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  • 151.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effects of branches, charge irregularities and tortuosity of the stepped leader channel on the current, electromagnetic fields and hf radiation of return strokes2008Conference paper (Refereed)
  • 152.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning parameters of engineering interest2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 153.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Interaction of multiple connecting leaders issued from a grounded structure simulated using a self consistent leader inception and propagation model SLIM2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 154.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Gunasekara, T.A.L.N.
    Nanayakkara, S
    Propagation Effects on Radiation Fields Known as Narrow Bipolar Pulses Generated by Compact Cloud Discharges2014Conference paper (Refereed)
  • 155.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Basic electromagnetic theory - a summary2012In: Lightning Electromagnetics / [ed] Vernon Cooray, The Institution of Engineering and Technology , 2012Chapter in book (Refereed)
    Abstract [en]

    The goal of this chapter is to provide a summary of the basic concepts of electro- magnetic theory as a complement to the subject matter, most of which is related to electromagnetism, discussed in this book. The chapter covers only the concepts that are necessary to understand the electromagnetics of lightning flashes.

  • 156.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Jayaratne, Rohan
    Cummins, Kenneth L.
    On the peak amplitude of lightning return stroke currents striking the sea2014In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 149, p. 372-376Article in journal (Refereed)
    Abstract [en]

    Data gathered from the US National Lightning Detection Network (TM) (NLDN) show that the peak currents of lightning flashes striking the sea are significantly higher than those of lightning flashes striking the land. We suggest that the unfavorable conditions for the formation of positive charge pockets in maritime clouds lead to lightning initiation at higher cloud potentials compared to their land counterparts, resulting in larger peak currents in negative lightning flashes striking the sea. As the positive charge pocket does not promote positive ground strokes, no such discontinuity should be expected in positive first return strokes to ground between land and sea. 

  • 157.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kumar, Udaya
    Rachidi, Farhad
    Lucci, Carlo Alberto
    On the possible variation of the lightning striking distance as assumed in the IEC lightning protection standard as a function of structure height2014In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, p. 79-87Article in journal (Refereed)
    Abstract [en]

    The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30m. However, for structure heights smaller than about 30m, the results show that the values assumed by IEC do not differ significantly from the predictions based on a lightning attachment model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. Results obtained from the model are also compared with Collection Volume Method (CVM) and other commonly used lightning attachment models available in the literature. The results show that in the case of CVM the calculated attractive distances are much larger than the ones obtained using the physically based lightning attachment models. This indicates the possibility of compromising the lightning protection procedures when using CVM.

  • 158.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montaño, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    A model to represent negative and positive lightning first strokes with connecting leaders2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, no 2-4, p. 97-109Article in journal (Refereed)
    Abstract [en]

    A channel base current model of the current generation (CG) type is introduced to describe both negative and positive first return strokes. The key feature of the model is the association of the slow front of the channel base current waveform with the upward connecting leader. This feature is mathematically represented by a discharge propagation speed profile, which is characterized by an initial exponential increase with increasing height. It is shown that the previous models of the CG type may be incapable of reproducing adequately the observed electromagnetic fields when the channel base current contains a slow front.

  • 159.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nucci, C.A.
    Rachidi, F.
    On the possible variation of the lightning striking distance as defined in the IEC lightning protection standard as a function of structure height2012In: Lightning Protection, 2012, p. 1-5Conference paper (Refereed)
    Abstract [en]

    The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30 m. However, for structure heights smaller than about 30 m, the results show that the values assumed by IEC do not differ significantly from the model's predictions based on a striking model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. In this respect, further analysis making use of lightning strike models developed by other authors is recommended.

  • 160.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nucci, Carlo Alberto
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rachidi, Farhad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Guest editorial2007In: Journal of Electrostatics, ISSN 0304-3886, Vol. 65, no 5-6, p. 281-Article in journal (Refereed)
    Abstract [en]

    From the 13th to 16th of September, 2004 researchers active in the fields of physics of lightning and lightning protection gathered in Avignon, France for the 27th International Conference on Lightning Protection (ICLP). Traditionally, the ICLP provides authoritative reviews of the progress and state of research, as well as opportunity for personal contact between the entire community of lightning researchers. The printed proceedings of previous ICLP conferences enjoyed considerable prestige on a worldwide basis. At the Avignon conference, over 150 papers presenting the entire range of lightning research and protection were presented by scientists from more than 30 countries throughout the world. We cannot claim to have collected a balanced overview of the entire conference, but we believe that the papers that survived the review process, first by the session chairmen and then by the strict anonymous review process of the Journal of Electrostatics, and that are included herein, represent some of the best current research in lightning and its effects. Naturally, any collection of papers in a single field creates a heavy burden of reviewing. We would like to thank session chairmen and many anonymous referees for their valuable, indispensable cooperation in the reviewing process of these papers. We also wish to thank Prof. Mark Horenstein, the Editor of the Journal of Electrostatics, for support of this issue.

  • 161.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rachidi, Farhad
    Ecole Polytech Fed Lausanne, Swiss Fed Inst Technol, Lausanne, Switzerland..
    Advances in lightning research2017In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 181-181Article in journal (Refereed)
  • 162.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rachidi, Farhad
    Swiss Fed Inst Technol, EMC Lab, CH-1015 Lausanne, Switzerland.
    Rubinstein, Marcos
    Haute Ecole Ingn & Gest Canton Vaud, Inst Informat & Commun Technol, CH-1401 Yverdon, Switzerland.
    Formulation of the Field-to-Transmission Line Coupling Equations in Terms of Scalar and Vector Potentials2017In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 59, no 5, p. 1586-1591Article in journal (Refereed)
    Abstract [en]

    More than 60 years ago, Prof. S. Rusck introduced a coupling model to take into account the interaction of lightning-generated electromagnetic fields with overhead power transmission and distribution lines. The model which assumes that the ground is perfectly conducting has served the power system research community for many decades. Recently, it was found that this model is not complete because some of the forcing terms in the relevant transmission line equations, which are based purely on the scalar and vector potentials, were missing. In the present paper, the correct transmission line equations pertinent to the interaction of external electromagnetic fields with overhead lines, described in terms of scalar and vector potentials, are derived by incorporating the effects of a finitely conducting ground. The model presented in this paper can be considered as a correction and an extension of the Rusck model to account for a finitely conducting ground.

  • 163.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Efficiencies for production of NOx and O3 by streamer discharges in air at atmospheric pressure2005In: 10th International Conference on Electrostatics, Helsinki, Finland, June 15-17, 2005Conference paper (Refereed)
  • 164.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Efficiencies for production of NOx and O3 by streamer discharges in air at atmospheric pressure2005In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 63, p. 977-983Article in journal (Refereed)
  • 165.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    On the Mechanism of X-ray Generation in Dart Leaders of Lightning Flashes2008In: EOS Trans. AGU, 89(53), Fall Meet. Suupl., Abstract AE21A-05, San Francisco, USA, 2008Conference paper (Refereed)
  • 166.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    On the relationship between the discharge current, energy dissipation and the NOx production in spark discharges2005In: International Conference on Lightning and static Electricity, ICOLSE, Seattle, Washington, USA, September 19-23, 2005, p. PHE-44.1-Conference paper (Refereed)
  • 167.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    On the NOx production by laboratory electrical discharges and lightning2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, p. 1877-1889Article in journal (Refereed)
  • 168.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Vladimir, Rakov
    On the NO x production by laboratory electrical discharges and lightning2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 799-829Chapter in book (Refereed)
  • 169.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Rakov, V
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    A current generation type return stroke model that predicts the return stroke velocity2006Conference paper (Refereed)
  • 170.
    Cooray, Vernon
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Rakov, V.
    Nucci, Carlo A.
    Rachidi, F.
    Montano, Raul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    On the Constraints Imposed by the Close Electric Field Signature on the Equivalent Corona Current in Lightning Return Stroke Models2004In: International Conference on Lightning Protection, Avignon, France, 2004Conference paper (Other scientific)
  • 171.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Valdimir A
    Dept of Electrical and Computer Engineering, University of Florida, Gainesville,FL, USA.
    Engineering Lightning Return Stroke Models Incorporating Current Reflection From Ground and Finitely Conducting Ground Effects2011In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 53, no 3, p. 773-781Article in journal (Refereed)
    Abstract [en]

    A return stroke model that incorporates a reflected wave from ground without introducing any current discontinuities at the return stroke front is introduced. The incident current is treated using current generation concepts and the reflected current using current dissipation concepts. It is shown that the effect of the reflected current wave is to cause flattening of close electric field waveforms within about 10 mu s. Additionally, it is shown how a return stroke model could be utilized to study the effect of ground conductivity on the return stroke current. The results show that the peak time derivative of current in lightning strokes terminating on poorly conducting ground is significantly lower than in the case of highly conducting ground. The model is also used to predict the spatial variation of return stroke velocity. The results show that the return stroke velocity increases initially, reaches a peak, and then decays with increasing height.

  • 172.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    A current generation type return stroke model that predicts the return stroke velocity2007In: Journal of Lightning Research, ISSN 1652-8034, Vol. 1, p. 32-39Article in journal (Refereed)
    Abstract [en]

    AbstractThe engineering return stroke models available in the literature can be divided into current generation andcurrent propagation types, which are also referred to as the traveling current source type and transmission linetype, respectively. In the current propagation models the return stroke channel serves as a guiding structure forthe return stroke current which is injected at ground level. In the current generation models each channelsection acts as a current source which is turned on by the arrival of the return stroke front at that channelsection. Once turned on, the current source associated with the channel section injects a current, called a coronacurrent, into the core of the return stroke channel. This current contribution is assumed to travel to groundalong the core of the return stroke channel with the speed of light in vacuum. In the current generation typereturn stroke models available today, the channel base current and the return stroke velocity together with eitherthe distribution of the charge neutralized during the return stroke or the temporal variation of the coronacurrent are assumed as input parameters. With these input parameters, model outputs are the spatial andtemporal variation of the return stroke current and either the temporal variation of the corona current or thedistribution of the charge neutralized by the return stroke, depending on the input parameters selected in themodel. In this paper, we utilize a current generation type return stroke model to predict the return stroke velocityusing the channel base current, distribution of the charge neutralized by the return stroke, and the temporalvariation of the corona current as input parameters. We will show that for physically reasonable inputparameters the predicted return stroke velocity initially increases with height, reaches a peak, and then decreaseswith increasing height.

  • 173.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    On the Striking Distance of Subsequent Return Strokes2014Conference paper (Refereed)
  • 174.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    Dept of Electrical and Computer Engineering, University of Florida, Gainesville, FL, USA.
    On the upper and lower limits of peak current of first return strokes in negative lightning flashes2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, no SI, p. 12-17Article in journal (Refereed)
    Abstract [en]

    It is shown that the peak current of a return stroke is determined by the background electric field that exists between the cloud and the ground. Assuming 150 kV/m as the largest background electric field that can exist below thunderclouds, it is estimated that the largest negative first return stroke peak current that can exist in nature is about 300 kA in temperate regions and about 450 kA–500 kA in the tropics. Since corona discharges from trees, bushes and other protrusions and upward initiated discharges from tall structures limit the maximum electric field that can exist below thunderclouds over land, there is a high probability for these strong discharges to take place over the oceans. In the study it is also estimated that the smallest value of the return stroke current that can exist in nature lies in the range of 3.0 kA to 1.5 kA with the most probable value located in the vicinity of 2 kA.

  • 175.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    The Effects of Ground Conductivity on the Electromagnetic Fields Generated by Lightning Return Strokes2014Conference paper (Refereed)
  • 176.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir A.
    Rachidi, Farhad
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nucci, Carlo Alberto
    On the Relationship Between the Signature of Close Electric Field and the Equivalent Corona Current in Lightning Return Stroke Models2008In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 50, no 4, p. 921-927Article in journal (Refereed)
    Abstract [en]

    Engineering return stroke models can be categorized either as current generation (traveling current source type) models or current propagation (transmission line type) models. The current generation models are described among other parameters by a corona current distributed along the channel. Recent studies show that there is equivalence between the models of current generation and current propagation types. Due to this equivalence, any engineering return stroke model of current propagation type can be described in terms of an equivalent corona current per unit channel length. The measurements conducted within 10-500 m from triggered lightning Hashes show that the electric field of subsequent return strokes at these distances flattens within 15 mu s or so. In this paper, the constraints imposed by this feature on the temporal and spatial variation of the equivalent corona current are investigated. The results show that in order for the close fields to flatten within 15 mu s or so, the equivalent corona current, should be bipolar and the corona current wave shape at late times should be identical to that of the longitudinal current time derivative. This is in contrast to most of the engineering models of current generation type, in which the corona current is assumed to be unipolar.

  • 177.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    Department of Electrical and Computer Engineering, University of Florida.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The lightning striking distance—Revisited2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 296-306Article in journal (Refereed)
    Abstract [en]

    First return stroke current waveforms measured by Berger [Methods and results of lightning records at Monte San Salvatore from 1963–1971 (in German), Bull. Schweiz. Elektrotech. ver. 63 (1972) 21403—21422] and Berger and Vogelsanger [Measurement and results of lightning records at Monte San Salvatore from 1955–1963 (in German), Bull. Schweiz. Elektrotech. ver. 56 (1965) 2–22] are used to estimate the charge stored in the lightning stepped leader channel. As opposed to previous charge estimates based on the entire current waveform, only the initial portion of measured current waveforms (100 μs in duration) was used in order to avoid the inclusion of any charges not involved in the effective neutralization of charges originally stored on the leader channel. The charge brought to ground by the return stroke within the first 100 μs, Qf,100 μs (in C) is related to the first return stroke peak current, Ipf (in kA), as Qf,100 μs=0.61 Ipf. From this equation the charge distribution of the stepped leader as a function of the corresponding peak return stroke current is estimated. This distribution (along with the assumed average electric field of 500 kV/m in the final gap) is used to estimate the lightning striking distance S (in meters) to a flat ground as a function of the prospective return stroke peak current I (in kA): S=1.9 Ipf0.90. For the median first stroke peak current of 30 kA one obtains S=41 m, while the traditional equation, S=10 Ipf0.65, gives S=91 m. In our view, the new equation for striking distance provides a more physically realistic basis for the electro-geometric approach widely used in estimating lightning incidence to power lines and other structures.

  • 178.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The relationship between the leader charge and the return stroke current: Berger's data revisited2004In: International Conference on Lightning Protection, 2004Conference paper (Refereed)
  • 179.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Shindo, T.
    Lightning attachment to power transmission lines2012In: Lightning Protection (ICLP), Vienna, 2012Conference paper (Refereed)
    Abstract [en]

    The effect of lightning channel inclination on the attachment of lightning flashes to UHV transmission lines is investigated using a lightning strike model that takes into account the competing connecting leaders issued from different conductors. The results show that the probability of screening failures increases with increasing inclination of the lightning channel.

  • 180.
    Cooray, Vernon
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Theethayi, Nelson
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Effects of corona on pulse propagation along transmission lines with special attention to lightning return stroke models and return stroke velocity2005In: VIII International Symposium on Lightning Protection, SIPDA, Sao Paulo, Brazil, November 21-25, 2005Conference paper (Refereed)
  • 181.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pulse propagation along transmission lines in the presence of corona and their implication to lightning return strokes2008In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 56, no 7, p. 1948-1959Article in journal (Refereed)
    Abstract [en]

    Transmission line equations in air in the presence of corona are derived. The analysis shows that the corona caused by a voltage or a current pulse propagating along a transmission line can be represented by a series of corona current sources distributed along the line. Corona has two effects on the voltage or current pulses propagating along a transmission line. First, it will clamp down the pulse amplitude at the front of the pulse to the corona threshold. Second, it will cause the portion of the pulse whose amplitude is larger than the corona threshold to travel with a speed less than the speed of light. The effects of corona on the voltage or current pulses propagating along a transmission line can also be evaluated by introducing a time varying capacitance and a conductance into the transmission line. If the time varying capacitance is assumed to be proportional to the ratio between the corona charge and the applied voltage then one requires both this and the time varying conductance to represent the corona effects more accurately. Analysis of the return stroke as a current pulse propagating along a transmission line undergoing corona shows that the corona effects may explain the reason why the measured return stroke speeds are considerably less than the speed of light. Moreover, based on the effects of corona, a physical justification for the concepts used in the current generation type return stroke models is provided.

  • 182.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The striking distance of lightning flashes and the early streamer emission (ESE) hypothesis2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 336-341Article in journal (Refereed)
    Abstract [en]

    The attachment of a lightning flash to a lightning conductor (or to any other structure) takes place through a connecting leader that rises from the structure towards the descending stepped leader of a lightning flash. The spatial separation between the tip of the stepped leader and the lightning conductor (or the grounded structure) at the initiation of the connecting leader is known as the striking distance. In this paper the striking distance of stepped leaders is derived as a function of conductor height, conductor radii and the prospective return stroke current. Based on these results the validity of the early streamer emission (ESE) hypothesis is discussed. According to the ESE hypothesis, the striking distance of a lightning conductor can be increased by the artificial initiation of streamers from a lightning conductor. The results cast doubt on the validity of the ESE hypothesis. This in turn calls for more experimental data and field validations before using the ESE hypothesis in standard lightning protection practice.

  • 183.
    Cooray, Vernon
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Zitnik, Mihael
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity.
    On attempts to protect a structure from lightning strikes by enhanced space charge generation2004In: International Conference on Lightning Protection, Avignon, Frankrike, 2004Conference paper (Other scientific)
  • 184.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, Mihael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Manyahi, Mighanda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Physical model of surge-current characteristics of buried vertical rods in the presence of soil ionisation2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, p. 193-202Article in journal (Refereed)
  • 185. De Conti, A
    et al.
    Visacro, Silvério
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simulation of the time-varying channel resistance: exponential decay versus strong-shock approximation2008Conference paper (Refereed)
  • 186. De Conti, Alberto
    et al.
    Visacro, Silverio
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A comparison of different approaches to simulate a nonlinear channel resistance in lightning return stroke models2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no D14, p. D14129-Article in journal (Refereed)
    Abstract [en]

    Different physical models that describe the time variation of the channel resistance are investigated in a lightning return stroke model. Such models consider one of the three following hypotheses: (1) the channel resistance decays exponentially with time, (2) the channel resistance decays with the radial expansion of the channel core, which is assumed to be described by the strong-shock approximation, or (3) the channel resistance varies with time according to three different arc resistance models (defined by Toepler, Barannik and Kushner et al.). Analyses illustrate the effect of a time-varying channel resistance on channel currents and corresponding electromagnetic fields. It is shown that the strong-shock approximation is able to predict typical features of experimentally observed lightning electromagnetic fields and return stroke speed profiles. It is also shown that results predicted by the strong-shock approximation can be qualitatively reproduced by either using simplified arc resistance equations (such as Toepler's and Barannik's ones) or considering an exponential decay of the channel resistance with attenuation constants linearly increasing with height.

  • 187.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leader channel models for long air positive electrical discharges2015In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 76, p. 208-215Article in journal (Refereed)
    Abstract [en]

    The models proposed for the positive long air gap electrical discharge can be considered to be either engineering or physical in their approach. In this work, we make a general review of the available models and use two of them for a comparison with experimental data. Common underlying assumptions were found in most of the models analyzed. The comparison with the experimental data revealed that the results obtained from the models were a good representation of the physical situation when the leader potential distribution and the leader-corona region evolution were described with certain physical assumptions.

  • 188.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. HVDC ABB AB.
    Methodologies for the charge estimation in the leader corona region used in modeling long air gaps underpositive voltage impulses2016Conference paper (Refereed)
    Abstract [en]

    Different methodologies have been proposed to represent the physical phenomena taking place in a laboratory electrical breakdown event. The implementation of these methodologies in numerical routines is based in several physical assumptions and a proper calculation of the electrostatic potential distribution. The whole electrical breakdown in air tested with switching-like voltage impulses can be subdivided into three main stages: first, the streamer inception (first corona), then the streamer to leader transition (second corona, leader inception) and the leader propagation. An important element in the last stage is the representation of the leader corona region (streamer region) in front of the leader tip channel as it propagates towards ground. In this paper, with the aid of a finite element method solver to determine the electric potential distribution, two new methodologies to quantify the amount of charge produced in the leader corona region were presented and compared with other ones available in the literature.

  • 189.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. ABB AB, HVDC PGGI, Div Res & Dev, S-77180 Ludvika, Sweden.
    Numerical Modeling of Electrical Discharges in Long Air Gaps Tested With Positive Switching Impulses2018In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 46, no 3, p. 611-621Article in journal (Refereed)
    Abstract [en]

    The numerical modeling of electrical discharges occurring in atmospheric air has been in continuous development during the past decades in different fields, such as high-voltage techniques and lightning protection. Different methodologies have been proposed to represent the physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of numerical methods to determine the electric potential distribution permits the creation of models whose predictions closely agree with the real case situations, where electrode arrangements might have nonsymmetric geometries. In this paper, we present an improved version of a simulation methodology for representing electrical discharges in long air gaps. This simulation methodology includes new elements like: 1) the 3-D leader channel tortuosity based on laboratory experimental measurements and 2) two new methods for the estimation of the electric charge contained in the so-called leader-corona region based on the electrostatic potential of fictitious potential rings representing the active region in front of the leader tip. Results from the simulation were compared with experimental records and a reasonably good agreement is found between them.

  • 190. Diaz, Oscar
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Roman, Fransicso
    Spark gap resistance for an electrostatic discharge at different pressures2008Conference paper (Refereed)
  • 191.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Schleimann-Jensen, Johan
    Energy dissipation in a new low voltage surge protective gas discharge tube2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 192.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Vayanganie, S P A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental study of leader tortuosity and velocity in long rod-plane air discharges2016In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 23, no 2, p. 806-812Article in journal (Refereed)
    Abstract [en]

    Long air gap electrical discharges are of particular interest among scientists and engineers working on high voltage techniques and lightning research. In the present work we report experimental results obtained while testing a long rod-plane air gap with positive switching-like voltage impulses to study the velocity and tortuous progression of the leader discharge. Voltage and current waveforms were recorded. Two still digital cameras were used to track the leader tortuous path. By using a fast digital camera, the leader temporal evolution was recorded and its propagation velocity was estimated. Three angles were used to describe the leader tortuous progression.

  • 193. Dwyer, J. R.
    et al.
    Saleh, Z.
    Rassoul, H. K.
    Concha, D.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Jerauld, J.
    Uman, M. A.
    Rakov, V. A.
    A study of X-ray emission from laboratory sparks in air at atmospheric pressure2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, p. D23207-Article in journal (Refereed)
  • 194. Edirisinghe, M.
    et al.
    Liyanage, A.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Critical electric field needed for the propagation of surface discharges on water2012In: 2012 31st International Conference on Lightning Protection, ICLP 2012, 2012, p. 6344350-Conference paper (Refereed)
    Abstract [en]

    The core objective of this study was to investigate the behavior of electric discharge exited in air over water and to study the way in which the lightning impulse is conducted into a water body. During the experiments, standard lightning impulses from -550 kV to 350 kV have been directed on water surfaces and surface discharges has been photographed using two cameras. The conductivity of the water has been varied from 41.5 μS/cm to 51.5 mS/cm. Analysis carried out in the study revealed that the current rather travels along the water surface than into the water when the conductivity of the water is low. A logarithmic variation was observed between the calculated electric field and the conductivity. For this variation a saturating trend could be observed and it appeared as if there is a critical value for the electric field below which no penetration will occur at any level of conductivity. Based on the experimental results of this study it can be estimated that to be less than 1.5×105 V/m for the positive breakdown and -5.0×10 5 V/m for the negative breakdown.

  • 195.
    Edirisinghe, M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Makela, J. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Fernando, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. e.
    Signatures of the lightning HF radiation at 10 MHz, 5 MHz and 3 MHz associated with leader and return stroke process2006Conference paper (Refereed)
  • 196.
    Edirisinghe, Mahesh
    et al.
    Department of Physics, University of Colombo, Colombo, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fine structure signatures in ground flashes as a source of HF Radiation2014In: International Letters of Chemistry, Physics and Astronomy, Vol. vol. 1, p. 91 – 104-Article in journal (Refereed)
    Abstract [en]

    Lighting radiation fields below 10 MHz are of considerable interest since these frequencies correspond to the natural resonance of structures with dimensions of a few meters to tens of meters. In this paper we present the fine structure signatures of sub-microsecond range pulses appeared at the leader phase and after the return stroke in negative ground flashes which act as a source for HF radiations at 10 MHz, 5 MHz and 3 MHz observed in Sri Lanka, in the tropics. Of the total sub-microsecond range pulses analyzed, 298 were due to positive field changes and 228 were due to negative field changes. The average rise time of those pulses for both polarities is 127 ns and it was found to be varying from 110-160 ns. The peak amplitude is in the range of 0.65-2.19 V/m. For the total 526 pulses analyzed for this study, the FWHM was between 190-310 ns with an arithmetic mean of 238 ns. Signatures of these pulses are similar to the leader like electric field pulses which acted as a strong source for HF radiations at 10 MHz, 5 MHz and 3 MHz. The initiation process of pulses reported in this study could be similar to the initiation process of leader like pulses.

  • 197. Edirisinghe, Mahesh
    et al.
    Montano, Raul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Response of Surge Protection Devices to Fast Current Impulses2004In: International Conference on Lightning Protection, Avignon, France, 2004Conference paper (Other scientific)
  • 198.
    Esa, M. R. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, M. R.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Mohd
    Occurrence of narrow bipolar pulses between negative return strokes in tropical thunderstorms2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), 2014, p. 1141-1142Conference paper (Refereed)
    Abstract [en]

    This paper reports a recent observation of Narrow Bipolar Pulses (NBPs) occurrence between return strokes (RSs) of negative cloud-to-ground (CG) flashes in tropical thunderstorms. A wideband electric field antenna measurement system has been used in this work and 173 isolated and non-isolated NBPs managed to be recorded. We found that 22 single NBPs and a pair of positive NBP embedded between RSs and some of them are located within the horizontal distance range from 20 to 45 km from the observation station.

  • 199.
    Esa, Mona Riza Binti Mohd
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Mohd Riduan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wavelet analysis of the first pulse of initial breakdown process in lightning discharges2013In: Progress in Electromagnetics Research Symposium, pp. 1377-1380, 2013, Stockholm, Sweden, 2013, p. 1377-1380Conference paper (Refereed)
  • 200.
    Esa, Mona Riza Binti Mohd
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Mohd Riduan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Distinctive features of initial breakdown process between ground and cloud discharges2012In: Proceeding of Asian Conference of Electrical Discharges, AECD2012, Johor Bahru, Malaysia, Johor Bahru, Malaysia, 2012Conference paper (Refereed)
1234567 151 - 200 of 332
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