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- Sabri, M. H. M., et al.
(författare)
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Initial electric field changes of lightning flashes in tropical thunderstorms and their relationship to the lightning initiation mechanism
- 2019
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Ingår i: Atmospheric research. - : ELSEVIER SCIENCE INC. - 0169-8095 .- 1873-2895. ; 226, s. 138-151
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the key finding is that all the examined first classic Initial Breakdown (IB) pulses in tropical flashes within the reversal distance were found to be initiated by a clearly detectable Initial E-field Change or IEC (45 -CG, 32 normal IC, and 3 IC initiated by +NBE). The durations of IECs for both -CG and IC flashes in tropical storms were longer than in Florida storms. On the other hand, for the magnitudes of the E-change, the values were smaller compared to Florida storms with averages of 0.30 V/m compared to 1.65 V/m for -CG flashes, and -0.81 V/m compared to -6.30 V/m for IC flashes. The IEC process of lightning flashes in tropical regions took longer to increase the local electric field in order to produce the first IB pulse because of the smaller magnitude of E-change. On the other hand, in Florida storms, the IEC process took a shorter time to increase the local electric field to produce the first IB pulse because of the larger magnitude of E-change. We found that very high frequency (VHF) pulses for tropical thunderstorms started sometime prior to the onset of the IECs. They started between 12.69 and 251.60 mu s before the initiation of the IEC for two normal IC flashes. The first two VHF pulses were detected alone without narrow IB pulses (fast antenna and slow antenna records) or any pulses from the B-field and dE/dt records. Furthermore, the VHF pulses for three IC flashes initiated by + NBEs were also detected before the onset of the IEC. The IEC started immediately after the detection of the + NBE. It is clear that the IEC is initiated by VHF pulses. It can be suggested that lightning is initiated by Fast Positive Breakdowns or FPBs (which emit strong VHF pulses and large + NBEs) and is followed by several negative breakdowns (weak VHF pulses and/or weak NBE-type pulses) before the IEC started. For the case of normal IC flashes, several weaker VHF pulses (mean values of 41.97 mV and 46.4 mV compared to the amplitudes of the VHF pulses of + NBEs of around 800 mV) were detected before the onset of the IEC. As FPBs can occur with a wide range of VHF strengths and E-change amplitudes, it can be suggested these weak VHF pulses accompanied by narrow IB pulses or weak NBE-type pulses detected before the onset of IEC are actually FPBs followed by negative breakdowns or several attempted FPBs.
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- Gomes, Ashen, et al.
(författare)
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Impulse flashover characteristics of oil palm trunk (OPT) veneer plywood
- 2018
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Ingår i: 34th International Conference on Lightning Protection, ICLP 2018. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- Oil palm is one of the largest crop industries in South East Asia, thus, it is of importance to use all parts of the Oil palm trees. Recently Oil Palm Trunks (OPT) have been used to make veneer, which can be processed to produce plywood. Even though OPT plywood doesn't have the same mechanical properties as timber, with proper treatment and adhesives during the processing of veneer to plywood, it can be made to compete with hardwood. OPT plywood has been used in various applications from wooden appliances to housing and roofing structures. These structures are at risk of surface flashovers through lightning and electrical breakdowns. However, no study has been conducted on the effects or characteristics of OPT plywood. In this paper, the effects of impulse surface flashover under different conditions on three-layered OPT plywood has been analyzed. Experiments were conducted to identify the characteristics of OPT under clean and dry, clean and wet, and contaminated surface conditions for both parallel and perpendicular fiber orientations. The 50% breakdown voltage was determined by the up and down method. Results identified the importance of the fibre orientation and the decrease in breakdown voltage under contaminants.
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- Jamil, N. A. M., et al.
(författare)
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Electrical stimulation for the growth of plants : With special attention to the effects of nearby lightning on mushrooms
- 2018
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Ingår i: Asian Journal of Microbiology, Biotechnology and Environmental Sciences. - : Global Science Publications. - 0972-3005. ; 20:4, s. 1332-1343
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Tidskriftsartikel (refereegranskat)abstract
- – Electrical stimulation could trigger biological activities of plants, enhancing their production rate. This paper addresses the application of this technology on mushroom which, possesses unique developmental process that depends on hyphae morphogenesis at growth stages; thus their response to electrical stimulation should be studied separately. The study analyses the information available on electrical environment of mushrooms with the view of investigating the efficiency of external electric stimulation approaches for the enhancement of their progress at various growth stages. Electric treatments at relatively low strengths, applied for a short exposure time have resulted positive impacts on growth rates, yields, length and size of various plants. In the case of mushrooms, the only information available on successful external electrical stimulation technique is the application of high voltage pulses. The technique has shown positive effects on the growth rate of varieties such as shiitake and nameko. This approach has been adopted based on the unconfirmed claims that lightning in the vicinity develops cracks in mushroom hyphae and stimulates their enzyme activities, which in turn boosts the growth rate. Based on the outcomes, we foresee a good economic viability of mushroom production with these modern technologies and methodologies.
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- Gomes, Ashen, et al.
(författare)
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Development of a portable type i to III lightning surge protective device for compact structures
- 2018
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Ingår i: 34th International Conference on Lightning Protection, ICLP 2018. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- Lightning Surge protection of large structures is done under zonal concept due to the requirement of a system with high current handling capacity and low voltage protection level. Induction of transient voltage in the wiring system within the building is another reason for such. However, in the case of compact structures such as base transmission stations (BTS) of tower sites, outside broadcast vehicles (OBV), various stages of railway systems etc. there are no sufficient lengths in the wiring network for implementing SPDs in such zonal-segment scenario. Also due to the remoteness of most BTSs and need for regular and/or continuous usage of OBVs and railway systems, the time-consuming replacement of outof-order fixed SPDs is most often not warranted. In this backdrop, it was proposed to develop a portable/pluggable system of coordinated SPDs with high current handling capacity and low voltage protection level. A compact SPD system that is capable of handling high currents (50 kA) with low let through voltage (1 kV) was designed using PSCAD and a thorough market research was conducted to identify products that satisfied the requirements of the system designed in PSCAD. Type I and III SPDs capable of handling 50 kA and 2.5 kA respectively, were identified and used for the hardware implementation of the system. Elimination of the type II SPD made the design more compact and better suited for applications at space-restricted locations.
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| 8. |
- Izadi, M., et al.
(författare)
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Estimation of Lightning Current and Return Stroke Velocity Profile Using Measured Electromagnetic Fields
- 2014
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Ingår i: Electric power components and systems. - : Informa UK Limited. - 1532-5008 .- 1532-5016. ; 42:2, s. 103-111
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate lightning current using measured electromagnetic fields, an inverse procedure algorithm is proposed in this article, where the variation of return velocity stroke velocity is considered as opposed to previous methods where the velocity is set at a constant value. The proposed algorithm considers all electromagnetic fields components directly in the time domain without needing to apply any extra conversions. Moreover, it can support the wide range of current models based on the general form of engineering current models. The proposed method is validated using a sample of triggered lightning data and measured electromagnetic fields at two stations with different distances from the lightning channel. The results illustrate that the proposed method could estimate the behavior of current along the channel and can thus be used for preparing a data bank to record lightning current parameters of a wide range of lightning occurrences based on measured fields.
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| 9. |
- Jamil, N. A. M., et al.
(författare)
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Effects of electrical stimulation on the yield of tuber of tiger's milk mushroom
- 2019
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Ingår i: Engineering in Agriculture, Environment and Food. - : Elsevier B.V.. - 1881-8366. ; 12:4, s. 526-533
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Tidskriftsartikel (refereegranskat)abstract
- The growth rate of mycelium of the tiger's milk mushroom (Lignosus rhinocerotis) at intermediate development stage was successfully increased up to 16% by the application of corona discharge through multiple needles at a steady state voltage of 5 kV generated by a Van der Graff generator, for 5 h a day, for four weeks. The same method could enhance the yield of tuber up to 56%. Myco-chemical analysis on the tuber of the corona treated group did not show any significant variation in the total flavonoid content and metabolite chromatogram pattern in comparison with that of the control groups and the reference groups. The experiment shows that the enhancement of the harvest of tuber of the tiger's milk mushroom is much more significant than the growth rate improvement of the mycelium of the same type of mushroom, as it was reported previously.
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| 10. |
- Izadi, M., et al.
(författare)
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Analytical fields expressions due to lightning channel considering variation of return stroke velocities along the lightning channel
- 2012
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Ingår i: Lightning Protection, (ICLP) 2012. - 9781467318976 ; , s. 6344252-
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Konferensbidrag (refereegranskat)abstract
- The return stroke velocity is an important factor for evaluation of lightning electromagnetic fields. Measurements showed that the return stroke velocity is varied at different heights along lightning channel while it is usually entered into field calculations with a constant value in previous studies. This paper presents the analytical electromagnetic fields expressions due to vertical lightning channel where velocity profile along channel is considered. The proposed fields expressions can be used to estimate electromagnetic fields directly in the time domain (without needing to apply any extra conversion to Frequency domain) whereas they are based on Heidler current function and can support widely used engineering current models. Likewise, the proposed field expressions are applied on a typical measured profile of velocity and also a function of velocity profile and the evaluated fields are compared to the corresponding simulated fields based on constant value of velocity and the results are discussed accordingly.
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