"Richard Clark" wrote

wrote:

Richard Harrison wrote:
Richard Clark, KB7QHC wrote:
"(don`t fall for the monster under the bed stories of gazillion volts
at
a bajillion amps)."

It's not a monster under the bed. But it is a heaven of a blast!

Hi Dave,

The point of the monster is that it is NOT under the bed, but in the
heavens. Let's look at the numbers you provide:

First peak 100,000 amperes with a second strike of
50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth]
of 100 useconds for each peak.

Expressed as power into a section of tower where the cumulative
resistance is 1 mOhm (not unreasonable) and giving the stroke a full
second sustained current flow (I've never seen such a long one) so we
can round the numbers into watt-seconds (never mind KWH); and figuring
a duty cycle of 0.01% based on your pulse width, but let's get
extravagant and say 0.1%; then both strikes express all of 150
milli-watt-seconds of power.

500 amperes sustaining current in the lightning channel for 300
milliseconds.

Again, expressed in watt-seconds (sneering KWH) this probably doubles
the power burden another 150 milli-watt-seconds. Total power: less
than half a watt-second or as much heat as 1/10th of a Christmas tree
bulb held for the same time as the strike. For those who remember
NE-2 bulbs in their radio's front end, these are rated at 1/4 Watt.
The paranoid may wish to parallel several, but such devices exhibit
what is called current hogging - one will fire to destruction before
the others light up.

To demonstrate the catastrophe that is so often associated with a
strike, divert the same strokes to a nearby tree that shows all of 10
Ohms resistance in its sap: 3 KW-Seconds. Try holding three clothes
irons for 1 second. :-)

Even this is barely remarkable given the heat is spread over a
considerable bulk. What makes the difference so destructive? That
same time element. The heat does not have the leisure of dissipation
in 100µS and concentrates. This accounts for the scoring of a strike
on metal, or the steam explosion in a tree trunk.

4) Electric field intensity prior to prestrike is greater than 10,000
volts per meter.

Conclusion: Lightning has lots of energy.

Energy is a strange thing, sunlight has vastly more energy than radio
waves at HF (or VHF or UHF or SHF or....) No one worries about their
radio at the beach, but they put sun screen on their skin. Walking
across a wool carpet generates far more energy than a pre strike, but
hardly enough power for a pinwheel. Separating two sheets of typing
paper is about the same risk.

This does not diminish the liability to sensitive components. The
electric fields created by the casual separation of paper can destroy
a transistor IFF it is not in a circuit. The power absorbed by
common, resistive components in relation to that same transistor
protect it simply. There are some circuit designs that seek a high
input resistance that easily fail to this assault. I should note that
in this day and age of surface mount that there are also resistors
that can be destroyed by these casually generated potentials.

Systems have been designed to
not only survive a direct strike but to operate through the direct
strike. All it takes is $$$$$$.

Well, for the amateur (not working through a strike) perhaps $$.

The risk is: "Do you maintain 0.001 Ohm or better strike paths?"

73's
Richard Clark, KB7QHC

Hi Richard - can you please explain this "duty cycle of 0.1%" ? I thought
it was expressed as a 10% duty cycle - but then a 50kva strike would be
expressed as 5kva sustaining current in the lightning channel, not 500
amperes. Dave - was that 500 amperes a typo or the figure used by the USAF
for protection design? My internal surge protection is designed for 10kva
max, and the rooftop downconductors would certainly be expected to carry at
least 5x that much for a short time from a direct attachment. Even internal
AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which
does incidentally happen from those 100kva strikes. It just happened less
than half a mile up the beach from me last month.

Thanks,

Jack Painter
Virginia Beach VA

On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter"
wrote:

Hi Richard - can you please explain this "duty cycle of 0.1%" ?

Hi Jack,

Duty cycle is a simple ratio of on time to off time. It would be
presumptuous to offer that the strike off time for any particular spot
on earth is hundreds of years, so the choice of one second is suitably
long enough given strike components have long since faded, but are
easily recent both.

The shape of the pulse complicates the estimate because Duty Cycle is
often expressed in the expectation of a square wave. What is the on
time? When you get into pulse work, most in the field arbitrarily
assign the width of the half-power, or half-voltage points. For
Dave's numbers, this would be some 100µS which, when compared to 1
second is actually 0.01%. Being generous, and given the shape of the
decay I simply threw in a 10X fudge factor.

I thought it was expressed as a 10% duty cycle

10% of what? Lightning current flows for 100µS and is off for 1mS?
Dave clearly expresses lingering current flow out to 300mS so that is
clearly wrong.

- but then a 50kva strike would be
expressed as 5kva sustaining current in the lightning channel, not 500
amperes.

Where did the volts come from? If the pre strike fields are running
10KV then your strike has only 5A in it. This is the pencil whipping
that comes with lightning: the voltage description. ALL of that
voltage is dropped across 10000 feet of discharge length, not in the
last 3 inches from the tip of the bolt to ground.

In normal, settled air, in the most benign weather without any
disturbance, the potential gradient from earth to sky is 180V/M. That
is to say, your head is at an elevated potential of 300V with respect
to your feet. At an altitude of 10000 feet the potential is
1,800,000V without any inducement to discharge.


Dave - was that 500 amperes a typo or the figure used by the USAF
for protection design? My internal surge protection is designed for 10kva
max, and the rooftop downconductors would certainly be expected to carry at
least 5x that much for a short time from a direct attachment. Even internal
AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which
does incidentally happen from those 100kva strikes. It just happened less
than half a mile up the beach from me last month.

You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether. As I offered in other
postings: where did the voltage come from? If your tower is of the
standard design, you are not going to develop any appreciable voltage
unless you introduce resistance or impedance to develop it from the
current flow. 100,000A through 0.001 Ohms may give you 100V at best,
and only if you can reach the top of tower where the strike hits.

For those who want to multiply this voltage with Z, calculate the
impedance of a 12" diameter wire 50' tall at a frequency of 1MHz.
Perhaps this will make an NE-2 glow, if its leads are long enough.

It just happened less
than half a mile up the beach from me last month.

No doubt, but what exactly was "It" that happened? Stick 50 feet of
tower up into the air, and interrupt it with insulation and YES! arcs
will spark. No one needs an insulated $$$$$$ tower - thousands of
commercial installations typically discard that feature in favor of
simple $$ lightning protection.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
. . .
You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether. . .

A joule is a watt-second.

Roy Lewallen, W7EL

On Sat, 14 Aug 2004 16:20:49 -0700, Roy Lewallen
wrote:

Richard Clark wrote:
. . .
You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether. . .

A joule is a watt-second.

Roy Lewallen, W7EL

Hi Roy,

Quite so. Still missing the volt reference (and no mention of Ohms).

73's
Richard Clark, KB7QHC

"Roy Lewallen" wrote -

A joule is a watt-second.

==========================

The only trouble with Richard (Clark) is his abuse of the English language.

;o) ;o) ;o)

Punchinello, G4FGQ

On Sun, 15 Aug 2004 02:26:15 +0000 (UTC), "Reg Edwards"
wrote:

The only trouble with Richard (Clark) is his abuse of the English language.

Glad to observe you don't challenge my technical language.

Figured out mud yet? :-P

73's
Richard Clark, KB7QHC

"Richard Clark" wrote

On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter"
wrote:
The shape of the pulse complicates the estimate because Duty Cycle is
often expressed in the expectation of a square wave. What is the on
time? When you get into pulse work, most in the field arbitrarily
assign the width of the half-power, or half-voltage points. For
Dave's numbers, this would be some 100µS which, when compared to 1
second is actually 0.01%. Being generous, and given the shape of the
decay I simply threw in a 10X fudge factor.

Thanks Richard.

- but then a 50kva strike would be

Meant to say "ka" sorry.

Dave - was that 500 amperes a typo or the figure used by the USAF
for protection design? My internal surge protection is designed for
10kva
max, and the rooftop downconductors would certainly be expected to carry
at
least 5x that much for a short time from a direct attachment. Even
internal
AC wiring is designed to carry 6kv/1kva before dialectric breakdown.
Which
does incidentally happen from those 100kva strikes. It just happened less
than half a mile up the beach from me last month.

You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether.

Only the those destructive MOV power strips get rated in joules ;-)

My normal-mode silicon diode surge suppression is rated in KA (not kva,
sorry again).

http://www.transtector.com/documents...s/1451-001.pdf

the 10ka model has a 12,000 amp surge rating. I located one at the main AC
entrance panel (load side) and one on the station's 240v branch panel.
Transtector also produces "power strip" surge protection that is all silicon
with NO MOV's and NO L-G references. My station has no AC surge protection
references to ground, and all equipment is connected to L-N surge protection
power strips. Except the computer which runs through an Amer.Pwr.Con. UPS -
which although it has an unavoidable L-G MOV, it is first protected by the
two Transtector Fortresses.

It just happened less
than half a mile up the beach from me last month.

No doubt, but what exactly was "It" that happened? Stick 50 feet of
tower up into the air, and interrupt it with insulation and YES! arcs
will spark. No one needs an insulated $$$$$$ tower - thousands of
commercial installations typically discard that feature in favor of
simple $$ lightning protection.

73's
Richard Clark, KB7QHC

A strike on a home and/or power lines in which the surge was so powerful
that it blew the electric meter clean off the wall of the home (burning the
powerline and the service panel inside the home). I visited when it was
still smoking but they discouraged my camera. I did get a good picture of my
neighbor's pine tree striped from 75' in the air to 6' above the ground,
where it jumped to and split a wood fence. That was about 50' from the end
of my 60 meter dipole which was operating at the time. I'm thinking the
surge protection is working as advertised this summer. At this rate I'll
soon have more examples that just nearby strikes......but hopefully not.

73,

Jack Painter
Virginia Beach VA