M.Phil. / Nearly every reference document, national and international standard, text book or web page discussing the topic of Power Quality has an introduction that refers to the demand from customers and regulators for better and more detailed reporting from electrical power utilities with regards power quality. Previously power quality was an internal utility measure with no external input. Today contracts are negotiated with customers and limits are set by regulators with regards Power Quality objectives. Current assessment methods defined in various international guidelines and standards recommend that for a “high percentage” of the assessment period, the measured performance must remain below specified levels (“compatibility levels” or contracted levels). In the case of NRS048-2:2008 the assessment criterion for voltage harmonics and voltage unbalance is based on 95% of the time and 95% of the space for an assessment period of 1 week, and that for voltage magnitude is based on 95% of the time and 95% of the space, with the additional requirement that no two consecutive values exceed the specified levels. A statistical research study was undertaken to analyse the performance of the Eskom transmission system in order to determine the impact of using different assessment methods (100% of the week, 99% of the week, 95% of the day etc). This thesis will present the results of the analysis done on the data in the Quality of Supply database. The analysis will mainly focus on the voltage waveform parameters: harmonic THD; unbalance; and regulation as measured in the Eskom Quality of Supply database. The objective of this thesis is to determine how the current performance of an electrical transmission network is characterised by different assessment methods. This thesis makes a contribution to the current international debate on appropriate assessment criteria and the conditions (“normal” vs. “abnormal”) under which these would apply.

Atualmente, a intensidade de campo elétrico, campo magnético e campo eletromagnético é um fator determinante não só para a implantação de novas instalações, mas também, para as instalações existentes no sistema elétrico. Apesar de não existir nenhum estudo conclusivo que comprove a evidência direta entre a exposição a estes campos e os efeitos nocivos na saúde das pessoas, muitos países, inclusive o Brasil, definiram em suas legislações limites básicos à exposição de campos elétrico e magnético provenientes dos sistemas elétricos. Este trabalho tem como objetivo contribuir para análise de campo magnético de linhas subterrâneas de alta tensão existentes ou linhas em fase inicial de projeto, visando atender os limites de exposição vigentes na legislação local. Nele é apresentada a metodologia de cálculo de campo magnético baseada na Lei de Biot-Savart e no princípio da superposição. Estudos analíticos para verificação da influência dos parâmetros de instalação e elétricos de linhas sobre o campo magnético são apresentados para linhas subterrâneas de alta tensão compostas por um e dois circuitos com diferentes tipos de instalação e aterramentos. Comparações entre valores analíticos e valores de medições de campo magnético de linhas subterrâneas de alta tensão existentes em operação também são abordadas neste trabalho. As principais técnicas de mitigação de campo magnético utilizadas em linhas subterrâneas de alta tensão, tais como técnicas de compensação envolvendo laços de cabos e técnicas de blindagens com materiais metálicos externos aos cabos, também são apresentadas. Devido ao campo elétrico externo ao cabo isolado ser praticamente zero, assuntos referentes a este campo não são abordados neste trabalho. Por simplicidade, campo magnético refere-se à densidade de fluxo magnético neste documento. / Nowadays, the intensity of electric field, magnetic field and electromagnetic field is a determining factor, not only for implantation of new installations, but also for existing installations in the power system. Although no exist conclusive study that proves the direct evidence between exposure to these fields and adverse effects on human health, many countries, including Brazil, have defined in their laws basic limits for exposure to electric and magnetic fields produced by the electric system. This work aims to contribute to analysis of magnetic field for both existing high voltage underground lines and lines in initial stage of project, aiming the actual exposure limits of the local legislation. In it, is shown the magnetic field calculation methodology based on the Biot-Savart\'s law and the superposition principle. Analytical studies to verify the influence of installation and electrical parameters of lines on the magnetic field are presented for high voltage underground lines consist of one and two circuits with different types of installation and earthing. Comparisons between analytical and measurement values of magnetic field of existing high voltage underground lines in operation are also addressed in this work. The main mitigation techniques of magnetic field used in high voltage underground lines, such as compensation techniques by loop of cables and shielding by metallic materials, are also presented. Due the electric field outside the insulated cable be practically zero, issues related to the electric field are not addressed in this work. For simplicity, the magnetic field refers to the magnetic flux density in this document.

Atualmente, a intensidade de campo elétrico, campo magnético e campo eletromagnético é um fator determinante não só para a implantação de novas instalações, mas também, para as instalações existentes no sistema elétrico. Apesar de não existir nenhum estudo conclusivo que comprove a evidência direta entre a exposição a estes campos e os efeitos nocivos na saúde das pessoas, muitos países, inclusive o Brasil, definiram em suas legislações limites básicos à exposição de campos elétrico e magnético provenientes dos sistemas elétricos. Este trabalho tem como objetivo contribuir para análise de campo magnético de linhas subterrâneas de alta tensão existentes ou linhas em fase inicial de projeto, visando atender os limites de exposição vigentes na legislação local. Nele é apresentada a metodologia de cálculo de campo magnético baseada na Lei de Biot-Savart e no princípio da superposição. Estudos analíticos para verificação da influência dos parâmetros de instalação e elétricos de linhas sobre o campo magnético são apresentados para linhas subterrâneas de alta tensão compostas por um e dois circuitos com diferentes tipos de instalação e aterramentos. Comparações entre valores analíticos e valores de medições de campo magnético de linhas subterrâneas de alta tensão existentes em operação também são abordadas neste trabalho. As principais técnicas de mitigação de campo magnético utilizadas em linhas subterrâneas de alta tensão, tais como técnicas de compensação envolvendo laços de cabos e técnicas de blindagens com materiais metálicos externos aos cabos, também são apresentadas. Devido ao campo elétrico externo ao cabo isolado ser praticamente zero, assuntos referentes a este campo não são abordados neste trabalho. Por simplicidade, campo magnético refere-se à densidade de fluxo magnético neste documento. / Nowadays, the intensity of electric field, magnetic field and electromagnetic field is a determining factor, not only for implantation of new installations, but also for existing installations in the power system. Although no exist conclusive study that proves the direct evidence between exposure to these fields and adverse effects on human health, many countries, including Brazil, have defined in their laws basic limits for exposure to electric and magnetic fields produced by the electric system. This work aims to contribute to analysis of magnetic field for both existing high voltage underground lines and lines in initial stage of project, aiming the actual exposure limits of the local legislation. In it, is shown the magnetic field calculation methodology based on the Biot-Savart\'s law and the superposition principle. Analytical studies to verify the influence of installation and electrical parameters of lines on the magnetic field are presented for high voltage underground lines consist of one and two circuits with different types of installation and earthing. Comparisons between analytical and measurement values of magnetic field of existing high voltage underground lines in operation are also addressed in this work. The main mitigation techniques of magnetic field used in high voltage underground lines, such as compensation techniques by loop of cables and shielding by metallic materials, are also presented. Due the electric field outside the insulated cable be practically zero, issues related to the electric field are not addressed in this work. For simplicity, the magnetic field refers to the magnetic flux density in this document.

Secure operation of electric power grids fundamentally relies on their dynamical stability properties. For the third-order model, a paradigmatic model that captures voltage dynamics, three routes to instability are established in the literature: a pure rotor angle instability, a pure voltage instability, and one instability induced by the interplay of both. Here, we demonstrate that one of these routes, the pure voltage instability, requires infinite voltage amplitudes and is, thus, nonphysical. We show that voltage collapse dynamics nevertheless exist in the absence of any voltage instabilities.

Transformers are the most expensive and critical asset in any electrical power network. Their failure results in long interruption of power supply with consequent loss of reliability and revenue. Understanding and detection of the failure mechanism helps in avoiding catastrophic failures, unplanned outages and improving the power system reliability. Oil impregnated paper (OIP) and pressboards form the main soild insulation in a transformer. Life of the transformer is governed mostly by the life of OIP insulation. Until recently, it was thought that ageing of the OIP insulation in power transformer and its eventual failure, is mainly a function of temperature and electrical stresses. However, it has now been realized that the moisture causes rapid degradation of OIP and needs a special attention. Considering its practical relevance, this research program was formulated with goals: (i) to study the ageing of OIP insulation under temperature and moisture stresses, (ii) to seek correlation between diagnostic ageing indices and end-of-life (EOL) and (iii) to develop a life model for OIP considering moisture along with the thermal stress. Observing that working with actual transformers or even the prototypes are rather inordinately expensive, experiments were conducted with paper strips immersed in oil in test tubes with paper to oil ratio kept same as that in power transformers. In order to cater for the statistical nature of the phenomena, adequate numbers of test specimens were employed (25 numbers for each experiment). Experiments were conducted for two years at temperatures 90°C, 110°C & 120°C and moisture 1%, 2% & 3%. Following the literature, the degree of polymerization (DP) was chosen as the primary index for ageing. As measurement of DP is not only destructive, but also impractical on most of the working transformers, with an aim to develop suitable diagnostic indices for ageing, 2-furfural (2-FAL) and oxides of carbon (CO and CO2) were also measured. Empirical relation between ageing and amount of stresses and time have been deduced for the relevant range. Limiting value of these indices to prescribe the end-of-life, as well as, their correlation with DP have been worked out and reported. In order to bring the role of moisture explicitly, based on earlier work on multi-stress ageing, a multiplicative power law supplementing the Arrhenius factor is envisaged. Accordingly, a phenomenological combined stress model involving the time to failure, temperature, and moisture content is deduced. Based on the experimental results, this model is statistically validated and the values of parameters appearing in the model is obtained. Thus the combined stress model enables one to estimate the life of OIP insulation at any temperature and moisture under synergy. In summary, this work through experimental and analytical approach has contributed to the evaluation of the aging of OIP insulation used in power transformers under the combined action of moisture and temperature.

Water distribution systems, electrical power transmission systems, and other civil infrastructure systems are essential to the smooth and stable operation of regional economies. Since the functions of such infrastructure systems often are inter-dependent, the systems sometimes suffer unforeseen functional disruptions. For example, the widespread power outage due to the malfunction of an electric power substation, which occurred in the northeastern United States and parts of Canada in August 2003, interrupted the supply of water to several communities, leading to inconvenience and economic losses. The sequence of such failures leading to widespread outages is referred to as a cascading failure. Assessing the vulnerability of communities to natural and man-made hazards should take the possibility of such failures into account. In seismic risk assessment, the risk to a facility or a building is generally specified by one of two basic approaches: through a probabilistic seismic hazard analysis (PSHA) and a stipulated scenario earthquake (SE). A PSHA has been widely accepted as a basis for design and evaluation of individual buildings, bridges and other facilities. However, the vulnerability assessment of distributed infrastructure facilities requires a model of spatial intensity of earthquake ground motion. Since the ground motions from a PSHA represent an aggregation of earthquakes, they cannot model the spatial variation in intensity. On the other hand, when a SE-based analysis is used, the spatial correlation of seismic intensities must be properly evaluated. This study presents a new methodology for evaluating the functionality of an infrastructure system situated in a region of moderate seismicity considering functional interactions among the systems in the network, cascading failure, and spatial correlation of ground motion. The functional interactions among facilities in the systems are modeled by fault trees, and the impact of cascading failures on serviceability of a networked system is computed by a procedure from the field of operations research known as a shortest path algorithm. The upper and lower bound solutions to spatial correlation of seismic intensities over a region are obtained.