The present society is highly dependant on complex electronics systems, which have a low damage t... more The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.
We present for the first time detection of X-rays from laboratory sparks created in air at atmosp... more We present for the first time detection of X-rays from laboratory sparks created in air at atmospheric pressure by applying an impulse voltage with slow rise time. It is in full analogy with the detection of X-rays from lightning stepped and
2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium on Lightning Protection (SIPDA)
This study employed wavelet transformation to disclose the spectrograms of IEC standard impulses ... more This study employed wavelet transformation to disclose the spectrograms of IEC standard impulses and real transient voltages generated by the cloud to ground discharges. The spectral details of each impulse were subdivided into different spectral clusters and the outcome was mapped into respective voltage levels and time to develop correlations. Eventually different protection voltage levels of commercially available surge protection devices (SPDs) and the voltage levels of different spectral clusters were compared to determine whether harmful energy infringements could be possible when the spectral clusters are wrapped by SPDs. This study revealed that all IEC impulses have identical spectral clusters whereas real transient voltages demonstrated that they are inherited with much random spectral distributions. Thus, planning for foolproof through benchmarking real transient impulses against IEC impulses would not produce guaranteed outcomes. Hence, a poor selection of clamping voltages may create a permanent window to infringing a small quantum of harmful energy on a constant basis into sensitive systems to trigger silent killing of basic functional units.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This paper presents an analysis done on the transient behavior of an external lightning protectio... more This paper presents an analysis done on the transient behavior of an external lightning protection system (LPS). The study was devised by modeling a Faraday's cage type LPS of a five-storied building on a MATLAB based electrical nodal network and simulating it against the 10/350 μ s lightning impulse with a peak current of 30 kA. The study focused on the down conductor material cross section area, ground impedance and the number of down conductors in the LPS to establish which factor or factors have more influence on the LPS performance. The simulation concludes that under the transient conditions the voltage dissipation on the LPS can reach several thousand volts and the peak branch current disbursements in the network are in the order of 2-2.5 kA. However, under poor ground conditions and less number of down conductors, voltage rise on the LPS system can elevate alarmingly, and branch currents tend to increase close to 7.5 kA. The study proved that the performance of the LPS and the magnitudes of the negative consequences of the associated secondary effects such as electromagnetic compatibility issues and risk associated with high step voltage issues, etc., have a close correlation with the ground impedance and the number of down conductors than that of the cross-section area of the down conductors.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study presents the behavior of surge protecting devices (SPDs) against transient over voltag... more This study presents the behavior of surge protecting devices (SPDs) against transient over voltages generated by cloud to ground (CG) flashes. Analysis revealed that lightning generated transient over voltages have a potential to impart detrimental effects on the SPDs. Moreover, it was concluded that comparisons between IEC laboratory impulse and the real transient voltages are remote due to factors such as peculiar time domain voltage profiles, random polarities, multiple surges with very narrow inter pulse durations in the order of microseconds. Further, observed that SPDs would not always retain within the limits specified by the manufactures under all circumstances.
Variation of fractal dimension of long laboratory sparks were studied using high speed video reco... more Variation of fractal dimension of long laboratory sparks were studied using high speed video recordings and still images. Four sparks were selected for the study, including both positive and negative polarities in lightning and switching impulses. Temporal and spatial variation of fractal dimension was studied. It was found that the fractal dimension is maximum at the breakdown. No particular pattern was observed for the variation of fractal dimension along the channel. Results show that the value of fractal dimension depends on the angle of view. Keywords-component; fractal dimension, long laboratory sparks.
Use of earthing enhancing compound (EEC) in electrical earthing system is a common practice in ma... more Use of earthing enhancing compound (EEC) in electrical earthing system is a common practice in many countries. Naturally available materials and commercially modified materials are used as EEC. This research will enlighten further the phenomenon of using EEC to improve the performance of an electrical earthing system. The EEC used for this experiment was a commercially available product which the exact chemical composition is unknown. Both high impulse current generator and a modular impulse generator with suitable data acquisition systems were used to study the impedance characteristics of the product specifically under fast transients. Both 1.2/50 μs lighting impulses and 8/20 μs wave shapes were applied to the sample and analyzed the responsive V-I and impedance curves. Both experiments provide convincing evidence for healthy conductive character of the selected material under impulse conditions. However, some of the evidence suggests dissimilarities in the behavior of the test s...
2018 34th International Conference on Lightning Protection (ICLP), 2018
The tortuosity of the channel is defined as “Mean absolute angle change of the angle change and i... more The tortuosity of the channel is defined as “Mean absolute angle change of the angle change and it measures how strongly the tortuous path of the channel of lightning/laboratory spark is twisting. 8 m Long laboratory sparks and high speed (20000 frames per second) technology used for this experiment. Using these data it has been calculated the channel tortuosity of 8 m long sparks and vertical profile of channel tortuosity. In addition to that spectral analysis of the angel change of the twisting path of the channel has been done in this study.
2018 34th International Conference on Lightning Protection (ICLP), 2018
Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric ... more Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric fields do. Thunder flashes of tropical lightning occurred in Hambantota (810 0’E, 60 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.
2018 34th International Conference on Lightning Protection (ICLP), 2018
For an effective earthing system, the resistance/impedance of the earthing system should be held ... more For an effective earthing system, the resistance/impedance of the earthing system should be held at the lowest possible level. In this study, a surge generator, which can inject a 2-kV signal of $1.2/50 \mu \mathrm{s}$ waveform or 1 kA impulse current waveform of 8/20 $\mu$ s, was constructed to investigate the impedance of single rod earthing system. The resistivity of the soil at the selected location varies from $300 \Omega \mathrm {m} - 1700 \Omega \mathrm{m}$. By using the fall of the potential method, it was observed that the impedance of single rod system varies from $900 \Omega$ at 1 m to $70 \Omega$ with the distance of 2-5 m. The earthing resistance of the same system was found to be $285 \Omega$, which is higher than the impedance.
2018 34th International Conference on Lightning Protection (ICLP), 2018
A basic broadband digital interferometer was developed, which is capable of locating Very High Fr... more 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.
General characteristics of K changes together with their fine structure associated with ground fl... more General characteristics of K changes together with their fine structure associated with ground flashes in Sri Lanka in the tropics are presented. It is found that on average there are about 2 K changes associated with each return stroke. Analysis of the fine structure of the K changes shows that the K change is a chaotic pulse burst. Some of these chaotic pulse bursts start and the others end as a regular pulse bursts. Sometimes the chaotic part occurs in between two regular pulse bursts. This is in agreement with the recent published results that claim that chaotic pulse bursts are a random superposition of regular pulse bursts. The results show that the small step fields identified in the literature as K changes are the static fields associated with these pulse bursts.
Propagation effects on the Narrow Bipolar Pulses (NBPs) or the radiation fields generated by comp... more 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 are 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.
In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and re... more In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.
The present society is highly dependant on complex electronics systems, which have a low damage t... more The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.
We present for the first time detection of X-rays from laboratory sparks created in air at atmosp... more We present for the first time detection of X-rays from laboratory sparks created in air at atmospheric pressure by applying an impulse voltage with slow rise time. It is in full analogy with the detection of X-rays from lightning stepped and
2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium on Lightning Protection (SIPDA)
This study employed wavelet transformation to disclose the spectrograms of IEC standard impulses ... more This study employed wavelet transformation to disclose the spectrograms of IEC standard impulses and real transient voltages generated by the cloud to ground discharges. The spectral details of each impulse were subdivided into different spectral clusters and the outcome was mapped into respective voltage levels and time to develop correlations. Eventually different protection voltage levels of commercially available surge protection devices (SPDs) and the voltage levels of different spectral clusters were compared to determine whether harmful energy infringements could be possible when the spectral clusters are wrapped by SPDs. This study revealed that all IEC impulses have identical spectral clusters whereas real transient voltages demonstrated that they are inherited with much random spectral distributions. Thus, planning for foolproof through benchmarking real transient impulses against IEC impulses would not produce guaranteed outcomes. Hence, a poor selection of clamping voltages may create a permanent window to infringing a small quantum of harmful energy on a constant basis into sensitive systems to trigger silent killing of basic functional units.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This paper presents an analysis done on the transient behavior of an external lightning protectio... more This paper presents an analysis done on the transient behavior of an external lightning protection system (LPS). The study was devised by modeling a Faraday's cage type LPS of a five-storied building on a MATLAB based electrical nodal network and simulating it against the 10/350 μ s lightning impulse with a peak current of 30 kA. The study focused on the down conductor material cross section area, ground impedance and the number of down conductors in the LPS to establish which factor or factors have more influence on the LPS performance. The simulation concludes that under the transient conditions the voltage dissipation on the LPS can reach several thousand volts and the peak branch current disbursements in the network are in the order of 2-2.5 kA. However, under poor ground conditions and less number of down conductors, voltage rise on the LPS system can elevate alarmingly, and branch currents tend to increase close to 7.5 kA. The study proved that the performance of the LPS and the magnitudes of the negative consequences of the associated secondary effects such as electromagnetic compatibility issues and risk associated with high step voltage issues, etc., have a close correlation with the ground impedance and the number of down conductors than that of the cross-section area of the down conductors.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study presents the behavior of surge protecting devices (SPDs) against transient over voltag... more This study presents the behavior of surge protecting devices (SPDs) against transient over voltages generated by cloud to ground (CG) flashes. Analysis revealed that lightning generated transient over voltages have a potential to impart detrimental effects on the SPDs. Moreover, it was concluded that comparisons between IEC laboratory impulse and the real transient voltages are remote due to factors such as peculiar time domain voltage profiles, random polarities, multiple surges with very narrow inter pulse durations in the order of microseconds. Further, observed that SPDs would not always retain within the limits specified by the manufactures under all circumstances.
Variation of fractal dimension of long laboratory sparks were studied using high speed video reco... more Variation of fractal dimension of long laboratory sparks were studied using high speed video recordings and still images. Four sparks were selected for the study, including both positive and negative polarities in lightning and switching impulses. Temporal and spatial variation of fractal dimension was studied. It was found that the fractal dimension is maximum at the breakdown. No particular pattern was observed for the variation of fractal dimension along the channel. Results show that the value of fractal dimension depends on the angle of view. Keywords-component; fractal dimension, long laboratory sparks.
Use of earthing enhancing compound (EEC) in electrical earthing system is a common practice in ma... more Use of earthing enhancing compound (EEC) in electrical earthing system is a common practice in many countries. Naturally available materials and commercially modified materials are used as EEC. This research will enlighten further the phenomenon of using EEC to improve the performance of an electrical earthing system. The EEC used for this experiment was a commercially available product which the exact chemical composition is unknown. Both high impulse current generator and a modular impulse generator with suitable data acquisition systems were used to study the impedance characteristics of the product specifically under fast transients. Both 1.2/50 μs lighting impulses and 8/20 μs wave shapes were applied to the sample and analyzed the responsive V-I and impedance curves. Both experiments provide convincing evidence for healthy conductive character of the selected material under impulse conditions. However, some of the evidence suggests dissimilarities in the behavior of the test s...
2018 34th International Conference on Lightning Protection (ICLP), 2018
The tortuosity of the channel is defined as “Mean absolute angle change of the angle change and i... more The tortuosity of the channel is defined as “Mean absolute angle change of the angle change and it measures how strongly the tortuous path of the channel of lightning/laboratory spark is twisting. 8 m Long laboratory sparks and high speed (20000 frames per second) technology used for this experiment. Using these data it has been calculated the channel tortuosity of 8 m long sparks and vertical profile of channel tortuosity. In addition to that spectral analysis of the angel change of the twisting path of the channel has been done in this study.
2018 34th International Conference on Lightning Protection (ICLP), 2018
Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric ... more Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric fields do. Thunder flashes of tropical lightning occurred in Hambantota (810 0’E, 60 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.
2018 34th International Conference on Lightning Protection (ICLP), 2018
For an effective earthing system, the resistance/impedance of the earthing system should be held ... more For an effective earthing system, the resistance/impedance of the earthing system should be held at the lowest possible level. In this study, a surge generator, which can inject a 2-kV signal of $1.2/50 \mu \mathrm{s}$ waveform or 1 kA impulse current waveform of 8/20 $\mu$ s, was constructed to investigate the impedance of single rod earthing system. The resistivity of the soil at the selected location varies from $300 \Omega \mathrm {m} - 1700 \Omega \mathrm{m}$. By using the fall of the potential method, it was observed that the impedance of single rod system varies from $900 \Omega$ at 1 m to $70 \Omega$ with the distance of 2-5 m. The earthing resistance of the same system was found to be $285 \Omega$, which is higher than the impedance.
2018 34th International Conference on Lightning Protection (ICLP), 2018
A basic broadband digital interferometer was developed, which is capable of locating Very High Fr... more 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.
General characteristics of K changes together with their fine structure associated with ground fl... more General characteristics of K changes together with their fine structure associated with ground flashes in Sri Lanka in the tropics are presented. It is found that on average there are about 2 K changes associated with each return stroke. Analysis of the fine structure of the K changes shows that the K change is a chaotic pulse burst. Some of these chaotic pulse bursts start and the others end as a regular pulse bursts. Sometimes the chaotic part occurs in between two regular pulse bursts. This is in agreement with the recent published results that claim that chaotic pulse bursts are a random superposition of regular pulse bursts. The results show that the small step fields identified in the literature as K changes are the static fields associated with these pulse bursts.
Propagation effects on the Narrow Bipolar Pulses (NBPs) or the radiation fields generated by comp... more 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 are 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.
In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and re... more In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.
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