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Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2008 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 8, 085204- p.Article in journal (Refereed) Published
Abstract [en]

The early emission of streamers in laboratory long air gaps under switching impulses has been observed to reduce the time of initiation of leader positive discharges. This fact has been arbitrarily extrapolated by the manufacturers of early streamer emission devices to the case of upward connecting leaders initiated under natural lightning conditions, in support of those non-conventional terminals that claim to perform better than Franklin lightning rods. In order to discuss the physical basis and validity of these claims, a self-consistent model based on the physics of leader discharges is used to simulate the performance of lightning rods in the laboratory and under natural lightning conditions. It is theoretically shown that the initiation of early streamers can indeed lead to the early initiation of self-propagating positive leaders in laboratory long air gaps under switching voltages. However, this is not the case for positive connecting leaders initiated from the same lightning rod under the influence of the electric field produced by a downward moving stepped leader. The time evolution of the development of positive leaders under natural conditions is different from the case in the laboratory, where the leader inception condition is closely dependent upon the initiation of the first streamer burst. Our study shows that the claimed similarity between the performance of lightning rods under switching electric fields applied in the laboratory and under the electric field produced by a descending stepped leader is not justified. Thus, the use of existing laboratory results to validate the performance of the early streamer lightning rods under natural conditions is not justified.

Place, publisher, year, edition, pages
2008. Vol. 41, no 8, 085204- p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-97283DOI: 10.1088/0022-3727/41/8/085204ISI: 000254329500024OAI: oai:DiVA.org:uu-97283DiVA: diva2:172149
Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2017-12-14Bibliographically approved
In thesis
1. On the Attachment of Lightning Flashes to Grounded Structures
Open this publication in new window or tab >>On the Attachment of Lightning Flashes to Grounded Structures
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the physical modeling of the initiation and propagation of upward positive leader discharges from grounded structures during lightning strikes. It includes the analysis of upward leaders initiated under the influence of the electric field produced by a dominant negative cloud charge and due to the combined action of a negative thundercloud and a descending downward stepped negative leader. Thus, a self-consistent model based on the physics of leader discharges is developed for the evaluation of the attachment of lightning flashes to any kind of grounded structure. The predictions of the model have been found to be in good agreement with the results of laboratory long air gap experiments and with classical and altitude rocket triggered lightning experiments.

Due to the high application level and predictive power of the developed model, several contributions to the physical understanding of factors influencing the initiation and propagation of upward positive leaders during thunderstorms have been made. For instance, it has been found that the initiation of upward connecting leaders is strongly affected by the average velocity of the downward stepped leader. Similarly, it is shown that the switching voltage impulses used in the laboratory do not “fairly approximate” the electric fields produced by a descending downward leader, as claimed by supporters of Early Streamer Emission (ESE) devices. Furthermore, it is found that the space charge layer created by corona at ground level significantly increases the thundercloud electric fields required to initiate upward lightning leaders from tall objects. On the other hand, it is also shown that the upward leader velocity depends on the downward leader average velocity, the prospective return stroke current, the lateral distance of the downward leader channel and the ambient electric field.

By implementing the model to the analysis of complex structures, it has been observed that the corners of actual buildings struck by lightning coincide rather well with the places characterized by low leader inception electric fields. Besides, it has been found that the leader inception zones of the corners of complex structures do not define symmetrical and circular regions as it is generally assumed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 438
Keyword
Engineering physics, Lightning, Lightning attachment, Positive leader discharges, Lightning protection, Thunderstorms, Numerical modeling, Teknisk fysik
Identifiers
urn:nbn:se:uu:diva-8871 (URN)978-91-554-7216-0 (ISBN)
Public defence
2008-06-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2010-04-23Bibliographically approved

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