On Sun, 12 Feb 2006 19:59:37 +0000, Don Pearce burbled:

snip
Dunno if it has been mentioned, but these high voltage transmission lines
are all three phase. When they are perfectly balanced, they don't need an
earth wire, as there is no earth current. the earth wire only needs to
handle any out-of-balance residue.


On the UK system the Neutral carries out-of-balance current as far as the
sub - after that it is reflected onto the delta-connected phases. At this
point Neutral (the star point of the transformer secondary) is connected
to earth. So, strictly speaking, earth is not used as a conductor at all.

There are one or two earth wires run at the top of pylons. I don't know if
these actually connect to the pylon metalwork though.

At one time you used to be able to light a small torch bulb between
Neutral and a true earth (spike) in some areas, simply because of the volt
drop on the Neutral conductor (it was quite a distance between subs). Of
course, that didn't do through the meter! I don't think that's possible in
many places nowadays, but it may still be possible in some outlying areas.

The very large feeders mentioned by Richard are HV DC though, with one
variation using just earth return. Interesting system and, as he says,
carrying many MW.

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info