3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item A Bayesian framework for forensic investigations involving lighting location system data(2018) Hunt, Hugh Gordon PatrickThe work presented in this thesis extends and contributes to research into the forensic use of Lightning Location Systems and the uncertainty present due to location errors. While previous work in this area has produced some approaches that can be used in forensic investigations, there has not been a consistent, standardised approach to presenting Lightning Location System stroke reports as evidence in a legal environment. In the research presented, a Bayesian framework for representing Lightning Location System data as likelihood ratios and posterior probabilities is developed. The statistical models necessary for use of the framework are discussed and verified through groundtruth events and bivariate statistical analysis. Photographs of multiple lightning events to the Brixton tower in South Africa and current measurements at the Gaisberg tower in Austria are used as ground-truth data and bivariate statistical techniques are used to fit and evaluate different statistical models. It is shown that the bivariate Students’ t-distribution is the best fit for Lightning Location System location errors, rather that the commonly assumed bivariate Gaussian distribution and that a bivariate Gaussian Mixture Model can be used to describe the prior probability of lightning occurrence in a region. It is demonstrated how the Bayesian framework can be used to present Lightning Location System data as evidence in a court of law. This represents a unique and valuable contribution to those working in the field of lightning location and, in particular, in forensic situations.Item Relationship between corona power loss and audible noise(1997) Engelbrecht, Michael SeanResults are reported on an initial investigation into corona power loss and its relationship to corona initiated audible noise. The work has the goal of being able to accurately predict the corona power loss, from a transmission line, from knowledge of the audible noise on the line. Corona power loss and its relationship to corona current, applied voltage and electric field is also exarr-ined. Experiments were performed using two single phase, different diameter, corona cages. Although the corona cage test results showed no correlation between corona initiated broad band audible noise and corona power loss, a linear empirical relationship, with excellent correlation, was found to exist between corona power loss and 100Hz Hum (dBA above 20jlPa). Results showed that, at the same magnitude of electric field, within the l h o different diameter corona cages, the corona current is the same magnitude and the corona power loss is proportional to the applied voltage.Item Electrical transient interaction between transformers and the power system: case study of an onshore wind farm(2016) Banda, Cedric AmittaiThrough the Renewable Energy Independent Power Producer Procurement Program (REIPPPP) the South African government has awarded opportunities for growth of renewable energy through bidding rounds. Round 1 saw a total capacity of 397 MW being awarded to independent power producers (IPP). Subsequently Rounds 2, 3 and 4 each had a total capacity of 333 MW auctioned. The advent of renewables on the market has brought upon its own associated problems with regards to power quality issues and failure of HV equipment. This thesis will address transformer failures that occurred at an onshore wind farm. The nature of the transformer failures suggest transient overvoltages are mainly to blame. A comparison between transformer failures in South African and Brazil suggest a common failure mechanism. The failure starts with an inter-turn insulation failure which propagates to an inter-layer insulation. In worst cases the failure mode results in a puncture through the LV-HV barrier and punctures through the LV winding. An extensive literature review was performed to find appropriate methods to predict and explain the failure mode in wind turbine LV-MV step-up transformers. Of the different models which were reviewed the most notable was the Multi-conductor Transmission Line (MTL) model which was chosen as the preferred model due to its ability to predict the inter-turn/inter-layer voltage stresses. Verification of the developed MTL model by the author was then compared to published results of an MTL model of a disc winding transformer. The results of the comparison revealed a relatively good agreement between the developed model and the published model. The application of the MTL model to represent the voltage stresses in transformer windings was then extended to two specially constructed wind turbine step-up transformer prototypes. The prototypes differed in the winding arrangement of the MV coil. The other used two separate MV coils separated by an oil gap whereas the other had a single MV coil. To validate the model accuracy, a comparison of measured results versus those obtained analytically was done for the two prototypes. The analytical and measured results also had a relatively good agreement for the two prototypes considered. Measurement of switching surges was done on-site at the wind farm to understand the nature of the transients. Using analysis tools such as FFT and frequency domain severity factor it was possible to understand the impact the nature of these transients would pose on the transformer insulation. Different mitigation techniques which can be used to alleviate the transient overvoltages to within safe levels were investigated. The most notable protection device considered was the RL choke device which offered a significant reduction of the pre-strikes and is virtually transparent under power frequency operation.Item A MATLAB based analysis tool for clearance and thermal violations in transmission power lines(2016) Mabuza, Ndumiso SimonClearances are an important aspect of High Voltage (HV) transmission line design, construction and maintenance. A software tool that combines clearance violation analysis and optimum loading operating conditions for power lines could save power utilities the capital cost of refurbishing transmission power lines that marginally exceed maximum power line clearance distances. This can be achieved by operating the power lines at an optimum amperage level for any given set of weather conditions. This research project proposes a low cost MATLAB® based software tool that detects clearance violations and determines operational limits on transmission power lines using prevalent weather conditions as well as the power line amperage. Various power lines around the states of Missouri and Illinois in the United States of America are analysed to test the viability and functionality of the software. In order to validate the accuracy of the program, the results obtained were compared to results from PLSCADD ®. Key Words: conductor, clearance, sag, software, temperatureItem Transmission line compaction using high phase order transmission(2016-08-17) Bortnik, JacobThis report discusses high phase order (HPO) technology, i.e. the use of more than the conventional 3 phases for transmission of electric power, its use in the compaction of lines, and power density maximization over existing servitudes. It is structured in four parts. The first part introduces the concepts, establishes the need, and lists the advantages ofHPO. The second part deals with the technology itself and shows that it is possible to analyze HPO systems using symmetrical component analysis, lists common transformer configurations, covers protection, and so on. The third part analyses 5 case studies, the first 3 being analytical, and the last 2 being the first experimental test line, and the world's :first utility application ofHPO lines. The fmal section is a South African case study and compares an HPO line to an existing 400 kV 3-phase line and shows that the former is 87.5% more expensive to implement than the latter. Comparing the 3-phase and 6-phase lines on a more even basis, yielded a breakeven distance of225.86 km, above which the 6-phase option becomes more economical. These results are then explained and discussed in the conclusions section.