2018 34th International Conference on Lightning Protection (ICLP), 2018
Thunder signatures have been categorized into three types using recorded peak pressure. The varia... more Thunder signatures have been categorized into three types using recorded peak pressure. The variation in fundamental frequency initiated by ground flashes has been studied by using an acoustic spectrum of thunder. Stransformation has 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. The mean fundamental frequencies of type 1 ground and cloud flashes are 88 Hz and 123 Hz respectively.
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.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study was conducted to understand what inherent limitations are associated with SPD arrays i... more This study was conducted to understand what inherent limitations are associated with SPD arrays in confronting with real transient over voltages. To devise the study 403 transient voltages were selected with different physical attributes covering a range of peak-to-peak voltages, starting from 175 V up to 2861 V. The sample comprises 218 cloud-to-clouds and 185 clouds to ground generated transient voltages with mean and median values of 676.80 V and 551.00 V respectively. Impulses were segregated into three subclasses based on their physical attributes and assessed the tendency to drift through the protection array once they placed at the+90, zero and -90 phaser angles. The study revealed that 100% of positive impulses in the sample could drift through the selected array once pitched at any phaser angle on 230 V, 50 Hz utility signal. It was observed that out of the negative pulses, 90.35% at +90, 74.39 % at zero and 42.21% at -90 phaser angles, could freely move through the array. In addition to that, almost 100% of the positive portions of bipolar impulses too can reach the sensitive systems through the protection array irrespective of the pitching phaser angle.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study was devised to investigate how the pitching phaser angle and the time domain voltage p... more This study was devised to investigate how the pitching phaser angle and the time domain voltage profile would compel surge protective devices (SPDs) to fall short in providing guaranteed protection. The study showed that the phaser angle at which the transient voltage pitching on the 230 V power frequency signal and its time domain voltage profile play a significant role in deciding the efficiency of the protection array and the amount of incident energy that infiltrates to reach the sensitive loads connected to the low voltage power installation. The analysis managed to prove that the selected SPD array can effectively reduce the harmful energy content of the impulse to around 40% and hence it is always advantageous to have a cascaded array than a single SPD. The study emphasized that it is practically impossible to have a universal protection system that can provide the same degree of protection under all circumstances. Moreover, the study further revealed that it is rational to design a SPD array considering regional and local lightning characteristics.
2017 International Symposium on Lightning Protection (XIV SIPDA), 2017
In many studies of lightning flash characterization, the lightning generated electric field measu... more In many studies of lightning flash characterization, the lightning generated electric field measuring system uses a circuit based on the buffer-amplifier LH0033. This circuit was proposed 35 years ago and there is no doubt of its excellent performance to measure the lightning electric field intensity. However, LH0033 is no longer manufactured, making it necessary to find a replacement. This paper proposes an improvement of the electric field measuring system, which consists of a new electronic circuit that uses the buffer-amplifier BUF602. This circuit presents a similar performance of the classic circuit, but has a lower energy consumption and allows its implementation in surface mount technology, which reduces the space required for the circuit. The field tests were performed in Bogotá, Colombia during a complete thunderstorm season and their results show that new circuit is a good alternative for measuring electric field signals with a bandwidth up to 11 MHz.
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
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.
Wavelet analysis of 18 Narrow Bipolar Pulses (NBP) captured of a single thunderstorm from a coast... more Wavelet analysis of 18 Narrow Bipolar Pulses (NBP) captured of a single thunderstorm from a coastal area in Sri Lanka is presented. The data sample consists of the narrowest measured bipolar pulses from both polarities. Data was recorded at Matara (5.95 0 N, 80.53 0 E), southern coast of Sri Lanka from a highly active thunderstorm day in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. The spread distribution and the energy percentages for each wavelet coefficient were measured and compared for each polarity. The negative NBPs had an average spanning of 83-273 kHz for the initial pulse's spread distribution. The overshoot of the same had an average range of 96-200 kHz. The positive pulses had an average spanning of 76-208 kHz for the initial pulse in the spread distribution. The overshoot of the same had an average range of 85-169 kHz. The energy percentages of the wavelet coefficients of negative NBPs had an average of 3.78 x10-5 for in...
2018 34th International Conference on Lightning Protection (ICLP), 2018
Thunder signatures have been categorized into three types using recorded peak pressure. The varia... more Thunder signatures have been categorized into three types using recorded peak pressure. The variation in fundamental frequency initiated by ground flashes has been studied by using an acoustic spectrum of thunder. Stransformation has 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. The mean fundamental frequencies of type 1 ground and cloud flashes are 88 Hz and 123 Hz respectively.
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.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study was conducted to understand what inherent limitations are associated with SPD arrays i... more This study was conducted to understand what inherent limitations are associated with SPD arrays in confronting with real transient over voltages. To devise the study 403 transient voltages were selected with different physical attributes covering a range of peak-to-peak voltages, starting from 175 V up to 2861 V. The sample comprises 218 cloud-to-clouds and 185 clouds to ground generated transient voltages with mean and median values of 676.80 V and 551.00 V respectively. Impulses were segregated into three subclasses based on their physical attributes and assessed the tendency to drift through the protection array once they placed at the+90, zero and -90 phaser angles. The study revealed that 100% of positive impulses in the sample could drift through the selected array once pitched at any phaser angle on 230 V, 50 Hz utility signal. It was observed that out of the negative pulses, 90.35% at +90, 74.39 % at zero and 42.21% at -90 phaser angles, could freely move through the array. In addition to that, almost 100% of the positive portions of bipolar impulses too can reach the sensitive systems through the protection array irrespective of the pitching phaser angle.
2018 34th International Conference on Lightning Protection (ICLP), 2018
This study was devised to investigate how the pitching phaser angle and the time domain voltage p... more This study was devised to investigate how the pitching phaser angle and the time domain voltage profile would compel surge protective devices (SPDs) to fall short in providing guaranteed protection. The study showed that the phaser angle at which the transient voltage pitching on the 230 V power frequency signal and its time domain voltage profile play a significant role in deciding the efficiency of the protection array and the amount of incident energy that infiltrates to reach the sensitive loads connected to the low voltage power installation. The analysis managed to prove that the selected SPD array can effectively reduce the harmful energy content of the impulse to around 40% and hence it is always advantageous to have a cascaded array than a single SPD. The study emphasized that it is practically impossible to have a universal protection system that can provide the same degree of protection under all circumstances. Moreover, the study further revealed that it is rational to design a SPD array considering regional and local lightning characteristics.
2017 International Symposium on Lightning Protection (XIV SIPDA), 2017
In many studies of lightning flash characterization, the lightning generated electric field measu... more In many studies of lightning flash characterization, the lightning generated electric field measuring system uses a circuit based on the buffer-amplifier LH0033. This circuit was proposed 35 years ago and there is no doubt of its excellent performance to measure the lightning electric field intensity. However, LH0033 is no longer manufactured, making it necessary to find a replacement. This paper proposes an improvement of the electric field measuring system, which consists of a new electronic circuit that uses the buffer-amplifier BUF602. This circuit presents a similar performance of the classic circuit, but has a lower energy consumption and allows its implementation in surface mount technology, which reduces the space required for the circuit. The field tests were performed in Bogotá, Colombia during a complete thunderstorm season and their results show that new circuit is a good alternative for measuring electric field signals with a bandwidth up to 11 MHz.
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
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.
Wavelet analysis of 18 Narrow Bipolar Pulses (NBP) captured of a single thunderstorm from a coast... more Wavelet analysis of 18 Narrow Bipolar Pulses (NBP) captured of a single thunderstorm from a coastal area in Sri Lanka is presented. The data sample consists of the narrowest measured bipolar pulses from both polarities. Data was recorded at Matara (5.95 0 N, 80.53 0 E), southern coast of Sri Lanka from a highly active thunderstorm day in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. The spread distribution and the energy percentages for each wavelet coefficient were measured and compared for each polarity. The negative NBPs had an average spanning of 83-273 kHz for the initial pulse's spread distribution. The overshoot of the same had an average range of 96-200 kHz. The positive pulses had an average spanning of 76-208 kHz for the initial pulse in the spread distribution. The overshoot of the same had an average range of 85-169 kHz. The energy percentages of the wavelet coefficients of negative NBPs had an average of 3.78 x10-5 for in...
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Papers by Mahendra Fernando