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Power cuts

electricity power wind pole weather

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16 replies to this topic

#1 George.

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Posted 10 November 2018 - 03:31 AM

Up here in the north of the island, there was a power cut - again. Shetland News state that it was caused by a burnt wooden electricity pole. All too often it's caused by wind damage, though. If the power was supplied underground then these problems wouldn't exist.

 

Why do they continue to supply power above ground?



#2 Roachmill

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Posted 10 November 2018 - 11:24 AM

Because they can't tell where a certain Westside shop owner may move to next? ;)

#3 paulb

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Posted 10 November 2018 - 02:53 PM

cost. repairs become harder.



#4 Ghostrider

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Posted 10 November 2018 - 03:59 PM

[Sarcasm] SSE have to save every penny they can so that they can afford to pay for their cut of Viking and the interconnector.....[/Sarcasm]



#5 tarsus

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Posted 10 November 2018 - 06:45 PM

Overhead is cheaper than underground ?.



#6 CrashBox

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Posted 10 November 2018 - 07:01 PM

Much quicker so cheaper to dig a hole, drop a pole in it, dig another hole some distance away, and string a cable between them. Repeat until completed. If the cable is fully underground then the hole becomes a very, very long trench which takes longer to dig and fill in. 



#7 Ghostrider

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Posted 10 November 2018 - 07:22 PM

^ Fair point, until you factor in that Scottish Water dug a trench from LK to Sumburgh (give or take) to lay a new main some years back.

 

Had they and SSE put their heads together and put both utiities in one trench which would have halved the cost to both, at least that part of Shetland could have been underground. There are probably other areas the same thing could have happened, I'm just not familiar enough with elsewere to know.



#8 Colin

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Posted 10 November 2018 - 08:06 PM

One problem with trenching is that, if you dig in peat, the peat eventually moves and will damage cables etc..  More trouble than it is worth.



#9 Ghostrider

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Posted 10 November 2018 - 09:20 PM

^ Is there any actual evidence of this ever having happened. Or is it a 'convenient' myth over-exaggerated by SSE for their own ends?

 

Its 'possible' for sure, but unless on sites where common sense should be screaming out its madness to lay anything, damage to things like water and sewer pipes laid through peat tends to be largely minimal and only very occasional. Why would an armoured, insulated cable be more susceptible to damage than say a piece of 3", 1/2" wall "asbestoes" type water line?

 

The cable is solid, flexible, and needn't be laid taught so as allow some leeway for movement. and they're usually laid on and within a protective layer of aggregate etc. The old water mains that were laid 50-60 years ago are hollow, rigid, relatively brittle, and were just backfilled in the trench with whatever had come out of it. Yet only very occasionally do they give probems, even yet.



#10 Colin

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Posted 11 November 2018 - 08:39 AM

Good points.  I suppose that it comes down to money.  It would be a lot more expensive, and take a lot longer, to put cables into trenches.

 

Come to think of it, the power into my house is underground from the nearest pole ! :roll:



#11 waarigeo

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Posted 11 November 2018 - 12:48 PM

Fault finding on overhead lines is much easier than locating a fault on underground cables, 

 

I speak from experience having worked for electricity supply companies.



#12 George.

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Posted 11 November 2018 - 03:00 PM

Fault finding on overhead lines is much easier than locating a fault on underground cables, 

I bet it would be, but how many faults do we come across on overhead cables as opposed to underground cables?



#13 Ghostrider

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Posted 11 November 2018 - 09:10 PM

Fault finding on overhead lines is much easier than locating a fault on underground cables, 

 

I speak from experience having worked for electricity supply companies.

 

There's probably a reasonable amount of truth in that, given where most of the overhead lines are sited at the moment, but they don't seem to need too much time and effort to locate faults in cables in urban settings, for which underground is mostly the only reasonable and workable solution.

 

BT don't seem to have too much bother locating faults either, and their cables are almost all exclusively underground, in both ubran and rural settings.

 

 

BT though chose to lay their's adjacent to public roads in most cases, making access and maintenance/repair considerably quicker easier. Maybe if SSE adopted a similar model to BT for cabling, rather than their long-standing 'as the crow flies, regardless of what almost impassable terrain and/or extreme exposure that involves' routing policy, it would obviously considerably more expensive for the initial investment, but its difficult to see how they wouldn't be quids in in the long run in repair, maintenance and replacement cost savings. BT seem to think it works for them, otherwise they'd be reverting back to their old style poles and wires at every opportinity.

 

The current lifetime in Shetland of everything about the overhead power supply system seems to be a max of approx 40 years. Then it all needs to be dismantled, removed and a totally new one built from scratch. Underground cables would last much longer, and even when it came time to replace them, *if* they copied BT's system of laying piping in the trenches and then laying the cable itself inside that pipe aong with a draw rope, nothing needs to be replaced other than the cable itself, no digging or construction work of any kind is required. Just up to manholes, draw the new cable and another draw rope through with the existing draw rope, disconnect the old one, pull it out, connect up the new one, and head for home, job done,


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#14 Ian_H

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Posted 12 November 2018 - 08:29 AM

A power cable isn’t the same beast at all as a phone cable. Photo shows how to lay one. Okay, equipment and machinery have become available and developed since that photo, but it wouldn’t be a small cable to supply any quarter of Shetland. If the link below doesn’t work, look for photo number W00027 on the museum website.

http://photos.shetla...AFnBSUynA/36952



#15 Ian_H

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Posted 12 November 2018 - 08:49 AM

One issue is that electricity flowing through a wire generates heat. With a bare wire way up in the air, that isn’t a problem. But cover it in insulation, bundle three wires together and add more insulation, bury in the ground, then heat does become an issue. The way around that is to use bigger wires to have less resistance and therefore produce less heat. But more copper costs more money, add insulation, armouring and laying; the result is that underground cables are expensive compared to overhead if moving a lot of power over a distance.







Also tagged with one or more of these keywords: electricity, power, wind, pole, weather