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Author Topic: Electrification - even of thin long lines  (Read 1117 times)
stuving
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« Reply #15 on: February 13, 2020, 05:32:38 pm »

With Atlantic gales and storms of the Ciara ilk, light-weight electrification on the Newquay branch might prove a bit flimsy. Although the line skirts the Cornish Alps, I'm not sure they provide quite the same shelter as the Swiss & Austrian ones.

Speak to Blackpool if you want advice on how to make it strong enough for gales on a coastline.

I suspect that's an imaginary problem. Direct wind damage to overhead wires and supports of any design, whether for railways or power distribution, should not happen if they are in good nick. It needs something extra, such as trees and other wind-blown stuff, or else rot and rust. For OLE, the main impact of wind isn't damage, it's the wires being pulled off too far sideways or bouncing about and preventing continuous contact. Series 1 is of course specified to cope, but so should earlier designs as this isn't anything new.

The big danger is icing, which can add huge extra loads, both weight and windage. However, icing is rare in Britain, and even rarer in Cornwall. Oh course it does occasionally happen - there was one famous big (very tall) example of icing damage, and the Queensferry Crossing was closed this week due to a form of icing (though for some reason it wasn't called that). In that latest case the bridge wasn't damaged, it was just dropping chunks of ice on cars.

While you'd expect better resilience where icing is common, such as the Alps, enyone can be caught out. A few months ago, around Lyon, a lot of small electricity poles were felled by very heavy icing on the wires - 7 kg/m where the design loading was 2 kg/m was mentioned. And the Chinese have had problems with their new electrified lines through mountains, though in their case icing of the pantographs and roof-mounted busbars is also a big issue.

Power lines also suffer from galloping, induced by the wrong kind of wind and growing to large amplitudes because of the large droop in the cables. Railway OLE has enough tension to keep that to very low levels, but again there can be adverse conditions. Asymmetry in the wire shape is one of those, and icing features again as it can add an aerofoil shaped tail to a wire. Again, it's the Chinese who have found out this can cause significant damage (because it can happen to a long stretch of line in one event). Series 1 does (of course) have a design requirement for icing, which is 9.5 mm thickness except on the GWML where it is 3.5 mm.
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CyclingSid
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« Reply #16 on: February 14, 2020, 06:54:38 am »

In the 1987 storm one of the main cause of the National Grid lines dropping out were plastic bags. Acting like a sail when they blew onto the lines.
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TonyK
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« Reply #17 on: February 14, 2020, 10:36:29 pm »

In the 1987 storm one of the main cause of the National Grid lines dropping out were plastic bags. Acting like a sail when they blew onto the lines.

Since then, the privately owned trampoline has become more common, usually bounced on a few times, then forgotten about until it's not there the morning after the storm.
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stuving
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« Reply #18 on: February 14, 2020, 11:04:56 pm »

In the 1987 storm one of the main cause of the National Grid lines dropping out were plastic bags. Acting like a sail when they blew onto the lines.

Do you mean National Grid? Or even national grid (still run by the CEGB in 1987)? I think that would relate to local distribution, via 33 kV lines on wooden poles. I've known one of those to be broken by a lad throwing a stick for his dog.

But in a big storm, there's much bigger stuff than carrier bags goes flying: not only industrial communal trampolines and bouncy castles (which were rare in 1987), but haystack tarpaulins, trees, and roofs. I vaguely recall metal roofing sheets landing inside grid substations makes quite a mess of the switchgear, and loudly.
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