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.

STREAMER

The streamer is the filament type electrical discharge that develops over distances as great as several tens of centimeters. 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.

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.

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 arc.

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).

LIGHTNING PROTECTION LEVEL

The Lightning Protection Level corresponds to the number related to a set of lightning current parameter values relevant to the probability that the associated maximum and minimum design values will not be exceeded in naturally occurring lightning. NOTE Lightning protection level is used to design protection measures according to the relevant appropriate set of lightning current parameters.

CAPTURE POINT

Also referred to as the shock point. This is a 30 to 50 cm high metal component, with a minimum diameter of 18mm and a tapered point.

DOWN CONDUCTOR

External lightning protection component of an installation. It allows conducting lightning current between the air-termination system and the earth-termination system.

DEDICATED EARTH ROD

Electrode or series of grouped electrodes in direct electrical contact with the ground. It ensures the run-off and distribution of a lightning current into the ground.

IMPACT POINT

Point where a lightning strike hits the ground, a structure or a lightning protection installation.

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.

EARLY STREAMER EMISSION AIR TERMINAL EFFICIENCY

The early streamer emission air terminal efficiency is the difference between the initiation time of an early streamer emission device (PDA) and the initiation time of a simple rod air terminal (SRAT). ESEAT efficiency (ΔT) difference expressed in micro-seconds between the emission time of an ESEAT and an SRAT measured in a laboratory under the conditions defined in the NF C 17 102 standard.

REFERENCE SIMPLE ROD AIR TERMINAL

geometrical shape metal rod defined in the NF C 17 102 standard to be used as a reference.

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.

EARLY STREAMER EMISSION AIR TERMINAL (ESEAT)

Simple rod air terminal 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 reference simple rod air terminal in the same conditions. The method for calculating the protection radius of an early streamer emission air terminal is described in NFC 17-102.

EARLY STREAMER EMISSION LIGHTNING PROTECTION SYSTEM

(ESESystem) complete system based on one or more ESEAT and all elements to safely conduct lightning to earth in order to protect a structure, facility or open area against direct lightning impact.

LIGHTNING ROD

Lightning rods (sometimes referred to as Franklin rods) have a practical height of 2 to 6 meters and a tapered point. They may be made up of one or more like material components, provided that electrical continuity is guaranteed (NF EN 62 305-3).