Downed power line on backyard swing set - Page 1
Forum section: electronics / general

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: June 20, 2016, 12:32:45 am
content: Keep watching, you'll see a bit of surprise in the middle:

author: uncle_bob
author_rank: Unknown
timestamp: June 20, 2016, 12:42:11 am
content: HiNow children ... *this* is what can happen to you fence if you don't make absolutely sure that your swing set is properly grounded. No soldered connections. No skippy ground wire. No wimp out when pounding in the ground rods (redundancy is good) ...Bob

author: Halcyon
author_rank: Unknown
timestamp: June 20, 2016, 01:24:48 am
content: It's almost therapeutic watching it.Although why wasn't the power cut automatically? We had a tree come down on power lines shorting out all three phases in a storm a few weeks ago and apart from periodic "test" pulses, there was no power on those lines.

author: uncle_bob
author_rank: Unknown
timestamp: June 20, 2016, 01:30:48 am
content: Quote from: Halcyon on June 20, 2016, 01:24:48 amHiOne would guess that the fuse on the line and the grounding of what it was hitting didn't quite make it into the "open the circuit category". Based on the comments in the background, it's not an automated grid system. Somebody has to come out with a big long pole if a manual disconnect it needed. Good old Chicago / Commonwealth Edison.... I wonder if they still give away free lightbulbs? I still have a few of theirs from 30 ...errr ... 40 ... years ago.Bob

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 20, 2016, 02:46:15 am
content: Looks like it was an arc fault below the rating of the breaker, not a dead short.

author: JoeN
author_rank: Frequent Contributor
timestamp: June 20, 2016, 04:27:51 am
content: What do you think that line voltage was? That feels like pretty high voltage for running through a neighborhood. Any idea?

author: Cubdriver
author_rank: Unknown
timestamp: June 20, 2016, 04:29:39 am
content: I think those neighborhood lines are generally in the 12-15kV range, but am not absolutely certain.-Pat

author: Brumby
author_rank: Unknown
timestamp: June 20, 2016, 05:02:19 am
content: Quote from: NiHaoMike on June 20, 2016, 02:46:15 amClearly.After the dramatic arc that livened the fence you can hear one of the firemen say "There - that might have did it." no doubt referring to the breaker having tripped - especially when another brief arc immediately afterwards caused him to add: "Nope".Seeing that fence arcing to the ground as it did was fascinating .... and sobering.

author: Richard Head
author_rank: Frequent Contributor
timestamp: June 20, 2016, 06:14:14 am
content: We had a tree come down on power lines shorting out all three phases in a storm a few weeks ago and apart from periodic "test" pulses, there was no power on those lines.Those test pulses you refer to are probably the auto re-closer trying to close the breaker again after a trip. Normally happens a couple of times before it realises that it has a permanent fault.In this case it looked like there was a serious amount of ground current flowing as can be seen by the steam coming out of the soil anywhere there is a grounded conductor. The fault current will flow from the live cable through the ground to the nearest utility ground point, probably at a pole mounted transformer. Touching anything metallic in the vicinity could be very dangerous, assuming you are grounded.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 08:18:15 am
content: This puts a new meaning to the term "Jacob's Ladder"Interesting to watch!

author: CJay
author_rank: Super Contributor
timestamp: June 20, 2016, 08:55:21 am
content: Quote from: uncle_bob on June 20, 2016, 01:30:48 amStill weird, the pole mounted breakers here trip out if they brush against tree branches or the wind gets up enough to make them arc against each other and require a man with a pole to close them.

author: Moshly
author_rank: Regular Contributor
timestamp: June 20, 2016, 09:27:50 am
content: ImpressiveBut if you are going to electri-fry the neighborhood, this is how its done ->Photonicinduction's Retirement Village

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: June 20, 2016, 09:42:57 am
content: ^ that's just insane

author: rsjsouza
author_rank: Super Contributor
timestamp: June 20, 2016, 11:58:50 am
content: Quote from: Moshly on June 20, 2016, 09:27:50 amWow... At four minutes, that is amazing. Probably the HV lines shorted the 110/220 ones.In the city where I live the electricity company recently put higher voltage (probably 69kV) in a residential area (street view), which probably pissed off a bunch of homeowners.

author: uncle_bob
author_rank: Unknown
timestamp: June 20, 2016, 01:16:03 pm
content: Quote from: rsjsouza on June 20, 2016, 11:58:50 amHiThat stuff is low voltage compared to what we have running through our neighborhood. Of course, there's a *lot* more separation between the lines. Not at all clear what they were doing with the cherry pickers before they hit the lines. I'm sure they maxed out what ever insurance they happened to have with that stunt.Bob

author: Ian.M
author_rank: Super Contributor
timestamp: June 20, 2016, 01:51:11 pm
content: QuoteFromhttp://www.bavfc.org/company_history.phpAlso:QuoteFrom:http://www.baltimoresun.com/ph-ag-25-years-0823-20130819-story.html

author: uncle_bob
author_rank: Unknown
timestamp: June 20, 2016, 02:05:23 pm
content: Quote from: Ian.M on June 20, 2016, 01:51:11 pmHiSo the cherry pickers were utility equipment. I would *hope* there was a major review of procedures after the event. If work was going on in the area, they should have been ready to cut power in a few seconds, not in minutes / hours. They may not have maxed out the insurance, but I'm sure the insurance rates went up the next year.Bob

author: Ian.M
author_rank: Super Contributor
timestamp: June 20, 2016, 02:25:42 pm
content: I would *guess* the utility was attempting to remove a damaged tree limb that was endangering the power line and it got away from them. As you say, if it was scheduled tree trimming, they should have had a plan to isolate the line quickly.

author: m100
author_rank: Regular Contributor
timestamp: June 20, 2016, 02:29:16 pm
content: High earth resistance, high fault impedance, incorrect protection settings, stuck breakerIf the circuit is fed from one end and there are no comms it can be difficult to distinguish between genuine load and a fault Just looking at volts and amps and their phase relationship from say five miles away can you tell in say 100ms if it is a resistance heater and a few motors or a phase conductor touching a swing frame and boiling a garden lawn?Safest place? Inside a vehicle heading rapidly awayIf on foot keep your legs close together. Hopping can also be usefulBut there was no exploding switchgear or burning transformer oil, or porcelain insulator shrapnel. Interesting in a domestic environment but quite tame on the grand scale of things:)Try thisThere was an even bigger one than that in the UK maybe 25 years ago.

author: Ian.M
author_rank: Super Contributor
timestamp: June 20, 2016, 02:42:03 pm
content: See post #6 here:http://www.electriciantalk.com/f2/hign-voltage-fire-49886/for an account of that transformer explosion.

author: uncle_bob
author_rank: Unknown
timestamp: June 20, 2016, 02:57:04 pm
content: Quote from: Ian.M on June 20, 2016, 02:42:03 pmHiThe information there on the root cause gets quickly back to a very basic point:The automated system failed so the operator could not know the problem existed and cut the power.Hmmm .... lets's see .... fire trucks on the scene. People running all over the place with cell phones. There is absolutely no way that information is not moving around. What you have is a setup that is now fully reliant on automatic cutouts and no longer really has the ability to do even a computer based manual intervention. Makes sense right up to the point the automatic sensors fail ...Yes, stuff happens. Plan for what to do *when* it happens.Bob

author: GEuser
author_rank: Frequent Contributor
timestamp: June 20, 2016, 03:06:35 pm
content: That HUMMING sound really creeps me out in the Op's VideoReally Really ReallyCreepsme out .

author: station240
author_rank: Unknown
timestamp: June 20, 2016, 03:24:53 pm
content: Another video, this time a crane truck makes contact with overheat wires.

author: m100
author_rank: Regular Contributor
timestamp: June 20, 2016, 03:38:36 pm
content: Quote from: Ian.M on June 20, 2016, 02:42:03 pmIn many countries there would be multiple separable and duplicated lines of defence in the protection schemes such that manual operator intervention would never be required. How they got it so wrong with that fault is mind boggling...but fun to watch...from the safety of a few thousand miles.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: June 20, 2016, 04:36:07 pm
content: It should be reasonable to assume the current returning via earth would have been enough to trip a breaker upstream, especially when it caught the fence with the lower contact resistance. But I guess the systems are/were pretty old, legacy stuff.

author: dmills
author_rank: Super Contributor
timestamp: June 21, 2016, 01:08:17 pm
content: On at least some of the US network they use the ground for a return path on single phase medium voltage lines!This makes a fault to earth less diagnostic then it would be for a network running three phase or even single phase with a neutral earthed only at the network substation.Regards, Dan.l

author: tooki
author_rank: Super Contributor
timestamp: June 21, 2016, 01:53:55 pm
content: Quote from: uncle_bob on June 20, 2016, 02:05:23 pmHeh, ages ago I dated a guy who lived in Bel Air.Anyway, here's someone's 3 part compilation of news coverage of that event:https://youtu.be/mvNA2kawKVEhttps://youtu.be/dRnwSmDWG0Ehttps://youtu.be/gGjRcXvs6M8Seems a tree cutting company hired by the electric company let a branch fall onto the line.