Department of Electrical and Electronic Engineering
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Electrical and Electronic Engineering is an exciting and dynamic field. Electrical engineers are responsible for the generation, transfer and conversion of electrical power, while electronic engineers are concerned with the transfer of information using radio waves, the design of electronic circuits, the design of computer systems and the development of control systems such as aircraft autopilots. These sought-after engineers can look forward to a rewarding and respected career.
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Browsing Department of Electrical and Electronic Engineering by browse.metadata.advisor "Beukes, Johan"
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- ItemDynamic modelling of traction loads and renewable energy systems on shared power lines for power quality assessment(Stellenbosch : Stellenbosch University, 2019-04) Naude, Hein; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Eskom has recently started investigating the effect of traction on renewable energy sources due to the power quality problems associated with traction networks. Poor power quality generated by means of traction networks have always been of concern. The impact of the traction load power quality issues has greatly increased due to the increasing number of renewable power producers (RPPs) being connected to the national grid. Studies has shown an increase in voltage unbalance and harmonic distribution at various points of concern in the network which leads to the loss of power production from the RPPs. Recent power quality assessment reports from Eskom has indicated that power quality problems, particular harmonic emissions, exist at RPPs. Harmonic sources such as non-linear (traction loads) are contributors to voltage harmonic distortion on the network in addition to harmonic emissions of RPPs. To gain insight into the problem the need exist to model and simulate traction drive systems and renewable power plants. DIgSILENT PowerFactory, was chosen as the software simulation package to design and build generic models of renewable system inverters and traction load rectifiers to conduct dynamic time domain simulations. To validate the accuracy of the models, the simulation results were compared to measured results. Due to good correlation, the models can be used for future network planning and power quality assessment. The aim of this thesis is further to investigate the power quality issues related to traction loads and to perform a power quality assessment at the POC of a local wind farm. The assessment of voltage unbalance indicated that traction loads is generally the largest contributor to voltage unbalance on a traction network and can cause inverter trips at RPPs at certain conditions. It is observed that various conditions such as the traction load type, operating conditions and control of the traction load, power demand of the traction loads and three-phase fault level will impact the voltage unbalance caused by traction loads. The impact of traction loads on the network voltage distortion is investigated and it is determined that small current harmonics emissions of traction loads can generate large voltage distortion at the presence of a parallel resonance. The impact of impedance and background harmonics is investigated and the results show that the methods often described in standards for calculating impedances to establish harmonic contribution will not always be valid, especially when having inverters as harmonic sources. A two-point measurement approach is followed for investigating the impact of traction load current emissions on the assessment of RPP current emissions based on international guidelines. A method is presented to approximate current emissions of the RPP without the impact of the traction load current emissions on the assessment. The results show that traction loads do impact the harmonic assessment of RPPs and therefore the current assessment method will not always be accurate.
- ItemEnabling low voltage grid visibility to detect safety hazards(2018-03) Wattel, Jacques Willem; Beukes, Johan; Mouton, H. du T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The low voltage (LV) network poses various hazards to humans and animals. In rural and deep rural areas the risk of electrocution and fire hazard is augmented, largely due to overhead conductors being used and illegal connections, with fatalities occurring each year on South Africa’s rural networks. The aim of this thesis is to investigate the possibility of detecting such hazards by employing smart meters and smart grid infrastructure. Four main hazard categories were identified as having the highest likelihood to the loss of life on Eskom’s rural LV distribution network. The hazards include: 1. PEN conductor failure. 2. LV earth electrode conductor high impedance failure. 3. Unaccounted current flow. 4. Earth leakage protection not operational. A model of each hazard is discussed and a possible detection method is proposed. An experimental setup of an LV feeder was built to verify the feasibility of the proposed detection methods. Experimental smart meters from Texas Instruments with ZigBee capabilities were installed at each customer installation and at the MV/LV transformer. The meters send measurement data to a data concentrator. The data concentrator was used to capture, store, manage and visualize data gathered from the smart meters. The thesis covers the hardware and software development that was done on the smart meters and data concentrator. Hazards were imposed on the experimental network to simulate each hazardous condition and the associated detection methods were evaluated. Lastly, the concept to monitor the feeder loop impedance using smart meters is introduced which provides an additional hazard detection parameter, providing an indication of the overall ‘health’ of a feeder. Experimental results showed that the feeder loop could successfully be measured using smart meters.
- ItemHarmonic resonance assessment of renewable energy power plants on the power system using resonant mode analysis(Stellenbosch : Stellenbosch University, 2021-03) Scheepers, David Johannes Jacobus; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Power quality problems and assessment methodologies associated with renewable energy power plants and resonant conditions are investigated.Resonant conditions are introduced by capacitive elements found in typical renewable energy power plant installations,namely the cabling capacitance and the inverter filter capacitors which resonates with inductive elements throughout the power system.A 40MW concentrated photovoltaic power plant serves as a case study. A simplified model of the power plant is developed and compared against a detailed DIg SILENT Power Factory model to validate the results. The Power Factory Python application programming interface is used to construct the Power Factory model’s admittance matrix for analysis.Propagation analyses are performed on the developed simplified models as well as the Power Factory model. Resonant mode analysis is applied to the Power Factory model to calculate the participation factors of various elements connected to specific bus bars. The participation factors indicate which system elements have dominant contributions to the creation of resonant conditions.
- ItemInverter control for voltage unbalance mitigation on low voltage electricity networks(Stellenbosch : Stellenbosch University, 2024-03) De Wet, Werner; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The use of single-phase power lines to electrify low consumption areas in South Africa leads to undesired levels of voltage unbalance at certain point on the distribution network. The increased use of inverter-based generation in the distribution network provides the opportunity for the utitlisation of these inverters to be increased by providing an ancillary service such as voltage regulation and voltage unbalance mitigation. This thesis provides a detailed design of a positive and negative sequence dq domain control system that can be implemented in grid-connected inverters to perform voltage regulation and voltage unbalance mitigation. This control system allows the inverter to perform voltage regulation by means of reactive power compensation and mitigate voltage unbalance by transferring active and reactive power between the three phases. The inverter system is experimentally tested by adapting an existing three-phase 80 kVA inverter and connecting it to the electricity grid. Resistive loads are connected to the inverter-grid system to generate undesired levels of voltage unbalance. The control system implemented in the inverter consists of an inner dual current controller which is supplied current references from an outer control loop than consists of the DC voltage controller, positive sequence voltage controller and a negative sequence voltage controller.
- ItemThe Measurement and Analysis of High-Frequency Conducted Disturbances in Power Networks(Stellenbosch : Stellenbosch University, 2022-12) Lambrechts, Johannes; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis discussed the measurement of high-frequency disturbances in power networks referred to as ”supraharmonics” in the power quality community. Supraharmonics are caused by modern power converter based loads and generators connected to the distribution power network. The amplitudes of the supraharmonics caused are very small compared to the fundamental 50 Hz grid frequency component. Thus, measuring these small signals in the presence of the fundamental power signal is a non-trivial task. All parameters related to frequency measurements, such as sampling frequency, Fourier transforms, windowing, aliasing and quantization was discussed. It was found that various parameters, such as measurement length, windowing and frequency grouping do affect the output spectrum of the measurement in a significant manner, and it was concluded that a measurement standard is required. At the time of writing, no measurement standard exists for the supraharmonic frequency range. All currently proposed measurement methods were evaluated and discussed with the CISPR 16 standard showing promising results in terms of accuracy and the type of signals which can be measured. It was shown that quantization and specifically quantization noise imposes a hardware limitation to the measurement of small signals. An active high pass filter was designed and tested as a solution to the quantization noise problem, which enabled the accurate measurement of supraharmonics. The supraharmonic emissions of various inverters were measured using the active high pass filter in both residential grid and microgrid environments. The measurement results showed inverters differ notably in their ability to filter out the generated supraharmonics and that some inverters do exceed the current compatibility levels for non-intentional emissions in the supraharmonic range.
- ItemSmart transformer communication and application in rural microgrid settings(Stellenbosch : Stellenbosch University, 2015-03) Verster, Cornel; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The Smart Grid is an initiative to make the existing utility grid more effective and efficient by making utility infrastructure smarter. The initiative affects all areas of the utility grid and all utility hardware. Communication to utility hardware for monitoring and remote configuration is central to the smart grid vision. The focus of this project is the Smart Transformer, a distribution transformer with built-in intelligence and communication capabilities. Data acquisition and remote configuration hardware and software was developed and installed on a distribution transformer for application in deep rural areas. The solution included communication capabilities and adheres to industry standards. The solution was tested and data acquisition and management were done using the OSIsoft PI System software. Field tests were performed to evaluate the effectiveness of the solution in a deep rural setting. It was found that the smart transformer can be effectively monitored, configured and controlled in a deep rural setting. The smart transformer concept was investigated in a microgrid context. The potential of a smart transformer within a microgrid was explored and the smart transformer as a microgrid market-enabler was focussed on. A simulation was performed to evaluate the role of a smart transformer as a microgrid market-enabling device. It was found that the smart transformer has the potential to serve as a market-enabling device.
- ItemThe use of small-signal impedance modelling of grid-tied inverters in harmonic studies of renewable power plants(Stellenbosch : Stellenbosch University, 2023-03) Du Plessis, Francois; Beukes, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Increased penetration of renewable power plants on the South African power network presents technical and regulatory challenges. Power quality problems and compliance assessment methods related to harmonic emissions of renewable power plants are studied. The elements which influence the harmonic emissions of renewable power plants are identified as the inverter harmonic source, the plant impedance, the grid impedance and background distortion levels. An accurate description of the plant impedance is discussed and includes the inverter filter inductor and control system. These elements have a significant impact in the low frequency region. The negative resistive characteristic of the controller and its interaction with system resonances is identified as a limitation on the controller bandwidth to ensure resonant stability. The inverter impedance description is used to investigate the impact of parameter variations on harmonic emissions of a simulated 2.3 MVA inverter system, including variations in controller topology and bandwidth, grid impedance and harmonic compensation. The harmonic contributions of a 100 kVA inverter and 2.3 MVA inverter on a shared feeder are identified using descriptions of the impedances. A harmonic study of an 80 kVA experimental inverter system is conducted. The effects of variations in controller bandwidth, filter capacitance and grid impedance on harmonic distortion are investigated. The inverter impedance description is used to accurately characterise the plant impedance of a 100 MW wind farm, which enables the attribution of harmonic contributions from measured data. Phasor analysis in the phase and sequence domains are compared and challenges of harmonic assessment methods are discussed.