Walter,

there is one more important reason why the high voltage cables are not dug inte ground. The interaction between the cables and ground will be eqvivalent to big capasitors. The value of these capasitors will be a formula which I don't remember from school, but it will be something like x*l/d, where l is the length of the cable, and d is the distance between the cable and ground. So the higher up in the air the cables are, the smaller value. And the power loss will be proportional to this capasity, and increase by the AC frequency.

When they need to transport high voltage over longer distances, and it's not possible to have them up in the air, they use DC. The reason for this is that the eqvivalent capasitors' influence is minimal at DC, in fact it can even have a positive effect. But they lose a lot of power in the conversion from AC to DC, and vice versa. From Norway there are a few huge power cables to Denmark, they simply lie on the bottom of the Nordic Sea.

>Tamar,
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>That would not explain it.
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>Here too, for longer distances and high voltages the transport goes through air, for a couple of reasons:
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>- cheaper.
>- easier to maintain
>- safer (can you imagine digging into a 100.000 volt cable?)
>- Higher voltages will create problems (shortcuts, leakage) if burried into the ground.
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>However as soon as the power is reduced for transportation to the actual end consumers, everything goes into the ground. In amsterdam you won't see any (end user) power cables going through the air, except for the trams.
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>In the small village I live, I don't know of any above ground cable. No power, no telephone, no cable television.
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>However, I must note that for example in Belgium, I'll find many cables above ground, just like in north america.
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>As for cheaper. It might be false economy. Power cables in the ground are not so susceptible to damage from icerains or accidents, so might be cheaper in the long term. I do not know the exact reasons why the do lay them underground here, but it sure is a lot prettier than having them above ground.
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>Walter,
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>>>It amazes me to see how many power lines run overhead in the USA and Canada. To me it seems funny to have, say, traffic lights hanging from cables strewn across the road. Over here all power goes underground after the cross-country pylons bring it into the main sub-stations. There aren't so many telephone lines coming from telegraph (as they're still called over here) poles anymore even (our street is quite exceptional but, being Victorian, there is no under-road infrastructure other than the drains).
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>>I suspect this is one of those cases where size is the big issue. North America is just so big that the difference in cost between running above-ground and underground cable is probably huge. It also may be related to when the cables were first put in. I also suspect that in much of North America, the cables were there before the inhabitants. (That is, electricity and phone were strung across huge spans of area to connect places that existed and then folks settled in between.)
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>>Tamar