Wisdom of Overhead Power Lines

[flickster]

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:
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


Why do we keep repeating a past mistake?

[kanicbird]

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.

[Metacom]

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...

[Sunspace]

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.

[flickster]

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.

[Polycarp]

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.

[GorillaMan]

Vast majority of the newer housing developments I've lived and been in all have underground utilities.
I doubt these are working at the multi-kilovolt levels of main power lines.

[Joey P]

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.

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.

[t-bonham@scc.net]

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:
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


Why do we keep repeating a past mistake?But who gets this economic advantage?

Lives lost due to downed lines doesn't cost the power company.
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.)
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.)
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.
Aesthetic value is completely meaningless to the power company bottom line.


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

[engineer_comp_geek]

Why do we keep repeating a past mistake?

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.


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...


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.

[Scruloose]

Yes, the wires in overhead power lines are bare.
[Johnny Carson]
I did not know that.
[/JC]

[kanicbird]

(nuke plants are the biggest, usually followed by a couple of coal fired plants).

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).

[flickster]

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


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.


But who gets this economic advantage?
Lives lost due to downed lines doesn't cost the power company.
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.)
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.)
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.
Aesthetic value is completely meaningless to the power company bottom line.

Repeating a mistake? It's certainly not a mistake for the utility company, just a smart economic decision!
So you're claiming we can only factor costs incurred by the power company?

[t-bonham@scc.net]

So you're claiming we can only factor costs incurred by the power company?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.)

[rexnervous]

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.)

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.

[Polycarp]

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.

[Metacom]

There is some evidence, not sufficiently documented IMO, that link living near high voltage lines to various chronic medical complaints.
Have you head of any non-anecdotal evidence? I was under the impression that the only evidence was anecdotal?

[Metacom]

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).
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).

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.
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...

[danceswithcats]

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.

[Polycarp]

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

[flickster]

I consider the question of high voltage lines to be a separate issue from the question of overhead vs. underground local electrical delivery lines.
I agree. My concern was more with the local lines than high voltage. At least where I grew up in Tennessee, the high voltage lines were on special towers at a higher elevation with the undergrowth cleared to prevent problems from snapping tree limbs.

[Exapno Mapcase]

Some earlier threads:

http://boards.straightdope.com/sdmb/showthread.php?t=271288

http://boards.straightdope.com/sdmb/showthread.php?t=54765

My answer from that first thread still applies. In the U.S. the cost would be in the trillions. Not billions: trillions.

So who pays for that? Legally, the customers of the company putting in the lines. Chance that any state Public Utility Commission would approve this? Zero.

Emergency costs, even in the billions, are a meaninglessly small fraction of this cost. And they are often allocated differently, i.e. they come out of a utility's set-aside money for such emergencies, out of the shareholders profits, or out of state emergency funds. In none of these ways do ordinary customers wind up paying for the costs.

Politically, and in every other way, the cost of retrofitting the country does not fly. Even the costs of retrofitting hurricane states like Florida and Louisiana are much higher than the occasional emergency cost.

Polycarp, the Quackwatch article, Power Lines and Cancer: Nothing to Fear (http://www.quackwatch.org/01QuackeryRelatedTopics/emf.html).

[flickster]

Thanks for the links. I should have figured this topic had been discussed in relation to hurricanes in the past.

[ouryL]

But who gets this economic advantage?

Lives lost due to downed lines doesn't cost the power company.
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.)
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.)
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.
Aesthetic value is completely meaningless to the power company bottom line.


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

I'd rather trim limbs than to dig up roots. :p :dubious:

[David Simmons]

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.I don't worry too much about the induction from high voltage AC lines because I don't live near any. If I did I might.

The 1 million volt (+-500000) volt DC line of the Pacific Intertie runs down the eastern side of the Sierra Nevada Range near here. I used to fish a lot at a campground on the Owens River through which the power line runs. There was a lot of sag in the lines in summer and they were only about 20-25' above the ground. I always was a little leery of walking under them and I never, ever pointed my finger at them. Silly? Maybe but it didn't cost me anything and why be half safe?

[flickster]

I'd rather trim limbs than to dig up roots. :p :dubious:
I've seen some pretty bad trimming jobs - trees never recovered and would have been better off being dug up.

[GusNSpot]

Try to watch an helicopter going down a right of way with a large rotation blade hanging down beneath it....... Now those are messy........ Even worse that brush hogs on a pole.....

[Joey P]

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?


But wouldn't they have to know where it is to start. I just hot them come out and mark my property so I could put up a fence. I wasn't hear when they did it, but I'd imagine they just used a map (and some common sence...hey there's a meter over there, I don't care what the map says, SOMETHING must go that way). Even if they had something to detect live lines underground, would they really go over every square inch of property, or just use it to help trace the lines on the map.

Anecdote. Years ago there was two bouts of construction in front of my dads business. During th first one he got a pretty good look at what runs under the street. A few years later when they came to tear up the road, my dad noticed that they were about to start digging in a place where he KNEW there was a utility line. He went out there to mention it to them and they pretty much told him to mind his own business. The lines weren't on the map, Diggers Hotline didn't mark them on the road, ergo they arn't there. (Even with my dad saying that he actually saw them with his own eyes). They dug anyways and wound up knocking the power out for a few days because of it.

[BubbaDog]

Note: Bubbadog has 28 years experience with electrical utilities -
But who gets this economic advantage?
[list]
Lives lost due to downed lines doesn't cost the power company.Our lawyers would disagree with this statement. Picture this - line falls on the ground, local citizen walks up to it and attempts to pick it up, and dies.
Court case with jury - poor grieving widow vs mean old power company. The power co lawyers usually settle these out of court by paying.

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.)Lawyers tell me that, this too, is untrue. Many times, in search for deep pockets, the electric company is sued for having the pole too close to the road, failing to paint it bright orange, flagrantly not hanging a lit blicking sign that says"do not run into this pole with your car", etc. Even if its frivolous the electric company has to staff and pay legal fees to defend the company.


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.)
Every outage has a significant cost to the power company. The utilities are mandated to record frequency and severity of outages. If these stats show any indication of lax effort on the utilities part the state regulators gleefully use this as ammunition to deny rate increases for the utility.
The utilities must pay response personel (call centers, dispatchers, on-call labor) to handle these outages.
You are correct that customer losses due to outages is usually not reimbursed by the power company. Years ago, during cleanup of a significant windstorm, I was yelled at by a guy who told me his freezer food was thawing. He had been out of power for 4 hours. I asked him how he knew it was thawing and he said that he checked it every half hour since the outage. :smack: Most freezers will maintaing frozen foods for at least 20-40 hours if you don't open the freakin door every 20 minutes to let the cool air out In this case we had all cutomers back on in 18 hours.


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. Utility budgets for trimming trees is easily in the millions of dollars each year. You are correct that this cost is less than the cost of burying existing power lines.

Aesthetic value is completely meaningless to the power company bottom line. In our service territory all new residential power is provided underground. Main distribution arteries that supply this are still overhead. You may be able to see this when you see poles along main streets which then feed underground into neighborhoods. It is significantly more expensive to dig the ditches and buy the expensive underground cable than it is to erect poles and feed bare conductor on to those poles. The utility understands the desire for aesthetics but it must also show prudence in its costs. This is not just a utility decision. Every dime a utility spends must be justified to state and federal regulators.


Repeating a mistake? It's certainly not a mistake for the utility company, just a smart economic decision!
An economic decision that realizes that the rates necessary to support a 100% underground system would bankrupt our customers. So this is correct. Most utilities carefully select where they put underground systems.