hover with the slightest error.
It is also interesting to see how dust is removed from power lines. Out west large amounts of dust can accumulate on lines so they are washed using jets of deionized water from the ground. The deionized water won't conduct electricity.
Helicopters can also generate large static charges. A helicopter carrying say a long metal tower to a location could find a powerful electric spark jump between the tower and ground as it is lowered. Gas tankers will sometimes drag chains to prevent static charges from building.
prestonsturges at October 14th, 2013 17:46 — #16
There was an article in Scientific American about 100 years ago about the terrible death toll among birds caused by telegraph and electrical wires. Apparently they were just running into them and breaking their necks and wings because these obstacles had never existed before.
I can only guess that couple generations of selective pressure created new instincts, the way a sheep dog has the urge to herd.
leicester at October 14th, 2013 18:32 — #17
There's only three things I've ever been afraid of: electricity, heights, and women.... And I'm married, too.
teapot at October 14th, 2013 20:54 — #18
There is an awesome BBC series called "Richard Hammond's Invisible Worlds" which captures otherwise unseeable phenomena on special cameras. One of the episodes (The first of three, if I remember correctly) shows the guys who do this in the UK but using cameras that show the high voltage charges being conducted by their bodies and the chopper.
The stupid Beebs geo-blocks their stuff on Youtube, so here's a link to the torrent. BBC: unleash your stuff to the world or we will steal it.
tetracyclic at October 15th, 2013 14:56 — #19
I was reminded of this show as well. The footage from the cameras is fantastic, as you can see the corona discharge.
Here's a YouTube video showing just that part of the program.
clamb at October 15th, 2013 15:04 — #20
I wonder how much of this neglect is actually public aversion to building of new power lines. When high voltage distribution lines are put up around here there is always a public outcry against them. I don't think a proposal to erect redundant wires would survive public scrutiny.
technogeekagain at October 15th, 2013 15:24 — #21
Many years ago, I was told about a brainstorming exercise a group of linemen were asked to do in order to come up with a better way to keep ice from freezing on lines, increasing the weight and causing them to snap. The best procedure at that time involved having linemen climb up to shake the wires so they'd flex and the ice would break free -- very labor-intensive.
After a period of more serious conversation, one of the linemen bought out the story of how he'd once been chased up an electric pole by a bear. From there, the conversation went roughly:
Hey, train bears to climb up and shake the wires.
How are you going to keep them motivated?
Oh, that's easy -- put a bowl of honey at the top of each pole.
How would you keep those bowls filled? If you run a pipe for the honey, you now have to worry about it freezing.
OK, so we'll fill the bowls from a helicopter.
But the downdraft from the chopper will blow the bowls off the poles.
Hey, wait a moment, guys -- wouldn't the downdraft from a helicopter also shake the wires? Has anyone tried that?
Turned out that was, indeed, the new solution to the problem -- fly a helicopter down the length of the transmission line and the ice falls right off as it passes over. Saved the company a bundle and earned the team a bonus.
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