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#165583 - 06/30/07 08:24 PM Overhead LV lines - self-destructing!  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
This incident took place in Rhode, Co. Offaly Ireland.

http://www.youtube.com/watch?v=OHvnXH1_6Kk

Warning : There is some coarse language in the video as local residents watch in horror as their town's overhead power lines literally fry before their eyes.

These are 220/380V 3 phase installations, extremely old installation.



Worrying aspects:
1) How did this happen?
2) Why didn't the fuses/breakers trip - it seems that the system almost burned itself out rather than tripping.
3) Why were the wires sagging...

Question has to be asked, was that installation completely overloaded and over-fused?

Worrying!

That installation dates from the original rural electrification era. So, could be anytime from 1946 onwards.

It would be quite a short run of 3-phase cable just serving a little village. Typically, that system would be fed from a 10 or 20kV local distribution MV line.

Apparently one of the poles further along had been damaged, resulting in the extreme sagging of the overhead wires.
However, I'm only going on someone's blog for that info!

The entire LV run would quite likely have been very short, just a few poles, so it's quite possible that an end pole was damaged.

There is an on-going project (multi billion euro) to replace and upgrade much of the original electrical gear that is now well life-expired.

However, that incident would leave a lot of questions for the local Networks team to explain!!!





Last edited by djk; 06/30/07 08:27 PM.

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#165594 - 07/01/07 07:52 AM Re: Overhead LV lines - self-destructing! [Re: djk]  
RODALCO  Offline
Member
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
Amazing video !
Obviously not fused or oversized fuses.
These wires must be bare to create those fireworks.
Obviously one wire sagged too much and caused the arcing.
The spacing for vertical rack OH wiring is tight, so correct tension is important.


The product of rotation, excitation and flux produces electricty.

#165596 - 07/01/07 08:46 AM Re: Overhead LV lines - self-destructing! [Re: RODALCO]  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Yikes! An impressive fireworks display, but rather worrying.

Was there too much sagging on two separate spans? Most of the action is on one span, but we can see a fair bit of movement on the cables off to the right as well, and at one point the camera pans round and shows arcing on that span as well.

I'd wonder whether it was breezy and this started the problem, but the weather looks rather foggy, which doesn't seem to go with windy weather.


#165599 - 07/01/07 09:02 AM Re: Overhead LV lines - self-destructing! [Re: RODALCO]  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
Yup the wires from the 1940s/50s era used on those overhead distribution systems were uninsulated. They've generally been replaced by quadruplex when upgraded.

I suspect the system being stretched beyond capacity may have caused the sagging as the wires were running warm also, the very misty weather possibly doesn't help much either.

Those wires are normally very tight and wouldn't move about in a breeze at all. There's something very wrong with that set up. I suspect something's moved/slipped. They seem to be using spacers quite a bit in some areas too to keep them apart. However, in general they'll just come in and replace that with a run of very ugly quadruplex.

The system did trip after a while, but it took over 1 min.
Then again, if you search around youtube, you'll see quite a lot of footage of LV systems not tripping out for quite a while. Clearly the older systems simply weren't fused very well at all.

E.g. : http://www.youtube.com/watch?v=cTDjq6K-qM4



Last edited by djk; 07/01/07 09:07 AM.

#165817 - 07/06/07 04:01 AM Re: Overhead LV lines - self-destructing! [Re: djk]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,223
SI,New Zealand
I have to agree with your comments Ray,
it looks to be un-fused.
But remember back to Electricity 101 when you started your time, when excess current flows in a wire, the Electro-motive Force within that wire can make it move in strange ways.
This is another reason why we support large cables with clamps and saddles and the like.
I once happened to see a car swipe a pole here in town, the force was enough to make the 230/400V lines clash.(Old lines that had long since lost thier PVC coating)
I noticed that down the road, the lines rose toward the sky, two even busted out of thier (old) insulator bindings.
But this fault cleared pretty quickly, unlike Dave's example.



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