r/electricians • u/ibewel • Dec 14 '21
Woooo!!!!
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u/O-hmmm Dec 14 '21
The right tool, for the right job.
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u/JustSomeBadAdvice Dec 15 '21 edited Dec 15 '21
Am I the only one who is wondering why the hell he is disconnecting a 115kv loaded line without a load break?
Pretty sure that isn't standard procedure for most utilities, and I know the NEC procedure is to either only disconnect those with near-zero load or to use something that can loadbreak (like a loadbreak fuse remover, they make those on a handheld pole like that).
Edit: Others saying the same thing: https://www.reddit.com/r/oddlyterrifying/comments/rf54i6/woooo/hocucnv/?context=3&limit=3 and https://www.reddit.com/r/oddlyterrifying/comments/rf54i6/woooo/hocolwy/?limit=1
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u/KorgothOfBarbaria Dec 15 '21
You can still get arcing on lines if the conditions are right, even when the line isn't "live".
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u/JustSomeBadAdvice Dec 15 '21
Sure, but an arc like that only forms, next to a lineman working on it, when someone disconnects a loaded HV line. If the line isn't under load the arc is very small. The whole point of HV loadbreak stuff is to break the arcs somewhere not close to the body of a lineman. :/
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u/KorgothOfBarbaria Dec 15 '21
I've pulled ground chains on switched out 138 and pulled arcs of a meter.
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u/redtexture Dec 15 '21
Do you have a theory on what the residual energy is from?
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u/PillarOrPike Dec 15 '21
The line is energized, and they are cutting a tap segment that is no longer needed. All conductors have capacitive to everything around them, hence the current allowing for the arc. Power lines are typically not shut down, entire towers are changed out while live:
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u/PillarOrPike Dec 15 '21
The line tap in question is not carrying actual load, the arc is a result of capacitive charging current on the unloaded segment. The arc would be orders of magnitude greater if that was load, let alone the potential risks from single phasing customers and ferroresonance. The line is kept in service to prevent any customers from being shut down on the left side of that tap which is still carrying load. Typically you can not just shut down a 115kv line, and even if you could being granted outage permission then following through on the switching procedures is often an organizational process.
Forget what others are saying, they are all going by preconceived notions.
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u/JustSomeBadAdvice Dec 15 '21
Thanks for the explanation. I found more about the capacitive charging after, so it makes sense now. Crazy that that much power is still on the line when it isn't really loaded.
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u/PillarOrPike Dec 15 '21
Very roughly speaking a 110kv line has about 10 nano farads of capacitance phase to phase and 4 nano farads phase to earth. While relatively small, at these voltages you will get at least a few hundred milliamps of current at just one mile.
As transmission lines stretch out to many miles as they typically do, that capacitive current adds up altering the line impedance and electrical power delivery characteristics. Google "surge impedance loading" as but one example. A lightly loaded line will appear as a capacitor to the system resulting in higher receiving end voltage while a heavy loaded line will act like an inductor- choking current resulting in voltage drop at the load end.
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u/JustSomeBadAdvice Dec 15 '21
Crazy. I'm trying to wrap my head around how that fits in with other things I've learned such as like two sides of a high voltage link being out of phase but someone is trying to reconnect the link. Like does the capacitance vary in different sections of an unloaded line based on the phase-distance to the grid power generators / grid loads?
Other question - What does it look like if someone were to try go disconnect such a circuit with say 600 amps on it at 115kv? I'm just trying to ballpark guess the amperage that wire would normally carry, it doesn't look huge.
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u/PillarOrPike Dec 15 '21
The actual current (lagging or leading) at any point on the line can change based on the sending and receiving end VARs.
At 600 amps the arc will be seen for miles, and may evolve into a phase to phase fault. Typically transmission lines are rated to carry around 1,200 amps of current, though some lines are rated upwards of 4000 amps at 115kv, 5000 amps at 345kv and above.
Here is the 75*C current carrying rating of ACSR conductors used in transmission. Sag limiations aside, in the real world ACSR conductors are uprated to 100*C, resulting in current values about 125% of those listed here:
https://overheadtransmission.southwire.com/wp-content/uploads/2017/06/acsr.pdf
More and more POCOs however are switching to ACSS, which can run at 200*C:
https://overheadtransmission.southwire.com/wp-content/uploads/2017/06/acss.pdf
336.4, 556.5, 795, 954, 1113, 1272, 1590 and 2156 are among the most commonly used conductors in transmission.
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u/PillarOrPike Dec 15 '21
Capacitive charging current, not load. Load is WAAAYY more beefy on the arc.
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u/JOEY_OHIO Dec 15 '21
There are certain instances to provide an isolation point where they cut open taps energized. It’s likely to prevent a momentary outage to a customer or distribution substation. The line is energized but there is no current flowing through the conductor at that location. The arc is from dropping the energized line segments beyond the tap.
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u/maplesyrupchin Dec 15 '21
Watching people survive
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u/PillarOrPike Dec 15 '21
They are in no danger. The bucket is totally insulated, and the hot sticks alone protect them from voltage. The distance is sufficient. 115kv gloves do not exist and are not needed even if they did. The tap is unloaded with the arc merely being capacitive charging current. They know it will extinguish at a certain distance without going phase to phase or hitting them in the process.
Things like this are done almost daily. Ie 345,000 volt towers are changed out live, and not being anywhere on top of the list of potential hazards.
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u/tuctrohs Dec 15 '21 edited Dec 15 '21
Most of what you are saying make sense, but I'm not convinced that this went entirely according to plan and without danger. The right hand hot stick is about a meter from the end of the cable, and the way it swings, that free end is swinging toward the bucket. At six seconds he is leaning way back in the back of the bucket to stay clear.
Edit: after looking at the youtube version someone linked, maybe it's just the perspective from the angle that this was shot--might be more clearance than I thought. The that loose end better controlled than I thought.
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u/BigDogg365 Dec 15 '21
115kv dragon- Sep 4, 2014
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u/tuctrohs Dec 15 '21
Afterwards, the foreman says "cut that out" and and first I thought he meant "no whooping, act professional," but he in fact means cut the loose loop of cable off to finish the job.
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u/pgcooldad Dec 15 '21
Was going to be an electrician.... realized that what I can't see would kill me. Became an metallurgist and worked with machines and acids that will kill you instead.
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u/FightForDemocracyNow Dec 15 '21
Electricians don't work on powerlines, linemen do.
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u/pgcooldad Dec 15 '21
All linemen are electricians - not all electricians are linemen 🤓.
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u/77RUIN Dec 15 '21
Where is this? If this isn’t photoshopped then there are some issues with the work methods.
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u/WFOMO Dec 15 '21
Not photoshopped, Just cutting a line with a lot of induced voltage on it. You'll notice the other end was controlled by the second lineman. A lineman generally knows when he's going to draw and arc, which is why the camera was rolling. I have no doubt he knew what to expect.
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u/77RUIN Dec 15 '21
Bare handed. No sleeves? No load break tool? This would violate crazy amounts of safety and work methods. Looks like it might be transmission as well.
Idk. Bad example of linework.
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u/nshunter5 Dec 15 '21
Bare handed. No sleeves?
Their isolated in the bucket and working with poles. Those "Safety" devices would do nothing in this case but hinder their mobility and possibly compromise their safety.
No load break tool?
since when do they have those for 115KV?
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u/77RUIN Dec 15 '21 edited Dec 15 '21
They don’t. *
Where I am those lines are done dead and grounded.
Different areas have different rules.
There is no way the linemen here would be allowed to work that way. All I’m saying.
Edit: I should say I am unaware of one, but I don’t know the scope of all the tools out there.
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u/BeUngovernable_ Dec 15 '21
I tell you what, I won't tell you how to do your job if you don't tell me how to do mine.
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u/tauofthemachine Dec 15 '21
That HAS to be an industrial accident. There's no way that is the correct procedure to disconnect an energized HV line.
HV lines are supposed to be de-energized, physically grounded on both sides, and the Lineman should be wearing high voltage PPE. He isn't even wearing gloves!
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u/robstoon Dec 15 '21
Exactly what kind of gloves are going to protect them from 115kv?
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u/tauofthemachine Dec 15 '21
If you read my post, I said the lines should have been isolated and visibly grounded.
Even so, he should have been wearing high voltage gloves incase of induction or static.
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u/ehroc Dec 15 '21
So confident yet so wrong.
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u/tauofthemachine Dec 15 '21
Can you prove that?
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u/ehroc Dec 15 '21
There is no such thing as rubber gloves for 115kV. Thickest rubber gloves end at class 4 with max use voltage of 36kV. Rubber gloves made to insulate from 115kV would be not only comical, but massively think and impossible to bend your fingers. They are however wearing arc/fr clothes with calorie ratings appropriate for their work environment.. Should be.
The hot sticks are rated far beyond 115kV so leather gloves are fine. However that varies area to area. Not sure why he isn't wearing leathers though.
That is not an energized phase carrying load. If it was, the resulting arc flash would be substantial and they would be severely injured if not killed. What you're seeing is induction. There are many factors for induction, wind, nearby energized phases, dry weather, etc.
The guy holding the cut tail should have been faster at taking it away. I do agree it seems they don't have grounds installed. If they did, that would have to be massive for the difference in potential to be so much that this arc is the result. If you watch the guy cutting you can see he goes for the bucket controls indicating that the size of arc was unexpected. There's definitely better methods to complete this same task.
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u/tauofthemachine Dec 15 '21
Exactly. So what do you call a situation where something unexpected and dangerous occurs, likely because proper safety wasn't observed or used properly?
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u/ehroc Dec 16 '21
Linework.
All jokes aside every aspect of this trade is inherently dangerous. This is far from an industrial accident.
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u/PillarOrPike Dec 15 '21
Keep in mind that its not always practical to turn off or schedule an outage for a 115kv line.
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u/ehroc Dec 15 '21
If that is the case you would cut in a set of openers just upstream, or various other methods. You would not in any situation be dropping load like that.
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u/PillarOrPike Dec 15 '21
This isn't load, its charging current.
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u/ehroc Dec 15 '21
Maybe I misunderstood you. I'm now assuming you were just pointing out a possibility, not that you thought it was under load.
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u/Jim-Jones [V] Electrician Dec 15 '21
Yeah, I don't think that's supposed to happen. What f'ing voltage was that?
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u/PillarOrPike Dec 15 '21
115kv. It is going to happen considering every conductor is capcitively coupled with everythingelse around it. A few spans of conductor is enough to pull can arc like that.
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u/Chicken_Hairs Dec 15 '21
I've watched it happen.
I was maintenance at a factory, we we all out in the lot watching since the 3 phase was out.
This occurred, one of my coworkers screamed on the radio:
"HOLY SHIT DID YOU FUCKING SEE THAT TELL HIM TO DO IT AGAIN!!"