Lightning accidents in Nigeria: with special attention to aviation mishaps

Lightning related accidents in Nigeria, a country of high lightning density, have been collected and analyzed. Results show that lightning related human injuries and deaths are very high in Nigeria, where the actual figure may reach as high as 500 deaths per year. However, due to the social stigma attached to lightning incidents and the lack of unbroken news chains reaching media, collection of accurate statistics has become a daunting task. Apart from human and livestock related hazards; property damage is also of high concern due to probable devastating consequences of such incidents. Extra attention has been paid on collecting damage records related to aviation industry as there are several serious accidents related to lightning have been reported in this area. The data collected and analysed is used to develop a set of national level recommendations for lighting safety and protection which can also be applicable in neighbouring countries, as they also experience extremely high lightning occurrence density

Reduction of earth grid resistance by addition of earth rods to various grid configurations

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 0.8 were lower than those with a compression ratio of 1

Preliminary results of the performance of grounding electrodes encased in bentonite-mixed concrete

Earth resistance of buried steel cages, encased in bentonite mixed concrete has been investigated. A reference pit was constructed with steel cage encasing in ordinary concrete. The land mass of the site has somewhat uniform surface soil resistivity which is in the range of 100 Ωm. The performance of earth resistance in each electrode has been measured for five months. The results show that for the first month, the lowest earth resistance and the highest decrement in earth resistance are shown by the pit with concrete having 20% bentonite. However, for the following four months, pits with bentonite mixed concrete showed increased earth resistance compared to the reference pit. These results indicate that the long-term reduction in earth resistance in electrodes encased with bentonite, as observed in previous studies, is not the case with electrodes embedded in bentonite mixed concrete. The initial reduction of earth resistance observed at pits with bentonite mixed concrete may most probably be due to the presence of hydrated bentonite which is not mixed with other constituents of concrete. Other than the pits with 20% and 70% bentonite, the outcome of this research thus far reaffirms the capability of concrete blocks to maintain earth resistance with small fluctuation

Impact of energization current on the safe design of distribution substation earth grid

Energization current is a fundamental consideration in designing of distribution substation earth grid. Arbitrary choice of energization current in earth grid design process may lead to technical and economic implications resulting in underestimated or overestimated designs. In this paper, a distribution substation earth grid was designed using SESCAD and executed in MALT module of CDEGS. The energization current was varied by 100, 75, 50 and 25% of the short circuit current available at the secondary terminals of the upstream transformer to determine the impact on safety criteria of the earth grid. Results indicated that, the EPR for 100% fault current was higher, whereas the step and touch voltages were lower. Also, compared to the other cases of short circuit currents, there was no difference in step and touch voltages when the energization currents were varied at 75, 50 and 25%

Design of distribution substation earth grid in high resistivity soil using CDEGS

Design of distribution substation earthing grid can be very challenging in high resistivity soils especially in two layer soils where the top layer resistivity is lower than the bottom layer. This paper presents the design of a distribution substation earth grid using Current Distribution Electromagnetic Field Grounding Soil Structure Analysis Software (CDEGS). Soil resistivity measurement was carried out at the substation site using a 4-pole Megger earth tester based on Wenner method. The soil structure was determined using RESAP module, while the design was implemented using SESCAD and executed by MALT module. Results indicated a slight reduction of earth grid resistance, 0.6%, 5.8% and 6.5%, respectively as the grid burial depth was varied from 0.5m to 1.5m in steps of 0.5m. The touch and step voltages were found to be lower when surface layer material was not applied and higher when surface layer materials of 3000Q-m and 5000Q-m resistivity were interchangeably applied on the grid surface. It was also found that, the calculated earth grid resistance from IEEE Std. 80-2000 equation was lower than the grid resistance computed by MALT

Effect of earth grid conductor spacing on the safety criteria of substation earthing

Site dependent parameters such as soil resistivity, maximum grid current, fault duration, shock duration, surface layer material resistivity, and grid geometry have substantial impact on the design and performance of an earth grid. The grid geometry, i.e. the area occupied by the grid system, conductor spacing and the depth of burial of earth grid specifically have much impact on the mesh, step, touch voltage and earth potential rise, while parameters such as the conductor diameter and the thickness of the surfacing material have less impact on the safety criteria. In this paper, a distribution substation earth grid was designed using the CDEGS software by varying the spacing between grid conductors (compression ratio) from 1 to 0.5 in steps of 0.1. The safety criteria were studied under three scenarios, without surface layer material, with surface layer material of resistivity 3000Ω-m, and surface layer material of resistivity 5000Ω-m. Results indicated that the grid resistance and earth potential rise were lower for a compression ratio 0.9, while the step and touch voltages were found to be similar for each case of surface layer material

Effects of naturally-produced lovastatin on feed digestibility, rumen fermentation, microbiota and methane emissions in goats over a 12-week treatment period

Twenty male Saanen goats were randomly assigned to four levels of lovastatin supplementation and used to determine the optimal dosage and sustainability of naturally produced lovastatin from fermentation of palm kernel cake (PKC) with Aspergillus terreus on enteric methane (CH4) mitigation. The effects on ruminal microbiota, rumen fermentation, feed digestibility and health of animal were determined over three measuring periods (4-, 8- and 12-weeks) and the accumulation of lovastatin in tissues was determined at the end of the experiment. The diets contained 50% rice straw, 22.8% concentrates and 27.2% of various proportions of untreated or treated PKC to achieve the target daily intake level of 0 (Control), 2, 4 or 6 mg lovastatin/kg body weight (BW). Enteric CH4 emissions per dry matter intake (DMI), decreased significantly (P<0.05) and equivalent to 11% and 20.4%, respectively, for the 2 and 4 mg/kg BW groups as compared to the Control. No further decrease in CH4 emission thereafter with higher lovastatin supplementation. Lovastatin had no effect on feed digestibility and minor effect on rumen microbiota, and specifically did not reduce the populations of total methanogens and Methanobacteriales (responsible for CH4 production). Similarly, lovastatin had little effect on rumen fermentation characteristics except that the proportion of propionate increased, which led to a decreasing trend (P<0.08) in acetic: propionate ratio with increasing dosage of lovastatin. This suggests a shift in rumen fermentation pathway to favor propionate production which serves as H+ sink, partly explaining the observed CH4 reduction. No adverse physiological effects were noted in the animals except that treated PKC (containing lovastatin) was less palatable at the highest inclusion level. Lovastatin residues were detected in tissues of goats fed 6 mg lovastatin/kg BW at between 0.01 to 0.03 μg/g, which are very low

Reduction of earth resistance by application of chemical and natural materials

Earthing systems provide continuous and conductive electrical path to the ground for dissipation of fault currents, lightning transient charges and ensures the safety of humans against contact with energised circuits and systems. Earthing systems also provide a zero signal reference for electronic systems and ensures reliable operation of power system both under normal and fault conditions. Local and international earthing standards have recommended minimum values of earth resistance required for earthing systems to provide adequate protection. However, it is difficult to achieve low earth resistance in ordinary soil conditions due to variation of soil resistivity from one location to the other. Hence, the objective of this study is to determine the performance of chemical and natural materials for reduction of earth resistance of vertically installed earth electrodes. A combined experiment based on soil enhancement and electrode enhancement was conducted in UPM, Serdang, Selangor, Malaysia (Latitude 2.990 N, longitude 101.710 E). The experiment based on soil enhancement was installed by driving five earth electrodes made of solid copper into the soil to a depth of 1.4m separated at intervals of 3m from each other. Five circular trenches of dimension 0.2m wide by 0.15m deep were dug around each of the earth electrodes for placement of 10kg each of chemical materials such as sodium chloride, sodium thiosulphate, magnesium chloride, calcium chloride and calcium-magnesium carbonate (dolomite) in separate trenches. The experiment based on electrode enhancement was installed by drilling five holes with dimension of 0.13m diameter and 1.5m deep which were each filled with different natural materials such as palm kernel fibre, kenaf fibre, paddy dust (rice husk),bentonite and Sungai Besar Marine Clay and compacted. Five earth electrodes made of solid copper were driven at the centre of each hole to a depth of 1.4m. Another earth electrode was installed without any enhancement material around it as a reference. All copper earth electrodes used were of similar dimensions of 0.013m diameter and 1.5m length. For all 11 earthing installations, 0.1m length of the earth electrode was allowed above grade for clamping of earth resistance meter. Plastic earth chambers were placed on all earthing installations to serve as inspection boxes. Earth resistance measurement was conducted using 3-point fall of potential method on daily basis for a period of one year using a Megger Digital Earth Tester, model DET3TC. After 365 days, results of earth resistance measurements indicated that the earth resistances have reduced from their initial values by 78.30%, 74.65%, 68.61%,64.49%, and 29.16%, for sodium chloride, calcium chloride, magnesium chloride,sodium thiosulphate, and calcium-magnesium carbonate installations, respectively when compared to the reference installation. Similarly, earth resistance for bentonite,palm kernel fibre, Sungai Besar Marine Clay, kenaf fibre and paddy dust (rice husk) installations over the same period have reduced by 56.43%, 34.65%, 17.32%, 16.81% and 2.92%, respectively. It is concluded from the study that chemical materials are a better choice for reduction of earth resistance compared to natural materials. The cost of installing earthing systems with natural materials is averagely 65% cheaper than earthing systems with chemical materials. In terms of installation technique, earthing systems with chemical materials are easier to install as earthing systems with natural materials require more equipment and operators during the installation process. It is also easier and cheaper to maintain earthing systems with chemical materials. Considering the impact on environment, the study did not reveal any effect from the two installations as the grasses germinated at the same rate and maintained similar colour. The only discolouration of grass that was observed is specifically at water logged spots

Mitigating the anthropogenic global warming in the electric power industry

One of the most current and widely discussed factors that could lead to the ultimate end of man's existence and the world at large is global warming. Global warming, described as the greatest environmental challenge in the 21st century, is the increase in the average global air temperature near the surface of the Earth, caused by the gases that trap heat in the atmosphere called greenhouse gases (GHGs). These gases are emitted to the atmosphere mostly as a result of human activities, and can lead to global climate change. The economic losses arising from climate change presently valued at $125 billion annually, has been projected to increase to$600 billion per year by 2030, unless critical measures are taken to reduce the spate of GHG emissions. Globally, the power generation sector is responsible for the largest share of GHG emissions today. The reason for this is that most power plants worldwide still feed on fossil fuels, mostly coal and consequently produce the largest amount of CO2 emitted into the atmosphere. Mitigating CO2 emissions in the power industry therefore, would significantly contribute to the global efforts to control GHGs. This paper gives a brief overview of GHGs, discusses the factors that aid global warming, and examines the expected devastating effects of this fundamental global threat on the entire planet. The study further identifies the key areas to mitigate global warming with a particular focus on the electric power industry

Impact of split factor value on the safe design of distribution substation earth grid

Split factor is a fundamental consideration when designing a distribution substation earth grid. Arbitrary choice of split factor in earth grid design process may lead to technical and economic implications resulting in underestimated or overestimated designs. In this paper, a distribution substation earth grid was designed using SESCAD and executed in MALT module of CDEGS. The energization current was varied by 100%, 75%, 50% and 25% of the short circuit current available at the secondary terminals of the upstream transformer to determine the impact on safety criteria of the earth grid. Results indicated that, the EPR for 100% fault current was higher, whereas the step and touch voltages were lower. It was also revealed that, there was no difference in step and touch voltages when energization current was set at 75%, 50% and 25%