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  • 51.
    Becerra, Marley
    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.
    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.
    A simplified model to represent the inception of upward leaders from grounded structures under the influence of lightning stepped leaders2005In: VIII International Symposium on Lightning Protection, SIPDA, Sao Paulo, Brazil, November 21-25, 2005Conference paper (Refereed)
  • 52.
    Becerra, Marley
    et al.
    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.
    A simplified physical model to determine the lightning upward connecting leader inception2006In: IEEE Transactions on Power Delivery, ISSN 0885-8977, Vol. 21, no 2, p. 897-908Article in journal (Refereed)
  • 53.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    A Simplified Physical Model to Determine the Lightning Upward Connecting Leader Inception2006In: IEEE Transactions on Power Delivery, Vol. 21, no 2, p. 897-908Article in journal (Refereed)
  • 54.
    Becerra, Marley
    et al.
    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. elektricitetslära och åskforskning.
    An improved upward leader propagation model2006In: Proceedings of the 28th Internat Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, p. 581-586Conference paper (Refereed)
  • 55.
    Becerra, Marley
    et al.
    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. elektricitetslära och åskforskning.
    Dynamic modeling of the lightning upward connecting leader inception2006In: Proceedings of the 28th International Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, p. 543-548Conference paper (Refereed)
  • 56.
    Becerra, Marley
    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.
    Early streamer emission principle does not work under natural lightning!2008Conference paper (Refereed)
  • 57.
    Becerra, Marley
    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.
    Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 8, p. 085204-Article in journal (Refereed)
    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.

  • 58.
    Becerra, Marley
    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.
    On the interaction of lightning upward connecting positive leaders with humans2009In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, no 4, p. 1001-1008Article in journal (Refereed)
    Abstract [en]

    Upward connecting leaders can be initiated from humans under the influence of lightning downward stepped leaders, thereby causing severe injuries. In order to improve the scarce knowledge about the interaction of upward connecting leaders with humans, a self-consistent model based on the physics of leader discharges is used in this paper. Furthermore, a current-generation-type return-stroke model is applied to calculate the current pulse produced during the neutralization of unsuccessful aborted upward leaders. It is estimated that an upward connecting leader can be initiated even when the victim is located several tens of meters away from the lightning channel. However, the lightning exposure to a direct strike and to an aborted leader is found to be reduced by 50% and 70%, respectively, when an individual standing straight adopts the squat position. In the case of an aborted upward leader, it is estimated that a short-duration pulse of opposite polarity in the kiloampere range would be produced by the neutralization of the leader charge. Rough estimates of the total energy dissipated in the victim's body by the current of an aborted unsuccessful upward leader range between hundred and thousand joules.

  • 59.
    Becerra, Marley
    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.
    On the physics of the interaction of aborted lightning upward connecting leaders with humans2008Conference paper (Refereed)
  • 60.
    Becerra, Marley
    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.
    On the velocity of positive connecting leaders associated with negative downward lightning leaders2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, p. L02801-Article in journal (Refereed)
    Abstract [en]

    A self-consistent leader propagation model is used to estimate the velocity of upward connecting positive leaders initiated from a tall tower under the influence of downward negative lightning leaders. The propagation of upward connecting leaders has been found to be influenced not only by the average velocity of the downward leader but also by the prospective return stroke current, the lateral position of the downward leader channel as well as by the ambient electric field. This result show that the velocity and propagation time of upward connecting positive leaders change from flash to flash due to the variations in these parameters.

  • 61.
    Becerra, Marley
    et al.
    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.
    Time dependent evaluation of the lightning upward connecting leader inception2006In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, no 21, p. 4695-4702Article in journal (Refereed)
    Abstract [en]

    The evaluation of the upward connecting leader inception from a grounded structure has generally been performed neglecting the effect of the propagation of the downward stepped leader. Nevertheless, field observations suggest that the space charge produced by streamer corona and aborted upward leaders during the approach of the downward lightning leader can influence significantly the initiation of stable upward positive leaders. Thus, a physical leader inception model is developed, which takes into account the electric field variations produced by the descending leader during the process of inception. Also, it accounts for the shielding effect produced by streamer corona and unstable leaders formed before the stable leader inception takes place. The model is validated by comparing its predictions with the results obtained in long gap experiments and in an altitude triggered lightning experiment. The model is then used to estimate the leader inception conditions for free standing rods as a function of tip radius and height. It is found that the rod radius slightly affects the height of the downward leader tip necessary to initiate upward leaders. Only an improvement of about 10% on the lightning attractiveness can be reached by using lightning rods with an optimum radius. Based on the obtained results, the field observations of competing lightning rods are explained. Furthermore, the influence of the average stepped leader velocity on the inception of positive upward leaders is evaluated. The results obtained show that the rate of change of the background electric field produced by a downward leader descent largely influences the conditions necessary for upward leader initiation. Estimations of the leader inception conditions for the upper and lower limit of the measured values of the average downward lightning leader velocity differ by more than 80%. In addition, the striking distances calculated taking into account the temporal change of the background field are significantly larger than the ones obtained assuming a static downward leader field. The estimations of the present model are also compared with the existing leader inception models and discussed.

  • 62.
    Becerra, Marley
    et al.
    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. elektricitetslära och åskforskning.
    Velocity of Laboratory Electrical Discharges at low Pressure2006Conference paper (Refereed)
    Abstract [en]

    Abstract AE42A-05

  • 63.
    Becerra, Marley
    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.
    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.
    Abidin, Hartono Zainal
    Location of the vulnerable points to be struck by lightning in complex structures2005In: International Conference on Lightning and Static Electricity, Seattle, 2005, p. GND-20.1Conference paper (Refereed)
  • 64.
    Becerra, Marley
    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.
    Acácio, Silva Neto
    Piantini, Alexandre
    Lightning attachment to power transmission lines: on the validity of the electrogeometric model2008Conference paper (Refereed)
  • 65.
    Becerra, Marley
    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.
    Hartono, Zainal
    Identification of lightning vulnerability points on complex grounded structures2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 9, p. 562-570Article in journal (Refereed)
    Abstract [en]

    The identification of the most vulnerable points on a given structure to be struck by lightning is an important issue on the design of a reliable lightning protection system. Traditionally, these lightning strike points are identified using the rolling sphere method, through an empirical correlation with the prospective peak return stroke current. However, field observations in Kuala Lumpur and Singapore have shown that the points where lightning flashes strike buildings also depend on the height and geometry of the structure. Since a lightning strike point is believed to be the place on a grounded structure where a propagating upward leader is first initiated, a physical leader inception model is used here to estimate the background electric field required to initiate a stable upward leader from the corners of some complex buildings. The computed location of the points from where leaders are incepted are compared with the damaged points on buildings struck by lightning. The observed lightning strike points coincide rather well with the corners of the buildings which are characterized by lower leader inception electric fields. Furthermore, it is found that the geometry of the buildings significantly influences the conditions necessary to initiate upward leaders and, therefore, the location of the most likely strike points.

  • 66.
    Becerra, Marley
    et al.
    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. elektricitetslära och åskforskning.
    Roman, F
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Striking distance of vulnerable points to be struck by lightning on complex structures2006In: Proceedings of the 28th International Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, p. 608-613Conference paper (Refereed)
  • 67.
    Becerra, Marley
    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.
    Roman, Francisco
    Lightning striking distance of complex structures2008In: IET Generation, Transmission and Distribution, ISSN 1751-8687, Vol. 2, no 1, p. 131-138Article in journal (Refereed)
    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.

  • 68.
    Becerra, Marley
    et al.
    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.
    Soula, Serge
    Chauzy, Serge
    Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no D12, p. D12205-Article in journal (Refereed)
    Abstract [en]

    Electric field measurements above ground have shown that the space charge layer created by corona at ground level shields the background electric field produced by the thundercloud. Therefore it is expected that this space charge layer can also influence the conditions required to initiate upward lightning from tall objects. For this reason, a numerical model that describes the evolution of the main electrical parameters below a thunderstorm is used to compute the space charge layer development. The time variation of the electric field measured at 600 m above ground during the 1989 rocket triggered lightning experiment at the Kennedy Space Center (Florida) is used to drive the model. The obtained space charge density profiles are used to compute the conditions required to initiate stable upward lightning positive leaders from tall towers. Corona at the tip of the tower is neglected. It is found that the space charge layer significantly affects the critical thundercloud electric fields required to initiate upward lightning leaders from tall objects. The neutral aerosol particle concentration is observed to have a significant influence on the space charge density profiles and the critical thundercloud electric fields, whereas the corona current density does not considerably affect the results for the cases considered in the analysis. It is found that a lower thundercloud electric field is required to trigger a lightning flash from a tall tower or other tall slender grounded structure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions.

  • 69.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Francisco, Roman
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning attachment to common structures: is the rolling sphere method really adequate?2008Conference paper (Refereed)
  • 70. Bodhika, J. A. P.
    et al.
    Dharmarathna, W. G. D.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A preliminary study on characteristics of thunder pulses of lightning2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 260-264Conference paper (Refereed)
    Abstract [en]

    Thunder is the acoustic emission associated with lightning discharges. Thunder signatures have been analyzed by many scientists with the aim of understanding the energy, channel tortuosity and localization of lightning channel. In describing thunder features, a few subjective terms such as clap, roll and rumble have been used in the literature inconsistently with no proper definitions. In this study the features of pressure pulses such as occurrence characteristics and their relative amplitudes were analyzed to understand some of the above mentioned thunder features. Those subjective terms, clap, peal, roll and rumble were quantified along with relative pulse amplitudes and confirmed by listening the recorded thunder signals carefully. The relative peak amplitudes of the pulses of rumble were less than 20% of the peak pulses of the thunder signal and for roll it was between 20% to 40%. Pulses with relative amplitudes greater than 40% were identified as claps. The most significant contribution to the sound in a thunder flash is due to claps, which was studied separately in this study. The number of claps in a thunder flash, their frequency variation, durations, and pulse characteristics has been studied. The frequency of pressure oscillations within these claps are being less than 300 Hz. According to this study, 62% of the flashes consist of 1 to 2 claps. The activity of the thunder signal is high in initial half than the latter half. Thunder signals analyzed in this study is recorded by a microphone system with wide bandwidth range from 6 to 20 kHz.

  • 71. Bodhika, J. A. P.
    et al.
    Dharmarathna, W. G. D.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Reconstruction of lightning channel geometry by localizing thunder sources2013In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 102, p. 81-90Article in journal (Refereed)
    Abstract [en]

    Thunder is generated as a result of a shock wave created by sudden expansion of air in the lightning channel due to high temperature variations. Even though the highest amplitudes of thunder signatures are generated at the return stroke stage, thunder signals generated at other events such as preliminary breakdown pulses also can be of amplitudes which are large enough to record using a sensitive system. In this study, it was attempted to reconstruct the lightning channel geometry of cloud and ground flashes by locating the temporal and spatial variations of thunder sources. Six lightning flashes were reconstructed using the recorded thunder signatures. Possible effects due to atmospheric conditions were neglected. Numerical calculations suggest that the time resolution of the recorded signal and 10 ms(-1)error in speed of sound leads to 2% and 3% errors, respectively, in the calculated coordinates. Reconstructed channel geometries for cloud and ground flashes agreed with the visual observations. Results suggest that the lightning channel can be successfully reconstructed using this technique.

  • 72. Bodhika, J A P
    et al.
    Dharmarathna, W.G.D
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Characteristics of thunder pertinent to tropical lightning2018Conference paper (Refereed)
  • 73. Bodika, J. A. P
    et al.
    Fernanado, Mahendra
    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.
    Dharmaratna, W G D
    A comparison of thunder signatures between cloud and ground flashes associated with audio frequency pressure variations over Sri Lanka2008Conference paper (Refereed)
  • 74. Chandimal, Lasantha
    et al.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nanayakkara, Sankha
    Sapumanage, Nilantha
    Fernando, Mahendra
    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.
    Impedance behaviour of earth enhancing compound under lightning transient conditions2018Conference paper (Refereed)
  • 75. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Application of electromagnetic fields of an accelerating charge to obtain the electromagnetic fields of a propagating current pulse2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 55-65Chapter in book (Refereed)
    Abstract [en]

    It was recently demonstrated that electromagnetic fields from accelerating charges can be utilized to evaluate the electromagnetic fields from lightning return strokes. It was documented in detail how to utilize the equations to calculate electromagnetic fields of various engineering return stroke models, both current propagation and current generation types.It was also demonstrated how the equations can be utilized to calculate radiation fields generated by currents propagating along transmission lines in the presence of bends. The basics of this technique are summarized in this chapter by applying it to evaluate the electromagnetic fields of a propagating current pulse.

  • 76. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Could Some Ball Lightning Observations be Optical Hallucinations Caused by Epileptic Seizures?2008In: The Open Atmospheric Science Journal, ISSN 1874-2823, Vol. 2, p. 101-105Article in journal (Refereed)
    Abstract [en]

    The great difficulty of encompassing all observed features of ball lightning into a single theory makes it highly probable that many observations and experiences which have no connection to ball lightning are also categorized as ball lightning experiences. In this note we compare the eyewitness reports of ball lightning and the symptoms of epileptic seizures of the occipital lobe as described in the medical literature and show that a person experiencing such a seizure for the first time may believe that he has witnessed a ball lightning event. Since many of the ball lightning reports are associated with nearby lightning strikes, the possibility that the rapidly changing magnetic field of a close lightning strike could trigger an epileptic seizure is analyzed. The results show that the time derivative of the magnetic field in the vicinity of an intense lightning flash is strong enough to stimulate neurons in the brain. This strengthens the possibility of inducing seizures in the occipital lobe of a person located in the vicinity of lightning strikes.

  • 77. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electromagnetic fields of a short electric dipole in free space - revisited2012In: PROG ELECTROMAGN RES, ISSN 1559-8985, Vol. 131, p. 357-373Article in journal (Refereed)
    Abstract [en]

    Maxwell's equations specify that electromagnetic radiation fields are generated by accelerating charges. However, the electromagnetic radiation fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r >> l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r(2), while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r(2) and 1/r(3).

  • 78.
    Cooray, V
    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.
    Fernando, M
    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.
    Gomes, C
    Sorensen, T
    The Fine Structure of Positive Return Stroke Radiation Fields2004In: IEEE Transactions on EMC, Vol. 46, p. 87-95Article in journal (Refereed)
  • 79.
    Cooray, V
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. Department of High Voltage Research.
    Fernando, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences.
    Sörensen, M
    Götschl, T
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences.
    Pedersen, A
    Propagation of lightning generated transient electromagnetic fields over finitely conducting ground2000In: Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 62, p. 583-600Article in journal (Refereed)
  • 80. Cooray, V.
    et al.
    Zitnik, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Manyahi, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Y.
    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 Ionisation2002In: 26th International Conference on Lightning Protection, ICLP-2002, Cracow, Poland, September 2-6, Vol. 1, p357-362, 2002, Vol. 1, p. 357-362Conference paper (Refereed)
  • 81.
    Cooray, V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Strandberg, G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Scuka, V.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A Novel Modification of the ’Transmission Line Model’ of Lightning Return Strokes2002In: 26th International Conference on Lightning Protection, ICLP2002, Cracow, Poland, September 2-6,                       Vol. 1, p50-55, 2002, Vol. 1, p. 50-55Conference paper (Refereed)
  • 82.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A novel procedure to represent lightning return strokes: current dissipation return stroke models2009In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, no 3, p. 748-755Article in journal (Refereed)
    Abstract [en]

    Engineering return stroke models available in the literature can be divided into two categories, namely, current propagation models and current generation models. Based on the theory of pulse propagation along transmission lines in the presence of corona, a third procedure to describe return strokes, which, in fact, is the inverse of current generation models, is introduced. Models based on the new concept are called current dissipation models. In the current generation models, the corona currents generated by the neutralization of the corona sheath travel downward and the cumulative effects of these corona currents generate the return stroke current. In current dissipation models, the return stroke is initiated by a current pulse injected into the core of the leader channel at ground level. This injected current pulse travels upward with speed vc . If the return stroke channel is treated as a transmission line, then this speed is equal to the speed of light. The propagation of this pulse along the central core initiates the neutralization of the corona sheath leading to the release of corona currents into the central core. In contrast to current generation models in which corona currents travel downward, these corona currents travel upward along the core. The speed of propagation of the corona pulses upward along the core is also equal to vc. The corona currents, being of opposite polarity, lead to the dissipation of the injected current pulse. As in the case of current generation models, a current dissipation model can be described completely by any three of the following four parameters. They are: 1) channel base current; 2) spatial variation of the return stroke velocity; 3) spatial variation of the corona decay time constant; and 4) the spatial variation of the positive charge deposited by the return stroke on the leader channel. It is also shown that current propagation models available in the literature are special cases of current dissipation models.

  • 83.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A novel procedure to represent lightning strokes – current dissipation return stroke models2008Conference paper (Refereed)
  • 84.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A return stroke model based purely on the current dissipation concept2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 61-65Article in journal (Refereed)
    Abstract [en]

    A return stroke model based purely on the current dissipation concept is introduced. With three model parameters the model is capable of generating electric and magnetic fields that are in reasonable agreement with experimentally observed electromagnetic fields.

  • 85.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A review of simulation procedures utilized to study the attachment of lightning flashes to grounded structures2011In: CIGRE ELECTRA, Vol. 257Article in journal (Refereed)
  • 86.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Attachment of lightning flashes to grounded structures2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 765-787Chapter in book (Refereed)
    Abstract [en]

    A grounded structure can interact with a lightning flash in two different ways. It can interact with either a downward or an upward lightning flash. The initiation of a downward lightning flash takes place in the cloud, whereas in the case of upward lightning flash, the point of initiation is usually at the tip of a tall structure. In other words, upward lightning flashes are created by the grounded structure itself. In this chapter, a brief description of various models used to study the lightning attachment is given together with some of their predictions.

  • 87.
    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.
    Authora reply to comments on On the concepts used in return stroke models applied in engineering practice2003In: IEEE Transactions on EMC, Vol. 45Article in journal (Refereed)
  • 88.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Basic discharge processes in the atmosphere2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 65-85Chapter in book (Refereed)
    Abstract [en]

    The main constituents of air in the Earth's atmosphere are nitrogen (78%), oxygen (20%), noble gases (1%), water vapour (0.03%), carbon dioxide (0.97%) and other trace gas species. In general, air is a good insulator and it can maintain its insulating properties until the applied electric field exceeds about 2.8 x 104 V/cm at standard atmospheric conditions (i.e. T= 293 K and P =1 atm). When the background electric field exceeds this critical value, the free electrons in air generated mainly by the high energetic radiation of cosmic rays and radio active gases generated from the Earth start accelerating in this electric field and gain enough energy between collisions with atoms and molecules to ionize other atoms. This cumulative ionization leads to an increase in the number of electrons initiating the electrical breakdown of air. The threshold electric field necessary for electrical breakdown of air is a function of atmospheric density. When the leaders reach an electrode of opposite polarity or a region of opposite charge density, a rapid neutralization of the charge on the leader takes place. This neutralization process is called a return stroke. The exact mechanism of the return stroke is not yet known, but different types of models have been developed to describe them. These models are described in several chapters of this book. Here, we will concentrate on the four discharge processes mentioned above. Some parts of this chapter are adopted and summarized from Reference 1 where an extensive description of basic physics of discharges is given.

  • 89.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric field of the return stroke channel2012In: 31st International Conference on Lightning Protection ICLP 2012, 2012, p. 6344241-Conference paper (Refereed)
    Abstract [en]

    Return stroke models specify the temporal and spatial variation of the return stroke current along the channel. This information is sufficient to evaluate the temporal development of the electric field along the channel of the return stroke. In this paper the mathematical procedure necessary to do this is introduced. The derived equations can be combined with any return stroke model to calculate the power and energy dissipation during the return stroke.

  • 90.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Horizontal electric field above and under ground produced by lightning flashes2009Conference paper (Refereed)
  • 91.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Horizontal Electric Field Above- and Underground Produced by Lightning Flashes2010In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 52, no 4, p. 936-943Article in journal (Refereed)
    Abstract [en]

    The horizontal electric field both at points above and below ground in the vicinity of lightning return strokes were evaluated by numerical solution of Sommerfeld's integrals. Results are presented for ground conductivities in the range of 0.01-0.0001 S/m. The results are compared with the following approximate procedures used in the literature to calculate horizontal electric fields: 1) the surface impedance approximation; 2) the quasi-static approximation frequently used in lightning protection standards; and 3) Cooray's simplified formula for the computation of underground electric field. Based on this comparison, the distance range in which these approximations are valid is obtained. The results obtained show that: 1) The surface impedance approximation can generate correct horizontal electric field when the distance to the point of observation is larger than about 50, 200, and 500 m for ground conductivities of 0.01, 0.001, and 0.0001 S/m, respectively. 2) It is necessary to include propagation effects in the magnetic field that is being used as an input in the surface impedance expression when it is being used to calculate the horizontal electric field. 3) Cooray-Rubinstein approximation gives exact results when it is being used to calculate the horizontal electric field aboveground generated by cloud flashes. 4) Cooray's simplified formula connecting the surface horizontal electric field to the underground one gives accurate results, provided that the horizontal electric field at the surface of the ground, which is used as an input, is calculated accurately and the depth of the point of observation is kept much less than the distance to the point of strike.

  • 92.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Horizontal electric field at ground level in the vicinity of lightning return stroke channels evaluated using Sommerfeld’s integrals2008Conference paper (Refereed)
  • 93.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning attractive radii of vertical and horizontal conductors evaluated using a self consistent leader inception and propagation model – SLIM2010Conference paper (Refereed)
  • 94.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning Protection2009Book (Other (popular science, discussion, etc.))
    Abstract [en]

    Lightning is a natural phenomenon that has always fascinated humans. It is also a destructive force, and the science of protecting humans and their belongings on earth is called lightning protection. This book provides the reader with a thorough background in almost every aspect of lightning protection. The contents of the book, distributed over 23 chapters, cover all aspects of lightning protection including lightning parameters of engineering interest, the evaluation of the risk imposed by lightning strikes, the art of installing lightning protection systems on various structures, basic principles and procedures necessary to protect electronic equipment in buildings from lightning flashes, grounding in lightning protection, the function of surge protection devices, protection of power transmission lines and telecommunication towers from lightning, the interaction of lightning flashes with wind turbines, various aspects of lightning strikes to trees, medical and engineering aspects of lightning strikes to humans, and lightning warning systems.

  • 95.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Non conventional lightning protection systems2011In: CIGRE ELECTRA, Vol. 258Article in journal (Refereed)
  • 96.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the accuracy of several approximate theories used in quantifying the propagation effects on lightning generated electromagnetic fields2008In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 56, no 7, p. 1960-1967Article in journal (Refereed)
    Abstract [en]

    The effect of finitely conducting ground on the signature of lightning generated vertical electric fields at ground level was evaluated by numerical solution of Sommerfeld's integrals. Results are presented for distances between 10 m to 1 km from the lightning channel and for ground conductivities in the range of 0.01 and 0.001 S/m. The results obtained from the exact theory are compared with the predictions of several approximate theories available in the literature. Based on that comparison the limits of validity of these approximate theories are obtained.

  • 97.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the attachment of lightning flashes to grounded structures with special attention to the comparison of SLIM with CVM and EGM2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 577-581Article in journal (Refereed)
    Abstract [en]

    Lightning attachment to vertical grounded conductors are presented with special attention to the lightning attractive radii of vertical conductors as predicted by self consistent leader inception and propagation model (SLIM), Electro Geometrical Model (EGM) and Collection Volume Method (CVM). Moreover, SLIM was utilized to model the attachment of a slanted stepped leader to a tall tower that resulted in a side flash to a point below the top of the tower. The important conclusions to be drawn from the results obtained are the following: (a) The error (caused by neglect of the connecting leader in EGM) in the predicted attractive radii and the striking distance of EGM increases with increasing structure height. However, for structures whose height is shorter than about 30 m the error associated with using EGM is less than about 20%. (b) The attractive radii predicted by the Collection Volume Method (CVM) are much larger than the ones predicted by SLIM and EGM. Thus, the use of CVM to locate the lightning conductors on a structure may undermine its safety. (c) Slanted stepped leader channels can cause side flashes in tall structures even though long connecting leaders are emitted from the top of the structure.

  • 98.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the Initiation of Lightning Flashes in Thunderclouds2014Conference paper (Refereed)
  • 99.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the mimimum length of leader channel and the minimum volume of space charge concentration necessary to initiate lightning flashes in thunderclouds2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 39-45Article in journal (Refereed)
    Abstract [en]

    Minimum length to which a leader channel has to grow before it can propagate continuously as a stable leader as a function of the background electric field inside a thundercloud is estimated. For electric field magnitudes comparable to the values measured inside thunderclouds, the minimum length of the leader channel that is required for it to propagate continuously is about 3-5 m. In other words, a leader discharge that originated inside a thundercloud has to grow to a length of 3-5 m before it can culminate in a stable and continuously propagating leader discharge that can give rise to a lightning flash. The minimum size of charge concentrations that can make this event possible have radii in the range of 2-4 m and should carry about 300-900 mu C of electric charge, respectively. This in turn shows that the high field regions inside the cloud where electrical discharges that can culminate in stable leader discharges, and hence in lightning discharges, may be confined to volumes which are no larger than a few meters in radius.

  • 100.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the upper and lower limit of peak current in return strokes of lightning flashes2010Conference paper (Refereed)
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