Re: [Phys-l] high voltage arcing

[brian whatcott <betwys1@sbcglobal.net>]

 I have some questions too:

1) Why are you giving thought to what seems to be occurring in a 
computer animation?
The same Utube channel has very many authentic helicopter transfers of 
linesmen.

2) Supposing that one can estimate the capacitance of man represented by
 a tube measuring 0.6 m diam, 2 m long, how much current would charge it
 to a representative high pylon voltage?

3) What is the usual breakdown voltage of air. Is it about 1kV/mm ?
So a 0.6 m discharge would represent how much voltage?

Brian W


On 7/6/2010 4:57 PM, Stefan Jeglinski wrote:
> http://www.youtube.com/watch?v=9tzga6qAaBA
>
> Questions:
>
> 1) If suit is faraday cage, how come it can be open at the face?
> Thinking in terms of something like an infinite conducting plane with
> small hole (see Jackson) - electric field lines will "intrude" but
> maybe the potential and the size of the opening are safe here?
>
> 2) Can't tell if sitting platform is insulated from helicopter. Audio
> implies helicopter is being brought to same potential but somewhat
> unclear (I would think this more or less required to prevent any risk
> of arc (wire to helicopter), even if possibility is remote.
>
> 3) Once charged, clamps appear to be used to maintain potential while
> moving over to the line, but of interest is when copter pulls away.
> He unclamps while using probe to presumably maintain potential, but
> as separation occurs, significant arcing again occurs. Why exactly
> would this be? Presumably the copter and line and suit are in
> equilibrium at this moment just before separation. Perhaps the copter
> cannot not fly off and maintain a massive charge on it (if it somehow
> did, think of the landing). But why not? Why would it all arc off
> right at that time and not just eventually "drain" off into the air
> due to it's high electric field?
>
> Summary:
>
> high E-field causes initial arcing to bring to equilibrium
> disconnect while at equilibrium causes equivalent arcing
>
> If asked to have predicted what would happen at disconnect, my
> (obviously incorrect) intuition would be to say "well there might be
> some small arcing" but the copter would fly off charged and
> consideration would have to be given to the charge eventually being
> drained off into the air. What is the time constant for such a drain
> - obviously MUCH shorter than I might have imagined, even considering
> factors such as humidity.
>
>
> Stefan Jeglinski
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