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Topic Title: routing a cable across a steep rocky field
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Created On: 03 October 2013 09:29 PM
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 03 October 2013 09:29 PM
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mabx

Posts: 46
Joined: 11 February 2008

I need to get a cable from a wind turbine across a field (~120m) - the soil is very thin with rocks showing through and it's too steep for any normal digger/ machine.

Any suggestions as to how this should/can be done? I don't fancy using a pickaxe and a shovel

I was thinking maybe run it on a line of posts instead of underground but getting posts sunk is itself a challenge with just an inch or two of soil.
 03 October 2013 09:57 PM
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slittle

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Poles and overheads would be my solution if the ground is that hard as a few holes will be easier than a trench.

The DNO boys manage steep hillsides in Scotland and Ireland to plant poles so it's do-able, just need a digger driver that can trust his machine.


Stu
 03 October 2013 10:13 PM
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mabx

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The DNO boys manage steep hillsides in Scotland and Ireland to plant poles so it's do-able, just need a digger driver that can trust his machine.


And here in wales too - but I've never seen 'em do it - I just can't see your average minidigger staying upright on this gradient. I was thinking a post hole borer on an alpine tractor, but even an alpine tractor will slide once your past a certain gradient...

Thx.

M
 03 October 2013 10:21 PM
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peteTLM

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You can get trenching machines/ chain cutters that will do the trench, but the angle is a big problem. Pole cats (truck that puts poles in) will go through no probs (they manage through cellar roofs in london) but the angle is a problem again.
Poles in difficult access ground can be put in by hand, you need a crew of 6-8 to dig a stepped hole and to be able to pick the thing up.

120m, isnt a lot, im guessing a pole at the start and a pole at the finish is all you need? How did they get the wind turbine in?

Edited to say that with a bit of left field thinking you could use cable troughs - network rail use them beside railways, but the theft risk is huge.
Presuming that the field isnt used that is. Could concrete a nest of ducts across the field and cast them into a block.......

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 03 October 2013 10:30 PM
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slittle

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I was about to add another post about a stepped hole or even a trench Pete. We've done that on farms before to get poles in where we can't auger them in.

We done one last week and managed to get a lad on the farm to hand dig a perfect pole hole. It was 4ft deep and the pole fitted like a glove.


Stu
 03 October 2013 10:46 PM
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mabx

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the windmill isn't there yet (I'm just planning ATM), and the field isn't so steep at the top, but as you go down the hill it steepens 'til at the bottom there's a 20' craggy drop.

at the risk of asking a silly question, what's a stepped hole? (I'm thinking you dig a wide hole, then dig a smaller hole in the bottom of the 1st hole, etc?).

a cable trough? well it's a private sheep pasture and anyone coming to nick the cable would have to drag it away by hand; but it sounds expensive.

I thinking I'm just going to have to manually chisel one or two post holes
 03 October 2013 10:49 PM
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statter

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Or just run it in a suitable pipe anchored down at points
 03 October 2013 10:51 PM
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mabx

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I assume I'm right in thinking it's not acceptable to lay an SWA on the ground and let the grass grow over it (that would be so much easier ).
 03 October 2013 10:52 PM
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mabx

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err... what would be a 'suitable' pipe?
 03 October 2013 10:55 PM
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peteTLM

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stepped hole, exactly that, but one side of the hole is a sheer drop, with the side nearest the pole laying on the floor stepped to enable it being walked upright.

120m of suitable cable isnt going to be cheap, neither is the wind turbine, horses for courses :-)

A suitable 'pipe' would be a 4'' rigiduct, but this cannot be laid above ground, so would need to be cast into a slab of concrete on the surface.

If you wanted to go exposed with anchor blocks cast on it, then your in the realms of 100mm screwed galv steel pipe.
Think of utility' aerial bridges; over railways and rivers that just jump across.

Never underestimate cable theifs. They will go at a 800v DC railway cable with an ordinary hacksaw and marigolds and be prepared to lose their arm so your bit of cable in a field will be dragged out by their teeth if they want it.

-------------------------
----------------------------------------
Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry


Edited: 03 October 2013 at 11:03 PM by peteTLM
 03 October 2013 10:57 PM
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UKPN

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the DNO do indeed use diggers on hillsides. while we dont get
that kind of issue in london/essex, i was on a short break in scotland
recently, in the pitlochery area, our colleagues in SSE are upgrading a
400kv network across the hillsides. they run a track up to the tower point for access, then cut out the ground/rock for the concrete blocks.
incidently, scores of wind turbines are being erected and new sub-stations are being built too.
a whole new network, £160 million i believe.

our posters project? talk to the DNO

Regards
 03 October 2013 10:59 PM
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slittle

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My local wholesaler can get ABC for sensible money which makes the overhead route quite a good option. Size is obviously going to depend on the output of the turbine :-)

Stu
 03 October 2013 11:01 PM
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statter

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You could use a screwed still pipe suitably earthed and deburred. Or you could use a length of heavy duty plastic Provided it is strong enough to provide mechanical protection for the likely hazards and is suitably marked along its length . If you use plastic this is vital as it will possibly be confused in future for water etc and down rated in hazard terms.
 03 October 2013 11:17 PM
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mabx

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OK, the ariel cable option seems to be winning - it's only a few 100's Watts, low 100's volts so a small cable. - now wondering where I might get suitable cable - ariel bundled cable didn't throw up any suppliers on google.

thanks for the suggestions folks.

m
 03 October 2013 11:22 PM
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slittle

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Google Uk electrical Chelmsford, give Keith there a call and tell him I told you. He'll point you in the right direction.

Stu
 03 October 2013 11:24 PM
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mabx

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Cheers Stu.

M
 04 October 2013 08:51 AM
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broadgage

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How big is the wind turbine ?
A utility scale machine requireing a substantial MV connection ? or a domestic battery charging unit ?

If utility scale, then despite the costs and diffeculty I would dig a trench and bury suitable armoured scale.
The erection of a utility scale wind turbine innvolves a lot of civil engineering, and a 120M trench even in adverse conditions might not add that much to costs.

If a domestic battery charging turbine, working at a safe voltage then I would go for either twin with earth attached to a catenary wire and strung between posts, or if theft is unlikely then lay SWA on the surface.
 04 October 2013 09:00 PM
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mabx

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domestic, offgrid, battery charging turbine, but due to the distance I was planning for an output of the order of 2-300 volts and down-converting at the battery to reduce cable losses (though I've not worked out the details yet and it may prove more practical to run low voltage/thick cable).
 04 October 2013 09:25 PM
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Fm

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Proven?
Hugh piggott design?
12 24 or 48 battery system?
Personally i would use cheap purple flexi duct, as found in street lights
 04 October 2013 09:26 PM
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Fm

Posts: 673
Joined: 24 August 2011

Proven?
Hugh piggott design?
12 24 or 48 battery system?
Personally i would use cheap purple flexi duct, as found in street lights
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