Change search
Refine search result
234567 201 - 250 of 332
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 201.
    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.
    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.
    Distinctive features of radiation pulses in the very first moment of lightning events2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 109, p. 22-28Article in journal (Refereed)
    Abstract [en]

    This paper investigates the existence of distinctive features between 4 different types of lightning discharges, namely negative cloud to ground discharge (-CG), positive cloud to ground discharge (+ CG), cloud discharge (IC) and isolated breakdown discharge (IB). A total of 110 very fine structure waveforms of 44 CG, 16 +CG, 39 IC, and 11 IB discharges have been selected from a collection of 885 waveforms measured using fast electric field broadband antenna system. The measurements were carried out in Uppsala, Sweden from May to August 2010. We found that there are significant distinctions within the first 1 ms among different types of lightning discharges (-CG, +CG, IC, and IB). For example, the pulses in -CG discharges are more frequent than other discharges; the pulses in +CG discharges have the highest intensity and the IC discharge pulses tend to have shorter duration. o 2014 Elsevier Ltd. All rights reserved.

  • 202.
    Esa, Mona Riza 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 electric field pulse of lightning flashes in Sweden2014In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 138, p. 253-267Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the wavelet characteristics of the first electric field pulse of four different flash types namely negative cloud-to-ground flash (-CG), positive cloud-to-ground flash (+CG), cloud flash (IC) and isolated breakdown flash (IB). A total of 110 fine waveforms out of 885 were selected which have been recorded during summer between May and August 2010 in Uppsala, Sweden. The measurement was done by using an electric field broadband antenna system with the time resolution of 20 Megasample per second. Evidence from our wavelet analysis suggests that the ionization process during the initial leader development (coincide with the detection of the first electric field pulse) of at least three flashes (-CG, IC, and IB) in Sweden was dictated directly by the existence and magnitude of localized free ions region and lower positive charge center (p region). In general, we found that both single peak and multiple peaks pulses of the negative CG and IC flashes radiated energy at higher frequencies and gain larger bandwidth when compared to positive CG and IB flashes. We suggest that the initial leader development of both IC and negative CG flashes underwent very rapid and much more extensive ionization process when compared to the positive CG and IB flashes. In specific comparison between negative CG and IC flashes, both temporal and wavelet analyses suggest that the first electric field pulses of IC flash radiated energy at higher frequency in both single spread categories and radiated energy at lower frequency in both multiple spread categories when compared to the negative CG flash. This finding may explain the observation of much slower and less bright type alpha leader (ionization process not so extensive) compared to much faster and very bright type beta leader (ionization process very rapid and more extensive). As for positive CG and IB flashes, the single peak pulses of positive CG radiated energy at much higher frequency while the multiple peaks pulses radiated energy at much lower frequency than IB flash. We suggest that the initiation mechanism of positive CG was dictated directly by the background electric field between the main positive charge center and the ground, which is distinct from the initiation mechanism of IB flash. The presence of small magnitude of localized free ions region facilitated the rapidity of the ionization process in the initial leader development of IB flash.

  • 203. Fernando, Mahendra
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurements of lightning-generated electromagnetic fields2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 567-581Chapter in book (Refereed)
    Abstract [en]

    The vertical component of the electric field generated by lightning flashes can be measured either using a field mill or using a flat plate (or a vertical whip) antenna ; each method having its advantages and disadvantages. The three components of the electric field can be measured by using specially adapted spherical antennas.

  • 204.
    Fernando, Mahendra
    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.
    Narrowband radiation associated with lightning ground and cloud flashes: A review2008Conference paper (Refereed)
  • 205.
    Fernando, Mahendra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mäkelä, Jakke
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning and trees2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 206. Fernandoa, Mahendra
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on the electric field time derivatives generated by return strokes in lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1388-1396Article in journal (Refereed)
    Abstract [en]

    The effects of propagation over finitely conducting ground on the features of radiation component of the electric field time derivatives are investigated. The results show that the peak, the half-width and the risetime of the electric field time derivative change significantly in propagating over finitely conducting ground. Furthermore, any correlation that may exist between various parameters could also change significantly due to propagation effects. Consequently, in return stroke model validations using experimentally measured fields, remote sensing of return stroke current time derivatives using measured electric field time derivatives and in the calculation of induced voltages generated by lightning flashes in electrical installations the distortions caused by propagation effects on the electric field time derivatives cannot be neglected.

  • 207. Gomes, C.
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electromagnetic transients in radio/microwave bands and surge protection devices2010In: PIER - Progress in Electromagnetics Research, ISSN 1559-8985, Vol. 108, p. 101-130Article in journal (Refereed)
    Abstract [en]

    A comprehensive review has been done on the types of electromagnetic transients that may affect low voltage electrical systems. The paper discusses various characteristics of lightning, swithcing, nuclear and intentional microwave impulses giving special attention to their impact on equipment and systems. The analysis shows that transients have a wide range of rise time, half peak width, action integral etc, with respect to both source and coupling mechanism. Hence, transient protection technology should be more specific with regard to the capabilities of the protection devices. Furthermore, we discuss the components and techniques available for the protection of low voltage systems from lightning generated electrical transients and the adequacy of International Standards in addressing the transient protection issues. The outcome of our analysis questions the suitability of 8/20 mu s test current impulse in representing characteristics such as the time derivative and the energy content of lightning impulses. The 10/350 mu s test current impulse better represents the integrated effects of the energy content of impulse component and long continuing current. A new waveform is required to be specified for testing the ability of protective devices to respond to the fast leading edges of subsequent strokes that may appear 100s of millisecond after the preceding stroke. The test voltage waveform 1.2/50 mu s should also be modified to evaluate the response of protective devices for fast leading edges of induced voltage transients. A surge protective device that is tested for lightning transients may not be able to provide defense against other transients.

  • 208.
    Gomes, Chandima
    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.
    Radiation field pulses associated with the initiation of positive cloud to ground lightning flashes2004In: J. Atmos. Terr. Phys., Vol. 66, p. 1047-1055Article in journal (Refereed)
  • 209. Gomes, Chandima
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Surge protection of low voltage systems and relevant standards2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 210. Gomes, Chandima
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Transients that may affect low voltage electrical systems2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 211. Gomes, Chandima
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ab Kadir, M Z A
    Vertical electric fields and field change parameters due to partly inclined lightning leader channels2013In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 135, p. 55-80Article in journal (Refereed)
    Abstract [en]

    Vertical electric ¯elds generated by lightning leaderchannels, the total leader ¯eld change and the total leader ¯eld changeto the total return stroke ¯eld change ratio, at a certain distance, weretheoretically analysed by varying the angle of orientation of a segmentof upper part. Ground was treated as a perfectly conducting horizontalplane. Results were able to discern signi¯cantly large di®erences in thestatic ¯eld due to leader channels which have the same total lengthbut a certain channel segment is oriented at di®erent angles. Theoutcome of our calculations consistently explains the scatter of thetotal leader ¯eld observed in previous studies. Without consideringsuch channel segment orientation, one has to assume unrealistic chargesource heights or unreasonable charge densities to calculate matchingvalues for many observed total leader ¯elds and leader ¯eld to returnstroke ¯led ratios, labelled as anomalous observations in the literature.In some cases, irrespective of the charge source height and the chargedensity, one cannot ¯nd a suitable ¯t for the observed ¯elds with thestraight channel model.

  • 212. Gomes, Chandima
    et al.
    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.
    Fernando, Mahendra
    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.
    Sonnadara, Upul
    Characteristics of chaotic pulse trains generated by lightning flashes2004In: Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 66, p. 1733-1743Article in journal (Refereed)
  • 213. Gomes, Chandima
    et al.
    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.
    Breakdown Characteristics and Optically Visible Discharge Paths of Surface Flashover2012In: 2012 IEEE Conference on Sustainable Utilization and Development in Engineering and Technology (STUDENT)Universiti Tunku Abdul Rahman, Kuala Lumpur, Malaysia. 6 - 9 October 2012, 2012Conference paper (Refereed)
  • 214. Gulyás, Attila
    et al.
    Mäkelä, Jakke
    Németh, Bálint
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kiss, István
    Berta, István
    Local detectors in preventive lightning protection2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 215.
    Gunasekara, T. A. L. N.
    et al.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Sonnadara, U.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka2016In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 138, p. 66-73Article in journal (Refereed)
    Abstract [en]

    A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBP5 analyzed in this work were recorded at a coastal location in the Southern part of Sri Lanka (Matara: 5.95 degrees N, 8.53 degrees E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. Both positive and negative NBP5 were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBP5 for these parameters were found to be 0.58 mu s, 3.01 mu s, 0.20 mu s, 138 mu s, 19.21 mu s and 0.19 respectively. Similarly, for positive events corresponding values were 1.38 mu s, 4.66 mu s, 0.48 mu s, 1.93 mu s, 16.42 mu s and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.

  • 216.
    Gunasekara, T. A. L. N.
    et al.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Sonnadara, U.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 173, p. 57-65Article in journal (Refereed)
    Abstract [en]

    Simultaneous measurement of both vertical and horizontal electric field signatures of lightning was carried out in an elevated location in Colombo, Sri Lanka. The experimental setup used in this work was similar to an earlier study carried out by a different group in the late 1980s. To our knowledge, this is the first instance that such a study is conducted in this region. Data were acquired during the active months (April-May) of the southwest monsoon period in 2014. Lightning flashes from the most active thunderstorm was analyzed by selecting 65 Return Strokes (RS), 50 Negative Narrow Bipolar Pulses (NNBP) and 40 Positive Narrow Bipolar Pulses (PNBP). The wave shapes were initially validated against results of a previous study and subsequently via a theoretical method as well. Since the direction and the distance information was not available, rather than the amplitudes, ratios of the peak amplitudes of vertical electric field (Ev) and corresponding horizontal electric field (Eh) were compared. The average ratio for the return stroke was 0.024 +/- 0.008. The same for the NNBP was 0.041 +/- 0.004. The PNBP had a ratio of 0.031 +/- 0.006. The average 10%-90% rise times (Tr) for Ev for RS, NNBP and PNBP was 2.124 +/- 1.088 mu s, 0.734 +/- 0.077 is and 1.141 +/- 0.311 mu s respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 +/- 1.200 mu s, 0.538 +/- 0.061 mu s and 1.086 +/- 0.423 mu s.

  • 217. Gunasekara, T. A. L. N.
    et al.
    Mendis, U.
    Fernando, M.
    Sonnadara, U.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric field signatures of narrow negative bipolar pulse activities from lightning observed in Sri Lanka2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 624-628Conference paper (Refereed)
    Abstract [en]

    Isolated Narrow Bipolar Pulses (NBP) have been observed in the past in sub tropical and tropical regions. This study presents detail electric field characteristics of NBP pulses observed in Sri Lanka in the tropic. NBP analyzed in this work were recorded at Matara (5.95 degrees N, 8.53 degrees E), southern coast of Sri Lanka from four highly active thunderstorm days in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. In contrary to previous observations at the same geographical region, both positive and negative NBP pulses were observed in this study. Parameters related to Narrow Negative Bipolar Pulses (NNBP) are presented in this study since majority of the observations were in that category. The parameters measured for NNBP's were rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width at half maximum (FWHM) and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values for these parameters were found to be 0.49 mu s, 2.83 mu s, 0.18 mu s, 1.18 mu s and 0.17 respectively. The above values conforms to a much narrower bipolar pulses when compared to values reported in earlier studies.

  • 218.
    Gunasekara, T. A. L. N.
    et al.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka..
    Vayanganie, S. P. A.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka..
    Jayalal, S. N.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka..
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka..
    Sonnadara, D. U. J.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Time-Frequency Analysis of Narrow Bipolar Pulses observed in Sri Lanka2016In: 2016 33RD INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), 2016Conference paper (Refereed)
    Abstract [en]

    Narrow Bipolar Pulses (NBP) of a single thunderstorm from a coastal location in Sri Lanka were subjected to S-transformation in order to study their time frequency information. This study is an extension to a similar study carried out by the authors where properties of NBPs were analyzed using the wavelet transformation. Keeping in line with the previous study, 18 events pertaining to equal number of positive and negative NBPs with the narrowest temporal widths were studied. The data was obtained from the southern coastal area of Sri Lanka (Matara - 5.95 degrees N, 8.53 degrees E) from a highly active thunderstorm, which occurred during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. The spanning (width) and the ratio of peak power amongst the initial and overshoot pulses were measured and compared for each polarity. The negative NBPs had an average spanning of 134 - 371 kHz. The overshoot of the same had an average range of 127 - 255 kHz. The positive NBPs had an average spanning of 103 - 245 kHz. The overshoot of the same had an average range of 102 - 195 kHz. The ratio of peak power of NBPs to overshoot had an average of 1.08 for both positive and negative pulses. The spectrogram reveals the initial and overshoots pulses to be relatively equal in power intensities.

  • 219.
    Gunasekara, T.A.L.N.
    et al.
    Department of Physics, University of Colombo, Sri Lanka.
    Jayalal, S.N
    Department of Physics, University of Colombo, Sri Lanka.
    Fernando, Mahendra
    Department of Physics, University of Colombo, Sri Lanka.
    Sonnadara, Upul
    Department of Physics, University of Colombo, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Time-Frequency Analysis of vertical and horizontal electric field changes of lightning negative return strokes observed in Sri Lanka2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 179, p. 34-39Article in journal (Refereed)
    Abstract [en]

    Simultaneously captured vertical and horizontal (total) electric field signatures of lightning negative Return Strokes (RS) were analyzed to obtain Time-Frequency (TF) variation using Stockwell Transformation (ST). In the study, ST was utilized since it is known to possess comparatively better time resolution at high frequency regions compared to other available TF methods. The data were obtained during the monsoon season of April–May 2014. The vertical and horizontal component of fifty negative RSs was utilized in the study. The resultant ST spectrum was analyzed and the regions of interest were demarcated based on the color which represented their relative power output intensities for different frequency components of the signal. The spread area was identified as the region of frequencies which consisted of power intensity equal or above 90th percentile when compared to the maximum possible value. The spectral area was identified as the area of frequencies in the borderline to the natural background noise. The spread region for the vertical E field had a range between 10 kHz and 650 kHz. Its average values were in between 126 kHz and 331 kHz. The spectral region of the vertical electric field change spanned from 1 kHz to 1020 kHz. Its average distribution was 44 kHz–660 kHz. Horizontal electric fields had a range of 20 kHz–1940 kHz in the spectral region. The same for the spread region was 80 kHz–910 kHz. The averages of the horizontal E field's spectral region were 46–1112 kHz and its spread region varied between 227 and 599 kHz. The results display a higher frequency range for all aspects of the horizontal E field changes which implies that its influence on the high frequency radiation is much higher than its vertical counterpart.

  • 220.
    Guo, Jun
    et al.
    Swiss Fed Inst Technol, Electromagnet Compatibil Grp, CH-1015 Lausanne, Switzerland.
    Rubinstein, Marcos
    Univ Appl Sci Western Switzerland, CH-2800 Yverdon, Switzerland.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rachidi, Farhad
    Swiss Fed Inst Technol, Electromagnet Compatibil Grp, CH-1015 Lausanne, Switzerland.
    On the Modeling of Non-Vertical Risers in the Interaction of Electromagnetic Fields With Overhead Lines2019In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 61, no 3, p. 631-636Article in journal (Refereed)
    Abstract [en]

    This paper proposes a simple method to take into account non-vertical risers through an equivalent partial inductance. The proposed approach was validated considering several examples and taking as reference full-wave results obtained using a numerical electromagnetics code numerical electromagnetics code (NEC)-4.

  • 221.
    He, Lixia
    et al.
    Nanjing Univ Informat Sci & Technol, Minist Educ KLME, Key Lab Meteorol Disaster, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, Nanjing, Jiangsu, Peoples R China;Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Azadifar, Mohammad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland;Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rachidi, Farhad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Rubinstein, Marcos
    Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rakov, Vladimir A.
    Univ Florida, Dept Elect & Comp Engn, Gainesville, FL USA;Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod, Russia.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pavanello, Davide
    Univ Appl Sci Western Switzerland, Inst Syst Engn, Sion, Switzerland.
    Xing, Hongyan
    Nanjing Univ Informat Sci & Technol, Minist Educ KLME, Key Lab Meteorol Disaster, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, Nanjing, Jiangsu, Peoples R China.
    An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Santis Tower2018In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, no 8, p. 4045-4059Article in journal (Refereed)
    Abstract [en]

    We present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Santis Tower in Switzerland. The electric field was measured 15km from the tower. Upward flashes always begin with the initial stage composed of the upward-leader phase and the initial-continuous-current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return-stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no-current time intervals; (2) mixed-mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively small junction heights; (3) classical M-component pulses superimposed on the continuing current following some return strokes; and (4) M-component-type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively large junction heights. We consider a data set consisting of 9 return-stroke pulses, 70 mixed-mode ICC pulses, 11 classical M-component pulses, and 19 M-component-type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed-mode and M-component-type pulses, which is based on the current waveform features. The characteristics of M-component-type pulses during the initial stage are found to be similar to those of classical M-component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed-mode ICC pulses were preceded by microsecond-scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond-scale electric field pulses observed for M-component-type ICC pulses and which can be attributed to the junction of an in-cloud leader channel to the current-carrying channel to ground. Classical M-component pulses and M-component-type ICC pulses tend to have larger risetimes ranging from 6.3 to 430s. On the other hand, return-stroke pulses and mixed-mode ICC pulses have current risetimes ranging from 0.5 to 28s. Finally, our data suggest that the 8-s criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M-components. However, mixed-mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28s, as observed in this study.

  • 222.
    He, Lixia
    et al.
    Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Rachidi, Farhad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Azadifar, Mohammad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland;Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rubinstein, Marcos
    Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rakov, Vladimir A.
    Univ Florida, Dept Elect & Comp Engn, Gainseville, FL USA;Natl Res Univ Higher Sch Econ, Moscow Inst Elect & Math, Moscow, Russia.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pavanello, Davide
    Univ Appl Sci Western Switzerland HES SO, Inst Sustainable Energy, Sion, Switzerland.
    Xing, Hongyan
    Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, CIC FEMD, Nanjing, Jiangsu, Peoples R China.
    Electromagnetic Fields Associated With the M-Component Mode of Charge Transfer2019In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 124, no 13, p. 6791-6809Article in journal (Refereed)
    Abstract [en]

    In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return-stroke-like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC-carrying channel at relatively short distance from the tower top, resulting in the so-called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M-component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Santis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M-component charge transfer mode (including classical M-component pulses and M-component-type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2-Dimentional Finite-Difference Time Domain method, in which the M-component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Santis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M-component and M-component-type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M-component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M-component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M-component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch-to-channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E-field and 1.9 for the H-field. For a junction height greater than 6 km, the E-field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, ) in which an electric field propagation factor of 1. 8 was inferred for return strokes and mixed-mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return-stroke-like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 mu s or so) for which the tendency reverses. Finally, model-predicted fields associated with different charge transfer modes, namely, return stroke, mixed-mode, classical M-component, and M-component-type ICC pulse are compared with experimental observations at the Santis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed-mode models (1.0 km for the return stroke and 0.8 km for the mixed-mode pulse) are lower than the value of 2.0 km typically used in the literature.

  • 223.
    Hettiarachchi, Pasan
    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.
    Diendorfer, Gerhard
    OVE Service GmbH, Kahlenberger Straße 2A, 1190 Vienna, Austria.
    Pichler, Hannes
    OVE Service GmbH, Kahlenberger Straße 2A, 1190 Vienna, Austria.
    Dwyer, Joseph
    Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Morse Hall 309, 8 College Road, Durham, NH 03824, USA.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    X-ray observations at Gaisberg Tower2018In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 1, article id 20Article in journal (Refereed)
    Abstract [en]

    We report the occurrence of X-rays at ground level due to cloud-to-ground flashes of upward initiated lightning from Gaisberg Tower in Austria which is located at a 1300 m altitude.  This is the first time that the X-rays from upward lightning from a tower top located in high altitude is observed. Measurement was carried out using scintillation detectors installed close to the tower top in two phases from 2011 to 2015. X-rays were recorded in three subsequent strokes of three flashes out of the total of 108 flashes recorded in the system during both phases. In contrast to the observations from downward natural or triggered lightning, X-rays were observed only within 10 µs before the subsequent return stroke. This shows that X-rays were emitted when the dart leader is in the vicinity of the tower top and hence during the most intense phase of the dart leader. Both the detected energy and the fluence of X-rays are far lower compared to X-rays from downward natural or rocket-triggered lightning. In addition to above 108 flashes, an interesting observation of X-rays produced by a nearby downward flash is also presented. The shorter dart-leader channels length in Gaisberg is suggested as a possible cause of this apparently weaker X-ray production.

  • 224.
    Hettiarachchi, Pasan
    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.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Energy Distribution of X-rays Produced by Meter-long Negative Discharges in Air2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 12, article id 244Article in journal (Refereed)
    Abstract [en]

    The energy deposited from X-rays generated by 1 m long laboratory sparks in air created by 950 kV negative lightning impulses on scintillated detectors was measured. Assuming the X-ray energy detected in such sparks results from the accumulation of multiple photons at the detector having a certain energy distribution, an experiment was designed in such a way to characterize their distribution parameters. The detector was screened by a copper shield, and eight series of fifteen impulses were applied by stepwise increasing the copper shield thickness. The average deposited energy was calculated in each series and compared with the results from a model consisting of the attenuation of photons along their path and probable photon distributions. The results show that the energy distribution of X-ray bursts can be approximated by a bremsstrahlung spectrum of photons, having a maximum energy of 200 keV to 250 keV and a mean photon energy around 52 keV to 55 keV.

  • 225.
    Hettiarachchi, Pasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lobato, André
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Time Domain Analysis of the Lightning Interaction with Wave Energy Converters2018Conference paper (Refereed)
  • 226.
    Hettiarachchi, Pasan
    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.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    X-rays from long laboratory sparks: Influence of the anode geometry2014In: International Conference on Atmospheric Electricity ICAE 2014, Norman, OK, U.S.A., 2014Conference paper (Refereed)
  • 227.
    Hettiarachchi, Pasan
    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.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Univ New Hampshire, Inst Study Earth Oceans & Space, Morse Hall,8 Coll Rd, Durham, NH 03824 USA..
    X-rays from negative laboratory sparks in air: Influence of the anode geometry2017In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 190-194Article in journal (Refereed)
    Abstract [en]

    In this experimental work, the influence of the grounded anode geometry is studied on the X-ray production from the laboratory sparks in air at atmospheric pressure when a negative impulse voltage is applied to a high voltage rod which served as a cathode. The result shows that the smaller the diameter of the anode, the higher the energy of X-ray bursts. This observation can be explained by the mechanism that the encounter of negative and positive streamer fronts just before the final breakdown is the event that accelerates electrons to X-ray generating energies, but may not be the only mechanism that generates X-rays.

  • 228.
    Ismail, M. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sharma, S. R.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, P.
    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.
    Johari, D.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    HF and VHF electric field radiation produced by preliminary breakdown process pertinent to Swedish thunderstorms2015In: 2015 Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan, 2015Conference paper (Refereed)
  • 229.
    Ismail, Mohd Muzafar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Teknikal Malaysia Melaka, Fac Elect & Comp Engn, Telecommun Engn, Durian Tunggal 76100, Malacca, Malaysia..
    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.
    Fernando, Mahendra
    Univ Colombo, Dept Phys, Colombo 03, Sri Lanka..
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Johari, Dalina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Teknol Malaysia, Ctr Power Elect Engn Studies, Fac Elect Engn, Shah Alam 40450, Selangor, Malaysia..
    On the possible origin of chaotic pulse trains in lightning flashes2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 2, article id 29Article in journal (Refereed)
    Abstract [en]

    In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.

  • 230.
    Ismail, Mohd Muzafar
    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.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sharma, Shriram
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Johari, Dalina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric field signatures in wideband, 3 MHz and 30 MHz of negative ground flashes pertinent to Swedish thunderstorms2015In: Atmosphere, ISSN EISSN 2073-4433, Vol. 6, no 12, p. 1904-1925Article in journal (Refereed)
    Abstract [en]

    In this study, the electric field signatures of negative ground flashes pertinent to the Swedish thunderstorms were recorded simultaneously during the summer of 2014 using wide (up to 100 MHz) and narrow (at 3 MHz and 30 MHz as central frequencies) bandwidth antenna systems. The electric field signatures were recorded for a time duration of 250 ms. In the analysis, the whole flash was considered and a total of 98 flashes were chosen where electric field signatures of all wideband, 3 MHz and 30 MHz signals were present. It is observed that preliminary breakdown pulses are stronger radiators at 3 and 30 MHz compared to the return strokes. A comparison of our results with those of the previous studies obtained from different geographical regions clearly shows that the strength of preliminary breakdown pulses is higher in the temperate region (Sweden for instance) and is a function of latitude.

  • 231.
    Ismail, Muzafar M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. FKEKK Univ Tekn Malaysia Melaka, Durian Tunggal, Malaysia.
    Cooray, Vernon
    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.
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Johari, Dalina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. FKE Univ Teknol Mara, Shah Alam, Malaysia.
    On the possible origin of chaotic pulse trains in lightning flashes2015In: 2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28th Sept. – 2nd Oct. 2015., 2015, p. 409-412Conference paper (Refereed)
    Abstract [en]

    it is suggested that the chaotic pulse trains observed in lightning flashes are created as a result of the superposition of several regular pulse bursts produced by dart leader type discharge processes in the cloud. The similarity between the individual pulses in both chaotic and regular pulse bursts strengthen this suggestion.

  • 232. Izadi, M.
    et al.
    A Ab Kadir, M. Z.
    Gomes, C.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical fields expressions due to lightning channel considering variation of return stroke velocities along the lightning channel2012In: Lightning Protection, (ICLP) 2012, 2012, p. 6344252-Conference paper (Refereed)
    Abstract [en]

    The return stroke velocity is an important factor for evaluation of lightning electromagnetic fields. Measurements showed that the return stroke velocity is varied at different heights along lightning channel while it is usually entered into field calculations with a constant value in previous studies. This paper presents the analytical electromagnetic fields expressions due to vertical lightning channel where velocity profile along channel is considered. The proposed fields expressions can be used to estimate electromagnetic fields directly in the time domain (without needing to apply any extra conversion to Frequency domain) whereas they are based on Heidler current function and can support widely used engineering current models. Likewise, the proposed field expressions are applied on a typical measured profile of velocity and also a function of velocity profile and the evaluated fields are compared to the corresponding simulated fields based on constant value of velocity and the results are discussed accordingly.

  • 233. Izadi, M.
    et al.
    Ab Kadir, M. Z. A.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hajikhani, M.
    Estimation of Lightning Current and Return Stroke Velocity Profile Using Measured Electromagnetic Fields2014In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 42, no 2, p. 103-111Article in journal (Refereed)
    Abstract [en]

    To evaluate lightning current using measured electromagnetic fields, an inverse procedure algorithm is proposed in this article, where the variation of return velocity stroke velocity is considered as opposed to previous methods where the velocity is set at a constant value. The proposed algorithm considers all electromagnetic fields components directly in the time domain without needing to apply any extra conversions. Moreover, it can support the wide range of current models based on the general form of engineering current models. The proposed method is validated using a sample of triggered lightning data and measured electromagnetic fields at two stations with different distances from the lightning channel. The results illustrate that the proposed method could estimate the behavior of current along the channel and can thus be used for preparing a data bank to record lightning current parameters of a wide range of lightning occurrences based on measured fields.

  • 234. Izadi, M.
    et al.
    Ab Kadir, M. Z. A.
    Gomes, C.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of lightning return stroke current using measured electromagnetic fields2012In: Progress In Electromagnetics Research (PIER), ISSN 1559-8985, Vol. 130, p. 581-600Article in journal (Refereed)
    Abstract [en]

    The lightning return stroke current is an important parameter for considering the effect of lightning on power lines. In this study, a numerical method is proposed to evaluate the return stroke current based on measured electromagnetic fields at an observation point in the time domain. The proposed method considers all field components and the full wave shape of the current without the use of a special current model as a basic assumption compared to previous methods. Furthermore, the proposed algorithm is validated using measured fields obtained from a triggered lightning experiment. The results show a good agreement between the simulated field based on the evaluated currents from the proposed method and the corresponding measured field at a remote observation point. The proposed method can determine current wave shapes related to a greater number of lightning occurrences compared to the direct measurement of the current.

  • 235. Izadi, M.
    et al.
    Ab Kadir, M. Z. A.
    Gomes, C.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Shoene, J.
    Evaluation of lightning current and velocity profiles along lightning channel using measured magnetic flux density2012In: Progress In Electromagnetics Research (PIER), ISSN 1559-8985, Vol. 130, p. 473-492Article in journal (Refereed)
    Abstract [en]

    In this paper, an inverse procedure algorithm is proposed in the time domain to evaluate lightning return stroke currents along a lightning channel using measured magnetic flux density at an observation point while the current velocity along a lightning channel is assumed to be a height dependent variable. The proposed method considers all field components and it can evaluate the full shape of currents and the current velocity at different heights along a lightning channel. Moreover, a sample of measured magnetic flux density from a triggered lightning experiment is applied to the proposed algorithm and the evaluated currents and current velocities are validated using a measured channel base current and magnetic flux density at another observation point.

  • 236.
    Izadi, M
    et al.
    Centre of Excellence on Lightning Protection (CELP), Universitl Putra Malaysia.
    Ab Kadir, M Z
    Centre of Excellence on Lightning Protection (CELP), Universitl Putra Malaysia.
    Gomes, C
    Centre of Excellence on Lightning Protection (CELP), Universitl Putra Malaysia.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical fields expression due to lightning channel considering variation of return stroke velocities along the lightning channel2012In: 31st International Conference on Lightning Protection ICLP 2012, 2012Conference paper (Refereed)
  • 237. Izadi, M
    et al.
    Ab Kadir, M Z
    Gomes, C
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Improved algorithm for evaluation of lightning current using measured field at far distances from lightning channel2012In: 31st International Conference on Lightning Protection ICLP 2012, 2012, p. 6344251-Conference paper (Refereed)
    Abstract [en]

    In this paper, the effect of radiation component of electric field on the total electric field at different distances with respect to lightning channel is considered. Results showed by approximating the total electric field with the radiation component at far and intermediate distances, some percentages of electric fields at different time periods will be neglected and this percentage will be higher when decreasing the distance from lightning channel. Whilst the most common inverse procedure algorithms are based on field's radiation component and the total field as input data, this paper proposed the same procedure that based on measured field with the consideration on the effect of radiation component on the total field in the calculations. The results on the prediction of channel base current illustrated that the proposed method is in very good agreement with real lightning channel base current compared to the corresponding predicted current based on existing methods.

  • 238. Jeyanthiran, V
    et al.
    Edirisinghe, Mahesh
    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.
    Study of lightning activity over Sri Lanka2008Conference paper (Refereed)
  • 239. Jeyanthiran, V
    et al.
    Edirisinghe, Mahesh
    Fernando, 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.
    HF radiation pertinent to cloud flashes observed in Swedish thunderstorms2008Conference paper (Refereed)
  • 240. Jeyanthiran, V
    et al.
    Edirisinghe, Mahesh
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gomes, Chandima
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    HF radiation at 3 MHz, 5 MHz and 10 MHz associate with preliminary breakdown pulses observed in Sri Lanka2008Conference paper (Refereed)
  • 241.
    Johari, Dalina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Teknol MARA, Shah Alam, Malaysia.
    Cooray, Vernon
    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.
    Ismail, Mohd Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Tekn Malaysia Melaka, Durian Tunggal, Malaysia.
    Some characteristics of leader pulses in positive cloud-to-ground flashes2015In: 2015 International Symposium On Lightning Protection (Xiii SIPDA), 2015, p. 283-287Conference paper (Refereed)
    Abstract [en]

    Compared to negative ground flashes, not much is known about the characteristics of leaders in positive ground flashes. This paper presents some characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analyzed in detail the electric field changes produced by 50 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses were observed in 22% of the cases. They were observed to occur 1.4 ms or less before the first return stroke. Interpulse duration ranged from 13.3-50.3 mu s with a mean value of 24.7 mu s. The largest relative amplitude ranged from 2.7-17.8 % of the return stroke peak. No dependence of the pulses occurrence were observed with distance. However, the relative amplitude were found to decrease with distance. The presence of these pulses suggests that the leaders propagate in a stepped manner. One case of positive ground flashes preceded by negative polarity pulses just before the return stroke is also reported.

  • 242.
    Johari, Dalina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Faculty of Electrical Engineering, Centre for Electrical Power Engineering Studies, Universiti Teknologi Mara, 40450 Shah Alam, Selangor, Malaysia.
    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.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ismail, Mohd Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Faculty of Electronics and Computer Engineering, Telecommunication Engineering Department, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Malacca, Malaysia.
    Characteristics of leader pulses in positive ground flashes in Sweden2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, p. 3-9Article in journal (Refereed)
    Abstract [en]

    This paper presents the characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analysed in detail the electric field changes occurring just before the first return stroke in 51 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses (having the same polarity as the return stroke) were observed in 22% of the cases. They were observed to occur within 1.4 ms before the first return stroke. Interpulse duration ranged from 13.3 to 50.3 μs with a mean value of 24.7 μs. The peak amplitude of the leader pulses relative to the return stroke peak ranged from 2.7 to 17.8%. The presence of these pulses shows that the leaders propagate in a stepped manner. Based on the leader pulses’ time of initiation and average speed of the leader, the distance travelled by the leader was also estimated. One case of positive ground flash preceded by opposite polarity leader pulses just before the return stroke is also reported. To the best of our knowledge, this is the first time that such a case in positive ground flashes is reported. We suggest that these opposite polarity leader pulses are due to the negatively-charged leader branch of a bi-directional leader inside the cloud that propagates towards observation point.

  • 243.
    Johari, Dalina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Teknol Mara, Fac Elect Engn, Ctr Elect Power Engn Studies, Shah Alam 40450, Selangor, Malaysia.
    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.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ismail, Mohd Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Tekn Malaysia Melaka, Fac Elect & Comp Engn, Telecommun Engn Dept, Durian Tunggal 76100, Malacca, Malaysia.
    Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 150, p. 55-62Article in journal (Refereed)
    Abstract [en]

    This paper presents the characteristics of the electric fields produced by the first and the subsequent return strokes observed in positive ground flashes in Sweden. Fifty one positive ground flashes containing 60 return strokes recorded during 2014 summer thunderstorms were analyzed. In our analysis, only 12% of the cases were multiple-stroke while 88% were single-stroke. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was four. The geometric mean (GM) value of the interstroke interval was 60 ms while the distance between the first and the subsequent strokes ranged between 4.9 and 46.4km. We found that the average duration of the subsequent strokes parameters were smaller than that of the first strokes. For the first strokes, the GM values of the slow front duration, the fast transition 10-to-90% risetime, the zero crossing time, the zero-to-peak risetime and the 10-to-90% risetime were 8.7 mu s, 1.4 mu s, 29 mu s, 11 mu s and 5.7 mu s, respectively while for the subsequent strokes, the values were 4.0 mu s 0.91 mu s, 11 mu s 5.8 mu s and 3.2 mu s, respectively. Possible reasons for the shorter duration of the subsequent return strokes parameters were discussed.

  • 244.
    Johari, Dalina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Teknol Mara, Fac Elect Engn, Ctr Power Elect Engn Studies, Shah Alam 40450, Selangor, Malaysia.
    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.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ismail, Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Tekn Malaysia Melaka, Fac Elect & Comp Engn, Telecommun Engn Dept, Durian Tunggal 76100, Malacca, Malaysia.
    Characteristics of preliminary breakdown pulses in positive ground flashes during summer thunderstorms in Sweden2016In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 7, no 3, article id 39Article in journal (Refereed)
    Abstract [en]

    This paper presents the characteristics of the preliminary breakdown pulses (PBP) in 51 positive ground flashes recorded during 2014 summer thunderstorms in Sweden. Electric field measurements were conducted remotely using a broadband antenna system (up to 100 MHz) for a recording length of 1 s with 200 ms trigger time. In the analysis, PBP trains were observed in 86% of the cases. Based on the number of trains preceding the first return stroke, the PBP were classified into single and multiple train PBP. Characteristics of the first PBP train were determined and based on the initial polarity of the pulses, three types of PBP were identified. Characteristics of the subsequent PBP trains in the multiple train PBP were also analyzed and they were compared with the first PBP train. Based on the conceptual charge cloud configuration, we found that the inverted dipole is consistent with our observation. We also found that PBP in positive ground flashes during summer thunderstorms in Sweden are weak since the average ratios of the PBP peak to the first return stroke peak lie only between 0.21 and 0.26. Possible reasons for no detection of PBP and the different types of PBP observed were also discussed.

  • 245. Kumara, L.A.D
    et al.
    Edirisinghe, Mahesh
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Behavior of Low Voltage Varistors under Very Fast Oscillatory Type Current Impulse Environment2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 1577-1582Conference paper (Refereed)
    Abstract [en]

    In this study, the behavior of low voltage varistors under very fast oscillatory type non standard current impulses were analyzed. The experiment was performed on 20 mm disk varistors with different nominal operating voltages of 14V, 30 V, 40 V, 75 V, 150 V, 250 V and 275 V. Non standard current impulses were generated using a Van De Graaff generator. The shape of the impulse was like a double exponential oscillatory type wave which has the oscillation frequency of 14.53 MHz. The rise time of the impulse was 8 ns with a maximum peak current rate-of-rise is of 2.41 x 10(11) A/s. According to the results, under vary fast non standard current impulse environment, clamping voltage could be depend on both nominal voltage of varistors as well as its disk diameter. Another important feature of the voltage signatures observed was the DC offset voltage causes between terminals of varistor immediately after it triggered due injected fast current impulses.

  • 246.
    Liyanage, Prasanna
    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.
    Correlation between current waveforms of electrostatic discharges and optical signatures for several selected wavelengths2005In: Journal of Electrostatics, Vol. 63, p. 627-633Article in journal (Refereed)
  • 247. Liyanage, Prasanna
    et al.
    Montano, Raul
    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.
    Correlation between current and monochromatic optical signatures of electrical discharges2008Conference paper (Refereed)
  • 248.
    Liyanage, Prasanna
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity.
    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.
    Optical Signatures of Laboratory Sparks with Currents Comparable to Return Strokes in Lightning Flashes2004In: International Conference on Lightning Protection, Avignon, France, 2004Conference paper (Other scientific)
  • 249.
    Lobato, André
    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
    ABB Power Grids HVDC, R&D Dept, Ludvika, Sweden.
    Attractive Zone of Lightning Rods Evaluated with a Leader Progression Model in a Common Building in Brazil2017In: 2017 INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (XIV SIPDA), IEEE, 2017, p. 380-388Conference paper (Refereed)
    Abstract [en]

    Modeling the lightning attachment process is required on any method to design the air-termination elements of a lightning protection system. An attachment model that adopts the leader progression concept is used to evaluate the three-dimensional attractive zone of a lightning rod on a common 54-m tall building in Sao Paulo, Brazil. Electric field and scalar potential distributions are calculated numerically with a finite element method. The result is compared with the interception volume predicted by the electro-geometric model, as applied by the rolling sphere method. The results show that the electrogeometric theory underestimates the striking distance and the attractive radius. Moreover, in the presence of upward connecting leaders, the striking distance varies according to the field enhancement on the geometry of the structure and the lateral displacement of the stepped leader. The simulated propagated distances and speeds of the downward and upward leaders are compared with a recently published high-speed video analysis of a natural lightning attachment case observed on the evaluated lightning rod. A reasonable agreement between the simulated and measured leader characteristics has been found.

  • 250.
    Makela, J. S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Jantunen, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Ahola, T.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Hämäläinen, A.
    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.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. e.
    "Simple technique for detection of HF radiation from lightning2006Conference paper (Refereed)
234567 201 - 250 of 332
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf