Direct lightning strikes to the human head can lead to various effects, ranging from burnings to death. The biological and physical mechanisms of a direct lightning strike in the human head are not well understood. The aim of this paper is to design an experimental setup to measure the spatial and temporal current distribution during a direct lightning strike to physical head phantoms to establish normative values for personal lightning protection equipment design and testing. We created head phantoms made of agarose, replicating the geometric and dielectric properties of scalp, skull, and intracranial volume. The bases of the three compartments were galvanically contacted via copper electrodes to measure the current per compartment. We used pulse generators to apply aperiodic voltage and current signals that modelled lightning components. Our experiments indicated that the scalp compartment was exposed to the current with a fraction of 80–90%. The brain and skull compartments were exposed between 6–13% and 3–6% of the total measured current respectively. In case of a flashover, most of the current (98–99%) flowed through the discharge channel. Unlike previous theoretical estimates and measurements in technical setups, we observed considerably longer times for the flashover to build up. In our experiments, the time to build up a fully formed flashover varied from approximately 30–700 μs. The observed current patterns in cases without and with flashover provided information on regions of possible damage in the human head. Consequently, we identified the phenomenon of a flashover as a potential mechanism for humans to survive a lightning strike. Our measured current distributions and amplitudes formed the base for normative values, which can be used in later experimental investigations regarding the possibilities of individual lightning protection equipment for humans.
The main disadvantage of horn spark gaps resulting from the blow-out of hot ionised gases in case of lightning impulse and follow currents is discussed for modern and compact DIN rail mounted arresters. The technical problems of fully encapsulated horn spark gaps are revealed. Based on technical specifications, basic calculations for the required arc voltages and the thermal loads were made in advance for dimensioning the arc splitter chamber and the arc area of the spark gap. A method to fully encapsulate such spark gaps is proposed and its efficiency is described based on experiments with different arrangements and loads.K e y w o r d s: horn spark gap, arc splitter chamber, extinguisher, methods for encapsulation, follow current limitation FUNCTIONS OF LIGHTNING CURRENT ARRESTERS AND MODE OF OPERATIONSurge protective devices which are mainly used as DIN rail mounted devices in low-voltage installations and are directly installed at the entrance point of the power supply lines into buildings or systems are also referred to as lightning current arresters (SPD type 1). They are used for lightning equipotential bonding and to reduce high-energy conducted interference. For this reason, they must be able to discharge high-energy lightning currents of 10/350 µs wave form and injected impulse currents of 8/20 µs wave form several times and must at the same time maintain a low voltage protection level.Sufficient energy coordination with downstream surge protective devices in sub-distribution boards (SPD type 2) or on terminal equipment (SPD type 3) must be ensured to prevent these so-called surge arresters from being overloaded.If lightning current arresters operate due to a surge pulse or a potential rise, there is a low-impedance connection between the active phases and equipotential bonding (PE, PEN) and the so-called mains follow current is flowing through the arrester after the discharge process. Lightning current arresters must considerably limit and quickly extinguish this follow current so that upstream overcurrent protective devices do not trip and mains power failure is prevented.The electrodes of todays encapsulated lightning current arresters with a high follow current extinguishing capability are often spaced at several millimetres. These great distances are due to the presently used principles to generate a high arc voltage. These arresters require complex trigger circuits to ensure sufficient energy coordination with downstream surge arresters.When using a spark gap with divergent electrodes (horn arrester) and connected arc splitter chamber, the ignition and arc extinction area are separated. A very small electrode spacing in the ignition area can be selected for this arrangement. This allows space-saving triggering by simple means and excellent energy coordination.Horn arresters are based on the efficient dc extinguishing principle and can therefore be used in dc and ac systems to control lightning and follow currents.Until now a major disadvantage of horn arresters with arc splitter chamber was that ...
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