397 research outputs found
Data for: EFFECTS OF ELECTRICAL STIMULATION ON THE YIELD OF TUBER OF TIGER’S MILK MUSHROOM
No full textA data set that supports the Paper on Effects of electrical stimulation on the yield of tuber of tiger’s milk mushroo
Distinct position of chaotic pulse trains observed in Malaysia
No full textThis paper presents the chaotic pulse train (CPT) waveforms of the vertical electric field generated by lightning observed in Malaysia. Focusing on the position where these electric field changes occur in a number of cloud to ground (CG) flashes, these CPTs were detected in different ways of occurrences, durations, intensities and amplitudes. Seventy-six chaotic pulse trains were found in this study from a sum of 172 CG flash records from three thunderstorm days. The fast field antenna was employed to do the field measurements. As opposed to the typical occurrence of chaotic pulse trains prior to subsequent strokes as reported in the literature, this study has found chaotic pulse trains occurring in different places along the CG electric field waveforms
Lightning environment in Burundi
No full textThis paper presents preliminary studies on the lightning accident details in Burundi, a landlocked country in East Africa. The reported lightning incident record in 2012 and 2013 depicts that there are 52 human deaths, 94 human survivals with injuries and 40 deaths of livestock. Makamba province recorded the highest human casualties with 14 deaths and 69 injuries whereas Nyanza-Lac commune of the same province topped the list with 8 deaths and 52 injuries. The statistics do not justify the 1:10 ratio of death : injury as it is reported in USA. The statistics may be a gross underestimation as many lightning accidents are not reported due to lack of communication, especially in the rural areas. Gomes-Kadir equation estimates the death rate as 52 per year, a figure twice as high as that was observed in this study. The analysis of information for incidents over few more years reveals that seeking shelter under ungrounded metal-roofed buildings is extremely dangerous as multiple deaths may occur in the event of a lightning strike to the roof
Lightning incidents in Mongolia
Get PDFThis is one of the first studies that has been conducted in Mongolia on the distribution of lightning incidents. The study covers a 10-year period from 2004 to 2013. The country records a human death rate of 15.4 deaths per 10 million people per year, which is much higher than that of many countries with similar isokeraunic level. The reason may be the low-grown vegetation observed in most rural areas of Mongolia, a surface topography, typical to steppe climate. We suggest modifications to Gomes–Kadir equation for such countries, as it predicts a much lower annual death rate for Mongolia. The lightning incidents spread over the period from May to August with the peak of the number of incidents occurring in July. The worst lightning affected region in the country is the central part. Compared with impacts of other convective disasters such as squalls, thunderstorms and hail, lightning stands as the second highest in the number of incidents, human deaths and animal deaths. Economic losses due to lightning is only about 1% of the total losses due to the four extreme weather phenomena. However, unless precautionary measures are not promoted among the public, this figure of losses may significantly increase with time as the country is undergoing rapid industrialization at present
Analysis of ground potential distribution under lightning current condition
No full textThe grounding system of a lightning protection scheme is designed basically to avoid arcing and
dangerous step potentials. The grounding impedance of the system varies depending on soil structure and frequency. This paper describes the effect of harmonic impedance (also called frequency dependence of soil) on potential distribution under lightning strike to a metal tower with single grounding path, for different soil types. The results show that the peak value of ground potential rise (GPR) and step voltage (SP) may reach extremely hazardous values even at distances in the order of 90 m from the tower footing, especially when soil resistivity is high. Hence, we emphasise that, in contrast to power grounding, when designing of grounding systems that are meant to handle transient or high frequency currents as well, the frequency dependent soil parameters should be considered to avoid hazardous situations, especially at locations with a high probability of lightning strikes such as metal towers
Estimating Resistance and Performance of Earthing Systems Electrode in Variably Saturated Soil Conditions
No full textA research report submitted in fulfillment of the requirements for the Doctor of Philosophy in Engineering, In the Faculty of Engineering and the Built Environment , School of Electrical and Information Engineering, University of the Witwatersrand, Johannesburg, 2024The design and determination of post-installed resistance of earthing systems are significantly influenced by subsoil resistivity profiles, which are prone to seasonal variations due to environmental and climatic changes. These fluctuations can compromise operational safety and reliability of transmission systems, necessitating periodic monitoring of earthing installations as recommended by national and international standards. However, compliance with these recommendations is often impractical due to the vast number of earthing installations and associated costs. To address this challenge, this thesis proposes a novel multiphysics earthing model that integrates hydraulic and electrical properties of subsoil and earthing enhancement materials (EEMs) with climatic parameters to predict earthing resistance under varying conditions. The model, developed by coupling partial differential equations governing electric current dispersion and fluid retention in porous media, is validated through COMSOL Multiphysics® simulations of vertical earth rods in single and double subsoil layers. The results demonstrate that earthing resistance variation is dependent on subsoil texture, water content, and distribution of soil water potential, which determines subsoil resistivity. The proposed method achieves a relative error range of 2.72% to 6.53% and 1.47% compared to analytical and finite element method solutions, ensuring accuracy and validity. This innovative approach enables site-specific and climate-adaptive assessments of EEM effectiveness, facilitating informed decisions for earthing improvements in diverse conditions, and ultimately optimising material selection and recommendation for various soils and climates.Eskom High Voltage Centre for ExcellenceMM202
Modifications proposed to the concepts of structural protection
Get PDFIn this paper we show that the scale of damage in buildings with steel reinforcement, due to direct lightning strikes, is insignificantly small compared to the lightning effects on buildings and structures with no such steel reinforcement. The observed small-scale damages are also confined only to the point of strike. A large number of such cases have been observed in Sri Lanka and Malaysia. The fact that almost all these damaged structures, observed in this study, have a steel reinforcement structure, but not verified to be in compliance with the specifications in lEC 62305-3 (2006) for it to act as down conducting system, prompted us to re-think regarding the specifications. Such specifications are difficult to be achieved in practice and also not applicable to buildings that have been already constructed. The recommendations prevents the engineers from using the steel reinforcement as the down conductor in many cases; a fact that leads to either non-installation of LP systems or adopting non-conventional systems which are convenient to be installed. In both cases, a noteworthy advantage that could have obtained by using the steel reinforcement is lost. Use of the steel reinforcement as the down conducting system, which is integrated to a properly designed air-termination system could have prevented even the small-scale damage occurred at the attachment point. Hence, we strongly recommend revising the relevant recommendations in the standards so that a mass public will be benefited. In the absence of such relaxation of the existing guidelines the manufacturers and proponents of nonconventional lightning protection systems enjoy an undue advantage in promoting their technology
A tutorial on the selection and installation of surge protection devices in a TT wiring system
Get PDFThis paper provides an easy-to-understand guidance for the selection and installation of transient protection devices, especially in a TT wiring system. Several fringe issues with respect to surge protection have also been discussed. The information presented can be used as educational material that guides electrical engineers in addressing lightning protection issues of LV power systems and ELV signal systems. A number of real life examples and survey outcomes that reflect misinterpretation of standards and scientific practices, gathered in the South Asian region have also been discussed
On the selection and installation of surge protection devices in a TT wiring system for equipment and human safety
Get PDFThis paper provides a comprehensive guidance for the selection and installation of transient protection devices, especially in a TT wiring system with the aim of safeguarding both the equipment concerned and the operators and users of equipment. A number of core and fringe issues with respect to surge protection have been discussed in details with the view of developing high level of electrical safety practices among engineers. The information presented can also be used as educational material that guides electrical engineers in addressing lightning protection issues of LV power systems and ELV signal systems. A number of real life examples and survey outcomes that reflect misinterpretation of standards and scientific practices, gathered in the South Asian region have also been discussed
Reducing water absorption characteristics of kraft paper reinforced with modified nanoparticles
No full textA thesis submitted in partial fulfilment of the requirements for the degree Doctor of Philosophy to the Faculty of Engineering and the Built Environment, School of Electrical and Information Engineering, University of the Witwatersrand, Johannesburg, 2023The inherent hydrophilic characteristics of cellulose wood fibre compromise the dielectric properties of kraft paper insulation that is used mainly in oil-insulated power transformers. This thesis, therefore, presents a novel material design model of nanocomposite kraft paper with improved hydrophobic properties for power transformer insulation applications. The concept of nanodielectric kraft paper design was used. Rutile-titanium dioxide nanoparticles (rutile-TiO2 NPs) were selected as the nanofiller. Compared with other metal-oxides, rutileTiO2 NPs are stable in chemical reactions, have good thermal stability and also have high electrical resistivity. Rutile-TiO2 of 19.72 nm diameter were fabricated using the sol-gel method and then used in reinforcing the kraft paper to produce a nanocomposite kraft paper with improved dielectric properties. Since the nanoparticles are inherently hydrophilic, and the intention is to produce a hydrophilic nanocomposite kraft paper, a technique was devised to make the NPs hydrophobic. The rutile-TiO2 NPs were surface conditioned with two alternative surfactants; Alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). Various quantities of the two surfactants were investigated to determine the optimal amount. The resultant surface-modified rutile-TiO2 NPs were studied to understand their hydrophilicity and thermal stability properties. It was found that the unmodified rutile-TiO2 NPs absorbed more moisture, compared with the surface-modified nanofiller, the mass increased by about 4% due to moisture absorption. The surface-modified rutile-TiO2 NPs with 5% AKD had 45% more thermal resilience than the unmodified rutile-TiO2 NPs surface and this is a significant knowledge contribution of this thesis. Using an unbleached kraft pulp, nanocomposite kraft paper specimens were fabricated with nanoparticles having varying surfactant loading. The specimens were then characterized to reveal various critical properties such as hydrophobicity, thermal, dielectric losses and dielectric strength. The version of the nanocomposite kraft paper that gave the most improved water and moisture absorption properties was that with 5vol/vol% ASA surface-modified NPs. The moisture absorption rate dropped by 74% compared to the unfilled kraft paper, and the water vapor transmission rate decreased by 30%. The contact angle of water droplets improved by 12%, and water absorption rate improved by being 4 times slower. The dielectric loss measurements showed that the nanocomposite kraft paper containing rutile-TiO2 NPs (5 vol/vol% ASA) also had 40% lower dielectric losses than the reference (unfilled) samples. The breakdown voltage of the nanocomposite kraft paper increased by about 15% while thermal withstand was improved by 5.4%. This research, therefore, has successfully improved the hydrophobic properties of kraft paper by filling it with surface-modified rutileTiO2 NP. It can be argued from the results that for power transformer application, the novel nanocomposite kraft paper developed in this thesis will improve power transformer insulation reliability design by mitigating the main agents of insulation degradation which are water and thermal stress.Tertiary Education Trust Fund (TetFund)TL (2024
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