Masters Degrees (Electrical and Electronic Engineering)

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Browsing Masters Degrees (Electrical and Electronic Engineering) by browse.metadata.advisor "Bekker, Johannes Cornelius"

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    Parameter estimation of a high-voltage transformer using pseudo-random impulse sequence perturbation
    (Stellenbosch : Stellenbosch University, 2022-12) Banks, Daniel; Bekker, Johannes Cornelius; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Transformers are essential devices to the power system. Transformer applications include transmission services, monitoring of line voltages and currents, and distribution services. High-voltage test transformers are commonly used in environments when high voltages are required to test power system equipment. Due to the cost of large transformers and their importance to the power system, it is essential to monitor their health and condition to ensure nominal grid operation. Access to an equivalent-circuit model that represents the physical construction of the transformer aids in condition monitoring and identifying the location of faults. Due to the proliferation of renewable generation, there are increased harmonics in the power system. Therefore, there is a growing need for equivalent-circuit models that provide physical representation and accuracy over a wide range of frequencies. System identification can be applied to transformers to develop wideband equivalent-circuit models from measured data. In this project, a methodology for determining wideband models for transformer windings and a high-voltage test transformer is presented. The Pseudo-Random Impulse Sequence (PRIS) signal is a wideband excitation signal for system identification in the power system environment. The PRIS perturbation arrangement is applied to two cascaded transformer winding models in simulation. Successful offline perturbation of transformer winding models with the PRIS signal is verified through good correlations between the simulated and analytically derived frequency responses of the input impedance and voltage ratios. The performance of various optimisation algorithms are investigated and compared. The algorithms are applied to various approaches, namely, frequency-domain, time-domain, or modal decomposition, in combination with various cost function formulations. It is found that although the time-domain and modal decomposition approaches perform superior, frequency-domain estimation that makes use of the model’s frequency responses derived analytically is the most computationally efficient. A PRIS source is built and subsequently applied to perturb a practical 7.5kVA, 230V/100kV high-voltage test transformer. The transformer measurements show minimal noise up to 20kHz. Four equivalent-circuit model topologies are investigated to identify a suitable model and associated parameters that best reproduces the transformer measurements. It is found that a single-section low-voltage winding and a six-section high-voltage winding model topology are of a high enough order to represent the number of observed resonances up to 10kHz. The measured frequency responses and estimated frequency responses produced by the model show a good correlation, with discrepancies below 1kHz due to the lack of any frequency-dependent model parameters.