uu.seUppsala University Publications
Change search
Refine search result
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • 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.
  • 1. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    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.
    Channel tortuosity of long laboratory sparks2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 8, p. 521-526Article in journal (Refereed)
    Abstract [en]

    Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120 degrees. The sparks were generated between a steel rod and. a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3 degrees. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8 +/- 1.4 degrees, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08 degrees/cm) was seen when the sparks propagated towards the plane electrode.

  • 2. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    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.
    Fractal dimension of long electrical discharges2015In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 73, p. 33-37Article in journal (Refereed)
    Abstract [en]

    The fractal dimension of 500 mm long electrical discharges is presented by analyzing a set of photographic images. Three popular fractal dimension estimation techniques, box counting, sandbox and correlation function methods were used to estimate the fractal dimension of the discharge channels. To remove the apparent thickness due to varying magnitudes of current in the discharge channels, edge detection algorithms were utilized. The estimated fractal dimensions for box counting, sandbox and correlation function for long laboratory sparks were 1.20 +/- 0.06,1.66 +/- 0.05 and 1.52 +/- 0.12 respectively. Within statistical uncertainties, the estimated fractal dimensions of positive and negative polarities agreed very well. (C) 2014 Elsevier B.V. All rights reserved.

  • 3.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the interception of lightning flashes by power transmission lines2011In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 69, no 3, p. 220-227Article in journal (Refereed)
    Abstract [en]

    The design of the lightning protection system LPS of transmission lines is based on the well knownelectro-geometrical model. The electro-geometrical model assumes that the first point on a powertransmission line that will come within striking distance of the tip of a down-coming stepped leaderchannel is the strike point of the lightning flash. The model neglects almost all of the physics associatedwith the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numericalmethods, it is feasible to apply the physics of the discharge process to the study of lightning attachment.Such models take into account the movement of the downward and the resulting upward leaders fromdifferent points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachmentphenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with thepredictions of the electro-geometrical method.

  • 4.
    Arevalo, Liliana
    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.
    'The mesh method' in lightning protection standards - Revisited2010In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 68, no 4, p. 311-314Article in journal (Refereed)
    Abstract [en]

    At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro - geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.

  • 5.
    Arevalo, Liliana
    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.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical simulation of long laboratory sparks generated by positive switching impulses2009In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 67, no 2-3, p. 228-234Article in journal (Refereed)
    Abstract [en]

    A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic - L.T.E. - physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.

  • 6.
    Arevalo, Liliana
    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.
    Wu, Dong
    ABB AB, Power systems HVDC, Ludvika.
    Jacobson, Björn
    ABB AB, Power Systems HVDC, Ludvika.
    A new static calculation of the streamer region for long spark gaps2012In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 70, no 1, p. 15-19Article in journal (Refereed)
    Abstract [en]

    Different electrostatic approximations have been proposed to calculate the streamer region without going in deep details of the behavior of density of particles under the effect of high electric fields; this kind of approximations have been used in numerical calculations of long spark gaps and lightning attachment. The simplifications of the streamer region are achieved by considering it to be a geometrical region with a constant geometrical shape. Different geometrical shapes have been used, such as cones or several parallel filaments. Afterward, to simplify the procedures, the streamer region was approximated by two constants, one denoted K-Q, called the geometrical constant and in other cases K named as geometrical factor. However, when a voltage that varies with time is applied to an arrangement of electrodes (high voltage and grounded electrodes), the background electric field will change with time. Thus, if the background electric field is modified, the streamer zone could cover a larger or smaller area. With the aim of reducing the number of assumptions required in the calculation of long gap discharges, a new electrostatic model to calculate the streamer region is presented. This model considers a variable streamer zone that changes with the electric field variations. The three-dimensional region that fulfills the minimum electric field to sustain a streamer is identified for each time step, and the charge accumulated in that region is then calculated. The only parameter that is being used in the calculation is the minimum electric field necessary for the propagation of streamers.

  • 7.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hartono, Zainal
    Identification of lightning vulnerability points on complex grounded structures2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 9, p. 562-570Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the attachment of lightning flashes to grounded structures with special attention to the comparison of SLIM with CVM and EGM2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 577-581Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, C.
    Karolinska institutet.
    Andrews, C.J.
    Lightning caused injuries in humans2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 386-394Article in journal (Refereed)
    Abstract [en]

    A lightning flash may interact with humans in several ways. The possible pathways of interactions are direct strike, side flash, touch voltage, step voltage, subsequent stroke, connecting leaders and shock waves. The permanent or the temporary injuries that a victim suffers depend, among other parameters, on the type of interaction through which the body is exposed to a lightning strike and the path and the strength of the electric current passing through the body. In addition to the effects of electric current passing through the body, strong light and shock waves may also interact with the body in various ways. In this paper, the different types of injuries that may result from a lightning strike are documented and they are summarized, from engineering rather than a medical perspective

  • 10.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Becerra, Marley
    On the streamer discharges emitted from the head of a person located in the vicinity of lightning strikes and their possible consequences2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 572-576Article in journal (Refereed)
    Abstract [en]

    In this paper the currents associated with the streamer discharges generated from the head of a person located in the vicinity of a lightning strike are investigated. In the analysis the location of the person with respect to the lightning strike is selected in such a way that only a streamer burst, without the formation of a connecting leader, is emitted from the head. The current associated with these streamer bursts could exceed several hundreds of mA and may last for several hundreds of microseconds. The results of the calculation show that the passage of the streamer currents through the body of the person could create electric fields in the brain large enough to excite neurons. Depending on the strength of lightning flash and the distance to the strike point these streamer bursts can give rise to phosphenes which are a form of visual experience that occurs when the visual cortex is stimulated by electric currents.

  • 11.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montaño, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    A model to represent negative and positive lightning first strokes with connecting leaders2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, no 2-4, p. 97-109Article in journal (Refereed)
    Abstract [en]

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

  • 12.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Efficiencies for production of NOx and O3 by streamer discharges in air at atmospheric pressure2005In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 63, p. 977-983Article in journal (Refereed)
  • 13.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    Department of Electrical and Computer Engineering, University of Florida.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The lightning striking distance—Revisited2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 296-306Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The striking distance of lightning flashes and the early streamer emission (ESE) hypothesis2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 336-341Article in journal (Refereed)
    Abstract [en]

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

  • 15.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, Mihael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Manyahi, Mighanda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Physical model of surge-current characteristics of buried vertical rods in the presence of soil ionisation2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, p. 193-202Article in journal (Refereed)
  • 16.
    Diaz, Oscar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leader channel models for long air positive electrical discharges2015In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 76, p. 208-215Article in journal (Refereed)
    Abstract [en]

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

  • 17.
    Liu, Yaqing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Investigating the validity of existing definitions and empirical equations of effective length/area of grounding wire/grid for transient studies2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 329-335Article in journal (Refereed)
    Abstract [en]

    There are various definitions for effective length/area of grounding wire/grid for lightning transients [A.S. Farag, T.C. Cheng, D. Penn, Grounding terminations of lightning protective systems, IEEE Trans. Dielectics, Elect. Insul 5(6) (1998) 869–877; B.R. Gupta, B. Thapar, Impulse impedance of grounding grid, IEEE Trans. Power Apparatus Syayem PAS-99(6) (1980) 2357–2362; Y. Liu, N. Theethayi, R. Thottappillil, An engineering model for transient analysis of grounding system under lightning strikes: non–uniform transmission line approach. IEEE Trans. Power Delivery 20 (2) (2005) 722–730; M.I. Lorentzou, N.D. Hatziargriou, Modelling of long grounding conductors using EMTP, in: IPST’99, International Conference on Power System Transients, Budapest, 20–24 June, 1999; L.D. Grcev, M. Heimbach, Frequency dependent and transient characteristics of substation grounding system, IEEE Trans. Power Delivery 12 (1997) 172–178.]. The present work investigates and discusses the validity of those existing definitions. Further, practical methods for estimating the effective length/area of different grounding structures are proposed for engineering applications. The calculations for effective length/area based on non-uniform transmission line approach (Liu et al., 2005) show that, for a single grounding wire, the empirical equation for effective length in Farag et al. (1998) is not valid when the injection current has very fast rise time. Also, the empirical equation for effective length of grid edge in Gupta and Thapar (1980) is not applicable for grids with large inner mesh size.

  • 18.
    Liu, Yaqing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Gonzalez, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, Mihael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    An improved model for soil ionization around grounding system and its application to stratified soil2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, no 2-4, p. 203-209Article in journal (Refereed)
    Abstract [en]

    An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times.

  • 19. Perera, C.
    et al.
    Fernando, M.
    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.
    Leader propagation speed and the final jump distance of 8 m long laboratory sparks2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 568-571Article in journal (Refereed)
    Abstract [en]

    Vertical profile of the leader in long laboratory sparks was analyzed using high speed video photographs. Sparks were generated in an 8 m gap of sphere - plane electrodes with positive impulse voltage of 250/2500 mu s wave form. The spatial resolution of the high speed frame camera was 19.6 mm per pixel with a time resolution of 50 mu s. It was found that the average final jump distance of five sparks was about 4 m and the average electric field in the final jump region is about 5 x 10(5) V/m the leader speed varies from 1.3 x 10(4) m/s to 3.1 x 10(4) m/s as it propagates toward the ground. The average leader speed of the leader was in the order of 1.8 x 10(4) m/s. The observations show that there is a significant increase in the leader speed just before the final jump.

  • 20. Perera, C.
    et al.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Liyanage, P.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The relationship between current and channel diameter of 30 cm long laboratory sparks2012In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 70, no 6, p. 512-516Article in journal (Refereed)
    Abstract [en]

    In this study the dependence of channel diameter of 30 cm long sparks on discharge current is analyzed using a photographic technique. The results show the radial channel intensity variation follows a Gaussian distribution. The channel diameter (D), defined as the width of the intensity profile at 10% level, increases with the increasing peak current (I-p) up to 3 kA. The relationship between the two parameters can be represented by the equation, D = 8.36 ln(I-p) + 1.598, where D is in mm and I-p is in kA. The experimental results agree reasonably well with the available theory.

  • 21.
    Rahman, Mahbubur
    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.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Liyanage, Prasanna
    Atmospheric Physics and Lightning research group, Dept of Physics, University of Colombo, Sri Lanka.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    NO(X) production by impulse sparks in air2011In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 69, no 6, p. 494-500Article in journal (Refereed)
    Abstract [en]

    An experimental study on the production of NO(X) by impulse sparks in air is presented. The emphasis is placed on the dependence of the NO(X) yield on the signature of the discharge current waveforms. A voltage and two current impulses were used in the experiments to create a spark and the NO(X) production was measured by the method of chemiluminescence. The results show that, for a given current waveform, the NO(X) production varies linearly with the peak current and the gap length. In addition, it was found that the NO(X) yield increases with the duration of the current for a given peak current.

  • 22.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Some Issues Concerning Lightning Strikes to Communication towers2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 10-11, p. 689-703Article in journal (Refereed)
    Abstract [en]

    It is a usual phenomenon that lightning strikes tall communication towers. Some of the questions about lightning interaction with communication towers are dealt with in this paper. Can tall towers influence the incidence of lightning in the area where the tower is situated? Are the parameters of lightning, such as peak currents, influenced by the presence of the tower where lightning strikes? What would be the difference in the electric and magnetic field environment in the near vicinity of the tower and far from the tower when compared to the corresponding values with lightning striking level ground? Are lightning protection methods designed primarily to protect the communication equipment sufficient to prevent lightning surge transfer to nearby local networks? This paper addresses the above issues based on the analysis, models and observations made in the recent past and also using some simple calculations by the authors.

  • 23.
    Thottappillil, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Uman, Martin
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Electric and magnetic fields from a semi-infinite antenna above a conducting plane2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 61, no 3-4, p. 209-221Article in journal (Refereed)
    Abstract [en]

    The electric and magnetic field structures around a semi-infinite thin-wire antenna vertically placed above a perfectly conducting ground plane are investigated when the antenna is supporting two different types of sources. It is shown that when the wire is carrying a uniform line charge, the electrostatic potentials are equal on the surfaces of imaginary cones of fixed cone angles with axis along the wire and apex at the conducting plane. The electrostatic field vectors are shown to be perpendicular to the imaginary cones and tangential to the meridian lines of half-spherical shells centered at the base of the line charge. The vertical components of the electrostatic field on the surface of these imaginary half-spherical shells of a given radius are constant, except at the wire itself. The magnetic field structure associated with a constant current in the semi-infinite antenna is that of an infinite wire. The electric and magnetic fields due to a time-varying charge or current pulse propagating with the speed of light along the vertical thin-wire antenna have a spherical transverse electromagnetic (TEM) field structure, identical to that for the case of a uniform line charge and a uniform current. The connection between the static and dynamic solutions is derived mathematically using two different approaches.

1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • 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