Doctoral Degrees (Electrical Engineering)

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DC coronation electroporation.
(2015) Chetty, Nevendra Krishniah.; Davidson, Innocent Ewean.; Chetty, Leon.; Govender, T.; Ijumba, Nelson Mutatina.
Cells are surrounded by a semi-permeable bilayer lipid membrane that acts as a barrier against the entry of foreign molecules. In the fields of molecular biology, biotechnology, and medicine, the ability to breach the cell membrane and introduce molecules into cells for therapeutic purposes is often necessary. Molecules, which are considered foreign to the cell like drugs and extraneous genetic materials, are administered to cells for numerous applications including the treatment and prevention of diseases. There are many accepted methods of facilitating the delivery of molecules to cells. Of all these methods, one important and well-established physical method is electroporation which has been utilised for decades. Electroporation is a widely adopted procedure for the temporary permeabilization of cell membranes due to the application of short electrical pulses. It is a phenomenon resulting from the effects of pulsed electric fields, which induces biochemical and physiological changes to a cell membrane. As a result, some of the molecules that are ordinarily unable to pass through the membrane are thereafter able to gain access to the cell interior via pores that are formed in the membrane. Even though electroporation is fairly safe, there are some drawbacks associated with this method. The traditional method of electroporation requires direct contact of high voltage electrodes and fairly high currents are involved. As a result, the procedure can cause pain, muscle spasms, discomfort, burning and cell and tissue damage. Alternative methods of molecular delivery are therefore being researched, especially non-contact methods such as the use of high voltage plasma and high voltage corona discharge. Successful cell permeabilization with corona discharge ions and plasma has been previously demonstrated. These methods offer the advantage of contact-free treatment with low associated current. In this thesis, the research investigates the delivery of tracer molecules, SYTOX Green, into HeLa cells and the consequential cell destruction by the phenomenon of corona discharge. A high voltage DC, multipoint-to-plane atmospheric-air corona discharge apparatus was designed and constructed to investigate the conditions as well as the characteristics of the corona discharge current pulses that resulted in an acceptable balance between high cell permeabilization and low cell destruction. Firstly, the salient variables that affect molecular delivery and cell destruction were established. Secondly, the variables were optimized to allow for reliable molecular delivery to cells with acceptable levels of cell destruction. Thirdly, the nature and variation of the corona discharge current pulses and its effect on molecular delivery and cell destruction were investigated. Finally, a new method of assessing cell destruction, which combined the measurements of cell viability and cell lysis were used. The variables that were identified, over the course of many experiments, were exposure time to corona discharge, incubation time with SYTOX Green, volume of liquid during exposure, and inter-electrode distance. Further experiments show that when the variables of the experiment are set at optimal values, cell permeabilization is reliable with minimal damage to cells. Once these conditions were obtained and optimised, the effect of different applied voltages on the level of cell permeabilization and the short-term destructive effects on cells were investigated. The general trend is an increase in fluorescence and therefore, molecular delivery, with an increase in applied voltage. Cell destruction also tends to increase with increasing applied voltage. The characteristics of the corona current pulses that were analyzed include amplitudes, repetition rates, widths, and rise-times. The characteristic frequencies of single pulses, obtained from the application of a discrete fast Fourier transform, were also analyzed. For the corona-generating device constructed and the voltages tested, it was found that the only characteristic that varies appreciably with voltage is the pulse repetition rate. A higher pulse repetition rate relates to a greater number of pulses per unit time and therefore, a greater exposure of the cells to the applied electric field. This would, therefore, translate to a higher extent of molecular delivery and a higher accompanying level of cell destruction. This study shows that permeabilization of HeLa cells due to corona discharge can be reliably achieved and the results provide a greater understanding of cell permeabilization due to the influence of corona discharge. It therefore forms an important basis for future research on practical applications that would promote the establishment and acceptance of corona discharge as a procedure for molecular delivery to cells.
Performance and cost benefit analyses of university campus microgrid.
(2021) Akindeji, Kayode Timothy.; Tiako, Remy.; Davidson, Innocent Ewean.
Affordable and clean energy is one of the sustainable development goals (SDGs) to be achieved by the year 2030. Renewable energy sources such as wind, hydro, solar are free and inexhaustible globally to produce clean, reliable and cost effective power. However, most renewable energy sources are intermittent, to overcome this barrier, the concept of microgrid has been deployed in many applications to aggregate renewable energy resources, energy storage system and energy management system for sustainable, reliable, economical and environmental - friendly power system. Furthermore, considering the continuous increase in the cost of electricity and recent load shedding in South Africa, universities can reduce cost of energy demand, avoid interruption of academic activities due to load shedding and develop a test-bed or laboratory in which students and faculty staff can conduct research to advance modern power system through a self-sustaining microgrid. The university is like a separate entity and can operate as an island with sufficient resources to meet her energy demands. This thesis analyses the performance of a university campus microgrid using the five campuses of the University of Kwa-Zulu Natal as case studies considering economical and environmental benefits. Three different studies are carried out to achieve the aim and objectives of this work. The first study considers a grid connected microgrid using the real time data from the university energy management system, the modelling and simulations are implemented in HOMER Grid®. The main objective is to determine the optimal generation mix and size of a hybrid system consisting of the utility (eThekwini Electricity), solar PV, wind turbine, diesel generator and battery system taking into consideration the cost of energy (COE), net present cost (NPC), return on investment (ROI), payback period (PBP), utility cost saving and CO2 emission reduction. The second study aims to optimize the operational cost of a hybrid power system (PV-Wind-Diesel Generator-Battery) using two campuses as case studies. The objective function is formulated as a non-linear cost function and solved using a MATLAB function, ‘quadprog’ considering daily demands during summer and winter study and vacation periods with the aim of comparing the fuel costs and assess the effectiveness of the hybrid system. The third study proposes a novel optimization algorithm, the Quantum-behaved bat algorithm (QBA) to solve combined economic and emission dispatch (CEED) problem in an off-grid microgrid with onsite thermal generators and renewable energy sources (PV and Wind). The results obtained from these studies show and validate the fact that renewable energy source (RES) can be used to meet university energy demands in an economical way and reduce carbon footprint on campuses. It is observed from the result that the annual utility bill savings range from R3.97 million to R17.42 million and directly proportional to the peak load. The average emission reduction for all campuses is 49.6% except Pietermaritzburg where it is 33.7 %. In addition, the results will help university management as well as city management to invest wisely in renewables for energy sustainability and reliability.
Power quality enhancement in secondary electric power distr[i]bution networks using dynamic voltage restorer.
(2018) Ogunboyo, Patrick Taiwo.; Tiako, Remy.; Davidson, Innocent Ewean.
This research study investigates and proposes an effective and efficient method for improving voltage profile and mitigating unbalance voltage, voltage variation disturbances in rural and urban secondary distribution networks. It also proffers solutions for improving the performance of future distribution networks in order to increase the optimum functioning, security and quality of electricity supply to end users, thus making the power grid smarter. This study involves the compensation of power quality disturbance in balanced and unbalanced, short and long distribution networks. The mitigation of result of this voltage variation, poor voltage profile and voltage unbalance with an effective power electronics based custom power controller known as Dynamic Voltage Restorer (DVR) conceived. DVR is usually connected between the source voltage and customer load. An innovative new design-model of the DVR has been proposed and developed using a dq0 controller and proportional integral (PI) controller method. Model simulation was carried out using MATLAB/Simulink in Sim Power System tool box. An analysis of the results obtained when the new DVR is not connected to and tested on LV networks shows that the voltage profile, percentage voltage deviation and percentage voltage unbalance for 0.5 km for balanced and unbalanced distribution networks are within standards and acceptable limits, hence, the voltages are admissible for customers’ use. It was further established that the voltage profile, percentage voltage unbalance, voltage drop and percentage voltage deviation for distribution networks of 0.8 km to 5 km range from the beginning to the end of the feeder are less than the statutory voltage limits of -5%, 2 %, 5 % and ± 5 % respectively, hence, voltages are inadmissible for customers’ use. Others results obtained when DVR was connected recognized that for distribution feeder lengths of 0.5 km to 5 km range for balanced and unbalanced, short and long distribution networks the voltage profile, voltage variation, voltage drop and percentage voltage unbalance are within statutory voltage limits of 0.95 p.u and 1.05 p.u, -5 %, and less than 2 % respectively. Based on this investigation, and in order to achieve efficient, reliable and cost-effective techniques for improving voltage profiles, decreasing voltage variations and reducing voltage unbalances, the new DVR model is recommended for enhancing optimal performances of secondary distribution networks.
Survey and assessment of the impact of embedded generation on the eThekwini electricity distribution grid.
(2016) Sewchurran, Sanjeeth.; Davidson, Innocent Ewean.; Olorunfemi, Stephen Ojo.
Under frequency load shedding, rising electricity tariffs, environmental concerns, reducing costs of renewable energy technology and delays in constructing new power stations has lead consumers and producers alike to explore various energy generation options to reduce their own electricity needs whilst assisting the sector. Embedded Generation (EG), Distributed Energy Resources (DER) or Distributed Generation (DG) is further predicted to play a substantial role in the electrical power system in the near future. Various EG technologies are entering a period of major growth and commercialization. Small scale Embedded Generation (SSEG) projects are quickly becoming a popular sight locally within the city of Durban and numerous projects are been connected to the eThekwini Electricity distribution grids. In these projects, there seems to be a reluctance to couple expensive energy storage technologies to these systems but rather synchronize and utilise the municipal grid as a virtual battery. Whilst the advantages make synchronization to the grid a logical choice, the municipal network architecture and framework was not designed to facilitate this. The municipal mandated core function is to procure electricity from Eskom (the national energy generator), transform it and distribute it to its customers. Power flow is from generation (Eskom), transmission (Eskom) and distribution to the end customer. This includes all technical, regulatory, administrative and legal aspects that have been structured to support this unidirectional power flow. The introduction of DER/DG/EG introduces bi-directional power flow on the existing distribution network. An analysis of the impact of this phenomenon is required as it affects fault level, protection selectivity and sensitivity, network losses, quality of supply, network planning, metering and control of power flow on the existing distribution grid. In order to address and understand the impacts of EG on the existing eThekwini Electricity distribution grid, an investigation was first carried out to identify the drivers and available renewable energy resources in Durban. 5 cases studies were selected based on the investigation which showed that there will be growth and projects in these sectors in Durban. These cases studies were selected to address growth in residential rooftop PV, commercial/industrial rooftop solar PV, PV farm potential on closed landfill sites, wind farm potential at identified sites around the city and landfill gas to electricity projects from existing landfill sites in the city. Accurate models of these sources and their interaction with the grid were then studies. Studies were also carried out on the recently published NRS guidelines for SSEG and the South African Renewable Energy Grid Code to understand how this will provide operational flexibility to the System Operator and assist with mitigating the negative impacts to the distribution network. The 5 case studies provide excellent results and greater understanding of the impacts of increased penetration of EG onto the existing eThekwini Electricity distribution grid. The impacts of increased penetration of EG on the existing eThekwini Electricity distribution network included impacts to the network voltage, fault level rise, losses, power flow, network planning and revenue loss. Based on the results and studies from the case studies methods were then derived to mitigate the impacts of increased penetration of EG on the existing distribution network. The following outcomes and key contributions, were achieved in this research investigation, namely:  An understanding of the drivers of EG in eThekwini Municipality.  Evaluation of the available renewable energy resources within eThekwini Municipality.  The feasibility of residential rooftop solar PV in Durban.  Identified factors affecting residential rooftop solar PV feasibility in Durban.  Assessed the feasibility of municipal landfill gas to electricity EG projects.  Developed and propose methods to improve operational and financial viability of landfill gas to electricity projects in Durban.  Provides results showing the impacts of increasing EG on the eThekwini Municipality distribution network design and performance.  Developed methods to assist and enable distribution network designers when designing distribution networks with increasing EG.  Developed a methodology for selecting EG size on an existing eThekwini Electricity distribution network.  Provide methods to minimise the impacts of preselected size of EG given that the municipality has no control over the size selection which may be dictated by the IPP.  An understanding of the local South African guidelines on small scale EG, and the South African Renewable Energy Grid code requirements.  Provide controllability options to assist manage EG plants on the existing distribution network in eThekwini Municipality. vii  Understand the operation and effects of different EG sources available within eThekwini Municipality. These have been accomplished using the 5 case-studies, modelling and simulation, field tests and measurements; as well as extensive research investigation and analysis.
Utilisation of line surge arrestors to improve overhead HVAC and EHVDC line performance under lightning conditions.
(2020) Singh, Hariram.; Davidson, Innocent Ewean.
In high lightning areas, lightning strokes play an important role in the performance of overhead EHV AC and DC lines. A single lightning stroke, that terminate on the earth wire and/or tower can lead to back flashovers. This flashover depends on factors such as conductor type, tower, soil resistivity and magnitude of the stroke. The flashover across the insulator and the resultant fault current surge will propagate along the line, until it is extinguished or the breaker operates. This movement of the surge currents tend to damage and reduce the life span of associated equipment such and circuits breakers, insulators, transformers and impact network performance adversely. Furthermore, this operation of the protective devices leads to power interruption to consumers on that network, and loss of production, thus negatively impacting the economy. This thesis investigates the incidences of network failure due to lightining strokes occuring on Eskom HVAC network as well as HVDC networks, considering soil resistivity, tower footing resistance and factors that influence the earthing resistances. Tower footing resistance needs to be kept uniform and as low as possible to extinguish the surge across the tower and hence reducing the back flashovers across the insulator under lightning conditions. Theoretical simulations were conducted on the different methods that are available to improve the tower footing resistance values. A case study was undertaken to ascertain the tower footing resistance of an 88kV Eskom line. The crows earthing configuration was then utilized to reduce the footing resistance to a value less than 30 ohms, using line surge arrestors (LSA) which are devices that can drain power surges to ground, if placed adequately and in sufficient numbers. Furthermore the thesis determines the relationship between the magnitude of the lightning stroke, the tower top voltage, tower footing resistance and hence the back flashover voltage that would appear on the line, which would lead to power interruptions. Surge arrestors were modelled using MATLAB software. The required number of surge arrestors per phase is thus determined that is required to drain the surge current down to earth., thus preventing power interruptions. EHV AC and DC cases studies are simulated and results are presented snd discussed.

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Browsing Doctoral Degrees (Electrical Engineering) by Author "Davidson, Innocent Ewean."