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  • 301. Sapumanage, Nilantha
    et al.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simulation of the performance of the external lightning protection system2018Conference paper (Refereed)
  • 302. Sapumanage, Nilantha
    et al.
    Nanayakkara, Sankha
    Abegunawardena, Sidath
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    How physical attributes of transient voltages limits the efficiency of SPD array2018Conference paper (Refereed)
  • 303. Sapumanage, Nilantha
    et al.
    Nanayakkara, Sankha
    Abeygunawardena, Sidath
    Chandimal, Lasantha
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study on responses of SPDs against the transient voltages generated by CG flashes2018Conference paper (Refereed)
  • 304. Sapumanage, Nilantha
    et al.
    Nanayakkara, Sankha
    Abeygunawardena, Sidath
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Insight of SPD limitations cause by incident phaser angle and the physical attributes of transient voltages2018Conference paper (Refereed)
  • 305.
    Seah, B. Y.
    et al.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Ahmad, M. R.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Shairi, N. A.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Periannan, D.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Sabri, M. H. M.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Aziz, M. Z. A. A.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Ismail, M. M.
    Univ Teknikal Malaysia Melaka UTeM, Ctr Telecommun Res & Innovat CeTRI, Atmospher & Lightning Res Lab, Fak Kejuruteraan Elekt & Kejuruteraan Komputer, Durian Tunggal, Melaka, Malaysia.
    Esa, M. R. M.
    Univ Teknol Malaysia, FKE, Inst High Voltage & High Current IVAT, Johor Baharu 81310, Johor, Malaysia.
    Mohammad, S. A.
    Univ Teknol Malaysia, FKE, Inst High Voltage & High Current IVAT, Johor Baharu 81310, Johor, Malaysia.
    Abdul-Malek, Z.
    Univ Teknol Malaysia, FKE, Inst High Voltage & High Current IVAT, Johor Baharu 81310, Johor, Malaysia.
    Yusop, N.
    Univ Kebangsaan Malaysia, Inst Climate Change, Space Sci Ctr ANGKASA, Bangi 43600, Selangor Darul, Malaysia.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lu, G.
    Chinese Acad Sci, Inst Atmospher Phys, Key Lab Middle Atmosphere & Global Environm Obser, Beijing, Peoples R China.
    The Performance Evaluation of Capacitive Antenna with Various Structures and Permittivity Values2018In: 2018 INTERNATIONAL CONFERENCE ON ELECTRICAL ENGINEERING AND COMPUTER SCIENCE (ICECOS), IEEE , 2018, p. 457-460Conference paper (Refereed)
    Abstract [en]

    This paper evaluates the capacitive antenna performance as a lightning sensor. The performance is evaluated by looking at two aspects, antenna structures and the background permittivity value of the antenna. Two experiments were carried out, Experiment A using two different structure antennas, one with its Bayonet Neill-Concelman (BNC) connector's core direct touching the top plate (DBNC) while the other was connected via single core wires (WBNC), capturing the electric field (E-field) generated by the small spark at a distance of 1 meter away from both antennas. Furthermore, both capacitive antennas with top plates directly soldered to their BNC cores were used to study their performance with and without being covered by plastic (dielectric constant of 2.25) during Experiment B. The result from Experiment A showed that WBNC has different onset polarity and significant decreased in amplitude of the signals captured compared to DBNC (mean ratio is 1.095 with range between 0.5838 and 4.528). Meanwhile, Experiment B shows that a comparable average ratio of 0.7835 and 0.7447 during the measurement where antenna A(wc) with and without the presence of plastic cover respectively.

  • 306.
    Sharma, S. R.
    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.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isolated breakdown activity in Swedish lightning2008In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 70, no 8-9, p. 1213-1221Article in journal (Refereed)
    Abstract [en]

    The initial breakdown processes or preliminary breakdown (PB) processes are generally associated with either cloud or cloud-ground lightning flashes, and hence have been studied mainly in connection with those subsequent activities. However, it has been observed in the summer thunderstorms of Sweden that there are breakdown processes that may not culminate into any subsequent activity. As these processes do not lead to any subsequent activity, they have been termed as isolated breakdown activities. Such isolated breakdown activities involve microsecond-scale pulses with both initial polarities. Based on their polarities, breakdown processes are divided into two groups, the negative breakdown pulses that are similar to the breakdown pulses leading to negative return strokes in ground flashes and the positive breakdown pulses similar to the breakdown pulses generally leading to the cloud flashes. The occurrence of the two types of breakdown processes is found to vary from a thunderstorm day to the other. In the present study, the signatures of isolated breakdown activities have been analyzed and are compared with those leading to the subsequent activities observed during the same measurement campaign. The average duration of the isolated breakdown activity associated with the negative initial polarity pulses is found to be 0.98 ms with average number of pulses 8.5. Similarly, the average duration and number of pulses in the isolated breakdown process with positive initial polarity pulses are 6.9ms and 3.9, respectively.

  • 307.
    Sharma, S R
    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.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Unique lightning activities pertinent to tropical and temperate thunderstorms2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 4, p. 483-487Article in journal (Refereed)
    Abstract [en]

    Observations from two geographical locations show that some lightning events are unique and specific to the respective thunderstorms. From the measurements conducted in a tropical country, Sri Lanka, and a temperate country, Sweden, it is observed that there are some lightning activities that are unique for each location. Narrow bipolar pulses (NBPs) have frequently been observed in the tropical thunderstorms and were not observed in the temperate thunderstorms, whereas isolated breakdown pulses (IBPs) have frequently been observed in the temperate thunderstorms and were not observed in the tropical thunderstorms. It can be speculated that NBPs are the unique features of tropical thunderstorms and that IBPs are the unique features pertinent to the temperate thunderstorms.

  • 308.
    Sharma, S R
    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.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Miranda, F J
    ept of Mathematics, Statistics and Physics, Federal University of the Valleys of Jequitinhonha e Mucuri Diamantina, Brasilien.
    Temporal features of different lightning events revealed from wavelet transform2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 4, p. 507-515Article in journal (Refereed)
    Abstract [en]

    Various lightning events are analysed using wavelet transform. The events include PB pulses, stepped leaders, first return strokes, subsequent strokes associated with negative ground flashes, positive return strokes and narrow bipolar pulses. Time domain electric fields were recorded from tropical and temperate thunderstorms. PB pulses pertinent to the tropical thunderstorms are found to radiate in the average frequency range 51-739 kHz. Leaders are found to radiate in the frequency range 87-720 kHz. The energy radiated by the negative return strokes is predominant in the range 2.8-40 kHz. The energy radiated by the first subsequent strokes predominantly lies in the frequency range 4.5-55 kHz. Positive return strokes are found to radiate predominantly in the frequency range 5.5-81 kHz. Narrow bipolar pulses are found to predominantly radiate in the frequency range 58-714 kHz.

  • 309.
    Sharma, S. R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Fernando, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Positive bipolar type radiation field from lightning in Sri Lanka2006Conference paper (Refereed)
  • 310. Sharma, S. R.
    et al.
    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.
    Narrow positive bipolar radiation from lightning observed in Sri Lanka2008In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, Vol. 70, no 10, p. 1251-1260Article in journal (Refereed)
    Abstract [en]

    Narrow positive bipolar pulses (NPBPs), whose origin largely remains unknown as yet, have occasionally been noticed in Sri Lanka. These discharges are found to be opposite in polarity to that of negative return strokes, and are found to occur at the beginning and active stage of thunderstorm activities in Sri Lanka. They are emitted from the thunderstorms that produce other activities also and are relatively narrower, bipolar and isolated in nature. They are neither preceded by leader-type pulses nor succeeded by the subsequent activities and hence, could not be associated with any other known activity. Similar radiations have previously been identified and termed as NPBPs. Their features are indeed unique and different from the other known thunderstorm electrical processes. These events have been found to be accompanied by the HF radiations at 5 and 10 MHz, at the trailing part of the pulse. However, such narrow, bipolar and isolated events have not been observed in Sweden, during a lightning measurement campaign at Uppsala, in 2006. So, it is speculated that the meteorological conditions to be responsible for the thunderstorm activity to produce such pulses. Features of such pulses recorded on different thunderstorm days in 2005 and 2006 have been analyzed and presented in this study. The average rise time (10-90%) (Tr), of the pulses was found to be 2.6 [mu]s, the average zero crossing time (Tz) was found to be 5.85 [mu]s, the average duration of slow front (Ts) was found to be 1.86 [mu]s, and the average ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa) of these pulses was found to be 0.39.

  • 311. Sharma, S.R.
    et al.
    Fernando, Mahendra
    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.
    Frequency Spectrum of the Electromagnetic Fields of a Positive Return Strokes2004In: International Conference on Lightning Protection, Avignon, France, 2004Conference paper (Other scientific)
  • 312. Shoory, A
    et al.
    Rachidi, F
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Moini, R
    Sadeghi, S. H. H.
    On simple approaches for the evaluation of lightning electromagnetic fields above stratified ground2009Conference paper (Refereed)
  • 313. Shoory, Abdolhamid
    et al.
    Mimouni, Abdenabi
    Rachidi, Farhad
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Moini, Rouzbeh
    Sadeghi, Seyed H. Hesamedin
    Validity of Simplified Approaches for the Evaluation of Lightning Electromagnetic Fields Above a Horizontally Stratified Ground2010In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 52, no 3, p. 657-663Article in journal (Refereed)
    Abstract [en]

    We review in this paper simplified analytical expressions derived by Wait using the concept of attenuation function for the analysis of the propagation of lightning radiated electromagnetic fields over a horizontally stratified ground. Considerations regarding the use of these formulations as well as their domain of applicability are given. For the case, where the upper ground layer has a lower conductivity than the lower layer, the magnitude of the attenuation function can take values greater than unity. Time-domain waveforms of the vertical electric field along a horizontally stratified ground, obtained using the simplified formulations feature, an oscillatory behavior in their early-time response. The peak value of the field is also found to be larger than that corresponding to the case of a perfect ground. The accuracy of the Wait's formulations is examined taking as reference full-wave simulations obtained using the finite-difference time domain (FDTD) technique. FDTD simulations confirm the oscillatory waveform of the far field above a horizontally stratified ground (with an upper layer characterized by a lower conductivity than that of the lower layer), as well as the enhancement of the field peak compared to the case of a homogeneous, perfectly conducting ground.

  • 314. Shoory, Abdolhamid
    et al.
    Mimouni, Abdenabi
    Rachidi, Farhad
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rubinstein, Marcos
    Lightning horizontal electric fields above a two-layer ground2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 315.
    Shoory, Abdolhamid
    et al.
    Electromagnetic Compatibility Laboratory, Swiss Federal Institute of Technology, Lausanne, Schweiz.
    Mimouni, Abdenabi
    Laboratoire de Génie Physique, Ibn Khaldoun University, Tiaret, Algeriet.
    Rachidi, Farhad
    Electromagnetic Compatibility Laboratory, Swiss Federal Institute of Technology, Lausanne, Schweiz.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rubinstein, Marcos
    Dept of Electrical Engineering and Computer Science, University of Applied Sciences of Western Switzerland, Yverdon-les-Bains, Schweiz.
    On the accuracy of approximate techniques for the evaluation of lightning electromagnetic fields along a mixed propagation path2011In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 46, p. RS2001-Article in journal (Refereed)
    Abstract [en]

    In this paper we review simplified analytical expressions derived by Wait using the concept of attenuation function for the analysis of the propagation of lightning-radiated electromagnetic fields over a mixed propagation path (vertically stratified ground). Two different formulations proposed by Wait that depend on the relative values of ground surface impedances are discussed. It is shown that both formulations give nearly the same results for the time domain electric field. However, depending on the values of the normalized surface impedance for each ground section, the use of one of the two formulations is computationally more efficient. The accuracy of the Wait formulations was examined taking as reference full-wave simulations obtained using the finite difference time domain technique. It is shown that Wait's simplified formulas are able to reproduce the distant field peak and waveshape with a good accuracy.

  • 316. Smorgonskiy, A
    et al.
    Egüz, E
    Rachidi, F
    Rubinstein, M
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Influence of the lightning triggering rocket wire and its corona on the electric field at ground level2012In: 31st International Conference on Lightning Protection ICLP 2012, 2012, p. 6344361-Conference paper (Refereed)
    Abstract [en]

    In this paper, we present analytical calculations and numerical simulations of the vertical component of the electric field close to a rocket-triggered lightning site during the ascent of the rocket and prior to the lightning initiation, taking into account the corona layer around the wire. In the analysis, the background electric field was modeled according to the available experimental data. The influence of the space charge layer extending upwards from the ground level was modeled and analyzed. The obtained values of the electric field reduction are shown to be consistent with experimental observations. The presented model can also be used to estimate the charge distribution in the rocket wire and the current flowing into the wire from the ground.

  • 317.
    Smorgonskiy, Alexander
    et al.
    Ecole Polytech Fed Lausanne, EMC Lab, CH-1015 Lausanne, Switzerland..
    Eguez, Eda
    Ecole Polytech Fed Lausanne, EMC Lab, CH-1015 Lausanne, Switzerland..
    Rachidi, Farhad
    Ecole Polytech Fed Lausanne, EMC Lab, CH-1015 Lausanne, Switzerland..
    Rubinstein, Marcos
    HEIG VD, Inst Informat & Commun Technol, Yverdon, Switzerland..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A model for the evaluation of the electric field associated with the lightning-triggering rocket wire and its corona2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 20Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the electric field at ground level during the first stage of triggered lightning experiments, i.e., during the rocket ascent and prior to the lightning initiation. At distances of some tens of meters from the triggering wire, the electric field decreases significantly, while at distances of several hundred meters, there is only a very small decrease of the electric field. Two effects determine the level of the electric field reduction: the corona layer at ground level and the corona sheath around the triggering wire. We present an analytical solution based on the charge simulation method to study the phenomenon. The model is validated by comparing its results to those obtained by numerical simulations using the finite element method. A ground space charge layer and a corona sheath around the rocket-triggered lightning wire are included in the simulation. It is shown that, depending on the charge distribution, the change of the sign of the electric field is correctly predicted by our model. The obtained reductions of the electric field are consistent with simulations and experiments presented in the literature. Moreover, the proposed analytical solution is faster, and it allows studying the influence of several parameters simultaneously, i.e., the radius of the corona sheath and the space charge layer parameters. The described analytical model allows the estimation of the corona sheath radius if the parameters of the space charge layer are known from experiment.

  • 318. Sonnadara, Upul
    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
    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.
    Lightning radiation field spectra of cloud flashes2004In: International Conference on Lightning Protection, Avignon, France, 2004Conference paper (Other scientific)
  • 319.
    Sonnadara, Upul
    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. Avdelningen för elektricitetslära och åskforskning.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    The Lightning Radiation Field Spectra of Cloud Flashes in the Interval From 20 kHz to 20 MHz2006In: IEEE Transactions on Electromagnetic Compatibility, Vol. 48, no 1, p. 234-239Article in journal (Refereed)
  • 320. Sonnadara, Upul
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Characteristics of cloud-to-ground lightning flashes over Sweden2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 74, no 5, p. 541-548Article in journal (Refereed)
    Abstract [en]

    A detailed study of the characteristics of cloud-to-ground (CG) lightning flashes over Sweden was carried out for the period 1987-2000 using data obtained from the Swedish lightning-locating network. Results are presented by analysing over half a million lightning ground flashes. The average variation of the annual mean of the total number of flashes was found to be 37%. About 12% of the CG flashes were positive flashes and their average variation about the annual mean was 26%. The average peak currents were fairly constant over the years with variations as little as 4% for negative flashes and 5% for positive flashes. The average peak current values for negative and positive flashes were -29.90 and +63.97 kA respectively. A correlation between the mean monthly flash count and percentage of positive flashes was seen. A similar relationship is seen with the mean monthly flash count and the peak currents for both polarities. In general, high flash density and high peak currents were observed in the southern part of Sweden where most of the major cities are located. Flash densities exceeding 0.4 flashes km(-2) were observed for several large cities. The maximum flash rate of 32 flashes h(-1) within a 10 km radius was seen in Jonkoping (14.18 degrees E, 57.78 degrees N) in the province of Smaland.

  • 321. Sonnadara, Upul
    et al.
    Kathriarachchi, Vindu
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance of lightning locating systems in extracting lightning flash characteristics2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 112, p. 31-37Article in journal (Refereed)
    Abstract [en]

    A study was carried out to compare the negative cloud to ground lightning discharges recorded using Swedish lightning locating system against time correlated direct field measurements. Only the first 200 ms time window was investigated. A total of 167 flashes were recorded and time matched against the lightning locating system records. The comparison shows that for negative cloud-to-ground lightning flashes, the stroke detection efficiency of lightning locating system is at 93% for detecting the first stroke accurately. The efficiency drops to about 77% in detecting all strokes accurately. Thus, the system tends to give a low value for average multiplicity and a significantly higher value for parameters such as percentage of single stroke flashes. In agreement with the direct field measurements, when the individual strokes are identified correctly, both systems show the expected 2:1 ratio between the first and subsequent stroke peak field. Data also shows that the LLS system has a tendency of identifying isolated cloud pulses as positive return strokes. Hence one must take into account the systematic deficiency in lightning locating systems when reporting characteristics of cloud to ground lightning flashes.

  • 322.
    Theethayi, Nelson
    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.
    On the representation of the lightning return stroke process as a current pulse propagating along a transmission line2005In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 20, no 2, p. 823-837Article in journal (Refereed)
    Abstract [en]

    Assuming that the representation of the lightning return stroke as a current pulse propagating along a transmission line is valid, the effects of different transmission line parameters both on the channel current and the electromagnetic fields are investigated. The transmission line parameters that are incorporated into the study are the spatial variation of the inductance and the capacitance, the channel resistance and its temporal variation and the finite conductance of the line. The results show that the introduction of the time varying channel resistance and the finite conductance will change the predictions of the model in such a direction that they will come closer to the experimental observations.

  • 323.
    Theethayi, Nelson
    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.
    Representation of the return stroke as a transmission line: the apparent return stroke velocity2004In: Proceedings of International Conference on Lightning Protection, Avignon, France, 2004, 2004Conference paper (Refereed)
  • 324.
    Theethayi, Nelson
    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.
    Liu, Yaqing
    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.
    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.
    Thottappillil, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Zitnik, Mihael
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. 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.
    Scuka, Viktor
    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 theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden2005In: Electric Power System Research, Vol. 74, p. 267-280Article in journal (Refereed)
    Abstract [en]

    Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.

  • 325.
    Thottappillil, Rajeev
    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.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lightning Return Stroke Models and Electromagnetic Field Computation2007Conference paper (Refereed)
  • 326.
    Thottappillil, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Theethayi, Nelson
    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.
    Lightning Return Stroke Models and Electromagnetic Field Computation, in Tutorial on EMC aspects of Lightning2006Conference paper (Other academic)
  • 327.
    Vayanganie, S. P. A.
    et al.
    Univ Colombo, Dept Phys, Atmospher Phys & Lightning Res Grp, Colombo 3, Sri Lanka.
    Fernando, M.
    Univ Colombo, Dept Phys, Atmospher Phys & Lightning Res Grp, Colombo 3, Sri Lanka.
    Sonnadara, U.
    Univ Colombo, Dept Phys, Atmospher Phys & Lightning Res Grp, Colombo 3, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Perera, C.
    Univ Colombo, Dept Phys, Atmospher Phys & Lightning Res Grp, Colombo 3, Sri Lanka.
    Optical observations of electrical activity in cloud discharges2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 172, p. 24-32Article in journal (Refereed)
    Abstract [en]

    Temporal variation of the luminosity of seven natural cloud-to-cloud lightning channels were studied, and results were presented. They were recorded by using a high-speed video camera with the speed of 5000 fps (frames per second) and the pixel resolution of 512 x 512 in three locations in Sri Lanka in the tropics. Luminosity variation of the channel with time was obtained by analyzing the image sequences. Recorded video frames together with the luminosity variation were studied to understand the cloud discharge process. Image analysis techniques also used to understand the characteristics of channels. Cloud flashes show more luminosity variability than ground flashes. Most of the time it starts with a leader which do not have stepping process. Channel width and standard deviation of intensity variation across the channel for each cloud flashes was obtained. Brightness variation across the channel shows a Gaussian distribution. The average time duration of the cloud flashes which start with non stepped leader was 180.83 ms. Identified characteristics are matched with the existing models to understand the process of cloud flashes. The fact that cloud discharges are not confined to a single process have been further confirmed from this study. The observations show that cloud flash is a basic lightning discharge which transfers charge between two charge centers without using one specific mechanism.

  • 328. Vayanganie, S. P. A.
    et al.
    Gunasekera, T. A. L. N.
    Nanayakkara, S.
    Fernando, M.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric Field Change of M Component2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 1725-1728Conference paper (Refereed)
    Abstract [en]

    Temporary increase of luminosity of lightning channel during the stage of long continuing current is known as the M components. In this study 17 M components of 14 lightning flashes recorded with 10 ns sampling resolution is analyzed. Results suggest that in all analyzed cases the electric field change of M components is embedded with chaotic pulses.

  • 329. Vayanganie, S.P.A.
    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.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Diaz, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    On the occurrence of ‘bead lightning’ phenomena in long laboratory sparks2016In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 380, no 7-8, p. 816-821Article in journal (Refereed)
    Abstract [en]

    The formation of bead lightning, where the lightning channel appears to break up into luminous fragments, is still an object of speculation. Here we report similar observations in laboratory discharges. Analysis of time resolved photographs shows that the discharge channel exhibits a 'bead pattern' in the decaying stage of the discharge and the occurrence of loops in the channel sections where the bead pattern is observed. This result presents the first evidence that the rapid cooling of non-uniform channel sections could lead to the formation of beads. It is suggested that periodically occurring non-uniform channel sections could explain the bead pattern of lightning discharges.

  • 330. Vayanganie, S.P.A
    et al.
    Fernando, Mahendra
    Sonnadara, Upul
    Perera, D.C.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    High Speed Optical Observations of Cloud Flashes2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 752-755Conference paper (Refereed)
    Abstract [en]

    Luminosity variations of natural cloud lightning channels were studied using high speed video recordings in Sri Lanka in the tropic. Five cloud flashes were selected for the study, which were recorded with 5000 fps with 512X512 pixel resolution. Luminosity variation along channels and along selected channel segment, duration of cloud activities was studied. It was found that the average duration of selected flashes is 266.44 ms. No particular pattern was observed for the luminosity variation along channel segments. However the luminosity variation across the channel followed a Gaussian distribution pattern. Pattern of the luminosity variation along channels were compared with existing models to understand the development process of cloud flashes. Results show that it is hard to collaborate the observation to a single process for cloud discharges.

  • 331. Vayanganie, S.P.A
    et al.
    Gunasekara, T.A.L.N.
    Nanayakkara, S
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric Field Change of M Component2014Conference paper (Refereed)
  • 332.
    Vernon, Cooray
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    NOx production in lightning flashes2007In: International Conference on Atmospheric Electricity, ICAE, Beijing, China, 2007Conference paper (Other academic)
4567 301 - 332 of 332
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