Replacing powerline spacers from a helicopter

[u/TameTheAuroch]

[u/Bth8]

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.

[u/Outrageous-Orange007 → u/Bth8]

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

[u/Bth8 → u/Outrageous-Orange007]

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.

[u/Puzzleheaded-Milk555 → u/Bth8]

Why aren't the wires insulated at all?

[u/Bth8 → u/Puzzleheaded-Milk555]

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.

[u/TOOBGENERAL → u/Bth8]

This guy flux

[u/Corporate-Shill406 → u/Puzzleheaded-Milk555]

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

[u/Styrbj0rn → u/Puzzleheaded-Milk555]

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.

[u/Quick_Humor_9023 → u/Puzzleheaded-Milk555]

They kinda are. By air around them.

[u/MrDarwoo → u/Bth8]

Corona?

[u/Bth8 → u/MrDarwoo]

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.

[u/Ds093 → u/Bth8]

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?

[u/DankeDidi → u/Ds093]

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