power lines?

[dkm0038]

I was always wondering something and hoped someone in hear had an answer...

Why do they set up power lines above ground on those elevated power line poles as opposed to burying them underground.

To me its seems more logical to run them underground, you dont have to buy all of those large steel or wooden polls and cherry pickers, less of a chance of the failing to weather or getting knocked over for any reason and it just seems safer to run them like we do our sewage and pluming.

Any opinons would help

 

[CarlB]

From a civil perspective..

I've always hears it's at least twice as expensive to go overhead versus undergound. probaly depends on a lot of factors, such as voltage, etc...
If underground you probably need a different, better insulated conductor. And it needs to be in a conduit for protection & easier replacement. Then you may need to grade the conduit to drain to maholes to infiltrate or be pumped out.
More hassles to replace UG versus OH lines.
If you need to excavate the line such as for a repair, expensive if not easily accessible.
More prone to damge from construction excavations.

The main arguments I've heard for underground being preferred is aesthetics, and protection from wind damage/falling trees.

 

[MiketheEngineer]

Cheaper - much cheaper - at least in the short run.

And easier to fix when it breaks - whcih can be quite often above ground. Just check out some the ice-storms we have had recently

 

[civilperson]

The soil gets hot from being adjacent to the power line. Only soil with high heat resistivity is suitable for burial.
Insulation for buried cable is expensive since it must prevent short circuits in wet conditions and with small distance separations. The overhead carrier is bare metal with large air gaps for insulation against arcing and shorts, (much cheaper and safer for the public).

 

[CarlB]

Oops...I meant to say the overhead is cheaper than the underground installation, which seems to be other's experience as well..

 

[bimr]

Much less expensive - first cost and operating.

As you move electricity, the wiring provides resistance to the flow of electricity and that resistance gives off heat. Above ground wires are air cooled.

If you buried the lines, you would have to cool the lines.

In the cities, the electrical wiring for medium and high voltage transmission sometimes requires cooling systems, manholes, etc.

 

[cvg]

contrary to common belief, lightning will hit and damage underground lines just as often as overhead poles and the result is harder to locate and repair underground.

 

[concretemasonry]

It all depends on the voltage and the conditions/exposure.

High voltage line are expensive to bury because of the heat, insulation and cooling.

In our area, distribution lines (lower voltage) are always buried because of reliability and aesthetics.

I had a lake home in northern Minnesota and the only reasonable supply was buried for the distribution. This is in a heavily forested area with considerable snow, but not much ice. Over 30 years and the clock never had to be reset except for the daylight conversions. This was several miles from the nearest above grade line.

The east has had a horrible history of outages from overhead lines that take forever to repair (one downed line per customer) that was inherited from the dark ages. With buried distribution lines, the repairs from ice, wind and trees are not necessary and all it take is to repair a single major line where resources can be quickly mobilized and finished.

There is also a method of using DC and advanced insulation/cooling that is available.

 

[chicopee]

There are too many backhoe operators in contrast to too few crane operators in the field.

 

[bimr]

"Reliability of Service
In general, underground transmission lines are very reliable. However, their repair times are much longer than those for overhead lines."

"However in general, underground lines do have more construction impacts, costs more, and have operational limitations."

http://psc.wi.gov/thelibrary/publications/electric/electric11.pdf