Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Seany on 06/04/2008 13:06:05
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They are so very ugly!
Why couldn't they put it underground?
Would it have short-circuitted the whole thing?
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There are moves to do just that but the programme to do so is much delayed. The reason it is not done very much (so far) is because the voltage is so high that it is hard to get good enough insulators to stop short circuits to ground. The high voltages are used because it allows more efficient power transmission. Power is lost by heating the wires and this loss is proportional to the resistance of the wire and to the current flowing. Using thicker wires to get very low resistance is expensive in material and the the extra weight would be a problem mechanically. By using transformers to step up to a high voltage (and Alternating Current) the same power can be transported with a lower current (Power = Voltage x Current). Other transformers step down the voltage before travelling the short distances to reach your home.
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Thank you very Much kind sir!! [:)]
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And it's hugely more expensive - like ten times the cost.
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It is not only the cost of installation, but the cost of repair. If something does go wrong with the wires, it costs a lot less to put a new wire up on a pylon (and less time to do it) that to dig up the roads to do it. OK, you can offset this by the fact that there will be fewer faults on underground cables, since they are generally better protected from weather than pylons - but things do, and will, go wrong wherever they are.
We have all of our services (including phone lines) underground around here. Every couple of years, the water seeps through the insulation on the phone lines, and the BT engineers have to come out to fix it. They would save themselves a lot of work by simply laying better cable underground, but because it is underground they are loathed to do so. If it was overhead, it would be fairly simple to just replace the whole length of cable.
The other problem with laying all your services underground is keeping track of it all (especially after they have lain there for several decades). Someone wants to come along and dig the foundations for a building, they can come along and instantly see where all the pylons they need to steer clear of are; but knowing what is underground is often more difficult. It can be done (records should be kept and filed, and then checked; and you could use ground penetrating radar or metal detectors - but it is less obvious, and easier to make mistakes). Even if you make sure that you do not actually cut through underground service ducts, you could be building over them, so making it more difficult to later maintain those services, and the weight of what you are building could put stress on the service ducts that could cause damage to them.
I am not arguing that pylons are ideal and underground is bad, and to show that putting things underground also poses its own problems.
As for pylons being ugly - I'm sure if you asked someone in the middle ages what they thought of all the castles being built they would have told you how ugly they were, and how they ruined the landscape. The problem with pylons is that familiarity breeds contempt. In another 100 years, when we no longer have any use for the pylons, and they will mostly have been pulled down or allowed to decay, people will be insisting that preservation orders should be placed on the few remaining iconic examples of beautiful 20th century functional engineering design. There is no accounting for taste.
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I find pylons beautiful especially when they carry the power across vast tracts of waste land.
Who could not be impressed by the massive towers that carry the power across the Thames at Dartford or the chains of towers that carry the power across the shallow waters to the islands off Brisbane.
What I do find ugly is the conglomeration of low voltage wiring and transformers that surround American suburbs.
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I read somewhere recently (I think it was related to the new transmission wires they're installing across Scotland to connect a new wind-farm) that to lay the highest-power cables underground requires the construction of a concrete duct approaching the size of a motorway. Bearing in mind that the Scottish terrain is pretty rugged, this is a mammoth engineering challenge, and hugely expensive. I wonder what happens if an underground duct has to cross a stream or brook?
Coupled with the reasons already given here, this explains why pylons are a far more viable option.
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Would you believe there is a Pylon Appreciation Society: www.pylons.org/
Underground High Voltage cables have considerable technical difficulty. They are pumped full of oil which often leaks and has to be topped up, so there can be damage to the environment.
A few year ago, in the Everglades (Florida) it used to be common practice to repair high voltage cabling faults live from a helicopter. The repairer would operate from a cage projecting from the helicopter and the whole lot, helicopter, pilot cage and repair man, would be charged to the AC voltage of the cable. This practice was eventually abandoned after Union objections to it being somewhat dangerous.
PS I posted a similar version of this post but it disappeared :-(
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There is also the consideration of Power Factor. The capacity between underground cables is markedly higher than between overhead cables, because of the separation of conductors. This affects the power factor which, for AC distribution, has an effect on losses.
Regarding the way they look, I spent my youth in the West Country and appreciate the wilds of Dartmoor. I have also done my share of walking and camping in Wales and Scotland. I really don't think that overhead cables are particularly objectionable out in the wilderness; they are few and far between, in any case and can have an air of romance about them. They can, however,turn industrial and semi industrial environments into even more depressing landscapes. They seem to look worse without some of Nature to dilute them.
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It has been suggested that there are ill effects on the health of people living close to high voltage power lines do to the electrostatic fields from them, I do not believe this explanation if there are any ill effects I think it is due to excess Zinc in the environment from the galvanised steel towers or ozone generated by the high voltage
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Thank you George and Sophie. I realise that it costs a lot for installation, and fixing..
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ill effects on the health of people living close to high voltage power lines do to the electrostatic fields from them
I always understood people to connect it with magnetic fields (I subscribe to neither, personally).
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Having recently done some work on buildings, inhabitants, and power lines, it transpires that buildings very greatly (or totally if there's much metal in the construction) attenuate the electric fields inside. The magnetic field does penetrate however... but drops off to negligible strength once you're a few 10s of metres from the power lines anyway (depending on the voltage/current and size of pylon).
I've been standing in muddy fields measuring E and H fields from powerlines myself, as well as discussing with a proper EMC consultant (not the snake-oil salesman type).
The magnetic fields are way below international safety limits. (The electric fields outside and right underneath the pylons can get moderately close to the limits).
If the cables were underground then people could actually get closer to the conductors and experience higher magnetic fields than from overhead wires. The ground/earth will completely sheild the electric field from buried cables though.
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There is also a problem getting rid of the heat produced in underground cables.
There was a plan to build a big windfarm on the Outer Hebrides which sparked a big debate about the cables coming through beauty spots. Pylons are about 10 times cheaper. Another option was to run the cables under the sea as much as possible.
I would think the best plan would be to build the wind farms where the power is used.
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There is also a problem getting rid of the heat produced in underground cables.
There was a plan to build a big windfarm on the Outer Hebrides which sparked a big debate about the cables coming through beauty spots. Pylons are about 10 times cheaper. Another option was to run the cables under the sea as much as possible.
I would think the best plan would be to build the wind farms where the power is used.
Isn't heat produced from the wires in the Pylons though?
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The heat isn't a problem because they're air-cooled.
Same problem as using a mains extension lead. Whilst it's wound round the drum it can melt the cable; when it's unwound the heat does no damage.
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Yes.. So underground.. Can they just leave it unwound? It's not going to be dangerous, as it is .. underground..
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I would think the best plan would be to build the wind farms where the power is used.
Problem is that they don't al;ways build the factories in the most windy places (and, since windy places are often beauty spots or SSI's, or some such, so building factories there might not be politically very easy, and that is aside from getting all the employees and support services to move there).
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This is going back to the 18 century Idea of industrialisation, near where I live there is a small river the Loose about 10 miles long which runs thru a beautiful valley into the Medway but it is littered along its path with the remains of at least 10 hydro power schemes
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Yes.. So underground.. Can they just leave it unwound? It's not going to be dangerous, as it is .. underground..
Of course not wound up! I'm just pointing out that cables need to be able to get rid of all the generated heat by having space around them.
An underground fire is not a good idea. Think of the repair cost. You need a big tunnel to run the cables in, with plenty of ventilation.
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one problem with laying transmission lines underground is rodents and insects, also harder to locate, and maintain in adverse conditions.
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Yes.. So underground.. Can they just leave it unwound? It's not going to be dangerous, as it is .. underground..
Of course not wound up! I'm just pointing out that cables need to be able to get rid of all the generated heat by having space around them.
An underground fire is not a good idea. Think of the repair cost. You need a big tunnel to run the cables in, with plenty of ventilation.
Oh.. Does the ground not take up the heat?
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Oh.. Does the ground not take up the heat?
Earth is a fairly good insulator of heat. This is why something underground will remain at fairly constant temperature even as the air above may go from freezing to baking sun over a 24 hour cycle.
Apart from any other issue, the ground, being solid, does not support convection currents, which are a very effective way of drawing heat away in a fluid such as air or water.
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Thank you George [:)]