| 1. |
- Arevalo, Liliana, et al.
(author)
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Attachment process of the discharge of competing grounded electrodes - Experimental observations and modeling
- 2021
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In: 2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium On Lightning Protection (SIPDA). - : IEEE. - 9781665423465
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Conference paper (peer-reviewed)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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| 2. |
- Arevalo, Liliana, et al.
(author)
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The leader propagation velocity in long air gaps
- 2018
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In: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
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Conference paper (peer-reviewed)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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| 3. |
- Chandimal, A. P. L., et al.
(author)
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Impedance Behavior of Earth Enhancing Compound Under Lightning Transient Conditions
- 2018
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In: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
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Conference paper (peer-reviewed)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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| 4. |
- Frost, Anna E., 1988-, et al.
(author)
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Do pre-recorded lessons in combination with formative assessments fulfil the learning necessity of engineering students?
- 2022
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In: Bidrag från 8:e Utvecklingskonferensen för Sveriges ingenjörsutbildningar. - : Karlstads universitet. - 9789178672813 ; , s. 21-25
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Conference paper (other academic/artistic)abstract
- As an effort to increase digitization of education during the ongoing pandemic in Spring 2021, the course ”Electromagnetism II with electric circuits” at Uppsala University has been conducted in a blended form with both pre-recorded sessions and live online sessions. About half of the lectures were live sessions, and the rest were pre-recorded. Among the lessons, more than 75 % were pre-recorded. When the teaching is pre-recorded, the teachers do not get reactions directly from the students, either verbally or from facial expressions. Therefore,self-correcting quizzes were implemented for every lecture, and short formative evaluations were implemented for every lesson. The main objective was to increase the number of students participating in the lessons, which hopefully would lead to more students passing the course. More students watched the pre-recorded lessons than attended the lessons on campus previous years on the course. More students passed the exam on the course compared to previous years, but it cannot be excluded that this is partially or completely due to the exam being different due to the pandemic. The short formative evaluations had at least seven respondents during the first four lessons, but from lesson five and onward, the number of respondents was two or fewer. The quizzes which most students attempted were right after or right before the pre-exams (”duggor” in Swedish), but otherwise relatively few students answered the quizzes. When asked in the course evaluation, it varied a lot whether the students liked, disliked, or were neutral to have pre-recorded lessons, with slightly more students saying they preferred live sessions.
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| 5. |
- Perera, Chandana, et al.
(author)
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Analysis of Channel Tortuosity using 8 m Long Laboratory Sparks
- 2018
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In: 34th International Conference on Lightning Protection (ICLP 2018). - : IEEE. - 9781538666357
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Conference paper (peer-reviewed)abstract
- 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.
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| 6. |
- Persson, Rebecca, et al.
(author)
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Analysis of Peak Currents Reported by the Swedish Lightning Location System During 2015-2020
- 2022
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Conference paper (other academic/artistic)abstract
- The purpose of this work is to process lightning data from the Swedish Meteorological and Hydrological Institutes (SMHI) lightning location system to analyze which currents occur during lightning strikes in Sweden. The result can then be compared with the values currently used in dimensioning lightning protection for the transmission network, to evaluate whether the design of the protection is relevant with regard to the currents registered by the lightning location system. The results based on the years 2015-2020 show that the current distribution fits a lognormal and generalized extreme value distribution, the latter yielding a slightly better representation. The national analysis shows a significantly lower median peak current in Sweden compared to the reference median peak current recommended by CIGRE.
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| 7. |
- Persson, Rebecca, et al.
(author)
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Distribution of the current from lightning in Sweden
- 2022
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In: 2022 International Symposium on Electromagnetic Compatibility (EMC Europe 2022). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665407885 - 9781665407892 ; , s. 285-289
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Conference paper (peer-reviewed)abstract
- Data from the lightning detection system owned by SMHI mainly from 2015-2020 was used to model the peak current. The log-normal distribution and the generalised extreme value distribution were tried and the later was slightly better. The median of the peak current was found to be lower than the value recommended by Cigre, in particular for the first stroke in a flash. In part, this can be due that the lightning detection system is calibrated for the subsequent negative strokes. The duration and the interval of the strokes were as expected. No correlation between current and rise time was found, whereas there were some differences between the regions in Sweden.
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| 8. |
- Roman, Francisco, et al.
(author)
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10/350 µs Lightning Impulse Current Behavior of a Conductive Fabric
- 2021
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In: 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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Conference paper (peer-reviewed)abstract
- Lightweight Portable Lightning Protection Shelters require the use of new materials capable of supporting the high current densities associated with lightning currents. In this paper, 30 x 30 cm(2) conductive fabrics samples are subjected to 10/350 mu s lightning current impulses. This experimental work, performed at the HV lab of Uppsala University, is aimed at understanding the transversal pattern of scratches or striations observed in conductive fabrics in previous experiments performed at the HV lab of Universidad Nacional de Colombia with 8/20 mu s lightning impulse currents. Striations were recorded with both a still camera and a fast-recording camera, while the samples current was measured. Additionally, the withstand current density of the tested conductive fabrics was obtained.
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| 9. |
- Wooi, Chin-Leong, et al.
(author)
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Observations of X-rays in 4-meters long laboratory sparks under positive lightning impulse
- 2021
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In: 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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Conference paper (peer-reviewed)abstract
- In this paper, the observation of X-rays in 4-meters long laboratory sparks is presented for the first time. In this study, a total of 20 standard positive lightning impulse voltages (1.2/50 mu s) with measured peak voltages between 3.0 to 3.2 MV were applied across 4-m long horizontal air gap of sphere-sphere configuration with 50-cm spheres. The results show that most of the X-ray emission were detected at about 12 mu s after the applications of the lightning impulse voltage during the rising part of the voltage or at around the peak of the voltage. Compared to previous shorter gaps studies, the longer air gaps seem leads to a delay in X-ray occurrence time. X-rays appeared at about 1-2 mu s after the applications of lightning impulse voltage which is slightly delayed compared to some of the previous shorter gap's studies. This study also finds an increase in the X-ray emission rate and deposited energies of Xrays in the case of higher applied peak voltages. Higher applied peak voltages seemed to change the X-rays appearance time as well. Additionally, multiple peaks X-rays pulses were observed near to the peak of the voltage in this study.
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