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Following the Great Power Outage of 2003, the media devoted a great deal of attention to ideas of how the distribution grid system could be upgraded to carry bigger loads. One of the ideas put forth by (maybe) GE (I don't want to be sued if I'm misremembering the guilty party here) was to design power lines that would consist of exotic alloys that would enable the lines to carry loads that would bring them up to temperatures nearing red hot without sag or burnout. This is so stupid! If a conductor is heating up from the current flow, than it's too small for that current flow. Altering its chemistry to withstand continuous high temperatures would only serve to increase the wastage of energy by encouraging the production of all this waste heat. Duh! Hey, I'll take on one of their engineers' jobs at half the price.

The "exotic alloy" used for this is steel. It's not for new construction, but for upgrades on existing towers. It's cheaper to buy new conductors and string them than to have a completely new line built.

What limits the thermal capacity of the line is the sag. The conductors get longer when they heat up. If it sags to much, you end up with a conductor below minium clearance.

The trick is to have an aluminium "shell" sliding on a steel core. The aluminium conducts the electricity, while the steel keeps the wires in the air. Steel doesn't expand as much with temperature as aluminium does. This means that you can allow a considerably hotter conductor compared to if it had been all aluminium. 200°C versus 90°C if memory serves me.

This is not the same thing as an ordinary conductor with steel core. In the latter case the steel and aluminium lack the sliding layer between them, and thus you can't allow it to runs as hot.

I'll see if I can dig up a reference.

It seems my memory wasn't quite as reliable as I thought. It should read 170°C, not 200°C. Foot in mouth!

And there are some exotic alloys used too. In addition is seems they do use this for new construction too. The article below provides a good overview.
http://tdworld.com/ar/power_transmission_line_conductor/index.htm

[This message has been edited by C-H (edited 02-29-2004).]

atwater_kent,
You're darn right there!.
I can't say that I've heard of warped thinking like that before.
Running wires until they are red hot sounds silly and only adds to the in-efficiency of the system, which to a degree, makes the use of HV transmission pointless!.
Another thing is, a wire running that hot would be a definite fire hazard, should it fall.

Thank you, your honor. I rest my case.

I'm entering this discussion late, however there is something important that is being missed here. The purpose behind the upgrade potential is to overcome the N.I.M.B.Y. factor that seems to exist everywhere. People want unlimited power availablility, but only if the transmission system is in someone elses back yard. One of the most serious obstacles to improving our distributuion grid are the endless lawsuits and environmental impact reviews that come about whenever a utility wants to add a line. It is far far easier for them to increase capacity on existing lines, however the wire material properties have now imposed limitations. The change to "exotic materials" would allow additional capacity on existing infrastructure without the cost, and more importantly the long wait, involved in building new lines. The increased operating temperature represents only an additional loss of about 0.01% efficiency given the extra capacity, by far an acceptable trade-off.

It would seem that instead of "running red hot to meet demand" the better answer would be to increase voltage, that would require larger/longer insulators on the towers and some towers would have to be upgraded to meet the additional height required for the longer standoffs.
As a nation we need to look at creating federal regs that mandate manufacturers of electrical devices to meet energy efficiency standards and developing more local cogens to reduce the need to transmit.
I keep hearing that Fuel Cells are cost prohibitive but I expect that with oil above $50 (and when things settle down the price will still be over 30) that natural gas and coal will soon follow with their own the increases. Then maybe fuel cells will be viable. Locating small units that serve a community at a hospital or a shopping mall, and running them on natural gas would provide a safer, more secure grid. Steam stripping the H2 form the natural gas and using the waist heat to for HVACs and chillers for refrigeration for food outlets in shopping centers would also reduce the electrical load of the facility that incorporated the cell.
Anyways it’s just a thought…

Ray,
I would tend to agree with you on the idea that Electricity needs to be generated locally.
And Fuel-Cells would tend to be the option that I would use if I had the choice.
But it makes you wonder though, the Fuel-Cell is by no means the "new kid on the block", it has been around for some years now and it is good to see that real research on this sort of technology is really taking off.
If you had a Fuel-Cell in each town, there would be no need for a Transmission Grid at all.

When my company upgrades a transmission line it is normally rerated from 65 degrees C rise to 100 degrees C. C-H is right, sag is the limiting factor. Just by increasing structure height the line can be more heavily loaded. There are at present no exotic materials involved in electrical transmission that I am aware of. Most likely because there are none that are economically feasible. Local generation of power is not done because it is not economically feasible. Fuel cells, ditto. Anyone suggesting the use of fuel cells is probably unaware of the HUGE amounts of electrical power generated by present technology and how relatively inexpensive it is.