Wan Fatinhamamah Wan Ahmad

Numerical expressions in time domain for electromagnetic fields due to lightning channels

In this paper, by considering the factors that influence the charge height variation along the lightning channel and using Maxwells equations, general expressions in time domain for the evaluation of electromagnetic fields at an observation point are proposed. The lightning channel is assumed to be perpendicular to the ground surface and the ground conductivity is considered to be perfect. Our results showed that the proposed method has good agreement with the measured values, as we validated the outcome using fields measured at close and intermediate distances from the lightning channel. A set of general equations, which has the ability of evaluating any given channel base current function and current model in time domain is also derived.

Analytical Expressions for Electromagnetic Fields Associated with the Inclined Lightning Channels in the Time Domain

Abstract This article describes general analytical equations that are developed for the calculation of electromagnetic fields due to an inclined channel directly in the time domain. The input parameters of the model, angle of inclination of the lightning channel and the angle at the observation point can be varied through all possible values to produce the relevant electromagnetic fields. The proposed model is validated with eight electromagnetic waveforms measured at close range of the lightning channel. The results of the model show good agreement with the measured data. Furthermore, the proposed equations are compatible with different channel base current functions. The equations could easily be applied in the coupling models that calculate induced voltages in conductors in the presence of lightning-generated electromagnetic fields.

Recent statistics on lightning fatalities in Malaysia

It is a fact that Malaysia encounters more than 70% of power outages due to lightning and it is known as the “Crown of Lightning” in the world. The effects of lightning on electrical/communication networks and structures account for equipment damage, downtime/data losses and malfunctioning of control and automated systems that may cost the nation over RM 250 million and thousands of human injuries and deaths. Good statistics about death and injuries around the world are just beginning to be collected. This paper presents an update of the statistics on lightning fatalities in Malaysia and some comparisons with other countries around the world. In addition, a case study that accounts the geographical location, lightning detection data and distribution system layout will be presented.

Chemical enhancement materials for grounding purposes

It is an aim of this work in finding the best performed chemical enhancement material in order to provide the lowest impede path for fault currents to be dispersed into the earth in the shortest time possible. These fault currents are typically due to transients and they could be dangerous to the power system, equipment in it and the personnel involved with the system. Hence, it is desired that a grounding system is installed to provide such path to clear these fault currents from the power system in the manner that danger could be reduced. Such transients are generated by lightning, or switching action. Note that in this study, only lightning strike is considered. Lightning could create impulsive transient during its direct or indirect strikes to power system. This problem is normally prevented by installing a suitable grounding system to the power system. A grounding system will create a path for transient to be safely dispersed into the earth by providing lowest resistance path. This can be easily done using either natural or chemical enhancement materials. However, this work only reported the findings of having chemical enhancement materials in the vicinity of grounding system for protection against lightning. It is found that sodium chloride demonstrated the best performance in being enhancement material for earthing system on top of sodium thiosulphate, magnesium chloride, cuprum sulphate, and ammonium chloride.

Natural materials as grounding filler for lightning protection system

Grounding resistance could significantly reduce with the usage of grounding filler for grounding rod in lightning protection system. However, the cost of the normally used grounding fillers such as bentonite and other chemicals is the main drawback. Therefore, it is an aim of this study to determine the electrical properties and durability of natural grounding fillers as an alternative to bentonite. The 61.8% rule from the fall of potential method was used to obtain values of grounding resistance of the lightning protection system installed with natural grounding fillers such as bentonite, coconut coir peat, planting-clay soil and paddy dust. The measured grounding resistances were then compared with the grounding resistance of the reference grounding rod. Results revealed that natural materials especially planting-clay soil is the best alternative to replace bentonite as grounding filler because it gave the lowest grounding resistance values at the end of the experiment and had generally the highest percentage reduction in grounding resistance.

Investigate the effect of variations of ambient temperature on HST of transformer

Temperature, especially the hot spot temperature (HST) and top oil temperature (TOT), have played the most effective factor on the insulation life of the transformer. To determine HST and TOT, ambient temperature enter to equation that show the importance of ambient temperature on hot spot temperature of transformers, and Clause 7 (classic model) has been used as a standard thermal model in this research. In this article has been tried to show the effect of the variations of ambient temperature on a power transformer and at last has been compared by situation that the ambient temperature has been assumed constant.

Modeling of a ground wire using TLM

This work is aimed at developing electromagnetic modeling techniques to enable researchers to predict the behaviors of substation grounding system to lightning strikes using a 1-D transmission-line model. Several simulations have been done using 1-D TLM algorithm with two different injection impulses for comparison purpose. The method has been validated by contrasting with an algorithm based on a distributed model of an electrode where a good agreement was found. And, it is important for the selection of allowable one segment length of the 1-D transmission-line model to be less than 20% of its total length to produce reliable and accurate results of the transient responses.

Study on various excitation voltage effects to the transient responses of a single long horizontal ground conductor

This study is carried out to determine a suitable excitation source that can be used to model the lightning return stroke on a single long horizontal ground conductor. It is used to determine the fastest results obtained for the transient response of a single long horizontal ground conductor and for computation efficiency purposes. In this study, three various excitation sources are used and been compared to each other; that are derivative Gaussian, double exponential and one-cycle sinusoidal functions. The transient node voltages and transient node currents due to the lightning strike are obtained using TLM method. It is found that the derivative Gaussian excitation source demonstrates the fastest results compared to the other two. However, if a study is for observing the behaviour of lightning return stroke, a double exponential excitation source is more suitable.

Backflashover analysis for 132 kV Kuala Krai-Gua Musang transmission line

Lightning has been a major concern to the power system researchers because it can cause damage to the connected electrical equipment and transmission failure. One study carried out is that where the level of voltage at a substation is observed following a backflashover analysis on a transmission line. Sample of worst case transmission line was taken from Tenaga National Berhad, which is 132 kV Kuala Krai-Gua Musang line for the purpose of simulation using PSCAD software. An integral part of this study is the model of transmission line components such as insulator coordination gap flashover, tower model, nonlinear current dependent resistance as footing model. All models are verified by accurate analysis of previous researchers. Results were analyzed and influences of line parameters to backflashover rate were discussed. Practical recommendations and conclusions based on the results are made for an improvement in the lightning performance of high voltage transmission line.

Lightning hazard mitigation in Uganda

This paper addresses a concurrent burning issue in Uganda; the mitigation of rapidly increasing lightning hazards in the country. By analyzing various economic, technical and social factors a feasible hazard mitigation module has been proposed. The module essentially needs government intervention for providing facilities and coordination of various contributors and stakeholders for channeling expertise and possible funding. Several lightning disaster mitigation strategies have been proposed whereas practicality and limitations of applying them in Uganda are discussed in detail. Proposed modules are applicable in many countries having similar socio-economic environment.