Lightning [RE-wrenches]

Bill Brooks billb at endecon.com
Sun May 30 23:49:03 PDT 2004


 

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Bruce,

Several years back John Berdner and I were discussing these types of
"air-gap" surge arrestors. They are used heavily in Florida so Gator Tom may
be able to chime in here. The problem with this concept is that they cannot
be used on the DC side of the system. Once an arc is established, a 500 Volt
PV system will easily maintain a 0.5 in air gap. Even at 60 volts, fairly
large arc distances can be sustained. I think this rules them out on the DC
side unless you are only planning to have lightning at night.

Bill.


-----Original Message-----
From: Bruce Geddes [mailto:b.geddes at clear.net.nz]
Sent: Sunday, May 30, 2004 1:28 PM
To: RE-wrenches at topica.com; RE-wrenches at topica.com
Subject: Lightning [RE-wrenches]

Hello Wrenches,
                            I have read the summary on lightning discussions
from this list and have an idea I would like to put out there for discussion
/ constructive criticism from minds greater than mine.

When working with electric fences I know that a degree of lightning
protection could be afforded by forming a coil of wire 2" diameter and 10
turns spaced 1/2" apart in the hot lead and running an earth wire 1/2" or so
away from it.  The idea was that this formed an inductor and the short
duration of a lightning pulse means it is high frequency and this inductor
would present enough reactance that the voltage developed would cause arcing
to the earth wire.  As each turn arced, the voltage would drop until the
last few turns the voltage was too low to jump the air gap and at that point
the electric fence energizer could handle it as the operate at around 8 to
10kV.

Could this idea be adapted for renewables?  I know the air gap would need to
be pretty small and the conductors would be quite large but I am interested
in ideas about how it would work.

The problem for me is that any surge arrrestors that have visual indication
of going o/c are very expensive and standard MOVs don't have any visual
clues as to operational ability.  This coil would work after repeated hits.

I throw it over to you all.

Bruce Geddes
PowerOn

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