| 1. |
- Ahmad, Mohd Riduan, et al.
(författare)
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Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 810-813
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Konferensbidrag (refereegranskat)abstract
- In this paper, temporal characteristics of several initial electric field pulses of preliminary breakdown process (PBP) from very close negative cloud-to-ground (CG) flashes are compared to close narrow bipolar pulses (NBPs) to observe any similarity that may exists. Interestingly, we found that the initial PBP pulses are similar to close NBP with zero crossing time less than 5 mu s, do not preceded by any slow field change and followed by pronounce static component. As NBPs are believed to be a result of relativistic runaway electron avalanches discharge, this finding is an indication that the initial electric field pulses of PBP are perhaps the result of the same discharge mechanism.
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| 2. |
- Arevalo, Liliana, et al.
(författare)
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Streamer to leader transition criteria for propagation of long sparks and lightning leaders
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 480-483
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Konferensbidrag (refereegranskat)abstract
- Certain models have been dedicated to analyze the breakdown of long spark gaps and the lightning attachment process based on the mechanism of leader propagation. One of the most important processes on the mechanism of leader is the transition between streamers to leader. The streamer to leader transition is characterized by a rapid increase in the electron density and gas temperature, which is a consequence of the onset of thermal-ionization instability. To simplify the complexity of the physical process lightning attachment and long spark gaps models assumed that a minimum charge of 1 mu C is necessary to thermalize a leader channel, independently of the electric field and atmospheric conditions as temperature, pressure and humidity. In this paper an approach that takes into account the continuity equations and the gas temperature balance equation is used to investigate the minimum charge required to start the streamer to leader transition. The obtained results are compared with the minimum charge criteria used for long spark gaps and lightning attachment modeling. Simulation shows that the required charge to thermalize a leader depends on the vibrational energy relaxation. Results also indicate that only a small part of the energy input, transferred by electrons to gas molecules in the stem, contributes immediately to the temperature rise.
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| 3. |
- Arevalo, Liliana, et al.
(författare)
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Upward leader inception caused by a sudden change of cloud electric field
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 484-487
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Konferensbidrag (refereegranskat)abstract
- Discharge processes such as glow, streamer, and leader inception among others take place before an upward leader can be launched from a grounded structure during thunderstorms. Electrostatic fields below the thundercloud could lead to the formation of glow charge from grounded objects. If the electric field is high enough and ionization keeps expanding into the gap, streamers can be incepted. Depending on the available charge and the thermodynamic properties of the gas, there is a possibility to incept or not a positive upward leader towards the cloud. Usually, the inception of positive upward leaders is directly related with the appearance of a downward coming leader from cloud towards the grounded object. Such a downward leader will intensify the electric field in such a way that the streamer discharges could thermalize and produce an unstable upward leader channel. However, experimental observations have indicated the inception of upward leaders from grounded structures without registering connecting downward leaders towards the structure. The present paper intends to explain the inception of positive upward leaders from the top of a rod, whenever the electric field produced by the cloud suddenly changes e.g. due to intra-cloud discharges or distance cloud to ground flash. A two dimensional model based on the gas-dynamic equations, the main processes responsible for gas heating such as vibrational excitation and transfer of energy into electronic, rotational and translational excitation, coupled with Poisson equation is presented in this paper. Rods of different lengths under thundercloud electric field were studied. Simulation results indicate that positive upward leaders can be incepted from long rods under certain conditions of thundercloud electric field without the need of a coming downward leader. However, for rods of tenths of meters the thundercloud electric field is not enough to incept positive upward leaders and an intensification of the electric field is required in order to incept a positive upward leader from the structure, e.g., a coming downward leader.
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| 4. |
- Bodhika, J. A. P., et al.
(författare)
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A preliminary study on characteristics of thunder pulses of lightning
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 260-264
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Konferensbidrag (refereegranskat)abstract
- Thunder is the acoustic emission associated with lightning discharges. Thunder signatures have been analyzed by many scientists with the aim of understanding the energy, channel tortuosity and localization of lightning channel. In describing thunder features, a few subjective terms such as clap, roll and rumble have been used in the literature inconsistently with no proper definitions. In this study the features of pressure pulses such as occurrence characteristics and their relative amplitudes were analyzed to understand some of the above mentioned thunder features. Those subjective terms, clap, peal, roll and rumble were quantified along with relative pulse amplitudes and confirmed by listening the recorded thunder signals carefully. The relative peak amplitudes of the pulses of rumble were less than 20% of the peak pulses of the thunder signal and for roll it was between 20% to 40%. Pulses with relative amplitudes greater than 40% were identified as claps. The most significant contribution to the sound in a thunder flash is due to claps, which was studied separately in this study. The number of claps in a thunder flash, their frequency variation, durations, and pulse characteristics has been studied. The frequency of pressure oscillations within these claps are being less than 300 Hz. According to this study, 62% of the flashes consist of 1 to 2 claps. The activity of the thunder signal is high in initial half than the latter half. Thunder signals analyzed in this study is recorded by a microphone system with wide bandwidth range from 6 to 20 kHz.
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| 5. |
- Diaz, Oscar, et al.
(författare)
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Sensitivity Analysis of Leader Channel Models Used in Long Air Gap Positive Discharge Modelling
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 564-567
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Konferensbidrag (refereegranskat)abstract
- Leader models used in electrical discharge simulation have been proposed in theoretical works by different authors. Their application can be found in the study of lightning upward connecting leaders or long air gap laboratory testing, and can be considered engineering or physical according to their detail level. Based on simplifications and assumptions, these models are capable of predicting the 50% breakdown voltage for certain electrode arrangements, time evolution of physical phenomena like particle densities, temperatures, electric fields, leader and streamer progress, among others. An important parameter in a leader model is the potential distribution along the channel as it propagates. In present work, we compare an engineering and a physical leader model against experimental data recorded while testing a rod-to-plane 10 m gap with switching-like voltage impulse. A sensitivity analysis was done with some basic input parameters of two leader models in order to compare the outcome for different cases. The results showed a strong dependence of the leader channel evolution with the assumed constant average potential gradient used in most of the leader models.
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| 6. |
- Esa, M. R. M., et al.
(författare)
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Occurrence of narrow bipolar pulses between negative return strokes in tropical thunderstorms
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - 9781479935444 ; , s. 1141-1142
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Konferensbidrag (refereegranskat)abstract
- This paper reports a recent observation of Narrow Bipolar Pulses (NBPs) occurrence between return strokes (RSs) of negative cloud-to-ground (CG) flashes in tropical thunderstorms. A wideband electric field antenna measurement system has been used in this work and 173 isolated and non-isolated NBPs managed to be recorded. We found that 22 single NBPs and a pair of positive NBP embedded between RSs and some of them are located within the horizontal distance range from 20 to 45 km from the observation station.
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| 7. |
- Gunasekara, T. A. L. N., et al.
(författare)
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Electric field signatures of narrow negative bipolar pulse activities from lightning observed in Sri Lanka
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 624-628
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Konferensbidrag (refereegranskat)abstract
- Isolated Narrow Bipolar Pulses (NBP) have been observed in the past in sub tropical and tropical regions. This study presents detail electric field characteristics of NBP pulses observed in Sri Lanka in the tropic. NBP analyzed in this work were recorded at Matara (5.95 degrees N, 8.53 degrees E), southern coast of Sri Lanka from four highly active thunderstorm days in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. In contrary to previous observations at the same geographical region, both positive and negative NBP pulses were observed in this study. Parameters related to Narrow Negative Bipolar Pulses (NNBP) are presented in this study since majority of the observations were in that category. The parameters measured for NNBP's were rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width at half maximum (FWHM) and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values for these parameters were found to be 0.49 mu s, 2.83 mu s, 0.18 mu s, 1.18 mu s and 0.17 respectively. The above values conforms to a much narrower bipolar pulses when compared to values reported in earlier studies.
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| 8. |
- Kumara, L.A.D, et al.
(författare)
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Behavior of Low Voltage Varistors under Very Fast Oscillatory Type Current Impulse Environment
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 1577-1582
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Konferensbidrag (refereegranskat)abstract
- In this study, the behavior of low voltage varistors under very fast oscillatory type non standard current impulses were analyzed. The experiment was performed on 20 mm disk varistors with different nominal operating voltages of 14V, 30 V, 40 V, 75 V, 150 V, 250 V and 275 V. Non standard current impulses were generated using a Van De Graaff generator. The shape of the impulse was like a double exponential oscillatory type wave which has the oscillation frequency of 14.53 MHz. The rise time of the impulse was 8 ns with a maximum peak current rate-of-rise is of 2.41 x 10(11) A/s. According to the results, under vary fast non standard current impulse environment, clamping voltage could be depend on both nominal voltage of varistors as well as its disk diameter. Another important feature of the voltage signatures observed was the DC offset voltage causes between terminals of varistor immediately after it triggered due injected fast current impulses.
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| 9. |
- Mohd Esa, Mona Riza, et al.
(författare)
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Time-Frequency Profile of Discharge Processes Prior to the First Return Stroke
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 1134-1137
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Konferensbidrag (refereegranskat)abstract
- We aim to investigate the time-frequency profile for sets of lightning processes that occurred prior to the first return stroke which include narrow bipolar pulses, preliminary breakdown pulses and stepped leaders. The work is mainly using the wavelet transformation in order to gain the frequency spectrum while not losing the time information of the located pulses. 2 sets of events that include the narrow bipolar pulse (NBP) followed by preliminary breakdown pulses (PBPs), stepped leaders (SLs) and the first return stroke (RS) are used in this paper. All selected data are recorded during northeastern monsoon season at the end of year 2012 in Malaysia. Parameters that used in this works includes the (1) upper and (2) lower frequency spectrum for both spectral and spread regions and (3) power spectrum. In average, the upper and lower frequency spectrum for NBP is at least 10 times higher when compare to the first return stroke. It is also found that the NBP radiates predominantly between 61 kHz and 168 kHz which much higher than the first return stroke with range from 2 kHz to 12 kHz. PBP pulses radiate intensely within 65 kHz to 1 MHz, whereas SL pulses radiate predominantly between 163 kHz and 455 kHz. In terms of power spectrum, PBP pulses tend to produce higher magnitude of power spectrum in the earlier stage and decreased towards the end of its process. In the contrary, SL pulses' power spectrum magnitudes are lower in the beginning and tend to increase when approaching to the first return stroke.
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| 10. |
- Nanayakkara, Sankha, et al.
(författare)
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K - change : Is it a static field of a chaotic pulse burst?
- 2014
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Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - 9781479935444 ; , s. 634-642
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Konferensbidrag (refereegranskat)abstract
- Electric field changes associated with K - changes have been studied since 1956. In this study, the electric field variations of K changes observed in the tropics, in Sri Lanka, was analyzed to study the inter K change duration, K change duration, and possible contribution from other activities on K changes. Selected 144 k-changes of 64 lightning flashes, measured with 6.4 ns sampling rate were used for the analysis. The inter K change time interval was found to vary from 0.62 ms to 75.92 ms with an average of 16.92 ms. The duration of K-changes were found to vary from 0.44 ms to 1.65 ms with an average value of 0.48 ms. In this study, it was observed that all K - changes were combined with chaotic pulse trains (CPT). This suggests that the K - changes may be a result of slow electric field changes associated with chaotic pulse activities.
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