Browsing by Author "Gaunt, C T"

Now showing 1 - 8 of 8
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    Adaptive radio resource management for mobile satellite systems
    (2007) Abel, Ajibesin Adeyemi; Gaunt, C T
    In this thesis, a set of unique strategies and enhanced schemes for adaptive CDMA modulation are devised. A graded resource system is proposed for better radio resource management. Subsequently, a successful adaptive CDMA algorithm is designed and a prioritised processing gain for adaptive CDMA algorithm in satellite system is introduced. The idea of the critical section in the downlink system when a user controller scheme has to be activated to improve the performance is initiated. The diversity technique and rate compatible punctured turbo-code (RCPT), which has been found to give improved throughput performance in a direct sequence (DS) CDMA, are exploited.
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    Benefits of smart grid technologies in South Africa
    (2014) Masembe, Immaculate Angela; Gaunt, C T
    The main purpose of a power system is to deliver the electrical energy requirements of its customer, at the lowest possible cost and at an adequate level of reliability. A power system may be divided into three sub systems: generation, transmission and distribution. Each sub system plays a different role for the entire network. The distribution sub-system in South Africa, much like many other countries in the world, is still based on 20th century technology. According to some sources, 20th century technology cannot efficiently sustain a 21st century economy, and that power networks need to be ‘modernized’. A report released in 2007 by the National Energy Regulator of South Africa (NERSA) on the state of the Electricity Distribution Industry (EDI) infrastructure, indicated that although there were pockets of good performance, assets needed urgent rehabilitation and investment. Further studies have revealed that the distribution grid infrastructure is aging and poorly maintained, and that its state was steadily deteriorating. Ageing infrastructure has been identified as the key challenge for the electricity generation, transmission and distribution sectors. It has also been estimated that between 2012 and 2020, more than 250 billion (2008) ZAR will be needed to maintain and expand the transmission and distribution network infrastructure. Smart grid technologies have been proposed as one of the possible means of implementing new technologies and techniques into the grids of different countries. The main motive towards smart grid technologies is to improve reliability, flexibility, accessibility and profitability; as well as to support trends towards a more sustainable energy supply. Besides aging infrastructure, inadequate generation capacity has also been a problem faced by the industry. Since 2007, South Africa has faced electricity supply problems due to inadequate generation capacity, which culminated in rolling black outs and load shedding in 2007 and 2008. The main causes of the blackouts were: insufficient generation capacity to meet growing demand, unreliable transmission and distribution networks, as well as inadequate operation of existing plants. Traditionally, generation capacity has not been present in the distribution zone. However, due to technological developments in distributed generation technology; constraints on the construction of new transmission lines and grid infrastructure; increased customer demand for highly reliable electricity; and environmental concerns; the presence of generation in the distribution subsystem has increased. This dissertation, entitled BENEFITS OF SMART GRID TECHNOLOGIES IN SOUTH AFRICA, aims to show the potential reliability benefit of smart grid technologies and distributed generation. There are a variety of smart grid technologies available on the market, each aimed at improving different aspects of power system performance. Smart grid technologies, which are said to improve distribution feeder reliability, were identified and selected in this study. These are fault passage indicators, distance to fault estimators and feeder automation. Distributed generation in the form of solar PV was also introduced into the study.
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    The characterisation and automatic classification of transmission line faults
    (2014) Minnaar, Ulrich; Gaunt, C T; Nicolls, Fred
    A country's ability to sustain and grow its industrial and commercial activities is highly dependent on a reliable electricity supply. Electrical faults on transmission lines are a cause of both interruptions to supply and voltage dips. These are the most common events impacting electricity users and also have the largest financial impact on them. This research focuses on understanding the causes of transmission line faults and developing methods to automatically identify these causes. Records of faults occurring on the South African power transmission system over a 16-year period have been collected and analysed to find statistical relationships between local climate, key design parameters of the overhead lines and the main causes of power system faults. The results characterize the performance of the South African transmission system on a probabilistic basis and illustrate differences in fault cause statistics for the summer and winter rainfall areas of South Africa and for different times of the year and day. This analysis lays a foundation for reliability analysis and fault pattern recognition taking environmental features such as local geography, climate and power system parameters into account. A key aspect of using pattern recognition techniques is selecting appropriate classifying features. Transmission line fault waveforms are characterised by instantaneous symmetrical component analysis to describe the transient and steady state fault conditions. The waveform and environmental features are used to develop single nearest neighbour classifiers to identify the underlying cause of transmission line faults. A classification accuracy of 86% is achieved using a single nearest neighbour classifier. This classification performance is found to be superior to that of decision tree, artificial neural network and naïve Bayes classifiers. The results achieved demonstrate that transmission line faults can be automatically classified according to cause.
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    Comparing the reliability of older and newer transformer designs
    (2011) Jagers, Janine Norma; Gaunt, C T
    This dissertation describes the findings of an investigation that was conducted to determine if the reliability of older designs was significantly different from newer designs, and whether the observed differences (if any) were the result of developments in design, manufacture and technology of transformers during different periods.
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    Dispatching emergency reserves
    (2015) Van de Venter, Al ' louise; Gaunt, C T
    This dissertation presents the analysis of cost-effective dispatching of emergency reserves with a specific focus on supply and demand side options. On the demand side options the focus is the demand market participation product. On the supply side options the use of hydro and gas specifically the open cycle gas turbines are studied. In capacity constraint systems, supplying the demand with the current generation mix needs to be met. With a diminishing reserve margin and increase in demand yearly this challenge increases. The South African scenario is reported in this paper. As demand grows the ability to meet that demand remains a focus; a responsibility that remains a priority for the system operator. In times of surplus or shortage generation with adequate or diminishing reserve margins the focus on dispatching optimally and economically is an important aspect. Currently the South African Interconnected Power System is constrained; at times there is more demand than supply. The reserve categories are the ancillary requirements and are different for all power systems. Reserves are to cater for disturbances on the power system to ensure a healthy frequency is maintained. Reserve categories according to the ancillary requirements are: instantaneous, regulating, ten minute, supplemental and emergency. This dissertation focuses on emergency reserve.
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    Electrification technology and processes to meet economic and social objectives in Southern Africa
    (2003) Gaunt, C T; Braae, Martin
    Bibliography: leaves 243-251.
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    Improvement in the modelling of geomagnetically induced currents in Southern Africa
    (2008) Bernhardi, E H; Cilliers, P J; Gaunt, C T
    One of the consequences of the geomagnetic storms resulting from adverse space weather is the induction of geomagnetically induced currents (GICs) in power lines. The GICs that flow in a power transmission network are driven by the induced electric field at the Earth's surface. The electric field, in turn, is affected by the changing magnetic field during a magnetic storm. These GICs can cause extensive and expensive damage to transformers in the power transmission system. Understanding the behaviour of the magnetic field during a magnetic storm is a crucial step in modelling and predicting the electric field and ultimately the GICs in a power transmission network. We present a brief overview of the present status of GIC modelling in southern Africa and then discuss whether it is sufficient to use geomagnetic data from a single magnetic observatory alone to model GICs over the subcontinent. A geomagnetic interpolation method is proposed to improve the modelling of GICs in southern Africa. This improved model is one step closer to our being able to predict GICs accurately in the subcontinent, which will enable power distribution companies to take the necessary precautions to minimize possible transformer damage.
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    Operational modelling of geomagnetic fields and geomagnetically induced currents
    (2021) Heyns, Michael John; Gaunt, C T; Lotz, S I
    Geomagnetically induced currents (GICs) have long been known to affect power systems adversely. Modelling these GICs usually involves consideration of a chain of coupled systems. The scope of the modelling chain spans multiple disciplines, from solar physics through to geophysics and power engineering. Most models split the chain into sequential and separate processes. Recent approaches focus on improving accuracy in the geophysical process and in network models to a transformer level. However, even complex models in the geophysical or engineering steps leave significant unmodelled uncertainties in the coupled systems. The focus of this work is to use data-driven approaches to probe the uncertainties and provide a framework for operational estimation from the geomagnetic field to GIC. Although the empirical approaches chiefly link measurements of geomagnetic fields and GICs, measured geoelectric fields and magnetotelluric surface impedance responses are also employed. Analysis is done in both the time and frequency domains. Various aspects of this novel empirical approach have been tested using datasets from power networks in four mid-latitude countries, with consistent results found across the different contexts. The novel empirical ensemble method shows improvements compared with previous empirical models, regardless of data fidelity or coverage. Frequency-related driving and filters are shown to have material effects on GIC modelling. The network parameters widely used to calculate GICs at nodes are shown to vary with the magnitude of the geomagnetic disturbance during an event. Modelling uncertainty can be quantified, and an operational level of modelling was possible across all cases. For GIC modelling in networks with sparse magnetic Field data coverage, the well-defined and often used planar spherical elementary current systems interpolation method is adapted to use low-cost variometers and describe mid-latitude current systems. For the first time, uncertainty is included in the results from this interpolation scheme. This research has direct applications for power system operators in mid-latitude regions. The use of variometers and low-cost GIC monitors supports the feasibility of large-scale data collection. The empirical modelling methods developed can augment existing approaches and inform decisions regarding operations, maintenance, planning and risk assessment.