[BC] AM transmitter lightning sensitivity issue

[Ron Nott]

To reiterate one more time, here is a quotation from an NFPA official 
report: "It appears to the Panel that the NFPA 780 document does not 
meet the NFPA criteria for a standard since the recommended lightning 
protection system has never been scientifically or technically 
validated and the Franklin rod air terminals have not been validated 
in field tests under thunderstorm conditions".  This says simply that 
neither system has been scientifically tested.  However, NFPA 
continues to list the lightning rod system.

Discussions found on the web become highly emotional with the term 
"abused" appearing frequently.  Check out the "International 
Lightning Protection Association" site for some colorful rhetoric on 
Mr. Mousa and others. However, if any of these devices are to be 
tested truly scientifically, then insults, ridicule and derogatory 
comments have no place in the discussion. They have nothing to do 
with true scientific testing.

Now lets define exactly what an ESE (Early Streamer Emission) device 
is and how it works.  An excellent example may be found by Googling 
INDELEC and then looking at their "Prevectron" products.  These 
devices look like an inverted cone with electrodes near the 
tip.  They function by initiating an upward streamer during the onset 
of a thunderstorm.  The streamer goes up and attaches to a downward 
streamer from a cloud at which time a lightning discharge 
occurs.  The idea is to discharge part of the electrical energy 
contained in the field between earth and a storm cloud.  They 
function by repeating this process over and over, hoping to control 
the lightning strikes by providing a target, rather than allowing 
them to strike at random.

Charge dissipation works on an entirely different theory.  An array 
of grounded multiple sharp points is placed at a relatively elevated 
location. Prior to the arrival of a thunderstorm, the electric field 
slowly begins to build between the cloud and the earth or tall 
structure thereon.  A small current begins to flow from each of the 
points due to air ionization.  Ben Franklin described a "silent 
current" that flows from a sharp point into the air during these 
conditions.  It is analogous to a bleeder resistor in the HV supply 
of a transmitter.  When a transmitter is shut down, the bleeder 
discharges the power supply capacitors in order to make it safe for a 
person to work inside the transmitter.  Yes, I know that the caps 
should be discharged using the "sissy stick", but capacitors can 
build up a charge even after they have been discharged this way.  The 
bleeder resistor continuously drains the charge to make it safe.

The only thing wrong with a single sharp pointed rod is that it has a 
limited capacity of current.  Placing many of them in parallel is 
analogous to placing many high value resistors in parallel to provide 
a lower resistance discharge path.  If enough sharp points are placed 
in the proper geometry, the electric field voltage will be decreased 
below the point where lightning strike will occur.  This field is 
measured in volts per meter from ground upward toward the 
cloud.  When it exceeds 10 KV/meter of elevation, a strike may occur.

There are in fact three methods of attempting lightning protection:

1. The Franklin rod (an array of them for a large building is not cheap).
2. ESE (Early Streamer Emission) which intentionally causes strikes.
3. Charge dissipation in which the field voltage is diminished by 
controlled discharge.

They are not the same.  Charge dissipation products do not use the 
principle of ESE.

Ron Nott

----- Original Message ----- From: <dynotherm at earthlink.net>

>You might try following the Lightning Protection and Power
>Quality list on Yahoo. The ESE failures are reported frequently.
>
>Unrelated to broadcast, it is a question of safety of life and
>property. In general, a well known party in the ESE "industry"
>who tried obtaining listing via law suit has been kicked so far
>off the field that much of the smoke and mirrors is beginning
>to dissipate. With the last round of decisions a few months ago,
>trying to use ESE in a code approved building is an interesting
>historical quirk that is over, finished and done.