[time-nuts] GPS shielding by power lines?
David Ackrill
dave.g0dja at tiscali.co.uk
Sun Aug 10 12:01:48 UTC 2008
Alan Melia wrote:
> Hi Tom Brilliant I hadnt thought of the fields actually affecting the
> operation of the electronics! that is certainly something that might be
> interesting to check. I note there lines have three "phase" feeds but no
> neutral wire so they must use ground as the return path to any unbalance
> currents.(?)
On the UK 11kV overhead network the phases are all distributed without a
neutral.
At the 11kV/415V transformer the HV side is delta wound and the LV is
star wound, so the neutral/earth for the supply is taken from that
point, not from the HV side. So, you are correct, the connection to
"the general mass of earth" at the transformers is used as the return
path. Which is why there are regulations about the acceptable earthing
impedances at HV/LV transformers on an overhead supply. Tales of
Linesmen watering earth rods to get away without having to drive in more
earth rods and connect up to the transformers, and so avoid having to
drive rods into hard ground, are legion in the ESI...
In fact, if you look at most of the overhead high voltage distribution
systems, they are all phase only, no neutral...
Dave (G0DJA)
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