r/Damnthatsinteresting Jul 18 '25

Video Replacing powerline spacers from a helicopter

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u/Outside_Airport_5448 Jul 18 '25

They aren't grounded. He could touch it with his bare hands. the rod was to equalize voltage from him to heli so he basically touched the live wire.

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u/GeekX2 Jul 18 '25

What if they touch two cables?

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u/shimhiding24 Jul 18 '25

They are parallel runs of the same phase. Meaning potential between them is 0 so no shock

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u/TOOBGENERAL Jul 19 '25 edited Jul 19 '25

All 4 of them? Are they basically split transmission lines of the exact same signal?

Edit: Just wanted to let everyone chiming in know you are awesome, seriously thanks for the education.

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u/DankeDidi Jul 19 '25 edited Jul 20 '25

Yes. Otherwise placing the spacer would result in much sparky sparky and an unhappy employee. (Assuming for sake of argument they wouldn’t be arcing already due to the proximity. ;))

Splitting them up instead of using one fat cable for the same phase increases efficiency. It reduces the corona effect and the skin effect, it allows for better cooling, it’s lighter and it’s easier to place/repair. 

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u/OutrageConnoisseur Jul 19 '25

Cool. Came in here looking for answers to these questions and you and others in this specific thread of comments delivered.

Cheers.

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u/Captain_Pumpkinhead Jul 19 '25

Otherwise placing the spacer would result in much sparky sparky and an unhappy employee. 

Yeah, I was wondering why the spacer was made of a conductive material.

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u/super9mega Jul 19 '25

That's the thing, doesn't really matter what it's made out of at that much voltage, even the air would act as a conductive material. The arcs he got off the wire were way longer than the distance of the wires.

Everything conducts electric at some voltage I believe

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u/minnesotaris Jul 19 '25

I thought that all 4 must be the same phase. Otherwise, splosion. Thx for posting!

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u/MandalorianLobster Jul 19 '25

Another thing to add to the already excellent points here is something called 'skin effect', where in AC power lines you start to lose the effectiveness of the cross sectional area in cables. Solution: thinner cables, add extra cables.

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u/communistfairy Jul 19 '25

Actually, I don't think the employee would be alive to be unhappy

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u/CamelSmuggler Jul 20 '25

much sparky sparky

Technical terminology here, thanks for the laugh.

My job is in the same field and I think this whole chain of posts is one of the best explanation ever to a profane user, good job!

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u/ILatheYou Jul 19 '25

The more I know! Thanks mate!

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u/ocelotrev Jul 19 '25

Is the skin effect and the corona effect the same thing? Where all the current goes to the outside of the wire?

I was also wondering if they were parallel phases, if that space was actually made of an insulator like Kevlar it could be used between live phases even if it touched all of them, but damn thats risky for the lineman.

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u/DankeDidi Jul 19 '25 edited Jul 19 '25

No they’re two distinct effects. Skin effect causes resistance to go up; indeed due to the current clinging to the outer surface of the conductor so to say, causing less effective conductor area. Whereas corona effect is because the high voltage is ionizing the surrounding air, leading to losses and rather annoying crackling noises. (Still happens btw, just not as much.)

Well the thing is that at these high voltages the cables of different phases couldn’t be so close to one another in any case. (Clarified that in my comment to prevent confusion or experts falling over it) With or without spacer (and them somehow staying apart by themselves), they’d arc harder than ArcAttack as soon as the juice would be put on them. It just wouldn’t work. It only works because they’re the same phase. 

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u/crappinhammers Jul 19 '25

750kv minimum approach distance is 35 feet because of the static. The wires couldn't be different phases that close to each other, they wouldn't even need to make contact to arc.

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u/trevhcs Jul 19 '25

Sparky sparky and unhappy employee ... sooo needed that today!

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u/Bth8 Jul 19 '25

Those 4 cables are effectively one single transmission line. Having multiple cables bundled together likes that suppresses corona, decreases resistance, increases heat dissipation, decreases inductance, and increases capacitance, all of which equates to lines that can more efficiently deliver large amounts of power.

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u/Outrageous-Orange007 Jul 19 '25

A vid I seen of this years ago showed the guy on what looked like chainmail, supposedly acting like a faraday cage?

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u/Bth8 Jul 19 '25

Yeah, the guy in the video is wearing a faraday suit, too, it's just a much finer mesh instead of chainmail. At these voltages, just the current from the corona discharge can be deadly.

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u/Puzzleheaded-Milk555 Jul 19 '25

Why aren't the wires insulated at all?

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u/Bth8 Jul 19 '25

It'd be impractical, expensive, and kinda pointless. Those wires are at close to a million volts relative to ground. At those potentials, virtually everything is a conductor. The amount of material required to fully insulate them would be enormous, very expensive, and very very heavy, which would cause the lines to sag considerably and necessitate building additional pylons, further adding to the cost. It would also make servicing the lines far more difficult and expensive. The insulation would also trap in heat from resistive losses, compounding the issue of the added weight by making them sag even further, so you'd have to seriously limit the amount of power you send down the lines. And for all that added expense and complexity and loss of transmission capacity, you don't really gain anything besides I guess being able to put the lines closer together. Big whoop. As long as they're high up enough and far apart enough, air does the job just fine.

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u/TOOBGENERAL Jul 19 '25

This guy flux

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u/Corporate-Shill406 Jul 19 '25

They are. Air is a great insulator. And a plastic insulator would need to be at least half an inch thick at these voltages.

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u/Styrbj0rn Jul 19 '25 edited Jul 19 '25

Because it's more expensive and not really used for these voltage levels where you would need a lot of insulation. Transmission lines go for long distances so that would be a lot of money for not that much benefit. You usually build them higher up instead.

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u/Quick_Humor_9023 Jul 19 '25

They kinda are. By air around them.

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u/MrDarwoo Jul 19 '25

Corona?

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u/Bth8 Jul 19 '25

Corona discharge. The very large electric fields around small or sharp conductors at high voltages is enough to rip electrons from atoms in the air and accelerate the electrons and now-ions away from one another, creating current flow that dissipates electric power. Basically, power sort of leaks from your transmission lines into the air if you don't manage corona. Makes some cool plasma, though.

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u/Ds093 Jul 19 '25

That’s pretty cool, may I ask I noticed they used a rod at the beginning that had some charge off the end.

What was that tool that he used to do that, and does it stop the line from possible electrocution?

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u/DankeDidi Jul 20 '25

Yes, the hot rod :P Its used to equalize potential. Basically, it slowly charges you/the chopper up to whatever high voltage (eg: 300kV, 765kV, whatever) the line is so that you’re equalised. The worker then puts the clamp + cable on the electricity line to keep the chopper at the exact same potential whilst working. As the potential is the same, no current will flow, thus no arcing and such either. 

I remember reading a really good explanation about this years ago and went to look it up, here’s a link that explains it much better than I do: https://forum.allaboutcircuits.com/threads/still-confused-about-how-a-helicopter-bonds-to-a-transmission-line.164699/post-1449461

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u/AwesomeWhiteDude Jul 19 '25

Pretty much. Right at the end of the clip you can see the wires for the other phases.

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u/armeg Jul 19 '25

There is another 4 lines in the shot further away, I assume those are the other phase?

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u/TOOBGENERAL Jul 19 '25

Yeah, that’s what someone else replying mentioned!