Glossary
CAPTURE POINT
CORONA EFFECT (CORONA DISCHARGE)
DEDICATED EARTH ROD
DOWN CONDUCTOR
EARLY STREAMER EMISSION LIGHTNING CONDUCTOR (PDA)
IMPACT POINT
IMPEDANCE
INITIATION ADVANCE
IONIZATION
LIGHTNING ROD
LIGHTNING STRIKE
PROTECTION LEVEL
STREAMER
TAUGHT WIRE LIGHTNING CONDUCTOR
TRACER
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CAPTURE POINT
Also referred to as
the strike point. This is a 30 to 50 cm
high metal rod, with a minimum diameter
of 18mm and a tapered point.
CORONA EFFECT
(CORONA DISCHARGE)
The corona effect
is the local electrical phenomenon that
occurs around an electrode with a low
curvature radius when it is subjected to
a high voltage. It is caused by
successive electron avalanches that
result in the ionization of air
following high amplification of the
electric field around this electrode.
The electric currents involved in this
type of discharge are well below 1mA.
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DARD (« STREAMER
»)
Le dard (« streamer ») est la décharge électrique filamentaire se développant sur des distances pouvant aller jusqu’à quelques dizaines de centimètres. Elle est produite par une succession d’avalanches électroniques créant un canal faiblement ionisé. Ce type de décharge se produit lorsque le champ électrique est supérieur au champ d’ionisation de l’air sur une distance au moins égale à la longueur de l’avalanche électronique. Cette valeur de champ est bien supérieure à celle que nécessite une décharge couronne. La décharge dard peut véhiculer des courants allant de quelques mA à quelques centaines de mA.
DEDICATED EARTH ROD
Electrode or series
of grouped electrodes in direct
electrical contact with the ground. It
ensures the dissipation of lightning
current into the ground.
DOWN CONDUCTOR
External lightning
protection component of an installation.
It allows a lightning current to be
conducted and dissipated by an earth
rod. |
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EARLY STREAMER EMISSION LIGHTNING CONDUCTOR (PDA)
Standard lightning
rod which, when fitted with an electric
or electronic system to generate early
streamer emissions (advanced initiation
of the rising pre-discharge), has better
performance when compared to a standard
lightning rod in the same conditions.
The method for calculating the
protection radius of an early streamer
emission device is described in NFC 17-102.
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IMPACT POINT
Point where a
lightning strike hits the ground, a
structure or a lightning protection
installation.
IMPEDANCE
The characteristic
impedance is the main parameter for
defining electrical signal propagation
along a line. This signal is always a
pair of two mobile waves, voltage u(t)
and current i(t), that are rigidly
linked and which propagate at the same
speed. The characteristic impedance Zc
(also referred to as "wave impedance")
is the constant ratio between these two
values, i.e. Zc = u(t) / i(t).
(Source: UTE/SEE
"Guide de la protection", June 2000
edition).
INITIATION
ADVANCE
The initiation
advance is the difference between the
initiation time of an early streamer
emission device (PDA) and the initiation
time of a standard lightning rod (PTS).
IONIZATION
Series of physical
processes by which ions are created. An
ion is an atom or group of atoms that
have gained (negative ion) or lost
(positive ion), by electrolysis or
through radiation, one or more
electrons.
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LIGHTNING ROD
Lightning rods
(sometimes referred to as Franklin rods)
have a practical height of 2 to 6 metres
and a tapered point. They may be made up
of one or more like material components,
provided that electrical continuity is
guaranteed (NF C 17-100).
LIGHTNING STRIKE
The lightning
strike is the phenomenon that occurs
when a thunder cloud is connected via
rising and falling tracers to the
ground. It occurs after two tracers have
joined. All the charge contained in the
thunder cloud rushes into the ionized
channel formed by the two tracers and
produces an electric discharge. |
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PROTECTION
LEVEL
The protection level corresponds to
the statistical effectiveness of the
protection expressed as the probability
of capturing a lightning strike
according to its intensity. As a
minimum, the protection captures all
lightning strikes of greater intensity
than that under consideration.
Effectiveness (E)
in %
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Intensity of lightning current
(in kA) |
Protection level (Np)
NF C 17-100 |
Protection level (Np)
NF C 17-102
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| E > 98 |
- |
1 + additional
measurements |
1 + additional
measurements |
| 95 < E ≤ 98 |
2,8 |
1 |
1 |
| 90 < E ≤ 95 |
5,2 |
2 |
2 |
| 80 < E ≤ 90 |
9,5 |
3 |
2 |
| E < 80 |
14,7 |
4 |
3 |
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STREAMER
The streamer is the filament type
electrical discharge that develops over
distances as great as several tens of
centimetres. It is produced by
successive electron avalanches that
create a weakly ionized channel. This
type of discharge occurs when the
electric field is greater than the air
ionization field over a distance that is
at least as long as the electron
avalanche. This field value is much
higher than that needed for a corona
discharge. The streamer discharge can
carry currents ranging from several mA
to several tens of mA.
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TAUGHT WIRE
LIGHTNING CONDUCTOR
This system is made
up of one or more wire conductors
stretched above the installations that
are to be protected.
Comment: in
practice, lightning rod systems act more
or less as a cage due to the presence of
roof and down conductors: this can
contribute in protecting the volume they
enclose. Inversely, when a mesh cage
system is fitted with capture points,
these have a slightly preferential
attraction of lightning.
TRACER
The tracer is the path followed by
successive streamer discharges that
create an ionized channel over greater
distances (up to 50m). The electric
currents involved in this type of
discharge vary between 1 Amp and several
tens of Amps.
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