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sorry for the odd title. We're working on a project to find a cheaper and safer way to install high voltage power lines in the Scottish highlands. One of my group mates had a really cool idea to instead of actually digging underground, you could just lay the cables and cover them with dirt/some other material which we haven't thought about at the moment.

I am asking because I assume the industry would currently be using the best available technology to them, and they don't use this method; they lay them underground. I'm trying to figure out the potential drawbacks to this proposed method.

1) Initially i thought it could be regulations, i.e. minimum depths etc, however, as far as I can tell from official documentation, there are only guidelines. In general, cables are laid between 0.45m -1m below ground, but not always. For example from a cable map I found, there was an 11kV line just 35mm undeground in Edinburgh. Official documentation seems to imply depths are situational, and as long as a risk assessment is performed, shallower or deeper depths can be allowed.

2) In terms of cost, digging through the rocky terrain of the Scottish highlands would pose significant challenge and cost. Getting heavy vehicles out onto that sort of terrain isn't easy. Using some sort of packing material, such as dirt, would surely be a cheaper option? There would of course be costs incurred due to rough terrain for transport trucks etc, but I don't see how it could cost more than digging through the terrain.

Potential drawbacks I can think of:

1) Using a mound structure would pose issues such as erosion. However, maintenance (which must be carried out on cables anyway) shouldn't be too difficult, especially since faults in the structure would be easy to spot since it is overground. It may require more regular maintenance due to weathering, but that would be offset by the fact that each maintenance trip wouldn't involve unearthing the ground?

2) Potential damage to cables. I don't even know if this is a real drawback (in comparison to the existing system since cable damage isn't very uncommon). I read some case studies from one of the regulatory bodies, and it seems damage came mostly when projects were undertaken without consulting the relevant authorities for cable maps. I assume the mound layout would be very similar, and probably wouldn't encounter a greater frequency of damage to the cables, but this is pure conjecture.

3) It would be an easier target for malicious activity since it would be easier to get to without the need for heavy machinery. However, cable maps aren't very difficult to get, and someone could just as easily target shallow cables using the current system.

Ultimately, does anyone have any criticisms of the potential solution? Or does anyone know of this idea having been implemented but not worked, or was determined to not be feasible? Thank you very much!

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    $\begingroup$ "Why must high voltage underground cables be physically underground?" Seriously? Where else do you expect underground cables to be, except under the ground? $\endgroup$
    – Olin Lathrop
    Sep 30, 2016 at 11:17
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    $\begingroup$ Your matey there should either be sent back to school to learn how to read up on 100 years of electrical power delivery systems design or just plain fired. $\endgroup$
    – Carl Witthoft
    Sep 30, 2016 at 14:19
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    $\begingroup$ The obvious reason why not is "because some idiot will try to steal the copper and sell it to a scrap metal dealer". Having to keep powering down the cable to remove dead humans would be expensive ;) $\endgroup$
    – alephzero
    Sep 30, 2016 at 20:40
  • $\begingroup$ Yes, I apologise for the title, it wasn't particularly descriptive. In terms of being sent back to school I regret to inform you that's where we are. We've been asked to come up with a 'better' method than one that currently exists. Obviously we are aware that what the industry is using is going to be what's best at the moment. The reason I was asking here is because none of us are experts and were looking for better qualified opinions. $\endgroup$
    – masiewpao
    Oct 1, 2016 at 11:37
  • $\begingroup$ You might find elpipes interesting. I don't know what to make of them. $\endgroup$
    – 410 gone
    Oct 6, 2016 at 20:37

4 Answers 4

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Your four drawbacks are very good reasons for not laying cables on the ground and just covering them with soil or "stuff".

Erosion will be a major issue. Exposed cables would be a safety hazard to humans and wildlife. It would also increase the risk of cable degradation and failures. Countering the affects of erosion, but covering the cable, will also add to the operating cost of the cable because the uncovered parts of the cable would need to be covered over again, repeatedly.

Another impact will be that the covered cable on the land surface will present an obstacle to other forms of land use. Crossing points will need to be constructed over the cable, to allow people to access the land on the other side of the cable. This would add additional cost to laying the cable.

The Trans-Alaska Pipeline, which has been placed of the surface, has an impact on the migration of wildlife

By burying a cable, it prevents people and animal from fiddling with the cable and thus prevents damaging infrastructure & personal injury.

Also, a buried cable is out if sight and out of mind to most people and thus has a better chance of not being interfered with and being able to function as it should for a long a possible.

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I do not know the laws in your country, but the key is "risk assessment". And the risk we are talking about is the risk of killing someone, not the risk of the cable being damaged.

Irrespective of laws, it is likely the project will be signed off by a professional engineer and protected by your companies malpractice insurance. If someone dies as a result of gross negligence, the professional engineer(s) go to prison and the company may lose its malpractice insurance.

The only place I could see it being ok to put high voltage lines on the surface is in a military controlled area where it is continuously monitored and kept free of people and equipment.

I have heard of lines being buried at shallower depths, but concrete is poured above them to ensure that even heavy equipment will not dig them up. Your risk assessment would have to include what the area is used for, number of people that will be in proximity to it on a daily basis, development that will occur in the area over the line's lifespan, soil work-ability, failure detection, and monitoring methods.

Perhaps a simultaneous construction of a service road may be needed to move the equipment. You may be able to crush some excavated rock on site and use that to cover the cable in low areas; reducing the total amount of trenching required. Coarsely crushed rock would not have as many erosion issues and would be more difficult to excavate accidentally; reducing risk. The road would need blocked from normal traffic and periodically driven by service trucks to check for erosion and unapproved human activity.

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When we had to run HV lines to a building, we put them in steel pipes 6 ft deep, covered the pipes with 2 feet of sand, then laid a foot of concrete on that and painted it red, and filled the trench with earth. People dig, maps get lost.

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Aside from safety and maintainability concerns, there are also costs with insulation and capacitive losses to consider. See for example: https://www.quora.com/Why-arent-underground-cables-used-for-power-transmission-in-India

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