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The tech level is roughly comparable to contemporary. There is a loosely populated planet, where any realistic power grid system should span over continents, with on average a few thousand kilometers between power plants and main industrial regions.

From technical perspective of just transmitting that, that should be no huge problem to use HVDC. Nevertheless there is one serious strategic issue - such system should be a serious vulnerability in case of any conflict. (huge distance to defend in middle of nowhere plus cutting a few key places would knock out the whole power grid)

Is it possible to make such cable realistically hard to detect? Would just burying it underground work? Or maybe it would create magnetic field that would make it blatantly detectable anyway?

EDIT:

Power dams are placed there where is a river with proper altitude difference and at best proper rock formation. Such place is somewhat not portable. Places where are ores are also not portable. Pleasant places to settle are also not portable. Thus, with inexpensive transport, at least resources exploration places would be spread all over the planet all transport networks would be somewhat vulnerable.

wiki:

Depending on voltage level and construction details, HVDC transmission losses are quoted as about 3.5% per 1,000 km

So from practical perspective producing ultra cheap hydropower but losing 10% still remains cheaper solution, than using some local, expensive source.

I know about ground radar detection, thus I toyed with possibility of digging such cable deep enough to make it damn hard to detect this way. (and make such power grid not so easy target) But such solution had only any point if that cable do not produce huge, electromagnetic field or radiation, that is simply blatantly easy to detect.

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    $\begingroup$ Why few thousands km between power plant and industrial regions? Usually you build power plants where you need power... It also makes sense strategically, you have one region to defend instead of two plus cables. This makes no sense to me. $\endgroup$ – Mołot Jun 28 '17 at 20:22
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    $\begingroup$ You'd generate the power closer to where you're using it, and avoid long distance transmission. $\endgroup$ – MichaelHouse Jun 28 '17 at 20:22
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    $\begingroup$ Hvdc is fairly new niche tech, iirc, and AC was the main technology used that enabled transmission. You might want to link to the dc tech you mean. $\endgroup$ – JDługosz Jun 28 '17 at 20:23
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    $\begingroup$ @JDługosz niche, yes. New, not. At least if we are talking about en.m.wikipedia.org/wiki/High-voltage_direct_current $\endgroup$ – Mołot Jun 28 '17 at 20:35
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    $\begingroup$ @Richard <4% per 1000km, less than with AC. A lot, sure, but there are existing lines longer than 1000km and there is no need for such shielding. Like, at all. Your comment is just misinformation. $\endgroup$ – Mołot Jun 28 '17 at 21:10
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You don't want that

The biggest threat to underground utilities isn't intentional sabotage, but excavation damage from construction workers, farmers, and whatnot who aren't aware of the buried cable or are given bad information about its location.

As a result, even in sparsely populated areas, utility rights of way are marked and maintained so that people can see that "hey, there's a cable/pipe here, I shouldn't go digging willy-nilly if I don't want to knock out the lights/get blown up by a gas line/get covered in crude oil"

Given your situation, then, it's better to build power plants more locally, especially if you can have a diversity of fuels for any one given city (solid fuels, fuel gasses, hydropower, solar, wind, geothermal, nuclear). Furthermore, critical systems will have backup power of their own (generators), and transportable generator infrastructure is nothing new either.

Deep burial gets deep sixed by deep problems

Deeply buried long-haul utilities are largely impractical for several reasons; one might envision such a thing for a singular highly critical utility where cost and engineering difficulty are no object, but geographically diverse redundancy is cheaper and better.

First and foremost is the cost of installation. Trying to cut-and-cover a relatively narrow trench several tens of meters deep is not practical, so trenchless techniques are needed (either microtunneling or directional drilling, with the use of suitable bits for the ground conditions).

Atop that, you wind up putting your utility well below the water table. This means that any spills from a pipeline are instant groundwater pollution problems, while electric and telephone cables need to run in an environment that isn't simply wet, it's flooded.

Furthermore, this doesn't eliminate the excavation damage risk -- drilled wells (whether they produce oil, gas, or water) extend far deeper than you can ever put a utility. Oil and gas producing wells can be reasonably managed by a permit scheme, but strict water well permit schemes could be a serious problem especially in rural areas where well water is essential for survival and irrigation.

Finally, maintenance access becomes a nightmare. While trenchless replacement techniques for piping are known (pipe bursting, for one), they would suffer similar cost problems as the original install. Corrosion protection is more critical, and junctions, splices, and the like would require extensive surface access support.

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  • $\begingroup$ While I agree that localized power plants are the way to go, I don't agree that burying is as big of a problem as you claim. If it's buried tens of meters below the ground, no farmers or the likes will ever dig that deep. With the exception of big construction sites like high rise buildings or miners - both things which can just require government approval. $\endgroup$ – Syzygy Jun 29 '17 at 16:25
  • $\begingroup$ @Syzygy -- well drillers go that deep routinely... $\endgroup$ – Shalvenay Jun 29 '17 at 22:29
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Long Distance Power Grids Are Virtually Impossible To Defend Against Terrorism Or Insurgencies

Even a very timid and small insurgency or terrorist group determined to disrupt the kind of power grid you envision is virtually unstoppable.

A group with fifty active members with a million dollar budget could shut down the power of a civilization with hundreds of millions or billions of people with virtually guaranteed success, without needing any terribly expensive or advanced technology, even if the defenders devotes a hundred billion dollars of resources and millions of people to the cause of defending the grid.

Lawrence of Arabia did something similar to disrupt rail transportation in North Africa.

This is a problem inherent in the nature of a long distance power grid across desolate areas that is pretty much impossible to overcome. No technological solution can solve this efficiently. If you have this security problem, you have only one viable choice: abandon the long distance power grid.

Even if the location of the cables could be perfectly hidden, there are so many people at a fairly low level in any bureaucracy with a need to know (e.g. planning commissions, maintenance crews), that any organization with a mildly motivated and halfway competent spy or two could easily learn the location of a host of vulnerable locations from power company records or word of mouth from power company employees.

The only reason that this isn't a problem in places like the United States or Canada is that nobody has a terrorist agenda devoted to taking down the power grid, and that the power grids are predominantly more decentralized and localized.

Option One: Move Energy Via Fuel Cells Rather Than Using Cables

One alternative is to ditch the idea of power transmission over long distance cables entirely.

If you could built a very efficient, high energy density fuel cells, and had a low energy cost way to move those fuel cells (e.g. by ship or barge over a major oceans and/or river systems), you charge your fuel cells at the generator, deliver them to the destination (with a fuel cell inventory cushion for foreseeable interruptions in deliveries), and you power the grid where the power is needed with the fuel cells. Once a fuel cell is out of juice, you can ship the empty cells back on the return trip of the ships/barges.

This leaves you with no immobile cables or transformer stations in the middle of nowhere that are hard to defend in the event of a conflict.

All you need to protect is the generation location, the local grid at the destination, and ships or barges carrying the fuel cells while they are en route (and the incentive for anyone to attack those ships or barges is going to be much lower on the return trip than on the trip from the generator to the place where the power is used). The ships and barges can be protected are small and mobile, and can be protected with point-defense strategies similar to those of modern warships. Also, while the route may be effectively fixed in a river system (although the timing can be made unpredictable if desired), once you are on an ocean or sea you can use an unpredictable and varied route rather than the absolutely most efficient route, to make it harder to target the ships.

A Variation: Use Ship Based Rechargeable Fuel Cells With Short Cables Connecting To Port Cities

In a slight variation on this plan, you could have a short power cable running from the power generation site to the nearest port town at which fuel cells would be charged (perhaps even while still on the ships returning with empty fuel cells).

Similarly, at the destination, a much shorter distance power cable could deliver energy from the fuel cells that would stay on the ship at all times to the local power grid until they were depleted and the fuel cell ship returned to the port near the generator to recharge.

As long as neither the generation site nor the destination are too far inland, this could be a very workable alternative to putting the generator and the destination grid on the same power grid over many 1000s of kilometers of mostly deserted territory where the security of that grid in deserted territory could not be assured.

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  • $\begingroup$ Besides, significant chunks of the public have a need-to-know about buried facilities. (Ever had to get utilities marked for an excavation?) $\endgroup$ – Shalvenay Jun 30 '17 at 2:38
  • $\begingroup$ Also, why fuel cells instead of something more energy-dense? $\endgroup$ – Shalvenay Jun 30 '17 at 2:38
  • $\begingroup$ @Shalvenay Any means of energy storage that can be transported by ship and reused many times would be acceptable. If it was something other than a fuel cell that filled the same role but was more energy dense that would work just as well with the concept. $\endgroup$ – ohwilleke Jun 30 '17 at 18:26
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I recommend you look up the CLH Pipeline System which was the UKs secret fuel pipeline to distribute jet fuel across the country during WW2.

Of course, the CLH did not have to deal with electromagnetic waves, and while it's not possible to block magnetic fields, it's possible to redirect magnetic field lines through conductive materials. Modern cables are often shielded by wrapping them in copper foil which creates a Faraday cage to prevent signals from interfering with each other. If you were to wrap your cables in several of such shielding layers, little of the magnetic field would still be detectable.

Someone else suggested that you can't really bury the cables without making it public, as people will damage them from just digging out their yards and stuff. However, you can bury cables deep (tens of meters) to prevent most accidental damage from property owners digging out cellars or whatever excavations are commonly done. Things that require deeper digging, like high rise buildings or mines, require government approval. In addition, this further helps with masking the magnetic fields. While this is expensive, it doesn't seem unreasonable in war situations.

In addition, you can make your power grid redundant by connecting each city to several power plants and create multiple power lines from each plant to each city. While this sounds outlandish, this is what we actually did here - not for power but for information. It's called the internet, although in it's early stages it was called ARPANET and one of its goals was to continue functioning, even if large parts of the network are taken out.

Those suggestions should be enough to not only make your power grid hard to detect, but also make it hard to destroy... except that at some point your power stations have become the weakest link. A well-placed air strike, sabotage or a full attack might easily take out your power dams... and create a fair bit of mayhem once the broken dam floods the surroundings. In 1979 the Teton Dam broke and damaged Fort Hall, a city that is more than 130 km far away (by car, I assume the flood followed the river which takes an even less direct route). Usually cities are built near water sources and to me, it seems that your power requirements seem to be bigger, as you have few centralized power generators. Thus the dams are a way more interesting target than the power grid itself, even if the grid is somewhat vulnerable.

So in your case, I would care less about the grid, but more about the few power generators.

  • They can not be hidden.
  • They're vulnerable to (high altitude) air strikes and carpet bombing.
  • They're costly to create and repair.
  • Repairing them will take much longer than simply replacing a cable.
  • If you take them out, there will be a lot of secondary damage.
  • If you take them out, you might take out power for several cities.

So my final suggestion is... go with decentralized power distribution. Maybe everyone uses solar or wind power, or there's a small thorium reactor in every neighborhood.

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I believe the observable magnetic field that surrounds HVAC/HVDC lines varies directly with resistance. Therefore, if you posited superconductors, I believe that the transmission lines will be a lot harder to find. It also would let you take less direct routes because transmission loss would be less.

Frankly, you also need something like superconductors, otherwise your several thousand kilometer transmission lines will lose too much energy.

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    $\begingroup$ There are actually a couple of thousand-kilometer scale power lines in China (the optimal hydro power station locations tend to be far from the major cities). Power loss = resistance of the cable * current^2 but power transmitted = voltage * current, so if you go from a 1GW/500kV@2kA line to a 1GW/1MV@1kA line, you'll be moving the same amount of energy but with only 1/4 the losses assuming you use the same cable both times. The magnetic field is related to current, not resistance, but same trick as above, crank up voltage, use less current and you get weaker fields and lower losses. $\endgroup$ – Samwise Jun 29 '17 at 0:38
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    $\begingroup$ Also note that the electromagnetic effect around power transmission lines is due to special relativity. By pushing power through the line, the electrons are forced to move (albeit very very slowly) and that causes a compression of space (via special relativity), resulting in fewer electrons per unit of distance than protons, which leads to the electromagnetic effect. You can't avoid that. (Also: physics is weird). See: physics.stackexchange.com/questions/341809/… $\endgroup$ – Draco18s no longer trusts SE Jun 29 '17 at 14:30

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