ERICO Practical Guide to Electrical Grounding - Manual (Page 34)

inception over 200 years ago, the nature and scope of
lighting protection has changed considerably. Lightning
protection then was principally a defense against fire.
Wooden buildings, when struck by lightning, would often
burn. Barns and churches were the main facilities seeking
this protection due to their height. Today, fire is still a
concern, but not always the main concern. A modern
facility of almost any kind contains electronic equipment
and microprocessors. Facility owners are concerned about
avoiding downtime, data loss, personnel injury &
equipment damage as well as fire.
The materials used to construct facilities have changed
dramatically also. Steel columns and the steel in reinforced
concrete compete as low impedance conductors for lightning
energy. The myriad of electrical/electronic equipment and
conductors that crisscross every level of the facility are at risk
just by being near conductors energized from nearby
lightning strikes. The lightning codes of the past don’t
adequately address these issues. Bonding of downconductors
to electrical apparatus within 3 to 6 feet is required and can
add substantial wiring to a facility if there are a lot of
downconductors. Further, the need for lightning protection
for these electrically sophisticated facilities is growing.
The amount of knowledge about lightning has increased
dramatically also. Information about the behavior of
leaders, the changing of electrical fields leading up to a
strike, the effects of impedance of various competing
downconductors, and diagnostic equipment has all
increased dramatically. This gives today's designers of
lightning protection systems a large advantage over those of
just 20 years ago.
These technological advances and market demands for
more cost effective lightning protection systems have
prompted many new and novel approaches to lightning pro-
tection. One such system is the ERICO System 3000
™ . This
system’s components are Dynasphere ™ Controlled Leader
Triggering (CLT) air terminals typically used with Ericore ™
low impedance, insulated downconductor. This system
enables the facility owner to use fewer air terminals with
fewer downconductors. The result is:
• fewer conductors to bond to nearby electrical apparatus.
• the ability to run downconductors down through the
middle of a building.
• less congestion on the roof of a building (this is
especially important when reroofing).
• a safer building roof for workers.
• the ability to protect open spaces as well as buildings.
• an overall more cost effective lightning
protection system.
The Dynasphere CLT is a passive terminal, which requires
no external power source, relying solely on the energy
contained in the approaching leader for its dynamic
operation. This remarkable terminal has the ability to
concentrate only that electric field which occurs in the
millisecond time slots as the leader charge approaches the
ground. The principle of operation of this terminal relies on
the capacitive coupling of the outer sphere of the terminal to
the approaching leader charge. This in turn raises the voltage
of the spherical surface to produce a field concentration
across the insulated air gap between the outer sphere and
grounded central finial. As the leader continues to approach,
the voltage on the sphere rises until a point is reached where
the air gap between the central finial and outer surface
breaks down. This breakdown creates local photo-ionization
and the release of excess free ions. These then accelerate
under the intensified field to initiate an avalanche condition
and the formation of an up streamer begins.
The DYNASPHERE CLT is designed to ensure that it only
launches an up-streamer when it has sensed that the electric
field ahead of it is high enough to ensure propagation. This
is unlike the way in which many other so called Early
Streamer Emission terminals operate. It was developed
through research and test equipment that wasn't available to
earlier designers, but also developed by building on the
wealth of knowledge created by those that came before us.
Fig. 2-2 Dynasphere ™ Controlled Leader Emission
(CLT) Air Terminal
26 Practical Guide to Electrical Grounding
Spark Gap
Corona Drain
Impedance
Insulated
Aluminum
Sphere
FRP Support
Mast
Conductor
Termination
Grounding Book 4/14/99 10/5/99 6:01 PM Page 26 (Black plate)