Re: OT: electric blankie time

In message <memo.20051027170800.2976B@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Paul
Dormer <prd@xxxxxxxxxxxxxxxxxxxx> writes
>In article <247ijeJQRMYDFwSq@xxxxxxxxxxxxxxxxxx>, nojay@xxxxxxxxxxxxxxxxxx
>(Robert Sneddon) wrote:

>>
>> It also drops off as the square of the distance -- 240V in an electric
>> blanket a couple of centimetres from the skin is going have a lot more
>> effect than 275kV overheads thirty metres away.
>
>Remember, it's mainly 400kV in England (and Wales).

Has most of the 275kV stuff in situ in the 60s been replaced\upgraded
to 400kV?
>
>Walking under a power line, you can feel the electric field, or some
>effect of it.

Never did myself when I was up in the hills around the 400kV lines
there -- I think the bottom conductor is about 20 metres or so up from
the ground on the Supergrid pylons. You can hear a hum but I always
reckoned that was induction in the steel pylon frames flexing at 50Hz.
Moving to high-voltage DC would have fixed that and reduced transmission
losses if the down-converters could be made efficient enough (the Mother
of all SMPSes...)

Assuming the electric field is proportional to the voltage and to the
square root of the distance from the conductor, plus all the usual
physics blackboard caveats (free space between conductor and detector,
assumed infinite length conductor to eliminate end effects yadda yadda)
-- an electric blanket carrying 235V at a distance of 5cm to the skin
produces x amount of electric field at a given point on the skin
surface. At 400kV the conductor would have to be about 2 metres away for
the same amount of electric field to be present on the skin. At twenty
metres (and very few people live that close to a 400kV line) the value
would be something like 0.001x.

Underground cables have several metres of earth shielding plus the
armour around the conductors so they have even less electrical field
effect on people than free-hanging pylon wires.
--
My gmail account is nojay1 Robert Sneddon
.

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