Chandima Gomes | University of Witwatersrand, Johannesburg, South Africa (original) (raw)
Papers by Chandima Gomes
Reduction losses in three-phase transformers have drawn the attention of researchers, in the rece... more Reduction losses in three-phase transformers have drawn the attention of researchers, in the recent years. In this study, an intelligent algorithm employing particle swarm optimization (PSO) has been used to get the optimum T-joint design of a core in a three-phase transformer. This technique was employed to design a new geometry of a joint to obtain the minimum loss in a three-phase transformer. In achieving this target, a 3D finite element method had been used to simulate the proposed transformer model. Power losses in the core and winding losses had been considered as the heat sources, and the results were validated based on the test data obtained from transformer factory. The results presented that the total losses have been decreased up to 10% compared to the corresponding values from common designs. Moreover, the core losses have been reduced in the range of 11% compared to similar parameters in the conventional design.
This study examined the risk of lightning-related deaths and injuries in Malaysia between January... more This study examined the risk of lightning-related deaths and injuries in Malaysia between January of 2008 to July 2015. The majority of lightning-related injuries and fatalities occurred during the months of April and May. Most lightning related casualties reported in the statistics since 2008 occurred in the states of Melaka and Selangor in the western coastal belt. The majority of victims, were engaged in outdoor and sports activities when injured or killed by lightning incidents.
This paper presents a simulation study of a polluted insulator under a direct lightning impulse c... more This paper presents a simulation study of a polluted insulator under a direct lightning impulse current. The pollution condition was considered and divided into two cases which are partial and full pollution. Under those conditions, the electromagnetic profiles of the insulator were evaluated. In the study, six points of measurement recognised as the weak points of the insulator were introduced to be evaluated. Meanwhile the electric field and magnetic field values at the points were related to the common discharge and damage of polymer insulators. It was found that the pollution condition effectively influenced the electric field and magnetic field profile. A significant difference in the electric field value indicated at least 65.15 % in both cases. For the magnetic field, at least a 10.9 % percentage difference was recorded.
Lightning Surge protection of large structures is done under zonal concept due to the requirement... more 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 out-of-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 spacerestricted locations.
Environmental Engineering and Management Journal, 2015
It has been shown that the scale of damage in buildings with steel reinforcement, due to direct l... more It has been shown that the scale of damage in buildings with steel reinforcement, due to direct lightning strikes, is insignificantly small compared to lightning effects on buildings with no such steel reinforcement. Observed small-scale damages are also confined to points of strike; hence the only risk for occupants and properties is injury or damage caused by falling materials. A large number of such cases have been observed in Sri Lanka and Malaysia. All damaged structures, observed in this study, have a steel reinforcement structure, which may not be in compliance with specifications in IEC 62305-3, for it to act as the sole down conducting system. Such observation prompts us to reexamine specifications set forth in standards, which are difficult to be achieved in practice and also not applicable to buildings that have already been constructed. Existing recommendations prevent engineers from using steel reinforcement as the down conductor in many cases; a fact that leads to the addition of large amount of copper unnecessarily into the environment, non-installation of protection systems or adoption of non-conventional systems.
2018 IEEE 7th International Conference on Power and Energy (PECon)
A new prototype of a portable natural enhancement material resistivity meter was successfully des... more A new prototype of a portable natural enhancement material resistivity meter was successfully designed and constructed based on an existing soil resistivity meter. This portable natural enhancement material resistivity meter consists of four circuits, i.e. current generator, voltmeter, ammeter and display circuits, which these circuits needed to be compatible with each other to ensure the meter would be able to measure a correct resistivity of any material under test. Tremendous simulations were performed on each part of the four circuits to find the best suitable circuits that were compatible to each other to be constructed physically where a portable natural enhancement material resistivity meter could be made into its first prototype. Note that there are three types of material under tests involved in this work, i.e. soil, Bentonite and Zeolite, under three conditions, i.e. dry, mid-wet and highlywet. The prototype of a portable natural enhancement material resistivity meter is demonstrated to be perfectly working as the meter could be used to measure not only the soil resistivity but also resistivities of Bentonite and Zeolite too, which displayed higher resistivity values of dry specimens compared to the wet specimens.
2018 34th International Conference on Lightning Protection (ICLP), 2018
There are many methods that can be used in order to increase the performance of a grounding syste... more There are many methods that can be used in order to increase the performance of a grounding system meant for power system protection, i.e. by lowering its earth resistance values, which one of them is where soil could be treated using chemical or natural enhancement materials. This technique is one of the effective ways to improve the performance of a grounding system in which this work employed 15 kg Bentonite, and 3 kg Kenaf in powder and fibre forms as the natural enhancement materials for grounding systems at which they were either mixed or layered. The main purpose of conduction this work is to compare the performance of natural enhancement material mixture grounding systems to a Reference grounding system, which is without any enhancement material in the vicinity of the ground conductor. Fall-of-potential method was employed to measure earth resistance for the performances of the four grounding systems to be compared. After 60 days, their performances in descending order were Bentonite and Kenaf powder layered, Bentonite and Kenaf powder mixed, Bentonite and Kenaf fibre layered and Reference grounding systems. Hence, the grounding system with Bentonite and Kenaf powder layered is proposed to be the best to be used in order to reduce the earth resistance as it has the lowest earth resistance and able to stabilize faster compared to the other three grounding systems.
2016 33rd International Conference on Lightning Protection (ICLP), 2016
When a tower is struck by lightning, an induced voltage can generate in conducting objects within... more When a tower is struck by lightning, an induced voltage can generate in conducting objects within its vicinity. This phenomenon is due to the interaction between the electromagnetic field of the lightning with the object. The magnetic field is part of this field. Previous studies have shown that the magnetic field is affected by ground reflection coefficient factors that are usually taken as constants. However, the ground reflection coefficient factors have correlation with tower and ground impedance whereby the ground impedance can be determined based on soil resistivity and grounding system. This paper investigates the effect of soil resistivity on the value of magnetic field for a case of lightning strike on tall structures. Lightning current has been modelled accordingly and a set of equations is proposed to evaluate the magnetic field. Also, the effects of soil resistivity on the value of ground reflection coefficient factor consequently of the magnetic peak have been investigated. The results indicate that the magnetic field changes substantially with a variation of the soil resistivity. The magnetic field peak also has a strong correlation with the changes of soil resistivity as well as the fast front time of the channel base current. The outcome of the result of this paper will be beneficial to utility companies in determining the appropriate level of lightning protection since the magnetic field will be a result of induced voltage when have interaction with power lines.
2018 34th International Conference on Lightning Protection (ICLP), 2018
Oil palm is one of the largest crop industries in South East Asia, thus, it is of importance to u... more 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.
In sites with high soil resistivity such as deserts and mountainous terrains, designing and insta... more In sites with high soil resistivity such as deserts and mountainous terrains, designing and installing an effective grounding system is a challenging task. Therefore introduction of Bentonite into concrete mix of Ufer grounding at various proportions was done in a previous study and its steady state ground resistance performance was investigated. In that study, itwas found that 30% Bentonite-concrete mix is the optimum compound which yields the lowest average ground resistance with the least fluctuation as well. Subsequent study at site with high soil resistivity found that its performance is among the best compared with several conventional setups. In current work, such mix and the standard concrete mix were installed in five sites with varying soil resistivity to determine the correlation between ground resistance and localized soil resistivity. These correlations serve as a guide for future applications by engineers in designing grounding system using the best mix.
ARPN journal of engineering and applied sciences, 2016
Achieving low earth grid resistance is highly desirable in power distribution substations design.... more Achieving low earth grid resistance is highly desirable in power distribution substations design. However, due to variation of soil resistivity from one location to another, it is not possible to obtain the same value of low earth resistance at all locations. Changing earth conductor dimensions such as cross sectional area and length may lower earth resistance. In this paper, six different earth grid configurations have been used to study the effect of adding vertical earth rods to the grid periphery and at all grid conductor intersections of each configuration with the aim of reducing the overall grid resistance. Three grids were designed with compression ratio of 1, while the other three had a compression ratio of 0.8. Results indicated that for grids with compression ratio of 0.8 and with earth rods at all conductor intersections, the grid resistance was lower than those with a compression ratio of 1. It was also found that, the resistance of all grids with a compression ratio of...
A data set that supports the Paper on Effects of electrical stimulation on the yield of tuber of ... more A data set that supports the Paper on Effects of electrical stimulation on the yield of tuber of tiger's milk mushroom
Performance of deep driven Galvanized Iron (GI) electrodes encased in several backfill materials,... more Performance of deep driven Galvanized Iron (GI) electrodes encased in several backfill materials, which are freely available as industrial waste or at a low cost in many countries, were investigated over a period of 2-3 years. The best performing material, metal oxide powder (a waste product of the steel industry), was tested against several commercially available and traditionally used backfill materials. It was found that these industrial wastes reach the level of performance of commercially available backfill materials after several months. It was also found that the percentage of material erosion of GI due to corrosion in the presence of metal oxide powder is less than 1% after more than two years in contact. Lime and coke breeze also show good performance with respect to corrosion while commercially available natural Bentonite performs the best. Sodium Chloride, a backfill material that is widely used in South Asia, gave a highly undesirable outcome; the earth resistance of the...
Engineering in Agriculture, Environment and Food, 2019
The growth rate of mycelium of the tiger's milk mushroom (Lignosus rhinocerotis) at intermediate ... more 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.
Weather, Climate, and Society, 2018
Weather risk perception research lacks multihazard and transcultural datasets. This hypothesis-ge... more Weather risk perception research lacks multihazard and transcultural datasets. This hypothesis-generating study used a cognitive behavioral approach and Brunswik’s lens model for subjective risk parameters across eight countries. In Germany, Poland, Israel, the United States, Brazil, India, Malaysia, and Australia, 812 field interviews took place with a uniform set of 37 questions about weather interest, media access, elementary meteorological knowledge, weather fear, preparedness, loss due to weather, and sociodemography. The local randomized quota samples were strictly tested for sample errors; however, they cannot be considered representative for individual countries due to sample size and methodology. Highly rated subjective risks included flood, heat, tornado, and lightning. Weather fear was most prominent in the Malaysian sample and lowest in the German. Subjective elements were further explored with bivariate correlations and a multivariate regression analysis. Sociodemograph...
2016 33rd International Conference on Lightning Protection (ICLP), 2016
Fulgurites are natural tubes of glass formed by the fusion of silica sand or rock from a lightnin... more Fulgurites are natural tubes of glass formed by the fusion of silica sand or rock from a lightning strike. The fulgurites have been produced artificially in HV conditions in the past. Recent studies have found that fulguritic structures can be formed in some other materials, such as bentonite and cement, as well. These fulgurites can change the overall physical and electrical properties of the original materials. Thus, formation of fulgurites can modify the performance of electrical earthing systems, both ordinary and those improvised with backfill materials. This study investigates the fulgurite formation under alternating, direct and impulse current application. Bentonite and sand were tested under high voltage conditions. The type of fulgurites and their effects on electrical earthing systems were studied by analyzing the resistivity and permittivity of original materials and fulgurites. It has been found that fulgurites formation has a severe effect on the earth resistance of grounding systems.
Applied Mechanics and Materials, 2015
This paper is to study the effect of electric field on an angle variation of copper down-conducto... more This paper is to study the effect of electric field on an angle variation of copper down-conductor due to voltage and current transient. Down-conductor which informs of numerous material, shape and dimension are mandatory for diverting the lightning current from air termination system to the grounding system in sheltered building. Hence, a numerical analysis method is applied emulating the comprehensible and particular model according to ordinarily used in the manufacturer’s datasheet specification. A rigorous assessment in term of electric fields was reviewed in comparison with the critical breakdown value of air for a crucial study. Later, a foremost angle is proposed for the installation of down-conductor in order to achieve a reliable protection system.
Indonesian Journal of Electrical Engineering and Informatics (IJEEI), 2021
A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region wit... more A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region with a high lightning occurrence density. The surge protection was sought by implementing three metal-oxide surge arresters and an overhead ground wire. The purpose of these arresters is determined by their location in the circuit and the points that are vulnerable to adverse lightning effects: an arrester is installed to protect insulators between overhead lines and the supporting metallic mast, an arrester is installed to protect the point of contact between a stationary power supply wire and the train, and an arrester is installed to protect apparatus associated with the running tracks (return rail). An isolated earthing system is explored, and the effects of surge impedances and footing resistances are discussed. The voltage dropped across relevant vulnerable components and energy absorbed by the system components are determined by the simulation software Simulink. Lightning currents are injected into the system using Heidler function where the parameters comply with lightning protection standards. It is observed that the protection mechanisms defend susceptible components to a specified level. This demonstrates the success of the design in accordance with arrester protection levels (73.3 kV) and equipment withstand capabilities (a basic insulation level of 143 kV). This offers a protection margin of 95%. The largest percentage overshoot in the system is 39%, and this value is substantiated using reflection phenomena.
Machines
Installing surge protection devices in a hybrid photovoltaic (PV)–wind system is essential to gua... more Installing surge protection devices in a hybrid photovoltaic (PV)–wind system is essential to guarantee the survival of the system’s components. If the surge arresters are connected without taking into account the recommendations given by standards, the equipment to be protected might be damaged despite the energy coordination of the arresters. In this study, nonlinear surge protective devices (SPDs) are designed for a multi-MW hybrid system based on lightning protection standards with optimised threat level ratings to investigate the mitigation of lightning transients to an acceptable level. The system is implemented using Power System Computer-Aided Design for Electromagnetic Transients including Direct Current (PSCAD/EMTDC) software. It comprises a 2 MW PV farm, a 2 MW wind farm, and a backup energy storage system (ESS), which are all connected to a 132 kV grid via a step-up transformer and a transmission line. The results were obtained at critical system nodes for two standard l...
This paper deals with calculating the most probable position of the point of strike of a lightnin... more This paper deals with calculating the most probable position of the point of strike of a lightning ground flash when the angles to the strike point and the strength of the flash are given by two or more direction finding (DF) stations whose positions and instrumental uncertainties are known. In principal, DF station measurements are subject to both random and systematic errors. By assuming that there are no systematic errors and that the random errors can be represented by Gaussian distributions, a Monte Carlo simulation computer ...
Reduction losses in three-phase transformers have drawn the attention of researchers, in the rece... more Reduction losses in three-phase transformers have drawn the attention of researchers, in the recent years. In this study, an intelligent algorithm employing particle swarm optimization (PSO) has been used to get the optimum T-joint design of a core in a three-phase transformer. This technique was employed to design a new geometry of a joint to obtain the minimum loss in a three-phase transformer. In achieving this target, a 3D finite element method had been used to simulate the proposed transformer model. Power losses in the core and winding losses had been considered as the heat sources, and the results were validated based on the test data obtained from transformer factory. The results presented that the total losses have been decreased up to 10% compared to the corresponding values from common designs. Moreover, the core losses have been reduced in the range of 11% compared to similar parameters in the conventional design.
This study examined the risk of lightning-related deaths and injuries in Malaysia between January... more This study examined the risk of lightning-related deaths and injuries in Malaysia between January of 2008 to July 2015. The majority of lightning-related injuries and fatalities occurred during the months of April and May. Most lightning related casualties reported in the statistics since 2008 occurred in the states of Melaka and Selangor in the western coastal belt. The majority of victims, were engaged in outdoor and sports activities when injured or killed by lightning incidents.
This paper presents a simulation study of a polluted insulator under a direct lightning impulse c... more This paper presents a simulation study of a polluted insulator under a direct lightning impulse current. The pollution condition was considered and divided into two cases which are partial and full pollution. Under those conditions, the electromagnetic profiles of the insulator were evaluated. In the study, six points of measurement recognised as the weak points of the insulator were introduced to be evaluated. Meanwhile the electric field and magnetic field values at the points were related to the common discharge and damage of polymer insulators. It was found that the pollution condition effectively influenced the electric field and magnetic field profile. A significant difference in the electric field value indicated at least 65.15 % in both cases. For the magnetic field, at least a 10.9 % percentage difference was recorded.
Lightning Surge protection of large structures is done under zonal concept due to the requirement... more 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 out-of-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 spacerestricted locations.
Environmental Engineering and Management Journal, 2015
It has been shown that the scale of damage in buildings with steel reinforcement, due to direct l... more It has been shown that the scale of damage in buildings with steel reinforcement, due to direct lightning strikes, is insignificantly small compared to lightning effects on buildings with no such steel reinforcement. Observed small-scale damages are also confined to points of strike; hence the only risk for occupants and properties is injury or damage caused by falling materials. A large number of such cases have been observed in Sri Lanka and Malaysia. All damaged structures, observed in this study, have a steel reinforcement structure, which may not be in compliance with specifications in IEC 62305-3, for it to act as the sole down conducting system. Such observation prompts us to reexamine specifications set forth in standards, which are difficult to be achieved in practice and also not applicable to buildings that have already been constructed. Existing recommendations prevent engineers from using steel reinforcement as the down conductor in many cases; a fact that leads to the addition of large amount of copper unnecessarily into the environment, non-installation of protection systems or adoption of non-conventional systems.
2018 IEEE 7th International Conference on Power and Energy (PECon)
A new prototype of a portable natural enhancement material resistivity meter was successfully des... more A new prototype of a portable natural enhancement material resistivity meter was successfully designed and constructed based on an existing soil resistivity meter. This portable natural enhancement material resistivity meter consists of four circuits, i.e. current generator, voltmeter, ammeter and display circuits, which these circuits needed to be compatible with each other to ensure the meter would be able to measure a correct resistivity of any material under test. Tremendous simulations were performed on each part of the four circuits to find the best suitable circuits that were compatible to each other to be constructed physically where a portable natural enhancement material resistivity meter could be made into its first prototype. Note that there are three types of material under tests involved in this work, i.e. soil, Bentonite and Zeolite, under three conditions, i.e. dry, mid-wet and highlywet. The prototype of a portable natural enhancement material resistivity meter is demonstrated to be perfectly working as the meter could be used to measure not only the soil resistivity but also resistivities of Bentonite and Zeolite too, which displayed higher resistivity values of dry specimens compared to the wet specimens.
2018 34th International Conference on Lightning Protection (ICLP), 2018
There are many methods that can be used in order to increase the performance of a grounding syste... more There are many methods that can be used in order to increase the performance of a grounding system meant for power system protection, i.e. by lowering its earth resistance values, which one of them is where soil could be treated using chemical or natural enhancement materials. This technique is one of the effective ways to improve the performance of a grounding system in which this work employed 15 kg Bentonite, and 3 kg Kenaf in powder and fibre forms as the natural enhancement materials for grounding systems at which they were either mixed or layered. The main purpose of conduction this work is to compare the performance of natural enhancement material mixture grounding systems to a Reference grounding system, which is without any enhancement material in the vicinity of the ground conductor. Fall-of-potential method was employed to measure earth resistance for the performances of the four grounding systems to be compared. After 60 days, their performances in descending order were Bentonite and Kenaf powder layered, Bentonite and Kenaf powder mixed, Bentonite and Kenaf fibre layered and Reference grounding systems. Hence, the grounding system with Bentonite and Kenaf powder layered is proposed to be the best to be used in order to reduce the earth resistance as it has the lowest earth resistance and able to stabilize faster compared to the other three grounding systems.
2016 33rd International Conference on Lightning Protection (ICLP), 2016
When a tower is struck by lightning, an induced voltage can generate in conducting objects within... more When a tower is struck by lightning, an induced voltage can generate in conducting objects within its vicinity. This phenomenon is due to the interaction between the electromagnetic field of the lightning with the object. The magnetic field is part of this field. Previous studies have shown that the magnetic field is affected by ground reflection coefficient factors that are usually taken as constants. However, the ground reflection coefficient factors have correlation with tower and ground impedance whereby the ground impedance can be determined based on soil resistivity and grounding system. This paper investigates the effect of soil resistivity on the value of magnetic field for a case of lightning strike on tall structures. Lightning current has been modelled accordingly and a set of equations is proposed to evaluate the magnetic field. Also, the effects of soil resistivity on the value of ground reflection coefficient factor consequently of the magnetic peak have been investigated. The results indicate that the magnetic field changes substantially with a variation of the soil resistivity. The magnetic field peak also has a strong correlation with the changes of soil resistivity as well as the fast front time of the channel base current. The outcome of the result of this paper will be beneficial to utility companies in determining the appropriate level of lightning protection since the magnetic field will be a result of induced voltage when have interaction with power lines.
2018 34th International Conference on Lightning Protection (ICLP), 2018
Oil palm is one of the largest crop industries in South East Asia, thus, it is of importance to u... more 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.
In sites with high soil resistivity such as deserts and mountainous terrains, designing and insta... more In sites with high soil resistivity such as deserts and mountainous terrains, designing and installing an effective grounding system is a challenging task. Therefore introduction of Bentonite into concrete mix of Ufer grounding at various proportions was done in a previous study and its steady state ground resistance performance was investigated. In that study, itwas found that 30% Bentonite-concrete mix is the optimum compound which yields the lowest average ground resistance with the least fluctuation as well. Subsequent study at site with high soil resistivity found that its performance is among the best compared with several conventional setups. In current work, such mix and the standard concrete mix were installed in five sites with varying soil resistivity to determine the correlation between ground resistance and localized soil resistivity. These correlations serve as a guide for future applications by engineers in designing grounding system using the best mix.
ARPN journal of engineering and applied sciences, 2016
Achieving low earth grid resistance is highly desirable in power distribution substations design.... more Achieving low earth grid resistance is highly desirable in power distribution substations design. However, due to variation of soil resistivity from one location to another, it is not possible to obtain the same value of low earth resistance at all locations. Changing earth conductor dimensions such as cross sectional area and length may lower earth resistance. In this paper, six different earth grid configurations have been used to study the effect of adding vertical earth rods to the grid periphery and at all grid conductor intersections of each configuration with the aim of reducing the overall grid resistance. Three grids were designed with compression ratio of 1, while the other three had a compression ratio of 0.8. Results indicated that for grids with compression ratio of 0.8 and with earth rods at all conductor intersections, the grid resistance was lower than those with a compression ratio of 1. It was also found that, the resistance of all grids with a compression ratio of...
A data set that supports the Paper on Effects of electrical stimulation on the yield of tuber of ... more A data set that supports the Paper on Effects of electrical stimulation on the yield of tuber of tiger's milk mushroom
Performance of deep driven Galvanized Iron (GI) electrodes encased in several backfill materials,... more Performance of deep driven Galvanized Iron (GI) electrodes encased in several backfill materials, which are freely available as industrial waste or at a low cost in many countries, were investigated over a period of 2-3 years. The best performing material, metal oxide powder (a waste product of the steel industry), was tested against several commercially available and traditionally used backfill materials. It was found that these industrial wastes reach the level of performance of commercially available backfill materials after several months. It was also found that the percentage of material erosion of GI due to corrosion in the presence of metal oxide powder is less than 1% after more than two years in contact. Lime and coke breeze also show good performance with respect to corrosion while commercially available natural Bentonite performs the best. Sodium Chloride, a backfill material that is widely used in South Asia, gave a highly undesirable outcome; the earth resistance of the...
Engineering in Agriculture, Environment and Food, 2019
The growth rate of mycelium of the tiger's milk mushroom (Lignosus rhinocerotis) at intermediate ... more 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.
Weather, Climate, and Society, 2018
Weather risk perception research lacks multihazard and transcultural datasets. This hypothesis-ge... more Weather risk perception research lacks multihazard and transcultural datasets. This hypothesis-generating study used a cognitive behavioral approach and Brunswik’s lens model for subjective risk parameters across eight countries. In Germany, Poland, Israel, the United States, Brazil, India, Malaysia, and Australia, 812 field interviews took place with a uniform set of 37 questions about weather interest, media access, elementary meteorological knowledge, weather fear, preparedness, loss due to weather, and sociodemography. The local randomized quota samples were strictly tested for sample errors; however, they cannot be considered representative for individual countries due to sample size and methodology. Highly rated subjective risks included flood, heat, tornado, and lightning. Weather fear was most prominent in the Malaysian sample and lowest in the German. Subjective elements were further explored with bivariate correlations and a multivariate regression analysis. Sociodemograph...
2016 33rd International Conference on Lightning Protection (ICLP), 2016
Fulgurites are natural tubes of glass formed by the fusion of silica sand or rock from a lightnin... more Fulgurites are natural tubes of glass formed by the fusion of silica sand or rock from a lightning strike. The fulgurites have been produced artificially in HV conditions in the past. Recent studies have found that fulguritic structures can be formed in some other materials, such as bentonite and cement, as well. These fulgurites can change the overall physical and electrical properties of the original materials. Thus, formation of fulgurites can modify the performance of electrical earthing systems, both ordinary and those improvised with backfill materials. This study investigates the fulgurite formation under alternating, direct and impulse current application. Bentonite and sand were tested under high voltage conditions. The type of fulgurites and their effects on electrical earthing systems were studied by analyzing the resistivity and permittivity of original materials and fulgurites. It has been found that fulgurites formation has a severe effect on the earth resistance of grounding systems.
Applied Mechanics and Materials, 2015
This paper is to study the effect of electric field on an angle variation of copper down-conducto... more This paper is to study the effect of electric field on an angle variation of copper down-conductor due to voltage and current transient. Down-conductor which informs of numerous material, shape and dimension are mandatory for diverting the lightning current from air termination system to the grounding system in sheltered building. Hence, a numerical analysis method is applied emulating the comprehensible and particular model according to ordinarily used in the manufacturer’s datasheet specification. A rigorous assessment in term of electric fields was reviewed in comparison with the critical breakdown value of air for a crucial study. Later, a foremost angle is proposed for the installation of down-conductor in order to achieve a reliable protection system.
Indonesian Journal of Electrical Engineering and Informatics (IJEEI), 2021
A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region wit... more A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region with a high lightning occurrence density. The surge protection was sought by implementing three metal-oxide surge arresters and an overhead ground wire. The purpose of these arresters is determined by their location in the circuit and the points that are vulnerable to adverse lightning effects: an arrester is installed to protect insulators between overhead lines and the supporting metallic mast, an arrester is installed to protect the point of contact between a stationary power supply wire and the train, and an arrester is installed to protect apparatus associated with the running tracks (return rail). An isolated earthing system is explored, and the effects of surge impedances and footing resistances are discussed. The voltage dropped across relevant vulnerable components and energy absorbed by the system components are determined by the simulation software Simulink. Lightning currents are injected into the system using Heidler function where the parameters comply with lightning protection standards. It is observed that the protection mechanisms defend susceptible components to a specified level. This demonstrates the success of the design in accordance with arrester protection levels (73.3 kV) and equipment withstand capabilities (a basic insulation level of 143 kV). This offers a protection margin of 95%. The largest percentage overshoot in the system is 39%, and this value is substantiated using reflection phenomena.
Machines
Installing surge protection devices in a hybrid photovoltaic (PV)–wind system is essential to gua... more Installing surge protection devices in a hybrid photovoltaic (PV)–wind system is essential to guarantee the survival of the system’s components. If the surge arresters are connected without taking into account the recommendations given by standards, the equipment to be protected might be damaged despite the energy coordination of the arresters. In this study, nonlinear surge protective devices (SPDs) are designed for a multi-MW hybrid system based on lightning protection standards with optimised threat level ratings to investigate the mitigation of lightning transients to an acceptable level. The system is implemented using Power System Computer-Aided Design for Electromagnetic Transients including Direct Current (PSCAD/EMTDC) software. It comprises a 2 MW PV farm, a 2 MW wind farm, and a backup energy storage system (ESS), which are all connected to a 132 kV grid via a step-up transformer and a transmission line. The results were obtained at critical system nodes for two standard l...
This paper deals with calculating the most probable position of the point of strike of a lightnin... more This paper deals with calculating the most probable position of the point of strike of a lightning ground flash when the angles to the strike point and the strength of the flash are given by two or more direction finding (DF) stations whose positions and instrumental uncertainties are known. In principal, DF station measurements are subject to both random and systematic errors. By assuming that there are no systematic errors and that the random errors can be represented by Gaussian distributions, a Monte Carlo simulation computer ...
Additional information is available at the end of the chapter http://dx.doi.org/10.5772/58238 eff... more Additional information is available at the end of the chapter http://dx.doi.org/10.5772/58238 effect. However, this phenomenon becomes negligible as the frequency increases . Consequently, for frequencies above 10 GHz, other phenomena, such as rain and clouds, impose a serious impact on the signal attenuation . The oxygen and water vapor particles in space have a significant effect at higher signal frequencies [3].