Browsing by Author "Gaunt Charles"

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    Open Access
    Development of a Network Design Tool for the Herman-Beta Extended Transform
    (2024) Khan, Isma-Eel; Oyedokun, David; Gaunt Charles
    The Herman-Beta method has been one of the most important network planning tools used in South Africa. Over decades, it has transformed from being able to perform probabilistic load flow studies for LV passive feeders to an algorithm capable of performing PLF studies for passive/active feeders of any voltage. Furthermore, the new algorithm reformulated the equations used to dispose of the underlying assumptions used in the original method. This reformulation came to be known as the Herman-Beta Extended Transform (HBET), a powerful network planning tool which could prove vital to network planners as the uncertainty in power systems increase. Previously, the HBET was implemented using MATLAB programming software. In this dissertation, a set of user requirements and data structure to enable efficient handling of input and output data in the HBET was developed for an open-source platform. Python programming language was chosen as the most suitable programming language to implement the program, due to its array manipulation capabilities and the plethora of information and help available online. Four scenarios were used to test the accuracy with which the tool was created. The four scenarios included a 12-bus passive feeder, a 12-bus active feeder, a 33-bus passive feeder with laterals and a 33- bus active feeder with laterals. These results were tested against the results produced by the MATLAB tool, where it was previously proven to be accurate. It was found that the percentile voltages, mean voltages and voltage standard deviations for all systems simulated in Python were identical to those simulated using the MATLAB tool, indicating that the tool had been implemented accurately, thereby validating the hypothesis.
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    Open Access
    Development of a Network Design Tool for the Herman-Beta Extended Transform
    (2024) Khan, Isma-Eel; Oyedokun, David; Gaunt Charles
    The Herman-Beta method has been one of the most important network planning tools used in South Africa. Over decades, it has transformed from being able to perform probabilistic load flow studies for LV passive feeders to an algorithm capable of performing PLF studies for passive/active feeders of any voltage. Furthermore, the new algorithm reformulated the equations used to dispose of the underlying assumptions used in the original method. This reformulation came to be known as the Herman-Beta Extended Transform (HBET), a powerful network planning tool which could prove vital to network planners as the uncertainty in power systems increase. Previously, the HBET was implemented using MATLAB programming software. In this dissertation, a set of user requirements and data structure to enable efficient handling of input and output data in the HBET was developed for an open-source platform. Python programming language was chosen as the most suitable programming language to implement the program, due to its array manipulation capabilities and the plethora of information and help available online. Four scenarios were used to test the accuracy with which the tool was created. The four scenarios included a 12-bus passive feeder, a 12-bus active feeder, a 33-bus passive feeder with laterals and a 33- bus active feeder with laterals. These results were tested against the results produced by the MATLAB tool, where it was previously proven to be accurate. It was found that the percentile voltages, mean voltages and voltage standard deviations for all systems simulated in Python were identical to those simulated using the MATLAB tool, indicating that the tool had been implemented accurately, thereby validating the hypothesis.
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    Item
    Open Access
    Saturation Effects in 3p3L Power Transformers due to Geomagnetically Induced Currents
    (2023) Kerr, Evan; Folly, Komla; Gaunt Charles
    Geomagnetically induced currents (GIC's) caused by solar storms or other sources of dc excitation can impact the normal operation of power transformers in transmission networks. The impact is caused by the dc current introduced into the windings of a transformer energised with ac, which leads to a simultaneous dc magnetomotive force (mmf) resulting in part-cycle saturation of the core and so, heat related ageing and failures. A generally accepted theory on the impact of GIC's on transmission networks is that three-phase three-limb (3p3L) power transformers are not affected by this phenomenon. The basis is that a three-limb core forms balanced return paths which oppose the dc flux evenly in each limb, thereby neutralising the effect. The challenge is this theory only remains true if the circuit resistance of the three-phase lines connected to the transformer are balanced, which has proven difficult to achieve in practice. This study set up laboratory experiments to evaluate the effect of simultaneous ac and dc in the windings of an unloaded 3p3L transformer while simulating realistic unbalanced conditions. To ensure a valid test protocol, the transformer was designed as a scaled-down model of a power transformer with a core constructed using four step-lap mitred joints and a high quality electrical steel. This was to closely resemble the performance of a normal power transformer. The source supply for the test circuit was carefully designed and tested to ensure that it was sufficiently robust that it would not affect the results of the transformer under test (TuT). The initial testing was of symmetrical ac conditions to establish a performance benchmark at normal operation and the TuT nameplate rating, and to emulate core saturated conditions by over-exiting the core for exploratory core stray flux recordings. The dc testing that followed required adjustable levels of dc current and the unbalance to emulate a range of GIC conditions. At each setting of dc and unbalance, the excitation parameters such as THD were recorded using a power analyser. Simultaneously, the core stray flux was recorded using search coils, while tank ‘hot-spot' temperatures from stray flux eddy current heating were recorded. Finally, the audio levels of the 3p3L transformer in balanced and unbalanced GIC conditions were analysed. The results of the tests challenge the assumption that 3p3L power transformers are immune to GIC primarily because it is not possible to ensure ideally balanced conditions in the field. The importance of the transformer core design was highlighted by showing its significant contribution to the GIC vulnerability. The core joints of a four step-lap core was shown to saturate before the bulk core areas that emphasised the need for continual careful attention to core design and construction in an effort to reduce inherent design vulnerabilities.