John Gilmer wrote:
wrote in message
...
On Oct 15, 10:54 am, Ian Jackson
wrote:

One reason for lightning conductors (and for grounding elevated
conductors, like radio antennas) is that it helps to stop a high
electrostatic charge from accumulating in the air immediately above
them. The intention is to PREVENT a direct lightning strike, rather than
conduct a strike to ground. Of course, if a direct strike DOES occur, an
antenna (and even a stout lightning conductor) may be seriously damaged.
--
Ian

"The only problem with that is that the charge is so quickly
replenished
that I think trying to bleed off the charge is a waste of time."

The turn of the century genius, Testla, patented some lighting protection
devices based on having an insulated "cap" at the highest object on the
protected property. The "cap" would rise thousands of volts above the
protected structure and this would reduce the tendency of lightning to
strike.


This is done in some HV test laboratories to avoid flashover to the
ceiling and to make the field more representative of "outdoors".. they
hang a semiconductive curtain in a horizontal plane above the apparatus
which charges up and makes what's above look less like "ground"


There's also the whole thing of surrounding a valuable structure (e.g.
ammunition storage bunker, rocket launch pad) with an array of high
towers with grounded wires from the tops of the towers. While no
guarantee that lightning won't strike elsewhere, it definitely ups the
odds of the protective structure taking the hit.

here's a pictu
http://commons.wikimedia.org/wiki/Fi...launch_pad.jpg

On Oct 16, 10:43*pm, Jim Lux wrote:
John Gilmer wrote:
wrote in message
...
On Oct 15, 10:54 am, Ian Jackson
wrote:

One reason for lightning conductors (and for grounding elevated
conductors, like radio antennas) is that it helps to stop a high
electrostatic charge from accumulating in the air immediately above
them. The intention is to PREVENT a direct lightning strike, rather than
conduct a strike to ground. Of course, if a direct strike DOES occur, an
antenna (and even a stout lightning conductor) may be seriously damaged.
--
Ian

"The only problem with that is that the charge is so quickly
replenished
that I think trying to bleed off the charge is a waste of time."

The turn of the century genius, Testla, patented some lighting protection
devices based on having an insulated "cap" at the highest object on the
protected property. * The "cap" would rise thousands of volts above the
protected structure and this would reduce the tendency of lightning to
strike.

This is done in some HV test laboratories to avoid flashover to the
ceiling and to make the field more representative of "outdoors".. they
hang a semiconductive curtain in a horizontal plane above the apparatus
which charges up and makes what's above look less like "ground"

There's also the whole thing of surrounding a valuable structure (e.g.
ammunition storage bunker, rocket launch pad) with an array of high
towers with grounded wires from the tops of the towers. *While no
guarantee that lightning won't strike elsewhere, it definitely ups the
odds of the protective structure taking the hit.

here's a pictuhttp://commons.wikimedia.org/wiki/Fi...aunch_pad.jpg- Hide quoted text -

- Show quoted text -

yeah, the nasa pads have towers and long sloped wires to try to catch
lightning also.

for hv work we mostly do it outside or in a very tall building (the
octagonal one just left of center in the top picture is open inside
and about 80' tall.
http://www.ewh.ieee.org/r1/schenecta...2007_lenox.pdf