Re: Lightning protection

w_tom wrote:
You are joking. Right? The Fourier analysis of lightning
reveals energy at numerous frequencies. Lightning is RF
electricity. That RF energy is why lightning even causes
noise on radios. So now you say all those RF sine waves,
demonstrated by Fourier analysis, really do not exist? 

You're demonstrating a basic lack of understanding of
Fourier analysis.  Fourier used the sine function as a
basis function.  That doesn't mean there are sine waves
"in" the pulse.  If he had used some other set of basis
functions, would that "prove" that those other bases were
present in the pulse?

Don't get me wrong -- I'm ok with you saying there's RF
energy in the pulse, but not with your extrapolation to
"RF sine waves."  We're talking about impulses here.

Why
not just say the world is still flat? If lightning did not
have so much energy in RF, then radios would not receive that
RF noise. 

The radios are responding to the pulses.  Fourier series are a
useful way to analyze the response.  But the radio is essentially
a filter that alters the signal it sees.  It's not locking on to
some RF sine wave as you seem to think.

An example that demonstrates the RF nature of 
pulses and of lightning.  Pulses are not DC.

  If lightning were DC, then wire impedance would not be
relevant.  But lets put numbers to it.  A 50 foot 20 amp wire
may be 0.2 ohms resistance.  But wire reactance means same
wire has something like 120 ohms impedance to a lightning
transient.


Sure -- put numbers to it.  But show your work.

Why is impedance so much larger than the 
resistance?  Because the RF components of lightning make
impedance relevant and significant.  If lighting were DC, then
wire resistance and wire impedance would be same.  If
lightning were DC, then lightning would not have such
destructive consequences.

Huh?  Have you seen those videos of (as I recall) DC arcs in
high voltage transmission tests that are floating around the Web?

Fourier analysis demonstrates lightning is AC electricity at
many frequencies. Putting a number to the impulse - 8/20
microseconds - explains why so much energy is in the Megahertz
range. 

That's why I asked you for risetime numbers.  Show your work.
What fraction of the energy is in the MHz range?

Using DC analysis to explain lightning means that
person never first learned basic transient analysis taught to
first year EE students. 

I haven't noticed anyone here advocating the use of DC analysis
per se, so that's a red herring.

Lightning has massive energy in radio
frequencies which makes lightning so uniquely destructive. Those radio frequencies even mean that an earthing wire
bundled with other wires will induce transients on those other
wires. DC electricity would not do that inducing.

Think pulse.

Why are induced transients a problem with lightning? Because lighting is AC electricity - as demonstrated by
Fourier analysis, as demonstrated by discussion about
impedance, as demonstrated by what first year EE students are
taught, as demonstrated by noise on the radio, and as
demonstrated by so many industry professional cited in:
http://makeashorterlink.com/?X61C23DCA

Show me. Show me how lightning is only DC. 

Who's that addressed to?  I never said lightning is only DC.
I did say you haven't established it's "AC [or RF] sine waves."

Provide 
supporting facts.  Provide industry citations as I have done
repeatedly.  Declaring something without supporting facts is
classic junk science reasoning.  Where are those supporting
facts, the numbers, and industry professional citations that
declare lightning as DC electricity?  Without supporting
facts, et al, then your claim is really nothing more than
personal speculation or urban myth.  Show me.  Provide facts
and numbers.  Provide the underlying math.  Show me that
capacitors and inductors are irrelevant to conducting
lightning's DC electricity.  Show me rather than make
unsubstantiated claims.  Show me how you know that lightning
is DC electricity.  Show me that you also know the difference
between ultrasonics and electricity.

CJT wrote: 
That a pulse is susceptible to Fourier analysis does not make it
"contain numerous AC sine waves."



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