Are overhead cables insulated

[murphy4869]

Just a quick question for the pros-

Are overhead power cables either HV from pylons or usual domestic overhead supplies insulated like for instance twin and earth cable in your house.

If not how come is it purley a case of the high current running through would destroy the insulation but surely under ground HV cables would have the same trouble? Just curious-Many thanks

 

[flameport]

Overhead wires to individual houses might be insulated. Some are not.

Virtually all others are not. This is because insulated cables cost significantly more and they would be much heavier (so more pylons/posts would be needed to support them).

 

[joinerjohn]

Cables on pylons such as you see all over the countryside are not insulated. The cables are multi strand aluminium. Underground cables need to be insulated for obvious reasons. Can't see your reasoning that high current would destroy the insulation. They are designed to handle the sort of current they carry.

 

[Spark123]

There is no need to insulate the overhead cables at high tension as air is a good insulator.
The purpose of transmission at high voltages is to reduce the current flowing in the conductors (and therefore I²R loss and volt drop) as the higher the voltage the lower the current required to give the same power output.

 

[jeepmadmike]

the only time i have heard of HV overheads being covered in any form of insultation is on those in corrosive environments but that has nothing to do with insulation its there to prevent damage to the conductors.

 

[maguire]

So what happens if a sky diver lands amonst them

 

[ColJack]

as long as he only touches one of the wires and not to earth then he's fine..

 

[maguire]

So here's a tale a mate heard, He's a keen hill walker and one day in a bothy on the nevis slope a old timer told him, one day on a descent the wind an rain were awfull with the rain almost horizontal, on the lower slopes he was traversing parallel with some pylons when a line of rooks were electrocuted with the current arcing from one line to the other, is this possible or is it an urban myth.
DM

 

[Chri5]

You might not have seen this ?

High Voltage Cable Inspection

http://www.youtube.com/watch?v=9tzga6qAaBA

 

[maguire]

Good greif that scary not my idea of a days work
DM

 

[Lectrician]

This is american, but quite good.

 

[jabuzzard]

They do similar work in the UK as well. Notice he was wearing a special metal suite that puts him inside a Faraday cage.

The thing is that accident/death rates are lower in live working than dead working for HV lines. Basically if you know it is live you take care and do everything by the book. If you think it is dead you can get sloppy, or perhaps it is not dead or perhaps someone turns it back on by mistake.

As a note to someone further up, while the bulk of overhead cables are indeed aluminum for weight purposes. They also have a high tensile steel core for strength.

 

[PrenticeBoyofDerry]

There is no need to insulate the overhead cables at high tension as air is a good insulator.
The purpose of transmission at high voltages is to reduce the current flowing in the conductors (and therefore I²R loss and volt drop) as the higher the voltage the lower the current required to give the same power output.

Also the lower the current, the smaller the cable size, saving on material costs.

 

[gman76]

as long as he only touches one of the wires and not to earth then he's fine..

Would he not suffer some sort of flashover with 450kV pylons?

Also (sorry to hijack) why do HV pylons chatter in the wind & rain?

Sorry, think that should be 400kV?

 

[wingcoax]

Used to test products of previous company at 128kv for transmission lines without problems