When a power pole falls down

[John Williamson]

And look how long *that* lasts in the sunshine. ;-)

[Fredxx]

Given that loading of carbon black increases the conductivity of plastics, are you really sure?

[Martin Brown]

Provided that you don't increase the amount of carbon black to the point where networks of carbon particles form then with each particle neatly coated in plastic it merely decreases the overall voltage rating, but you don't need much plastic insulation to stop 240v ac.

Eventually it does deteriorate with age and hang off in strips - ours did that shortly before it was replaced. There would be some arcing as sparking as wet pieces from different phases moved about in the wind.

It tended to be rather hard on filament light bulbs. We now have a robust new generation three phase cable with a steel core which has demonstrably survived having a tree fall on it (bending all the poles).

[Martin Brown]

But they can be used so that the bulk of the plastic is protected from the effects of sunlight. Many sunblocks now use TiO2 nanoparticles. It scatters the light away from the target and you can get a dense enough layer of pigment to stop almost all the light. Carbon black is cheaper but only slightly more effective at protecting plastics.

But TiO2 would scatter it away in a similar depth, although I expect it would cost more which is probably the reason they don't bother.

EHT lines are bare metal. It is only low domestic voltages on poles where they put insulation on the wires.

[F Murtz]

High voltage, no insulation, low voltage usually insulated. fly kites with wire?

[charles]

Low voltage is defined as anywhere between 50v and 1000v. the standard overhead 240/415v cabling is not insulated.

[Martin Brown]

It is in the UK. Or at least it was when installed new. I would not rely on it being fully insulated after a few decades in service. There are strips of the insulation hanging down on our rural lines. They arc and spark nicely in wet and windy weather. Ours used to be like that before it got so bad that they had no choice but to replace it.

A rough heuristic is that low voltage

[tony sayer]

Well as said the other day we do get involved in some serious aerial rigging projects on rather high sites, and over the years I've not seen black tie wraps fail clear ones yes in a very short time space and over a long time Black self welding tape and PVC tape but thats over say 10's of years!...

[tony sayer]

Even the Pikeys have now learnt not to;!...

[Gefreiter Krueger]

Where I live now it's all underground once it's low voltage. But where I used to live (with an old pole mounted transformer), I could see bare wires coming from it and going along the street. The only insulated one was to my neighbours roof (he had a very old house built before the electricity was put in). That wire ended up burning his roof down, but I've told that in here before.

Shouldn't the automatic restart wait a long while? In fact why do they restart without human intervention at all?

[charles]

probably because a great many (most?) short circuits are caused by a momentary event.

[Gefreiter Krueger]

You mean a tree falling on them or something?

[Martin Brown]

Most failures are transient in nature and the autorestart will have two or three tries separated by increasing wait times before giving up and alerting a network operator (or just giving up and waiting for consumers to complain that the electrics gone off at dinner time again!)

I have never seen domestic mains on poles without insulation in the UK but in practice the older cables it is hanging off and pretty dodgy.

[Gefreiter Krueger]

These are the wires opposite where I used to live. I'm 95% sure they're not insulated.

[Dave Liquorice]

automatic

Autorecloser, essentially a glorified RCBO with automatic reset. The one feeding us reconnects about a second after tripping be that trip overload, earth short, lighting... If it trips more than 3 times in a minute or two it will lock out and need to be manually reset. It also "phones home" when in lockout, as when I call the DNO to report the outage within minutes of the loss their system already knows even if they don't.

In the rally car context the power will be reapplied twice before it locks out. The normal reason for a trip is a bit of tree getting too close, the errant bit of tree gets blown apart, so the power can be safely restored. Saves calling out an engineer at 0300 on a wet and windy night to drive an hour in just to push a lever and drive home. Also means us customers are not off supply waiting for the engineer.

[Gefreiter Krueger]

Is that why we get way less powercuts than we did 30 years ago?

[Tim+]

Tim

[docholliday93]

What I have commonly seen is a single uninsulated conductor plus three insu lated ones for the phases. The last time I saw one (relatively) close up th e insulation appeared to be braided, like the rubber insulated and cotton b raided wires that were used before PVC took over.

As for the higher voltages, just about all the 11kV lines I've seen look as described above, with pole mounted transformers feeding consumers at 240/4

40V. There are a lot of 33kV lines that look similar, with longer insulator s, but I've never seen one with a pole mounted transformer. You also get tw in poles and occasional small pylons with two 33kV circuits on.

[Tim+]

You can lead a horse (or goat) to water but....

Tim

[Vir Campestris]

Well,since it's beyond you - snow crystals are ice. Ice is transparent.

Snow is not white because it reflects light at the surface; it penetrates and is scattered by the crystals.

You'll also find it isn't opaque.

Andy