EARLY STREAMER EMISION : HISTORY AND OPERATION PRINCIPLES

EARLY STREAMER EMISION : HISTORY AND OPERATION PRINCIPLES

Early streamer emission (ESE) lighting protection air terminals appeared in 1984, initially in France, and later in Spain, which were also the first countries to adopt specific standards (NF C 17102 in France, UNE 12 186 in Spain). This type of air terminal is currently sold by foreign manufacturers (European, American,Chinese, Australian, Argentine, Turkish, etc.).In recent years, various devices designed to improve the efficiency of Franklin-type rod lightning protection terminals have appeared, particularly to replace prohibited radioactive devices. France has been extensively involved in this research,alongside other countries such as Spain. Research results have now been validated with laboratory tests, and even site testing.The industrial products developed based on this research improve the efficiency of capturing an upward connecting leader compared with a lightning rod air terminal.All discussions on efficiency aim to determine how the upward connecting leader can be activated as early as possible (at the best possible time) with the best possible initial speed. The principle is therefore to adjust and/or drive the corona discharge.Two physical principles are applied for this concept:

- Using high voltage pulses: repetitive high voltage pulses are applied to the end of the air terminal; the basic principle is to control the initial corona discharge and benefit from the "memory" effect left by previous discharges.

- Using a spark near to the tip: a spark is triggered near to the tip in order to ensure the presence of initial electrons in correlation with the increase in electric field. In practice, an ESE with the same size as a Franklin rod leads to a faster initiation of the upward connecting leader, which may, according to some authors, lead to a larger radius for the protected area or,with an identical radius of the protected area, to significantly higher reliability (probability of capture) compared with a rod terminal. However, the efficiency of such a terminal must be validated with specific tests.

In 2001, INERIS listed ESE-related technologies: technologies with electronic or piezoelectric activation, or with special profiles.

In 2016, only ESE technologies with electric/electronic activation and special profiles exist, and many manufacturers have combined both a profile and an activation mode.Piezoelectric terminals are no longer sold in France.In 2001, INERIS listed 100,000 ESE air terminals manufactured after 1985, GIMELEC2currently lists 440,000 for French members alone, i.e. ¼ of production occurred over the first half of the 30-year period and ¾ over the second half. This demonstrates the strong growth recorded in the market availability of these products.

How does an ESE air terminal operate?

If a lightning protection terminal generates an upward connecting leader before a nearby object, it will naturally win any competition with upward connecting leaders. This is the basic principle behind ESE. ESE air terminals must demonstrate early triggering ΔT compared with a lightning rod (LR) air terminal.

If a terminal benefits from early triggering ΔT, the upwardconnecting leader or leader generated will cover a distance D, greater than for an LR air terminal, to meet the downward leader. The terminal will capture the lightning at a larger distance, its range is therefore increased. The increase in range is therefore obtained from the propagation speed of the upward connecting leader as ΔL=VΔT.

The standard NF C 17102 defines the Early Streamer Emission air terminal as a lightning protection terminal with an earlier emission than a lightning rod air terminal in identical conditions.No information on the technology used is given.An ESE air terminal comprises a capture lightning rod, an attachment device, a fixation and a connection to the downward conductors.

Two main ESE groups can be identified:1. air terminals with special profiles including passive components (L, R, C: coil, resistor, capacitor);2. air terminals with electronic activation including one or more active electronic circuits for managing the activation of the upward connecting leader at a specific point in time.Most of the ESE systems of the manufacturers operate whether the ambient electric field is negative or positive, which is compatible with a downward negative or positive lightning strike.

No early triggering is required for an upward connecting lightning strike (positive or negative), the terminal will emit at the highest point connected to the earth and the ESE air terminal,if installed at the highest point as required by standard, will represent the preferred starting point for this type of lightning strike.