| 1. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
A Novel Interpretation of the Electromagnetic Fields of Lightning Return Strokes
- 2019
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Electric and/or magnetic fields are generated by stationary charges, uniformly moving charges and accelerating charges. These field components are described in the literature as static fields, velocity fields (or generalized Coulomb field) and radiation fields (or acceleration fields), respectively. In the literature, the electromagnetic fields generated by lightning return strokes are presented using the field components associated with short dipoles, and in this description the one-to-one association of the electromagnetic field terms with the physical process that gives rise to them is lost. In this paper, we have derived expressions for the electromagnetic fields using field equations associated with accelerating (and moving) charges and separated the resulting fields into static, velocity and radiation fields. The results illustrate how the radiation fields emanating from the lightning channel give rise to field terms varying as 1/r and 1/r2, the velocity fields generating field terms varying as 1/r2, and the static fields generating field components varying as 1/r2 and 1/r3. These field components depend explicitly on the speed of propagation of the current pulse. However, the total field does not depend explicitly on the speed of propagation of the current pulse. It is shown that these field components can be combined to generate the field components pertinent to the dipole technique. However, in this conversion process the connection of the field components to the physical processes taking place at the source that generate these fields (i.e., static charges, uniformly moving charges and accelerating charges) is lost.
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| 2. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Comment on "Straight lightning as a signature of macroscopic dark matter"
- 2022
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 105:8
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In the discussed paper [N. Starkman, H. Winch, J. S. Sidhu, and G. Starkman, Straight lightning as a signature of macroscopic dark matter, Phys. Rev. D 103, 063024 (2021)], the authors have made several assumptions and statements concerning the initiation and propagation of lightning flashes induced by macroscopic dark matter passing through the atmosphere. The authors suggest that the path of dark matter can be identified by looking for lightning with straight channels, although such channels have not been previously reported. Even though we agree with the suggestion of the authors that macroscopic dark matter could, in theory, give rise to straight lightning channels, there are several statements in the paper that are not sufficiently clear and which could lead to misinterpretation. Our comments on the paper are the following.
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| 3. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Could Macroscopic Dark Matter (Macros) Give Rise to Mini-Lightning Flashes out of a Blue Sky without Clouds?
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- A recent study pointed out that macroscopic dark matter (macros) traversing through the Earth's atmosphere can give rise to hot and ionized channels similar to those associated with lightning leaders. The authors of the study investigated the possibility that when such channels created by macros pass through a thundercloud, lightning leaders may be locked in by these ionized channels, creating lightning discharges with perfectly straight channels. They suggested the possibility of detecting such channels as a means of detecting the passage of macros through the atmosphere. In this paper, we show that such macros crossing the atmosphere under fair weather conditions could also give rise to mini-lightning flashes with current amplitudes in the order of a few hundred Amperes. These mini-lightning flashes would generate a thunder signature similar to or stronger than those of long laboratory sparks and they could also be detected by optical means. As in the case of thunderstorm-assisted macro lightning, these mini-lightning flashes are also associated with straight channels. Moreover, since the frequency of mini-lightning flashes is about thirty times greater than the macro-generated lightning flashes assisted by thunderstorms, they could be used as a means to look for the paths of macroscopic dark matter crossing the atmosphere.
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| 4. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Electromagnetic fields of accelerating charges : Applications in lightning protection
- 2017
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Ingår i: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 145, s. 234-247
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic fields generated by accelerating charges can be utilized to evaluate the electromagnetic fields generated by systems where moving charges and/or propagating currents are present. The technique can be used easily to evaluate the electromagnetic fields generated by systems in which propagating currents are present. This is illustrated by utilizing the equations to derive expressions for the electromagnetic fields generated by systems in which current pulses injected by lightning flashes are propagating.
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| 5. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Exact Expressions for Lightning Electromagnetic Fields : Application to the Rusck Field-to-Transmission Line Coupling Model
- 2023
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 14:2
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Tidskriftsartikel (refereegranskat)abstract
- An exact analytical expression for the electric field of the return stroke as excited by a propagating step current source is derived in this paper. This expression could be advantageously used to evaluate the disturbances caused by lightning on overhead lines. There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal-Price-Gurbaxani model, the Taylor-Satterwhite-Harrison model, and the Rachidi model. In the case of a vertical return stroke channel, the coupling model developed by Rusck becomes identical to these three coupling models. Due to its simplicity, the Rusck model is frequently used by engineers to study the effects of lightning on power distribution and transmission lines. In order to reduce the time involved in the electromagnetic field calculation, the Rusck model is incorporated with an analytical expression for the electromagnetic fields of the return stroke excited by a propagating step current pulse. Our research work shows that the Rusck expression can be used to calculate the peak values of lightning induced voltages to an accuracy of about 10%. However, the use of this analytical expression to calculate the time derivatives of lightning induced voltages may result in errors as large as 50%. The derived expression in this paper can be used to correct for this inaccuracy. We also provide an exact expression for the electric field at any given point in space when the propagating current is an impulse function. This expression can be combined with the convolution integral to obtain the electric field corresponding to waveforms similar to measured return stroke currents.
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| 6. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Generalized Electric Field Equations of a Time-Varying Current Distribution Based on the Electromagnetic Fields of Moving and Accelerating Charges
- 2019
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- In several studies conducted recently, it was shown that equations pertinent to the electric and magnetic fields produced by electrical charges in motion can be used to calculate the electromagnetic fields produced by current pulses propagating along linearly restricted paths. An example includes the case of current pulses propagating along conductors and conducting channels such as lightning. In this paper, it is shown how the technique can be applied to estimate the electromagnetic fields generated by current and charge distributions moving in arbitrary directions in space. The analysis shows that, depending on the way the problem is formulated using the field equations pertinent to accelerating charges, one procedure leads to the generalized dipole equations, which are independent of the velocity of propagation of the current, and the other procedure leads to a set of equations that depend on the velocity. Using the well-tested transmission line model of lightning return strokes as an example, it is shown that both sets of field equations give rise to the same total electromagnetic field.
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| 7. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Ionization Waves Enhance the Production of X-rays during Streamer Collisions
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data show that in laboratory sparks, X-rays are produced in time synchronization with the meeting of streamers of opposite polarity just before the final breakdown of the discharge gap. It has been suggested that the electric field enhancement created during the collision of streamers could provide the necessary conditions for electron acceleration, even though some of the theoretical studies show that the duration of the electric field is not long enough to do so. The experimental data on laboratory discharges show that. when streamers of opposite polarity meet each other, a potential or ionization wave that renders the streamer channels conducting is initiated. This paper shows that these ionization waves that convert the discharge channels from weakly conducting to highly conducting are associated with electric fields large enough to accelerate electrons to relativistic energies.
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| 8. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Modeling Compact Intracloud Discharge (CID) as a Streamer Burst
- 2020
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Narrow Bipolar Pulses are generated by bursts of electrical activity in the cloud and these are referred to as Compact Intracloud Discharges (CID) or Narrow Bipolar Events in the current literature. These discharges usually occur in isolation without much electrical activity before or after the event, but sometimes they are observed to initiate lightning flashes. In this paper, we have studied the features of CIDs assuming that they consist of streamer bursts without any conducting channels. A typical CID may contain about 10(9) streamer heads during the time of its maximum growth. A CID consists of a current front of several nanosecond duration that travels forward with the speed of the streamers. The amplitude of this current front increases initially during the streamer growth and decays subsequently as the streamer burst continues to propagate. Depending on the conductivity of the streamer channels, there could be a low-level current flow behind this current front which transports negative charge towards the streamer origin. The features of the current associated with the CID are very different from those of the radiation field that it generates. The duration of the radiation field of a CID is about 10-20 mu s, whereas the duration of the propagating current pulse associated with the CID is no more than a few nanoseconds in duration. The peak current of a CID is the result of a multitude of small currents associated with a large number of streamers and, if all the forward moving streamer heads are located on a single horizontal plane, the cumulative current that radiates at its peak value could be about 10(8) A. On the other hand, the current associated with an individual streamer is no more than a few hundreds of mA. However, if the location of the forward moving streamer heads are spread in a vertical direction, the peak current can be reduced considerably. Moreover, this large current is spread over an area of several tens to several hundreds of square meters. The study shows that the streamer model of the CID could explain the fine structure of the radiation fields present both in the electric field and electric field time derivative.
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| 9. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
On the Action of the Radiation Field Generated by a Traveling-Wave Element and Its Connection to the Time Energy Uncertainty Principle, Elementary Charge and the Fine Structure Constant
- 2017
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- Recently, we published two papers in this journal. One of the papers dealt with the action of the radiation fields generated by a traveling-wave element and the other dealt with the momentum transferred by the same radiation fields and their connection to the time energy uncertainty principle. The traveling-wave element is defined as a conductor through which a current pulse propagates with the speed of light in free space from one end of the conductor to the other without attenuation. The goal of this letter is to combine the information provided in these two papers together and make conclusive statements concerning the connection between the energy dissipated by the radiation fields, the time energy uncertainty principle and the elementary charge. As we will show here, the results presented in these two papers, when combined together, show that the time energy uncertainty principle can be applied to the classical radiation emitted by a traveling-wave element and it results in the prediction that the smallest charge associated with the current that can be detected using radiated energy as a vehicle is on the order of the elementary charge. Based on the results, an expression for the fine structure constant is obtained. This is the first time that an order of magnitude estimation of the elementary charge based on electromagnetic radiation fields is obtained. Even though the results obtained in this paper have to be considered as order of magnitude estimations, a strict interpretation of the derived equations shows that the fine structure constant or the elementary charge may change as the size or the age of the universe increases.
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| 10. |
- Cooray, Vernon, 1952-, et al.
(författare)
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On the Apparent Non-Uniqueness of the Electromagnetic Field Components of Return Strokes Revisited
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- Recent research work shows that there are four procedures that can be used to calculate the electromagnetic fields from a current source. These different procedures, even though producing the same total field, give rise to field components that differ from one procedure to another. This has led to the understanding that the various field terms that constitute the total field cannot be uniquely determined. In this paper, it is shown that all four field expressions can be reduced to a single field expression, and the various field terms arising from acceleration, uniformly moving, and stationary charges can be uniquely determined. The differences in the field terms arising from different techniques are caused by the different ways of summing up the contribution to the total electric field coming from the accelerating, moving, and stationary charges.
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| 11. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Polarity Asymmetry in Lightning Return Stroke Speed Caused by the Momentum Associated with Radiation
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- In positive lightning return strokes, the net momentum transported by the radiation field has the same direction as the momentum associated with electrons, whereas the momentum associated with electrons is in opposite direction to the momentum of radiation in negative return strokes. It is shown here that this polarity asymmetry could limit the maximum speed of positive return strokes with respect to the negative return strokes.
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| 12. |
- Cooray, Vernon, 1952-, et al.
(författare)
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The Upper Bound of the Speed of Propagation of Waves along a Transmission Line
- 2020
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Ingår i: Progress In Electromagnetics Research M. - : ELECTROMAGNETICS ACAD. - 1937-8726. ; 93, s. 119-125
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Tidskriftsartikel (refereegranskat)abstract
- According to theory, once certain conditions are fulfilled, current and voltage pulses propagate along ideal transmission lines with the speed of light. One can reach such a conclusion only when the conductors are assumed to be perfectly conducting, which cannot be realized in practice. A wave can only propagate along a transmission line with the speed of light if no energy has to be spent in establishing the current in the conductor. However, in establishing a current in a transmission line, energy has to be supplied to the electrons to set them in motion since they have a mass. The energy transfer to the electrons manifests itself in the form of an inductance which is called the kinetic inductance. The effect of the kinetic inductance has to be taken into account in signal propagation along high carrier mobility conductors including super conductors. In the case of transmission lines, the kinetic inductance leads to a change in the characteristic impedance and a reduction in the speed of propagation of waves along the transmission line. The goal of this paper is to show that the kinetic inductance will set an upper bound to the speed of propagation of waves along transmission lines, which is smaller than the speed of light.
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| 13. |
- Abegunawardana, Sidath, et al.
(författare)
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Audible Frequency Analysis of Ground Flashes
- 2018
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Konferensbidrag (refereegranskat)abstract
- Thunder signatures categorized into three types based on peak pressure and variation in fundamental frequency, have been studied by using acoustic spectrum of thunder. S-transformation has been used to estimate the dominant frequency variation around the peak pressure. The mean fundamental frequencies of type 3 ground and cloud flashes are 160 Hz and 98 Hz respectively. The mean frequencies of type 2 ground and cloud flashes are 108 Hz and 82 Hz respectively.
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| 14. |
- Abegunawardana, Sidath, et al.
(författare)
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Sound Source Localization of Lightning Discharges
- 2018
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Konferensbidrag (refereegranskat)abstract
- The lightning channel can be retraced by thunder signature recorded with an array of microphones. Four microphones were arranged to capture thunder sound, and acoustic cross-correlation of captured pressure signals estimated the time lag of each pair of microphones. A wave segment with 0.25 s or 0.5 s of duration was compared with the acoustic signal recorded by other microphones to estimate time lapse. The direction of channel propagation has been estimated by the time difference of arrival of each pair of microphones. Thunder source locations estimated by this method can be extended to investigate the channel propagation inside clouds.
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| 15. |
- Abewardhana, Ruwan, et al.
(författare)
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Lightning Localization Based on VHF Broadband Interferometer Developed in Sri Lanka
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- A basic broadband digital interferometer was developed, which is capable of locating Very High Frequency (VHF) radiation sources in two spatial dimensions and time. Three antennas sensed the time series of broadband electromagnetic (EM) signals and digitized with 4 ns sampling interval for a duration of several milliseconds. A technique based on cross-correlations has been implemented for mapping lightning source locations. A map of the first return stroke (RS) and the preceding stepped leader was mapped successfully, using the system with a time resolution of few milliseconds. The result was compared with the visible events of the ground flash to validate the system.
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| 16. |
- Ahmad, Mohd Riduan, et al.
(författare)
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Emission Heights of Narrow Bipolar Events in a Tropical Storm over the Malacca Strait
- 2017
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Ingår i: 2017 International Conference On Electrical Engineering And Computer Science (Icecos). - : IEEE. - 9781479976751 - 9781479976768 - 9781479976744 ; , s. 305-309
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Konferensbidrag (refereegranskat)abstract
- Emission heights for narrow bipolar events (NBEs) have been reported mostly from observations at mid latitudes but none have been reported from tropical regions. In this paper, we are reporting for the first time the heights of NBE emissions from a tropical storm over the Malacca Strait, a narrow water passage between the Malay Peninsula and Sumatra Island. A total of 49 positive NBEs (+NBEs) were detected from the storm. The NBE activity can be divided into two stages according to the emission heights and radar reflectivity data. The first stage (or S1) lasted for only 6 minutes, started with the first detected NBE, and produced 20 NBEs (41%). The emission heights ranged between 12.0 and 16.7 km. Radar reflectivity data showed that the storm reached maximum values at 55 dBZ within the period S1. In contrast, the second stage (S2) lasted longer (32 minutes) and produced 29 NBEs (59%). The emission heights were lower and ranged from 8.5 to 13.7 km. Radar reflectivity data showed that the storm reached maximum values at 50 dBZ within the period S2.
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| 17. |
- Arevalo, Liliana, et al.
(författare)
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Attachment process of the discharge of competing grounded electrodes - Experimental observations and modeling
- 2021
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Ingår i: 2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium On Lightning Protection (SIPDA). - : IEEE. - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- The lightning attachment discharge process theory is based on studies of the physics of the discharge obtained from high voltage laboratory tests. The process of propagation of positive and negative discharges has been studied independently and then the gathered information has been used to understand and explain the lightning attachment development. In this paper, an experimental set-up is built to describe the dynamic behavior of positive and negative discharges. Electrodes of different dimensions placed at different distances are used as grounded electrodes and a high voltage electrode is subject to negative switching impulses. Test results allow to identify different stages of the dynamic process of attachment of the discharge between a downward negative discharge and a positive upward leader discharge. The principles of physics of discharge for positive and negative polarities are used to model the laboratory test measurements. The model can reproduce in an accurate manner majority of the dynamic processes of the discharge. In addition, statistical results of the effect of nearby and competing upward discharges is obtained.
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| 18. |
- Arevalo, Liliana, et al.
(författare)
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The leader propagation velocity in long air gaps
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- Experimental measurements of long gap discharges and its interpretation are the base of engineering equations and complex models to design clearance distances, lightning protection systems, among others. Parameters like leader propagation velocity, average electric field of the leader channel, stability electric field of the streamer region, etc. are derived from experimental measurements for rod-plane arrangements. However, in high voltage engineering geometries are not only rod-plane arrangements but also rounded electrode geometries. Experimental measurements of sphere - plane arrangements are presented in this paper. Attention is given to the velocity of propagation of the leader. The velocity of propagation of the leader is compared for two different applied voltage conditions, such as overvoltage and non-overvoltage. Experimental observations indicate that the velocity of the leader does not have a linear relationship with the increment of the applied voltage, as described by other authors for rod-plane arrangements. By means of a model based on the physics of the discharge, it is observed that the velocity of propagation of the leader depends on the injected charge to the leader channel. The injected charge depends on the background electric field, the potential at the leader tip, the steepness of the applied voltage waveform, among other parameters.
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| 19. |
- Arevalo, L., et al.
(författare)
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The mesh method in lightning protection analyzed from a lightning attachment model
- 2016
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Ingår i: 2016 33RD INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - 9781509058433
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Konferensbidrag (refereegranskat)abstract
- Based on the well-known rolling sphere method, international standards recommend the location of the external lightning protection system of structures. The design of the external lightning protection system of structures of height of less than 60 m can be done by installing a mesh on top of a roof of the structure or by creating a mesh with wires at certain distance from the roof of the structure. The prospective downward leader current that the mesh can incept depends on the size of the mesh and the current magnitude is given as recommendation in the international standards. This paper analyses the relation prospective negative downward leader current vs. mesh size from a lightning attachment model. The model is applied to a perfectly grounded structure with maximum height of 50 m protected by two different external lightning protection systems recommended by the international standards. The results showed difference on magnitude of the prospective downward leader current the standards recommend and the ones obtained using the lightning attachment model for meshes of shorter size. Discrepancies concerning the minimum downward leader current that can be incepted by a mesh made by wires located at certain distance from the ground structure and a mesh located on top of the building are obtained.
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| 20. |
- Arevalo, Liliana, 1978-, et al.
(författare)
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Unstable Leader Inception Criteria of Atmospheric Discharges
- 2017
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 8:9
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Tidskriftsartikel (refereegranskat)abstract
- In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.
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| 21. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Electromagnetic Interference From Natural Lightning on 4G Communication Links
- 2024
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 12, s. 14870-14881
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Tidskriftsartikel (refereegranskat)abstract
- In this study, microwave radiation pulses emitted from natural lightning have been found to interfere with the Fourth Generation Long Term Evolution (4G LTE) mobile communication data transmission. Two sets of measurement instruments have been synchronized where lightning electric field sensor together with 4G LTE network were evaluated its performance under two conditions namely fair-weather (four cases) and storm (four lightning cases). The microwave radiation emitted from lightning was directly measured without the use of a mixer and down-convertor to ensure the preservation of information such as the number of pulses and amplitude. A client-server architecture has been set up for data transmission utilizing User Datagram Protocol (UDP) where the packets have been generated by using Internet Performance Working Group Third Version (Iperf3) platform. Under fair-weather conditions, the 4G LTE connection at both the client and server nodes demonstrated stability and experienced minimal impact. On the other hand, natural lightning electromagnetic interference disrupted the 4G LTE communication links. Among the four reported storms, three storms have affected the 4G LTE data transmission. The first and fourth storms resulted in a complete connection drop to zero, lasting for 4 minutes and 2 seconds and for 44 seconds, respectively. The observation of hundreds microwave radiation pulses, each characterized by individual oscillating features suggests a potential disruption to packet transmission. Moreover, negative could-to-ground (-CG) and intra-cloud (IC) lightning flashes have been identified as the primary sources of interference to the 4G LTE data transmission. This information could be useful for future studies and for developers working on improving the reliability and performance of 4G LTE networks, particularly in areas prone to thunderstorms.
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| 22. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave and Very High Frequency Radiations of The First Narrow Initial Breakdown
- 2021
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Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- This paper reports the observation of microwave and very high frequency (VHF) radiation pulses associated with the first narrow (<10us) initial breakdown (IB) pulses of ten negative cloud-to-ground (-CG) flashes. The centre frequency of microwave and VHF sensors was 0.97 GHz and 60 MHz, respectively. We found that all microwave pulses were the initiation event led the first VHF pulses ranging between 0.03187 and 2.57968 mu s and led the first narrow IB pulses ranging between 0.02382 and 2.70202 mu s. Half of the VHF pulses were observed to lead the first narrow IB pulses ranging between 0.03453 and 0.128 mu s. Moreover, polarity of microwave radiation pulses was always positive while the polarity of the first narrow IB pulses always negative. On the other hand, half of VHF radiation pulses had the same polarity as microwave radiation pulses.
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| 23. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave radiation associated with positive narrow bipolar events
- 2023
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examined seven isolated positive Narrow Bipolar Events (NBEs), one positive NBE that initiated an IC flash progressed to a single-stroke Cloud-to-Ground (CG) flash, and one positive NBE that initiated an IC flash. Seven NBEs have been accompanied by significant Very-High Frequency (VHF) and microwave radiation pulses. We recorded all NBEs from two measurement stations (ST1 and ST2) separated at 13.3 km apart which consisted of fast antenna (FA) and slow antenna (SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (0.97 GHz). The waveforms were sampled at 2.5 GHz (400 ps). The key finding is that all microwave radiation pulses have been found to precede both the VHF radiation pulses and NBEs with average lead time of 63 +/- 39 ns and 122 +/- 143 ns, respectively. In comparison to stepped leader pulses or SLPs (conventional breakdown), the average lead time of microwave to VHF for NBEs (fast breakdown) was 88% faster compared to the average lead time of microwave to VHF for SLPs. Moreover, the average lead time of VHF to NBEs was 56% faster when compared to the average lead time of VHF to SLPs. The VHF interferometer map for an isolated NBE (NBE6) showed upward propagation of VHF radiation sources (fast negative breakdown) with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 10.2 +/- 0.3 km, 2.9 +/- 0.6 km, and 1.8 x 108 and 2.8 x 108 ms-1, respectively. On the other hand, interferometer map for an NBE that initiated a single-stroke CG (NBE3) showed bidirectional fast streamers propagation with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 14.0 +/- 0.4 km, 2.9 +/- 0.82 km, and 1.6 x 108 and 2.8 x 108 ms-1, respectively. Clearly, the microwave and VHF radiation pulses associated with positive NBEs have been emitted by different processes of fast breakdown mechanism. Therefore, it can be suggested that the microwave radiation is emitted by electron avalanches/corona while the VHF ra-diation is emitted by fast propagating streamers.
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| 24. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave radiation associated with stepped leaders of negative cloud-to-ground flashes
- 2022
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Ingår i: Atmospheric research. - : Elsevier. - 0169-8095 .- 1873-2895. ; 270
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, Very-High Frequency (VHF) and microwave radiation pulses associated with stepped leader pulses (conventional breakdown) are examined. A total of 100 stepped leader pulses (SLPs) with the associated 100 quiet periods (QPs) from ten negative cloud-to-ground (CG) flashes within the reversal distance (<8 km) have been analyzed. The QP is defined as the period between two SLPs when no electrical activity within the fast antenna sensor bandwidth was detected. The measurement system is made up of fast antenna (FA) and slow antenna (SA) sensors, a VHF sensor (60 MHz center frequency with 40 MHz bandwidth), and a microwave sensor (0.97 GHz center frequency with 20 MHz bandwidth). The waveforms were sampled at 2.5 GHz (400 ps). The total durations of the SLPs and QPs were 2.648 +/- 1.152 mu s and 2.708 +/- 1.670 mu s, respectively. All microwave and VHF radiation waveforms have been detected as clear individual oscillating pulses. The key finding is that the microwave radiation can be classified into three categories based on the total number of detected individual oscillating pulses during the QP. Two microwave pulses detected during the QP (Category 1) are suggested to be associated with the electron avalanche/corona process at the tip of an existing negative leader and a space stem. The VHF pulses associated with the microwave pulses are suggested to be emitted by propagating streamers. On the other hand, a single microwave pulse detected during the QP (Category 2) is suggested to be emitted by the electron avalanche/corona process of a space stem. The VHF pulses associated with the microwave pulse are suggested to be emitted by propagating streamers. In both categories, 70% of the microwave radiation pulses have been observed to precede VHF radiation pulses with an average lead time of 0.848 +/- 1.336 mu s. The head-on collision of a downward propagating negative streamer and an upward propagating positive streamer (from space stem) emitted significant microwave radiation. A new negative leader was formed when the head-on collision took place. The microwave radiation pulses emitted by the head-on collision process were observed to precede SLPs with an average lead time of 0.423 +/- 0.378 mu s. Around 80% of the microwave radiation pulses preceded VHF radiation pulses with average lead time of 0.540 +/- 0.596 mu s. Therefore, microwave and VHF radiation pulses are suggested to be emitted by different processes of the electrical breakdown mechanism. The microwave radiation is emitted by electron avalanche/corona/head-on collision while the VHF radiation is emitted by propagating streamers.
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| 25. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
-
Very high frequency radiation emitted by negative narrow bipolar events occurred over malacca strait
- 2024
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 259
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, Very -High Frequency (VHF) radiation pulses associated with 11 negative Narrow Bipolar Events (NBEs) produced by a tropical storm over Malacca Strait are examined. The lightning data were recorded from a measurement station (ST) which consisted of a fast antenna (FA) and three VHF sensors (two 5 m perpendicular baselines interferometer). The average rise time (RT), average zero -crossing time (ZCT), average pulse duration (PD), and range of peak currents of the negative NBEs were 1.4 +/- 0.4 mu s, 2.7 +/- 1.0 mu s, 12.0 +/- 6.9 mu s, and -10 to -64 kA, respectively. The key finding is that all VHF radiation pulses have been found to precede the negative NBEs with an average lead time of 0.7 +/- 0.3 mu s. An interferometer map for one negative NBE (labelled as NBE10) detected at 35.7 km from ST has shown a characteristic of mixed propagation direction of fast streamers. The first VHF radiation source was detected at 12.4 +/- 0.4 km above sea level. The total length and estimated velocity of the main propagation of the VHF radiation sources were 2.2 +/- 0.7 km and between 1.4 x 10 8 and 2.8 x 10 8 ms -1 , respectively. Moreover, based on the Himawari satellite image, the maximum extent of the cloud top height was estimated to be around 20.9 km over sea level (over Malacca Strait). All the VHF radiation sources associated with NBE10 were suggested to be detected above the main negative charge region (6 km altitude that corresponds to -10 degrees C). Thus, it could be suggested that NBE10 was initiated most likely in the environment of the ice crystals alone, based on the first altitude of the VHF radiation source and maximum extent of cloud top height.
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| 26. |
- Baharin, S. A. S., et al.
(författare)
-
Wavelet Analysis of the Onset of VHF and Microwave Radiation Emitted by Lightning
- 2018
-
Ingår i: 2018 INTERNATIONAL CONFERENCE ON ELECTRICAL ENGINEERING AND COMPUTER SCIENCE (ICECOS). - : IEEE. - 9781538657218 ; , s. 297-300
-
Konferensbidrag (refereegranskat)abstract
- Lightning flash is an electrical discharge in air (dielectric breakdown) which emits electromagnetic (FM) fields across very wide spectra from a few Hertz up to visible wavelength. Electrical breakdown process is an important event that initiates lightning. For electrical breakdown process to occur, it must fulfill two conditions which are at least has one free electron and the electric field region is more than 3 MV/m. This process starts with electron avalanche in millimeter scale then grows into streamer in centimeter scale. Lastly, from streamer it will grow into leader in meter scale. It has already established that streamer emits intensely at Very High Frequency (VHF) band as it's already proven both theoretically and experimentally. A study by Cooray, theoretically proved that emission of electron avalanche peaks at microwave band. Air-gap parallel plate antenna which could operate at 1 GHz with remote sensing is designed and simulated to measure the microwave radiation emitted by lightning. Both temporal and wavelet analyses are used to compare the onset of microwave radiation and VHF radiation in both time and frequency domains to determine electron avalanche appears at which electromagnetic band.
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| 27. |
- Bodhika, J. A. P., et al.
(författare)
-
Characteristics of thunder pertinent to tropical lightning
- 2018
-
Ingår i: 34th International Conference on Lightning Protection (ICLP) (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric fields do. Thunder flashes of tropical lightning occurred in Hambantota (81(0) 0'E, 6(0) 10'N) close to the southern coast of Sri Lanka were studied. About 90 thunder flashes recorded with the sampling rate of 100 kS/s in 45 s windows were analyzed to identify their characteristics and damaging effects. Results of the analysis on duration of thunder flashes, peak sound pressure levels, occurrence of thunder claps and frequency distribution were presented. The shortest and longest duration of thunder recorded were 2.2 sec and 33.7 sec respectively. About 75% of thunder flashes were remained for about 5-20 sec. The frequency spectrum of a thunder signal could spread up to 1500 Hz. The peak sound pressure level of 30% of recorded thunder flashes at least 3 km away from the lightning were higher than 2 Nm(-2) (100 dB). One to five claps were identified in thunder flashes with 62% having 1 or 2 claps. Sound pressure level, frequency range and its duration are required quantities to estimate the harmful effects of thunder.
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| 28. |
- Chandimal, A. P. L., et al.
(författare)
-
Impedance Behavior of Earth Enhancing Compound Under Lightning Transient Conditions
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- This study was aimed at finding the performance of commercially available earth enhancing compound (EEC) under lightning conditions. Further to that, this is an extension of a previous study conducted by the same authors referring to the same EEC. The selected material seems to perform impressively under lightning conditions passing considerably large current values. The prepared EEC mixture and the setup was tested under dry conditions and exhibited low dynamic impedance characteristics for lightning impulse voltages. Ten-stage Marx-generator was used for the experiment, and due to high conductive nature of the material, HV supply between the sample was unable to increase more than few kV. Thus the 12 cm gap inside the material was complemented with an external air gap of 90 cm. The study was a comparison between "air-gap breakdown" and "air-gap plus material-gap breakdown". The results confirmed a low impedance characteristic for the selected EEC and suggested a very low electric field inside the material gap. An approximate value for the impedance of the test setup was calculated from the collected data. A time window was selected during the steady current discharge appeared just after the point of current peak and the impedance curves for both experiments were compared at a previously defined point at the time axis. The impedance value for EEC setup was estimated to be in the region of 1 - 2 Omega.
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| 29. |
- Chandimal, Lasantha, et al.
(författare)
-
A field study on the energy dissipation associated with step and touch voltage in earthing systems encased in earth enhancing compounds
- 2024
-
Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 231
-
Tidskriftsartikel (refereegranskat)abstract
- An extensive field experiment was conducted to investigate the effects of earth -enhancing compounds on earthing systems. Four identical vertical earth rods were installed, each encased in concrete, Bentonite, and two commercial enhancing materials. Lightning impulse signals were injected into all electrode arrangements, and the measured responses were used to analyse the associated risks of step and touch voltages. The peak voltage values and the corresponding energy dissipation for each measurement were calculated and compared to those of a reference electrode. The analysis of step voltage measurements and the corresponding energy dissipation demonstrated that the use of concrete exhibited greater advantages than the use of Bentonite. However, touch voltage measurements and the associated energy dissipation indicated that despite the lower touch voltage exhibited by Bentonite, its energy dissipation exceeded that of the reference electrode. Consequently, the unique findings reveal that specific variations of earth -enhancing compounds can exhibit reduced earth impedance and lower step or touch voltages while also yielding higher energy dissipation, introducing an unforeseen risk of injury.
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| 30. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
A Self-Consistent Return Stroke Model That Includes the Effect of the Ground Conductivity at the Strike Point
- 2022
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 13:4
-
Tidskriftsartikel (refereegranskat)abstract
- A current generation type return stroke model which can take into account the possible modifications of the return stroke properties by the soil conductivity at the strike point of the lightning flash is introduced. The model is also capable of incorporating the reflection of the current at the ground end of the return stroke channel. In this paper, this return stroke model is used to investigate (a) the effect of the ground conductivity at the strike point on the source electromagnetic fields generated by return strokes and (b) the effect of current reflection at ground level on the electromagnetic field generated by return strokes. The source electromagnetic fields are the electromagnetic fields generated by lightning flashes calculated in such a way that they are not distorted by propagation effects. The results obtained show that the ground conductivity at the strike point does not significantly influence the return stroke current peak or the radiation field peak for ground conductivities higher than about 0.001 S/m. However, strike points with very poor conductivities (lower than 0.001 S/m) would result in a decrease of the peak electric field. In contrast to the peak values of the lightning current and the electric field, the peak values of the time derivatives of the lightning current and electric field are significantly reduced when the strike point of the lightning flash is located over a finitely conducting ground. The inclusion of the current reflection at ground level influences significantly the saturation of the close electric fields. The current reflection also gives rise to residual electric fields, a difference in the field levels generated by the dart leader and the return stroke. The residual field decreases as the fraction of the reflected current decreases.
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| 31. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Advances in lightning research
- 2017
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1364-6826 .- 1879-1824. ; 154, s. 181-181
-
Tidskriftsartikel (refereegranskat)
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| 32. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Current propagation type self-consistent leader-return stroke model
- 2023
-
Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 217
-
Tidskriftsartikel (refereegranskat)abstract
- A current propagation type return stroke model which is consistent with the estimated distribution of the charge on the leader channel is described. The model takes into account the dispersion of the return stroke current along the return stroke channel. The model is capable of generating lightning return stroke electromagnetic fields that are in close agreement with experimental observations. The model could also be used to estimate the electric fields from the leader-return stroke combination at any given distance.
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| 33. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground
- 2018
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 9:5
-
Tidskriftsartikel (refereegranskat)abstract
- Propagation effects on the narrow bipolar pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results were obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the full width at half maximum (FWHM), zero-crossing time, and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason, the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.
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| 34. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Field-to-Transmission Line Coupling Models With Special Attention to the Cooray-Rubinstein Approximation
- 2021
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9375 .- 1558-187X. ; 63:2, s. 484-493
-
Tidskriftsartikel (refereegranskat)abstract
- There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal-Price-Gurbaxani model, the Taylor-Satterwhite-Harrison model, and the Rachidi model. The Cooray-Rubinstein approximation is a procedure used by scientists and engineers to estimate the horizontal electric field from the lightning that is used in the induced voltage calculations for lines located over a finitely conducting ground. The Cooray-Rubinstein approximation is usually incorporated in calculating the induced overvoltages using the Agrawal-Price-Gurbaxani model. In this article, it is shown how this approximation could be incorporated into the other two coupling models. The resulting coupling equations are compared to each other by calculating the voltages induced on two idealized overhead transmission lines.
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| 35. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Formulation of the Field-to-Transmission Line Coupling Equations in Terms of Scalar and Vector Potentials
- 2017
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X. ; 59:5, s. 1586-1591
-
Tidskriftsartikel (refereegranskat)abstract
- More than 60 years ago, Prof. S. Rusck introduced a coupling model to take into account the interaction of lightning-generated electromagnetic fields with overhead power transmission and distribution lines. The model which assumes that the ground is perfectly conducting has served the power system research community for many decades. Recently, it was found that this model is not complete because some of the forcing terms in the relevant transmission line equations, which are based purely on the scalar and vector potentials, were missing. In the present paper, the correct transmission line equations pertinent to the interaction of external electromagnetic fields with overhead lines, described in terms of scalar and vector potentials, are derived by incorporating the effects of a finitely conducting ground. The model presented in this paper can be considered as a correction and an extension of the Rusck model to account for a finitely conducting ground.
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| 36. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Latitude and Topographical Dependence of Lightning Return Stroke Peak Current in Natural and Tower-Initiated Negative Ground Flashes
- 2020
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 11:6
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental data show that the peak currents of first and subsequent lightning return strokes in negative ground flashes increase with decreasing latitude. In this paper, the reason for this dependence of peak return stroke current on latitude is explained using the fact that the height of the charge centers increases with decreasing latitude. Results show that in tropical regions where the height to the negative charge center is about 8 km, the median values of the first and the subsequent return stroke peak currents are about 42 kA and 15 kA, respectively. If the height to the charge center is larger than 8 km, the peak currents will also become larger. For example, if the location of the charge center is increased to about 9 km, the median values of the first and subsequent return stroke peak currents will increase to about 45 kA and 16 kA respectively. The same reasoning shows that, even in the same geographical region, the peak return stroke current may decrease as the elevation of the ground where the lightning strikes take place increases. The results also indicate that the peak subsequent return stroke current in tower-initiated negative lightning flashes decreases as the height of the tower increases. These theoretical predictions are in general agreement with the available experimental data.
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| 37. |
- Cooray, Vernon, 1952-
(författare)
-
Latitude dependence of peak lightning return stroke current : A theoretical explanation
- 2018
-
Ingår i: 34th International Conference on Lightning Protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- The experimental data show that the peak currents of first and subsequent lightning return strokes increase with decreasing latitude. In this paper the reason for this dependence of current amplitude is explained using the fact that the height of the charge centers increases with decreasing latitude. The results obtained show that in tropical regions peak first and subsequent return stroke currents are located in the vicinity of 42 kA and 15 kA, respectively. This theoretical prediction is in agreement with available experimental data.
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| 38. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Merging of current generation and current dissipation lightning return stroke models
- 2017
-
Ingår i: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 153:SI, s. 10-18
-
Tidskriftsartikel (refereegranskat)abstract
- Current generation and current dissipation return stroke models are engineering models based on the theory associated with the propagation of current pulses along transmission lines undergoing corona. However, neither of these models incorporates the complete theory associated with the phenomenon. One can make the physical scenario complete by combining the current generation concept with the current dissipation concept. In this paper how this can be done is demonstrated by creating a return stroke model which is a combination of these two model types. The new model encompasses the full theory associated with the pulse propagation along transmission lines under corona. The paper provides a full description of the model together with a description of the spatial and temporal variation of the return stroke current and the electric and magnetic fields generated at different distances as predicted by the model.
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| 39. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Modeling the Stepping Process of Negative Lightning Stepped Leaders
- 2017
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 8:12
-
Tidskriftsartikel (refereegranskat)abstract
- A physical model based on the mechanism observed in experimental investigations is introduced to describe the formation of negative leader steps. Starting with a small length of a space leader located at the periphery of the negative streamer system of the stepped leader, the model simulates the growth and the subsequent formation of the leader step. Based on the model, the step length, the step forming time, and the propagation speed of stepped leaders as a function of the prospective return stroke peak current are estimated. The results show that the step length and the leader speed increase with increasing prospective return stroke current. The results also show that the speed of the stepped leader increases as it approaches the ground. For prospective return stroke currents in the range of 15 kA–60 kA, the step lengths lie within the range 5 m–100 m, the step forming times lie within the range 10 μs–250 μs, and the leader speed lies within the range 105 m/s −1.5 × 106 m/s. The results obtained are in reasonable agreement with the experimental observations.
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| 40. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field-MTLD Model
- 2021
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:2
-
Tidskriftsartikel (refereegranskat)abstract
- In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse transformation, the procedure is illustrated by extracting the current attenuation curve from the typical wave shape of the return stroke current and from the distant radiation field of subsequent return strokes. The derived attenuation curve is used to evaluate both the subsequent and first return stroke electromagnetic fields at different distances. It is shown that all the experimentally observed features can be reproduced by the derived attenuation curve, except for the subsidiary peak and long zero-crossing times. In order to obtain electromagnetic fields of subsequent return strokes that are in agreement with measurements, one has to incorporate the current dispersion into the model. In the case of first return strokes, both current dispersion and reduction in return stroke speed with height are needed to obtain the desired features.
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| 41. |
- Cooray, Vernon, 1952-
(författare)
-
Origin of the Fine Scale Tortuosity in Sparks and Lightning Channels
- 2018
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 9:6
-
Tidskriftsartikel (refereegranskat)abstract
- The physical reason for the small-scale tortuosity observed in sparks and lightning channels is unknown at present. In this paper, it is suggested that the small-scale tortuosity of the discharge channels is caused by the natural tendency for subsequent leader streamer bursts to avoid each other but at the same time to align as much as possible along the direction of the background electric field. This process will give rise to a discharge channel that re-orients in space during each streamer burst creating the small scale tortuosity.
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| 42. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
The Energy, Momentum, and Peak Power Radiated by Negative Lightning Return Strokes
- 2020
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 11:12
-
Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic radiation fields generated by return strokes transport both energy and momentum from the return stroke to outer space. The momentum transported by the radiation field has only a vertical or z component due to azimuthal symmetry (cylindrical symmetry) associated with a vertical return stroke. In this paper, the energy, momentum, and peak power radiated by return strokes as a function of the return stroke current, return stroke speed, and the zero-crossing time of the radiation fields are studied. The results obtained by numerical simulations for the energy, vertical momentum, and the peak power radiated by lightning return strokes (all parameters normalized by dividing them by the square of the radiation field peak at 100 km) are the following: A typical first return stroke generating a radiation field having a 50 μs zero-crossing time will dissipate field normalized energy of about (1.7–2.5) × 103 J/(V/m)2 and field-normalized vertical momentum of approximately (2.3–3.1) × 10−6 Kg m/s/(V/m)2. A radiation field with a zero-crossing time of 70 μs will dissipate about (2.6–3.4) × 103 J/(V/m)2 in field-normalized energy and (3.2–4.3) × 10−6 Kg m/s/(V/m)2 in field-normalized vertical momentum. The results show that, for a given peak radiation field, the radiated energy and momentum increase with increasing zero-crossing time of the radiation field. The normalized peak power generated by a first return stroke radiation field is about 1.2 × 108 W/(V/m)2 and the peak power is generated within about 5–6 μs from the beginning of the return stroke. Conversely, a typical subsequent return stroke generating a radiation field having a 40 μs zero-crossing time will dissipate field-normalized energy of about (6–9) × 102 J/(V/m)2 and field-normalized vertical momentum of approximately (7.5–11) × 10−7 Kg m/s/(V/m)2. The field-normalized peak power generated by a subsequent return stroke radiation field is about 1.26 × 108 W/(V/m)2 and the peak power is generated within about 0.7–0.8 μs from the beginning of the return stroke. In addition to these parameters, the possible upper bounds for the energy and momentum radiated by return strokes are also presented.
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| 43. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
The Geometry and Charge of the Streamer Bursts Generated by Lightning Rods under the Influence of High Electric Fields
- 2022
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 13:12
-
Tidskriftsartikel (refereegranskat)abstract
- The streamer bursts generated during the initiation and propagation of leaders play an important role in the creation and maintenance of hot discharge channels in air. The most important parameters related to streamer bursts in this respect are the length of the streamer bursts, their lateral extent and the charge associated with them. The lateral extent of the streamer bursts may play a significant role in deciding the path and the tortuosity of the discharge channels of laboratory discharges and lightning. The charges associated with the streamer bursts are needed in understanding the physical processes associated with the streamer-to-leader transition. In this paper, the length, the lateral extension and the charge of the streamer regions generated by grounded conductors when exposed to external electric fields are estimated. This estimation is based on two assumptions: (i) once a streamer is incepted, the streamer head follows the direction of maximum background electric field at the location of the streamer head and (ii) the streamer continues to extend along this direction until the potential drop along the streamer channel matches the potential drop caused by the background electric field between the initial and end points of the streamer channel. The same technique could be used to estimate the streamer bursts generated in laboratory discharges and lightning stepped leaders. It is shown that in estimating the geometry of the streamer region, it is necessary to include the spread of streamers caused by branching. Moreover, the charge associated with the streamer region increases as the frequency of branching increases. The results obtained confirm that the charge in the streamer region can significantly change the potential ahead of the streamer region from the background potential and this has to be taken into account in any study that simulates the initiation and propagation of lightning leaders. Since the streamer bursts of leaders control the direction and speed of the leaders, the technique we have used here could be implemented in lightning leader progression models.
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| 44. |
- Cooray, Vernon, 1952-
(författare)
-
The influence of lightning conductor radii on the attachment of lightning flashes
- 2017
-
Ingår i: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 153:SI, s. 138-143
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the tip radius of lightning conductors on their lightning attractive distance as predicted by the self-consistent leader inception and propagation model (SLIM) is presented. The results show that in the absence of any glow corona from the tip of the conductor a smaller tip radius gives rise to a larger attractive radius than a larger radius. It is suggested that the reason for the experimental observations which show that blunt conductors are more efficient lightning receptors than sharp ones is the presence of glow corona at the tip of the sharp ones during the time of lightning strikes. Moreover, in a given background electric field, the probability of the inception of glow corona at the conductor tip increases with increasing conductor height and decreasing conductor radius. Thus, in a given electric field, as the conductor height increases its radius has to be increased to avoid the inception of glow corona at the tip. For this reason, the conductor radius that performs best as a lightning interceptor depends on the height of the conductor and the best performance shift from smaller radii to larger ones with increasing height of the conductor.
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| 45. |
- Cooray, Vernon, 1952-
(författare)
-
The power, energy, momentum and the action of the electromagnetic radiation fields of lightning return strokes
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- The energy, momentum and the action associated with the radiation fields generated by a typical subsequent lightning return stroke is estimated. The action is defined as the product of the total radiation energy emitted and the duration of emission, and the momentum refers to the vertical component. The results obtained show that a typical subsequent return stroke generates 2 x 10(6) J, 2 x 10(6) Kgm/s and 2 x 10(6) Js respectively of energy, momentum and action.
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| 46. |
- Cooray, Vernon, 1952-
(författare)
-
The Similarity of the Action of Franklin and ESE Lightning Rods under Natural Conditions
- 2018
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 9:6
-
Tidskriftsartikel (refereegranskat)abstract
- In the lightning rods categorized as Early Streamer Emission (ESE) types, an intermittent voltage impulse is applied to the lightning rod to modulate the electric field at its tip in an attempt to speed up the initiation of a connecting leader from the lightning rod when it is under the influence of a stepped leader moving down from the cloud. In this paper, it is shown that, due to the stepping nature of the stepped leader, there is a natural modulation of the electric field at the tip of any lightning rod exposed to the lightning stepped leaders and this modulation is much more intense than any artificial modulation that is possible under practical conditions. Based on the results, it is concluded that artificial modulation of the electric field at the tip of lightning rods by applying voltage pulses is an unnecessary endeavor because the nature itself has endowed the tip of the lightning rod with a modulating electric field. Therefore, as far as the effectiveness of artificial modulation of the tip electric field is concerned, there could be no difference in the lightning attachment efficiency between ESE and Franklin lightning rods.
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| 47. |
- Cooray, Vernon, 1952-
(författare)
-
Unification of engineering return stroke models
- 2021
-
Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- Engineering models burrow various features from transmission line theory and combine them using empirical data to create models that can predict the electromagnetic fields of lightning return strokes in space and time. At present, engineering models are the most successful in predicting the features of lightning electromagnetic fields in close agreement with the experimental data. Today, most scientists who are interested in lightning protection use engineering models in their studies. A large number of engineering return stroke models exist in the literature. Depending on the assumptions made they can be categorized as Current Propagation models (CP-models), Current Generation models (CG-models) and Current Dissipation models (CD-models). The goal of this paper is to describe the different approximations used in constructing these engineering return stroke models and to show that all these models are a special case of a more general model which we call Current model (C-model). We will show how various return stroke models can be precipitated from the C-model by neglecting different features associated with it.
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| 48. |
- Diaz, Oscar, 1980-, et al.
(författare)
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Arc Modeling for a low current Impulse Discharge in an Enclosed Microspark Gap
- 2012
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Konferensbidrag (refereegranskat)abstract
- Enclosed microspark gaps are commonly used as voltage controlled closing switches in gas discharge tubes -GDT-. These devices can be used as low voltage spark gap switches or surge protective devices. In this work, the arc discharge in a GDT under a current impulse was modelled. Mass, momentum and energy conservation equations are solved in a computer fluid dynamics model that includes turbulence, radiation and joule heating. The thermodynamic properties of the gas fluid were taken from the literature. Net emission coefficients are used for the calculation of radiation losses. Since the electrical stimulus is a low energy current impulse, the magnetic pinch forces acting on the plasma are disregarded. The GDT is filled with argon at 0.1 MPa pressure, enclosed in an aluminium oxide ceramic cylindrical container. This container is brazed together with two copper electrodes for an equivalent gap distance of 600 µm.
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| 49. |
- Diaz, Oscar, 1980-, et al.
(författare)
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Cold-electrode voltage fall for impulse arcs in argon between copper electrodes
- 2011
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596. ; 301, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- The full electric arc discharge in gases for short gaps in homogeneous electric field and pressuredistance (pd) below 150 Torrcm, can be described as a transition between different discharge mechanisms such as: Townsend, glow, and arc. Once the arc is achieved the measured voltage drops to some volts and the current density increases several orders of magnitude. Depending upon the type of gas used, the electrode surface characteristics and type of electrical excitation, the cathode and anode voltage fall might change. The present work is directed to study the electrode fall (sum of anode and cathode falls) during a current impulse arc discharge between copper electrodes in ceramic tubes filled with argon between 0.01 and 6.5 Torrcm. The copper electrodes were cleaned, degassed and hydrogen reduced. The arc voltages were measured with fast/slow rise times and short/long duration current impulses produced by a RLC circuit. An increasing variation of the electrode fall was found at the pressuredistance range analyzed.
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| 50. |
- Diaz, Oscar, 1980-, et al.
(författare)
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Effect of pressure on the electrode fall for impulse arcs in argon betweencopper electrodes
- 2011
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Konferensbidrag (refereegranskat)abstract
- The complete electric arc discharge in gases for short gaps in homogeneous electric field and lowpressure·distance (pd) values (< 150 Torr·cm), can be described as a transition between differentdischarge mechanisms like Townsend, glow, streamer and finally arc. Once the arc state isachieved, the measured voltage drops to some volts and the current density increases several ordersof magnitude at the arc spot. The arc voltage can be interpreted as the sum of the voltage dropalong the conductive gas column and two transition regions between the electrodes and the gas, theanode and cathode fall. The physical processes in these transition regions affect the measuredelectrode fall (sum of anode and cathode falls). In this work, the effect of the gas pressure on theelectrode fall is analyzed for a pressure range of 20 to 85 Torr. The results showed an increment ofthe measured voltage when the pressure is increased until 1 Torr.
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