" I see the diasharge brushes on remote sites, radar, repeaters, surveillance,
even airports surrounded by towers with brush arrays a few tens of feet
across?"
"Not effective at all? What about a row of air terminals on a house?"
Motorola's R56 grounding standard for comm sites does cover air terminals (not
brushes though):
"The use of air terminals (lightning rods) on a tower may be appropriate in
some circumstances to protect
antennas from a direct lightning strike. If the tower is over 45.7 m (150 ft.)
tall, side-mounted antennas
are vulnerable to direct lightning strikes. Side-mounted antennas installed at
a height greater than
45.7 m (150 ft.) may be protected through the use of horizontal lightning rods.
The horizontal lightning
rods are attached to the tower, just above and below the antenna."
So it's an attempt to absorb the strike, not prevent it. And they also show
them used on building roof tops probably to meet NEC code.
In Roger Block's (PolyPhaser's) "The Grounds for Lightning and EMP Protection"
(no longer published), there is a reference to a US Navy report and FAA video,
but no report numbers or specifics:
"A US Navy report, done in cooperation with the USAF, NOAA, and the FAA, states
that after several years of study, brushes have not prevented any lightning
strikes. (If they worked, NASA would be using them extensively.) The FAA even
did another study on the brushes and have video tapes showing them being hit
again!"
I have witnessed a broadcast tower being hit that had the "brushed-ring"
mounted on top of the tower/antenna. It was the only one in the area that had
a brushed-ring. So it didn't seem to work from my perspective.
Some articles on lightning have claimed that some of the steel-brush air
terminals on radio towers have ended up causing fires when the melted steel
from the brushes fell onto flammable or dry materials. However, no examples
were given. Seems plausible though.
73, de ed -K0iL
-----Original Message-----
From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On Behalf
Of KD7JYK DM09
Sent: Sunday, July 01, 2012 11:22 PM
To: rfi@contesting.com; Kim Elmore
Subject: Re: [RFI] Lightning Protection
"I asked them about these corona brushes and was told that they are
ineffective. Once the electric field exceeds about 50-100 kV per meter,
everything -- grass, trees, fences, antennas -- are all in corona and the
air is about as "saturated" with corona ionization as it can get. These
corona brushes have no effect"
Several of htese at a site won't lower the potential in the immediate area
preventing charges in the 50-100 kV per meter range?
I see the diasharge brushes on remote sites, radar, repeaters, surveillance,
even airports surrounded by towers with brush arrays a few tens of feet
across?
Not effective at all? What about a row of air teminals on a house?
Kurt
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
----------------------------------------------------------------------
This e-mail contains Omaha Public Power District's confidential and proprietary
information and is for use only by the intended recipient. Unless explicitly
stated otherwise, this e-mail is not a contract offer, amendment, or
acceptance. If you are not the intended recipient you are notified that
disclosing, copying, distributing or taking any action in reliance on the
contents of this information is strictly prohibited.
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|