Wisdom of Overhead Power Lines

Factual Questions
1

I understand the economic advantage of stringing power lines overhead on poles, but in hindsight wouldn’t it have been cheaper in the long run to bury them instead of having to repair them every time a storm blows through?
Not to mention:
[ul]The number of lives that have been lost due to downed lines.
The number of lives lost due to accidents involving cars and utility poles.
The costs residents have had to bear due to loss of utilities for extended periods (frozen food spoilage, etc)
The repeated costs of trimming tree limbs away from power lines
The astetic value of buried lines
[/ul]

Why do we keep repeating a past mistake?

2

Though u/g lines break less often, they are more difficult to repair when they do (more likely for food spoilage due to requiring more time to repair a u/g line). Also I would wag that the total cost is less w/ aeral lines then u/g, even considering those advantages. Also aeral lines give birds more places to rest. Also another wag, all the red tape required to dig up roads to lay the line.

3

A question for those who can answer this question: Does transformer placement have anything to do with it? Laying a power line underground seems easy enough, but finding a safe place to stick the transformer seems a little more difficult/expensive…

4

Air is an electrical insulator under normal conditions.

When you build an overhead power line, you just need to space the wires sufficiently far apart for the air to insulate them. You can carry very high voltages with large spaces, and thus less current for the same transmitted power, which means thinner wires. All you need provide is the hanging insulator that supports each wire.

Yes, the wires in overhead power lines are bare.

When you build an underground power line, you must provice continuous insulation over its whole length, because the water underground conducts electricity. Underground lines are vulnerable to leaks and breaks in the insulation, and are more inconvenient to access for repair when they do break. I believe that it is difficult or at least expensive to provide underground insulation against the same voltages that overhead lines can handle with a couple of metres of air.

5

Vast majority of the newer housing developments I’ve lived and been in all have underground utilities. Don’t ever recall having seen any of them having to be dug up for repairs. All of these developments have ground based transformer units for the houses.

I’ve never seen bare wires overhead, they’ve always been insulated.

6

After the fourth line-downing storm in eight years, my hometown inquired of our local utility why they didn’t put in underground lines. The answer is that they do a cost/benefit study with regard to how often the lines/poles must be replaced owing to storms, etc., vs. the probable number of times they must excavate to fix underground lines. In new developments where lines must only go short distances to serve a large number of residences, underground lines are preferable; in areas where lines must go longer distances, the pole and overhead lines approach is more preferable.

7

I doubt these are working at the multi-kilovolt levels of main power lines.

8

The keyword is “newer.” Give it 10, 15, 20 years and they’ll need to do work on them, then you’ll see the mess. Also, since the lines were buried as the houses/business/streets were built (or even before), it was much easier, no traffic, no trees no houses etc… to go around.

Also, the wires overhead are bare. If you’ve seen insulated you’ve seen one of two things. Either phone/cable lines OR bare wires with a weatherproofing coating on them to protect them from the elements. But that coating isn’t an insulator.

9

But who gets this economic advantage?
[ul]
[li]Lives lost due to downed lines doesn’t cost the power company.[/li][li]Lives lost due to car-utility pole accidents doesn’t cost the power company. (And generally, the car owners insurance is responsible for replacing the pole & transformer.)[/li][li]Residents’ costs (thawed food, etc.) doesn’t cost the power company. Their only cost is lower bills from people whose power is off. (And much of that is collected when power comes back on, as appliances, air conditioners, etc. run longer to get back to normal temps.)[/li][li]Costs of trimming tree limbs is paid by the power company. But it’s pretty minor, comparitively. And some have even tried to bill this to the homeowner, if the trees are on his property rather than public property. [/li][li]Aesthetic value is completely meaningless to the power company bottom line. [/li][/ul]

Repeating a mistake? It’s certainly not a mistake for the utility company, just a smart economic decision!

10

Every new neighborhood I’ve seen has underground lines. Why do you think we are repeating past mistakes?

I don’t buy a couple of your arguments either. Around here, whenever the power has gone out, it has been restored within hours, which is not long enough for food to spoil. Also, if a car has gone off the road already, it’s probably going to hit something. The fact that it hits a utility pole isn’t the fault of a pole being there. If the pole wasn’t there it would likely just hit something else. The points about safety, reliability, and asthetics are valid though.

Power is generated at a relatively low voltage at the generators. The losses in the line have a lot more to do with the current than the voltage, though, so transformers are used to step up the voltage. The higher the voltage, the less loss you have in the lines, but higher voltages are also more dangerous. You have to keep them up higher so people can’t climb up and electrocute themselve, and you have to keep the lines spaced farther away from things so that the electricity doesn’t arc over (the higher the voltage, the farther it will arc). Power is often generated very far from where it is used. Just because you have a power plant nearby doesn’t mean your power comes from there. Most power companies have a bunch of small plants, but only a small number of really big plants, and the big guys supply most of the power for the entire system (nuke plants are the biggest, usually followed by a couple of coal fired plants). In order to get the power to where it needs to go, they transform the voltage to a very high level (tens of thousands of volts), and run it over the really high voltage transmission lines that you see (the ones with the really big towers). This goes to a substation, which transforms the voltage down to a lower level (a few thousand volts), which then goes around to all of the neighborhoods. Inside the neighborhoods, transformers take the voltage down to what goes into your house (240 center tapped, so you can get both 120 and 240 circuits out of it). It’s very inefficient to carry power at this low of a voltage, so usually only a few houses will be fed from a single transformer, so in that respect transformer placement is important. These transformers are in large boxes on the ground (or in older above ground systems they’ll be in big cans on the utility poles). Substation placement is important too, since fewer substations means longer distribution wires and more wire losses, but then no one wants a substation in their back yard (there are many folks who are convinced just being near this stuff is bad for your health).

I’ve never seen a high voltage transmission line that had insulated wires. The distribution lines will sometimes be insulated, but usually won’t. If they are underground they will always be insulated.

Underground wire breaks are rare, but when they do happen they can be a real bitch to find. A friend of mine who works as a transmission and distribution engineer was telling me how they go out “thumping” sometimes. What they do is “thump” the broken line with a high voltage, and literally walk around in the area where they think it might be broken, listening for the thumping sound, and watching to see where the worms all come up out of the ground.

Also, people will often break underground lines when doing construction work. At least with overhead lines it is easy to see where they are. With underground lines, the only thing you have are diagrams showing you where the wires are suppsoed to go, and sometimes they aren’t accurate. People have dug into the ground and found a wire, only to have the power company come out and shrug, having no idea where the wire came from or where it goes.

11

[Johnny Carson]
I did not know that.
[/JC]

12

I thought nuke plants were kind of small while coal is usually larger in MW’age. For that matter hydro I though is usually bigger then a conventional nuke plant (given enough water).

13

When storms like hurricanes continually rip out power lines, we keep replacing the them so the cycle can start all over again. Now I realize that the quickest fix is to hang new wire, but I don’t see many efforts being made to bury utilities in existing overhead wire service neighborhoods and break that cycle.

So you’re claiming we can only factor costs incurred by the power company?

14

It’s the power company doing this, isn’t it?
And, yes, they generally only factor in their own costs (unless under some government regulation.)

15

Not necessarily. Connecticut Light & Power is trying to put in a 345kw trunk in SW Connecticut (which would help alleviate massive electrical burden in CT and eliminate huge federal penalties leveed against the state of CT), and after several years of study came to conclusion that the trunk should be built underground - at a significant additional cost.

They went through all the approval process.

And right before the plan was to start, a few local politicians raised a major stink because the plan would be disruptive to a few localized areas. Want to know why CL&P isn’t doing overhead lines. (Despite the fact that it’s all laid out in documentation)

So who knows what’s gonna happen now.

16

It is definitely worth looking into the possible dangers of 765 KV lines. At that level of voltage (and a to lesser degree with 345 KV lines) induction currents are induced in objects under or near them. There is a quite valid demonstration of this: if you walk directly under a 765 KV line carrying a tube for use in a fluorescent lamp, the bulb will begin to glow, by induction from the high-voltage line. There is some evidence, not sufficiently documented IMO, that link living near high voltage lines to various chronic medical complaints.

I consider the question of high voltage lines to be a separate issue from the question of overhead vs. underground local electrical delivery lines.

17

Have you head of any non-anecdotal evidence? I was under the impression that the only evidence was anecdotal?

18

I wasn’t looking so much for a discourse on how electricity is distributed but on the economics of a pole pig vs. the “large boxes on the ground.” And are they “on the ground” or “in the ground” (in a manhole) or some mix of the two?
Also, some newer neighhorhoods are certainly using above-ground poles. At least in these parts, most of the low-density neighorhoods are going with poles (although the service entrance cable is usually run underground from the pole pig to the meter).

Er, are you sure this is accurate? I thought that, with a live line, they had equipment available that could show you where it was?

I recently had the utilities come out to my place and mark my underground services before I put in a fence, and the electric company guys were by far the most specific, going so far as to spraypaint along exactly where it was crossing the fence line.

In fact, a google for “burried line locator” turns up plenty of manufacturers of such equipment…

19

One additional incentive for above ground placement of conductors is heat dissipation. Take those same conductors and bury them with insulation in close proximity to one another, the physical size must increase to acheive equal ampacity of an aerial set.

20

The state agency I used to work for did some accumulation of evidence when a 765 KV line was proposed that crossed our defined service area. But, as I said earlier, the evidence was not sufficient to give any sort of definite proof.