"As I understand it", Lightening is "more or less" the simple discharge
of static electrical charges of greatly differing potentials. Cloud to
ground to cloud, etc. The discharge alternates up and down with steep
rise and fall times with an average peak around 1 KHz and many
frequencies, up and down with diminishing strengths as you move away
from the peak. These charged areas are relatively large, with the
stroke "tending to hit the tallest object (where the charged areas are
closest AND the charge differential the greatest). HOWEVER the energy
in these charged areas is tremendous and as I said earlier, "Irregular"
so the tallest object often does not represent the spot where the
highest potential is located. For instance, although a 100' tower is
statistically the most likely target, the strike may hit the ground, or
a house no more than 150 to 200 feet away from that tower. The energy
stored in that moving charge is far more than a porcupine, or lightening
rod could bleed off to the point of preventing a strike, but they can
serve a purpose.
The Franklin Rod's (as reminded by several on the group) purpose is not
to prevent a strike, but rather to direct the strike away from doing
damage. The porcupine is incapable of preventing a lightening strike,
but they appear to do well with reducing precipitation static. OTOH I
claim no experience with their use.
As I've said many times, the first few years my 45G was up, it took 3
visually verified direct hits per summer, for 5 years, 2 the 6th, and
none (that I know of) for the last 7 years How many it actually took
those first 6 years? I have no way of knowing.
Typically the strokes between cloud and ground are between two large,
irregular shaped, moving charges. The descriptions of which remind me
of two giant Amoebas (for lack of a better term.) The potential
gradients are also irregular, so they are not represented accurately as
a spot with a high potential in the center
I'm glad Kim posted that information, but I wish the scientific
community would go back to averages rather than median. The average is
much more meaningful than knowing the number that lies half way between
the highest and lowest figure measured, at least they are for me.
Median is an interesting number, but average seems to be much more
informative and typically what is used for design. With a number of
samples large enough to be statistically valid a single, significant
outlier, be it high or low can substantially skew the median, but have
little effect on the average.
The so called "super strikes", or Positive lightening, which is
associated with sprites can move the median, but happen so seldom, they
have little effect on the average and when it come to lightening, do we
design for the median, average, maximum, or the best we can afford?
I know my relatively elaborate ground system did well, but how much
concrete would I need in this soil for an equivalent ground? When I
think of a lightening protective ground, I think of the area covered by
that system, not the contact area of the ground rods, or concrete.
Although the contact area of 32 8' rods is small, the ground system's
effective area is over a quarter acre. There is more to the protection
than the contact area and resistance.
I'm also interested in why we had so many strikes in this area for at
least 6 years, and so few since then. During that peak, this area
suffered a lot of damage. Trees completely blown apart, electrical
appliances, wells and even house wiring destroyed. Fortunately, no fires.
73
Roger (K8RI)
On 8/8/2015 5:40 PM, R Morris wrote:
I can't stop myself.....
That's the job of the wench, holding the plastic owl, facing true north.
Sent from my iPhone
On Aug 8, 2015, at 17:06, kr2q@optimum.net wrote:
With proper placement, these are great for keeping birds from landing on
surfaces.
TIC
de Doug KR2Q
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73
Roger (K8RI)
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