On 29/07/2014 11:36, Tim Watts wrote:
On 29/07/14 11:13, newshound wrote:
On 28/07/2014 13:29, John Williamson wrote:
On 28/07/2014 08:23, harryagain wrote:


Where exactly is this arc drawn for 30 minutes and for what purpose.?


The arc *can* be drawn by using the DC charge stored in the cable. No
claim was made that it ever had been drawn either deliberately or
otherwise, though it's the kind of trick that installation engineers
have been known to pull as a joke, or that happens when things go wrong
when commissioning plant of this sort.


If you watch footage of repairs to 400 kV overhead lines (typically shot
from helicopters) you will see long and impressive arcs being drawn from
these for several seconds while they are brought down to earth potential.

No - that's not what they are doing. Those lines are live.

What they are doing is making an equipotential bond between the line and
helicopter. The helicopter as basically a conducting object in free air
has inherent capacitance to ground and the the reactance is sufficient
to cause a not insignificant current to flow at 1/2 mil volts 50-60Hz

If your thinking of the bit of video footage I am thinking of, then I
have a suspicion that may have been a DC HV line anyway.

If the line were made dead, it would have been earth strapped at both
ends before anyone was let near it (standard operating procedure).

Indeed.

--
Cheers,

John.

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