Why Aren't Powergrids Underground?

jonging asks: "It is common knowledge that an underground power grid is less susceptible to the effect of a large thunderstorm. The American Transmission Company cites numerous reasons why it (and other power companies I assume) do not bury their transmission lines underground (e.g. environmental concerns, cost of installation and repair, etc.). Exactly how detrimental are underground transmission lines to the environment? Wouldn't the time spent without a power outage generate more than enough revenue to offset initial costs? Aren't the need for repairs in cities with successful underground power grids rare?" The linked article goes into extensive detail about the disadvantages in initial costs of putting in underground lines, but doesn't go into any detail about the maintenance costs of either option. With storms getting worse and worse (Maryland, DC and Northern Virginia have weathered torrential downfalls this week), might underground lines prove more resistant to storm-related power outages?

Comments

It costs money?

[NotQuiteReal]

That is all I have to say.

Sure, it would be nice to put it underground, but it costs more that way...

Re:It costs money?

[tomhudson]

Long term it still costs more.

Its a lot harder to maintain buried conduit. Plus, there's the problems of accumulated gases in any piping you lay down, plus drainage, plus trash/dirt/crap accumulation at the manholes.

Look what happens when buried conduit deteriorates - the resulting fire is nasty because its more concentrated than in the open air.

Re:It costs money?

[Sam Ritchie]

I would actually like to see some figures to back that up.

I don't have any hard numbers, but I seem to recall a figure of AUD 1 million/km being bandied about for burying high-tension lines in Perth (Western Australia). Most local councils here are already in the process of putting the residential supply underground, but the higher voltage distribution network is just too expensive. Interestingly, one of the main reasons for underground power here (besides 'suburban beautification') is to prevent poletop fires.

I doubt you could run cable in a conduit next to high voltage power?

Re:It costs money?

[kv9]

I doubt you could run cable in a conduit next to high voltage power?

you could run fiber.

Re:It costs money?

[alehman]

I am an electrical engineer and work in the utiltiy industry. My firm recently performed a series of studies on this very topic. Believe me, this subject has been studied *extensively* in many different ways by the utility companies. If anyone understands TCO it is the utilities. In almost all situations, even where subjected to the worst weather conditions, it does not work out financially for the utility companies to put the lines underground. There are plenty of factors besides money that can influence the decision (e.g. neighborhoods conerned about aesthetics, customers concerned about reliability, etc). In some locations, franchise agreements require underground installations in certain areas. In other cases, some customers are willing to pay for it for percieved reliability improvements (difficult to prove).

We studied conversion of some existing neighborhoods for a few cities in the midwestern U.S. a couple of years ago. The costs for conversion in those cases were unmanageable. Conversion has been done in a (very) few small areas where neighborhoods were willing to pay for it. Other programs that have been implemented include thoroughfare visual improvements and residential service drop undergrounding. These can make sense in some circumstances.

Re:It costs money?

[Technician]

There is a big cost diffrence if putting in a subdivision and burying the 7200 volt line into the subdivision transformers and burying a 500,000 transmission line. Safety is also a concern. Which line would you rather hit with a backhoe?

On a high tension line, the capacitance per foot is much higher for a buried line than for an overhead line. For long distance feeding this capacitive load adds greatly to the power loss in the line. Burried is OK in New York City, but forget it for the grid. There are too many losses. Putting the 2 top grounded lines above the high tension lines have greatly reduced lightning strikes to the power conductors and their resulting outages from damaged insulators and substation equipment.

Disclaimer.. My father was a substation operator for Bonniville Power Administration. I've seen the MegaVar meters on some long lines.

Re:It costs money?

['nother poster]

Well, I know people who work in the power generation and distribution business in the midwest U.S. Arcs cause resets, too many resets, and the circuits are taken out and it takes serious human intervention to bring them back in. This costs time and money. I find it shocking that there are utilities that scrimp on a few links of insulator to lengthen the path to ground through the dust buildup so that they don't have periodic fault to ground or fault to phase events. Those can get expensive fast. Once again, if any area experiences more than a few of these events and the plant engineers don't schedule a fix on the next maint outage they should be fired. Dumping an 18.8 kV feeder sucks. Dumping a 46 kV feeder is a major pain. Dumping a 230kV trans line will inconvenience lots of customers and will cost a fortune to cycle and bring back up. A utility doesn't let that happen more than about two times before heads roll. About the only thing that would piss off the management worse would be doing something really stupid and getting a 600MW alternator kicked out of the grid and having to spin it back up and sync it back in.

Re:It costs money?

[amorsen]

On a high tension line, the capacitance per foot is much higher for a buried line than for an overhead line. For long distance feeding this capacitive load adds greatly to the power loss in the line.

Go DC and forget about capacitance. That's what seems to be done for 150kV and up around here.

Re:It costs money?

[ray-auch]

I would actually like to see some figures to back that up.

http://www.highland.gov.uk/NR/rdonlyres/CBDD84F3-3 326-4DB9-AAA1-44537AE9B885/0/text.pdf

Has a lot of good info on underground vs. overhead for proposed new powergrid in Scotland.

Estimates of lifetime cost ratios (table 8 at the end of the document) are between 6.9 - 10.2 for traditional fluid-filled cable and still 4.9 - 7.8 for newer (and arguably less proven) XLPE insulation technology.

Also, this is recent tech which you would use to build your grid _now_ - go back a couple of decades and the difference was much larger. At Dinorwig - http://en.wikipedia.org/wiki/Dinorwig_power_statio n - they had to run the first few miles of cable underground because of national-park restrictions, and there you're looking at water-cooled cable requiring acutal cooling stations (size of small house) every couple of miles. While it's very impressive to see an entire power station underground, with no visible power lines, it was definitely not cheap to do it that way.

Bottom line is that the overhead option is using a few feet of air to get its insulation for free, and it's always tough to compete with free.

Re:It costs money?

[the_xaqster]

One of the main problems with underground cables is locating faults. Most faults are caused by water seeping into the cable via a damaged insulator. When enough water has seeped in, the cable shorts and blows the breaker. Unfortunatly, this also dries the cable out nicely, which means that testing for the fault becomes a problem. The best method for locating these faults is to switch bits of cable in and out, and narrow down which section it is, then dig it up.

And how do the insulators get damaged? One way that happens more than most people would admit is it gets clipped by someone digging up something else. Say you are digging up the gas pipe in the street. If you just nick the electricity cables insulation, would you tell your boss so he can get the electric company out to replace the cable, delaying your work by hours, or are you just going to throw some dirt over it, so no-one will be able to tell?

I have worked for 2 Electric companies, so I know a little about this.

Re:It costs money?

[tomhudson]

Ithink it shouldn't be to hard to design those tunnels in a way where you can use robots like in the sewage systems.

Really? The reality is that sewage work is still done by humans, not "robots". There's no way that a "robot" can dig up a street to replace a broken water main or sewer pipe, and the fibreglass inserts/patches are NOT a long-term fix when a pipe breaks.

Besides, you've overlooked the installation costs. It can easily be 100x more expensive to run a wire underground than overhead. Overhead - 2 cherry pickers, 5 guys, a few spools of wire, a day, and a couple of blocks are rewired (they just upgraded all the wiring on the street 2 blocks over last week - took 2 days because of the trees. On the other hand, 3 years ago they did a major upgrade along about 40 blocks - in one day - with a larger crew of cherry-pickers and support vehicles). Underground - backhoes, loaders, dump trucks, flatbed, concrete saw, gravel, conduit, manholes, manhole covers, asphalt repaving, cement mixer, sidewalk repair, 2 weeks, easily 30-40 people involved (gas, sewer, waterworks also have to be coordinated).

Then there are the transformer rooms (since you can't just hang them from a pole) - concrete pads, etc. Money money money.

Re:It costs money?

[b0s0z0ku]

Part of the thing *not* discussed here is that there are huge amounts of the power distro system in DC which *is* underground.

AFAIK, all of it, except for substations and the electrification of the Northeast Corridor rail line coming in from Baltimore. There's some old law prohibiting basically any overhead wires, and it's strictly applied - even the new trolley line in DC will have to use third rail (AFAIK, electrified only when a tram is passing on a given section) because of it.

-b.

Re:It costs money?

[mothlos]

I can personally attest to the problems of buried electrical cable. I am a dispatcher for a local power company. About 3/4 of our grid is above ground with the rest earth buried (not tunnel buried as in some cities). Buried cables account for fully half of our line failures. The most common issues are the result of earth shifting and water seepage. Repair of underground cable requires extra equipment and manpower to locate and excavate to fix problems. Also, there is a danger of damaging underground cables and pipes maintained by other utilities. Utilities spend a lot of money locating their underground infrastructure for each other.

Re:It costs money?

[AB3A]

Mod parent up, please. Overhead power lines are much more tolerant of higher loads. There is also the issue of insulation breakdown underground. Furthermore, burying power lines means you need to keep extremely detailed records for a very long time.

As someone who works in a water utility (where pipes are laid in the ground and expected to stay there for the next 100 to 150 years) let me be the first to point out the hazards of trying to keep such records for such a long period of time. Standards change. Reference markers get lost. Assumptions are forgotten. And yes, the earth does shift here and there. Folks, it's bad enough when you accidentally dig up a water line. It's much worse when you hit a high power electric line.

Underground electric lines look really good until you start getting in to the details. There are good reasons to leave things as they are.

Re:It costs money?

[Dare nMc]

Higher capacitance doesn't make for all that much loss. It's the heat from the resistive losses

True enough for DC voltages. however with AC voltages, any resistance between the capacitor and the inducter is greatly multiplied. IE you will have a ringing current passing between the capacitor and inductor, and that ringing will pay the price to resistance every pass. so if the capacitance is spread out over hundreds of miles, away from the inductance, you will have huge increases in resistive losses because of that distance. So although your power supply never see that current, it will have to compensate for the extra resisitve losses.

Re:It costs money?

[Anonymous Coward]

Maintenance is the issue here. The old saying "Out of sight, out of mind" is dangerous for electrical systems. I used to be an substation engineer for our company which had it's own substation transformers and distribution system and it was expensive to maintain. But our local power company kept on waiting for outages before maintenance...er, repair before we got fed up and purchased our own substation during the power de-regulation in our state. The cost have over time made up the cost in 3 years. Schedule maintenance is expensive but is worth it considering if you lose data or lose revenue since you cannot book sales when you computers are down is minimal.
Above an certain voltage level, 30,000 volts if I remember correctly, the voltage lost to conduit is too high so that is why high voltage line above a certain voltage is hung in towers. This is current technology now so if the new technologies (ie super conductors and new insulating materials) come out this may get some of the high voltage lines underground.

Simple physics

[loony]

Each cable that transports AC is subject to drain by the capacity the parallel lines themselves represent. The closer the wires, the higher the capacity. At about 30 km on a regular high voltage cable, you reach a point where the reactive power drain reaches the maximum power the cable can transport - the cable is saturated without draining a single watt at the end.

DC does not have this issue however then you have all the problems that killed Edison's original DC power distribution in favor of Telsa's AC distribution.

Peter.

Re:Simple physics

[coyote-san]

Are you sure that isn't inductance?

Anyway, we're almost certainly talking about different things. Nobody is suggesting burying long-distance high-tension lines. Just the last half-mile or so. That's enough to eliminate the visual clutter and keep the neighborhood from losing power after a tree limb breaks, etc.

Re:Simple physics

[Technician]

Are you sure that isn't inductance?


Yes he is sure. In any wire there are a few factors causing problems getting power from one end to the other without loss. First is resistance. Too much current simply heats the wire. Power lost in the wire is power put in and not delivered to the other end.

In addition to resistance, two conductors near each other are a capacitor. Capacitance goes up if the conductors are placed closer together or are larger, or the material between them is something other than a vacuumm Overhead high tension lines are 8 feet or more apart and are insulated by air which has a dielectric constant very close to the same as a vacuum. Making a direct burial cable places a grounded shield conductor quite close to the hot conductor (reduced distance). It surrounds the conductor (bigger area). The area in between is no longer air but an insulator with a dielectric constant several times greater then air. Feeding this long capacitor lots of AC voltage requires lots of AC current. As the parent poster noted, in a relatively short distance the current needed to feed the cable can equal the total amount of Amps the cable is designed to carry without drawing any power from the other end.

Inductance is also a factor in getting power from one end of a wire to the other. All wire has inductance. Inductance caused loading is unaffected by applied voltage. It is unaffected by the insulation used on a wire. The amount of inductive current is influenced by the current fed on the wire.

Hmmm is there a balance where the inductive current will cancel the capacitive current? I am glad you asked!! The answer is YES!! The solution lies in what is called the impedance of a cable. If you put a load resistor on the far end of a cable that matches the impedance of a cable, then the inductive current will match the capacitve current in a cable and they null each other out.

Is this the answer? Nope. Why.. The load is not a fixed resistance on the end of a transmission line. The load changes as lights, heat, AC, etc changes with demand.

To get a lot of power with reasonable cost transported long distance, high tension is used to keep the size of the conductors reasonable to keep the cost down and the huge magnetic fields that tend to induce current into anything nearby like rail tracks, fences and such. Losses from heat and magnetic fields are much less at higher voltage and lower current. Now you have a line with an impedance that does not match the load and power factor correction is needed.

A buried line at very high voltage needs a lot of corrective inductive current due to the very high capacitance per foot as the parent stated.

Sorry for the crash course in power factor correction and transmission line theory but it is on topic.

FYI, that is why a CAT5 cable is terminated into 120 ohms. It's the impedance of the UTP cable.

Higher transmission losses with UG lines...

[Ellis D. Tripp]

Underground powerlines would suffer higher capacitive losses than overhead lines, and losses between the generating plant and the user would be power that the utility company can't (directly) bill for.

With all the public concern about EMF exposure, the situation would be made much worse when all those distribution transformers move from 40' up a pole to concrete pads at ground level. And then there is the everpresent problem of "backhoe fade"...

Re:Higher transmission losses with UG lines...

[peragrin]

actually this is the big point. Power companies can massively undersize wires that are traveling in free air.

Three conductors in free air 15 feet off the ground the power companies can run a #2 sized cable for 200 amps. Yet that same wire underground needs to be 4/0 or 250 MCM which is several times larger.

The cost of goods to run lines over head is considerable less even if you take into account storms trashing it. Just from a dollar point of view you can competely rebuild a surface grid two or three times for the cost of doing it once underground. Digging costs that much more. Digging near roads is even worse.

I think it makes long term sense to go underground but I do see the cost advantages of going above. Plus the union can hire more people.

Re:Higher transmission losses with UG lines...

[Chirs]

North American power is 240V as well, it's just split into +/- 120 and ground rather than ground and 240V. My table saw runs on 240V, and my dust collector is capable of 240V but is currently wired for 120V.

Re:Higher transmission losses with UG lines...

[TubeSteak]

New York City loses a lot of power because of their old and beaten underground power grid. Everything from rotting insulator to wires that aren't in use, but never had their current shut off.

Their layout also manages to zap people & pets during the winter/wetter parts of the year.

Re:Higher transmission losses with UG lines...

[njh]

Actually, 240V power is distributed as 415V three phase with power tapped off separate phases. Three phase power is more efficient than the two phase you describe.

You prove the point

[PizzaFace]

Downtown Washington rarely has power outages because the power lines are underground.

Re:You prove the point

[5KVGhost]

FWIW, I live in rural Maryland. We have aboveground lines here and we've had similar heavy rain and flooding in nearby areas. Our power hasn't so much as blipped. The UPS hasn't even beeped to signal an under- or over-voltage condition. I'm more worried about brownouts later this summer than storm-related outages.

In fact, it's only gone out, fairly briefly, once or twice in the four years I've lived here. In that same timeframe the underground fiber at work, a few miles away, has been severed twice by construction.

And I have no idea what the OP means by "storms becoming worse and worse". I've lived in the Maryland/DC area all my life, and I remember some pretty hellacious storms, hurricanes, and blizzards over the last 30 years. We haven't had anything nearly as bad lately.

Re:Water

[geekoid]

your electric company has either improperly maintain there line, or incorrectly designed the underground system. In general undground lines or less prone to outage.
over a 10 years study, outages where less and the duration of outages was shorter.

what aren't people electrocuted when the rain has soaked the power polls and lines?

Footpaths

[MavEtJu]

Here in Australia, or at least large (for big values of large) amounts of it, it's all above ground too. Where I'm coming from, the Netherlands, it's all below ground.

When I discuss it with the people here, they give me all kind of reasons why it should be above ground (limited but not only to unable to quickly repair, the famous cable cut from people digging and, believe it or not, the people who are doing the repairs now would be jobless).

Just a quick glance about how it could be done and you'll see that it would be quite a trick anyway: All footpaths in Australia are large blocks of concrete or asphalt, and the nice small tiles you see in shopping centers are also just laying above a concrete layer. Opening up that would be a major++ operation. Compare it to the Netherlands where all footpaths (and most of the bicyclepaths) are just 30x30 cm tiles laying on top of yellow or black sand, you'll see that it has a historical tradition to put things underground and have them easily accessible.

Re:Footpaths

[Anonymous Coward]

New housing estates in Sydney are being built with the local (low tension) powerlines underground. I live in one such suburb, and we have remarkably few power outages compared to other, older suburbs where the powerlines are above ground.

On the other hand, high tension power is still distributed above ground by those massive towers. On the gripping hand, though, various authorities are considering how to move those high tension lines underground.

Official report from Edison Electric Institute

[philgross]

We could continue to debate this endlessly, but maybe you could save time and just read the official report?

I'll also mention that 4 of the 5 NYC boroughs (Manhattan, Brooklyn, Queens, and the Bronx) have their electricity distribution almost entirely below ground. It was a massive investment, but it was long ago.

Re:Maybe in Hawaii?

[snuf23]

Not exactly. Here's some good information on it:

State's utility system in better shape now

Some key points:
Since 1966 new neigborhood's have been built with underground electrical cabling.
Since hurricane Iniki devestated the island of Kauai in 1993 a lot of utility wiring has been moved underground.
Only about 40% of Hawaiian Electric Company power lines are underground.

At least here on Oahu we have plenty of power lines and during bad storms some areas of the island often lose power.

Not an option in high water table areas

[EQ]

The same reasons most houses in coastal areas of Florida and other sandy-soil areas near water don't have basements. Water pushes right into them.

Try putting underground *anything* in gulf-coast Florida, etc.

Re:Water

[Anonymous Coward]

Here'a a free copy of the same story. It also says that the problem also has to do with the worksmanship of the junction box.

Re: shared costs

[johnrpenner]

competition creates its efficiencies; but it also creates its inefficiencies.
it has been remarked by a german that america is often very innefficient.

why? well, in america, first they construct a road. then they remember
that they need sewers, so a different department goes and tears up the
street the road crew had built, and lays in sewers, and puts the road back
together again.

then the power company comes along, they want to lay power -- so they
dig another ditch, tear up the road, and put in the power. then comes the
gas company, and then the phone company, and then the cable company,
all digging their own ditches -- that's america.

in germany, the town gets together, find out all who need to be involved,
and then lay down one large pipe -- road and concourse are built together
from the outset, and then you can lay in your: gas, water, cable, etc. as you
wish. anyone who wants to use it pays a fee. --road doesn't need to get
torn up, community works TOGETEHER.

now, whether it be america and germany -- or whoever
(or pick your favourite parties) -- the efficiency of good community
is not always factored in by those who only value competition.

2cents
j

Re:Water

[Technician]

pets (and people) getting electrocuted from lines that were buried 40 or more years ago and were now corroding or fraying.

We have learned from our mistakes. All newer high voltage buried cable is coaxal in design. The hot conductor is surrounded by a grounded jacket. A fault shorts the cable to the grounded jacket tripping the overcurrent protection instead of putting lots of voltage to the ground.

The situation in Ukraine

[Zx-man]

As weird as it may sound, quite a number of small towns here, in Ukraine have their powergrids (mostly) underground. It is so because in the 90s it was not uncommon for every piece of cable/wiring to get stolen sortly after being installed. So, back in day it used to be financially effective. Now with crime rates down it, probably, would not be worth the price, thought. But it stays as it was.

Or downtown DC is close the the Whitehouse...

[Zadaz]

Why this is modded +5 informative shows how bad the average person's logic is. Unless you pegged my sarcasm meter (which is possible) it seems more plausible that keeping the nations government stably powered is a more significant factor than the placement of the lines.

Power has gone out at least once a year for the past five years to my (Downtown San Francisco) neighborhood. Due to underground power lines. A couple months ago an underground substation exploded and burned the hell out of a woman walking on the sidewalk. A couple years ago directly in front of my apartment a short underground ignited flammable (sewer) gases which blew the manhole covers 40 feet in the air (And the power out for the whole day). No one was hurt, but one of the covers did go most of the way through a car.

My UPS gets a good work out.

A: Cost

[BeProf]

Speaking as the son of a retired rural co-op lineman, underground counduit is a very bad idea in most situation. Whatever conduit you put the lines in breaks down and can leak. You would have to insulate the lines, buy new excavating equipment that most utilities don't own (and train/hire people who know how to operate them), shut down surface streets for extended periods of time. You'd also have to punch holes in the basements of all the hosues served by this underground line and move most, if not all of the meters. It'd be a nightmare, and in many rural environments like ours the terrain would absolutely prohibit it.

Overhead lines are cheap and easy to break, sure, but they're also cheap and easy to repair. Which would you prefer? Having your heat and lights go out in the dead of winter maybe once or twice every year, but you get to have it back in an hour or two; or having your heat and lights go out once every couple of years and not being able to have it back for a day or more (i.e. after grandma's dead because she's frozen to death or because she fell down the stairs or couldn't find her pills in the dark or her respirator's backup batteries died)?

Its a cost vs. distance problem.

[CFD339]

Powerline transmission in the US covers vastly more distance per end user than in most of the world. At the same time, the pace of change and growth in virtually every town in city in the country is so very rapid that underground placement would require much more frequent changes and retrenching. Above ground transmission is better suited to this environment.

As a firefighter, I have had on many occasions to stand by near broken transmission lines or transformers to wait for power company repair trucks. While it seems to the person sitting at home to take a very long time, let me assure you it seems longer for the poor bastard standing in the rain or snow waiting. That said, when there is a problem that is isolated they usually show up within minutes. During a storm, they make every effort to prioritize based first on danger, second on the number of outages that can be fixed in a single repair, and dead last based on cost. When we have a reported fire, they drop everything to get to where we are as quickly as possible to disconnect service to the location -- so that we can be able to do our work more safely.

I've never met a single careless or lazy power company lineman. I suppose any that start out as such are soon quit or dead.