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Lightning striking distance of complex structures
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: IET Generation, Transmission and Distribution, ISSN 1751-8687, Vol. 2, no 1, 131-138 p.Article in journal (Refereed) Published
Abstract [en]

Traditionally, the location of lightning strike points has been determined by using the rolling sphere method, but recently the collection volume method (CVM) has also been proposed for the placement of air terminals on complex structures. Both these methods are empirical in nature and a more advanced model based on physics of discharges is needed to improve the state of affairs. This model is used to evaluate the striking distance from corners and air terminals on actual buildings and the results are qualitatively compared with the predictions of the rolling sphere method and the CVM. The results show that the striking distance not only depends upon the prospective return stroke current and the geometry of the building, but also on the lateral position of the downward leader with respect to the strike point. A further analysis is performed to qualitatively compare the lightning attraction zones obtained with the CVM and the leader inception zones obtained for a building with and without air terminals. The obtained results suggest that the collection volume concept overestimates the protection areas of air terminals placed on complex structures, bringing serious doubts on the validity of this method.

Place, publisher, year, edition, pages
2008. Vol. 2, no 1, 131-138 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-97288DOI: 10.1049/iet-gtd:20070099ISI: 000252958100015OAI: oai:DiVA.org:uu-97288DiVA: diva2:172154
Available from: 2008-05-14 Created: 2008-05-14 Last updated: 2016-04-12Bibliographically 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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