Research Publications (Engineering and Built Environment)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215
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Item Enhancing the performance of Eskom’s Cahora Bassa HVDC Scheme and Harmonic Distortion Minimization of LCC-HVDC Scheme using the VSC-HVDC link(MDPI AG, 2022-04-20) Davidson, Innocent Ewean; Oni, Oluwafemi Emmanuel; Aluko, Anuoluwapo; Buraimoh, ElutunjiCahora Bassa, a thyristor-based High Voltage Direct (HVDC) link, transmits 1920 MW of power from a hydro-power plant in Zambezi River, north of Mozambique, to Apollo Substation in Johannesburg, South Africa. The high degree of harmonics distortion that is transferred into the AC side of the transmission network and the continuous increase in the rate at which commutation failure occurs during systems disturbance are both flaws in the utilization of this HVDC converter technology. AC and DC filters with rugged controllers are often used to minimize this effect but are limited in scope. Modern converter technology, such as the Voltage Source Converter (VSC), was proposed in this study to reduce harmonics content level, increase power transfer capabilities, enhance network stability, and reduce the rate of commutation failure occurrence. This paper, therefore, evaluates the performance analysis of the Cahora Bassa HVDC link and its level of harmonic distortion in the line commutated converters. A proposed method of utilizing VSC HVDC is provided as a suitable solution using three modular-level voltage source converter technology. Current and voltage waveform characteristics during a three-phase short circuits fault were analyzed, and the latest developments in the area of VSC HVDC were discussed. The results show a lower total harmonics distortion with the usage of VSC HVDC converter technology at the inverter station. The continuous occurrence of commutation failure was minimized by implementing a new converter architecture. The network simulation and analysis were carried out using the DIgSILENT PowerFactory engineering software tool.Item A review of long-distance UHVDC technology : a future energy disrupter(IEEE, 2020-03) Davidson, Innocent E.It is proposed to use highly complex power system controllers to integrate African power grids into one super-grid that can accept large penetration of renewable powers, without compromising power quality, active and reactive power flow, and voltage and power system stability. The proposed super-grid constructed with ultra-high voltage direct current (UHVDC) and flexible ac transmission systems (FACTS) along with dedicated ac and dc interconnectors with intelligent systems applications to produce a Smart Integrated African Super-Grid. DC interconnectors will segment the entire continent's power systems into five large asynchronous segments (regions). Asynchronous divisions will prevent ac fault propagation between sections while allowing power exchange between different parts of the super-grid, with minimum difficulty for grid code unification or harmonization of regulatory regimes across the continent as each segment maintains its autonomy. A Smart Integrated African Electric Power Super-Grid powered by these technologies is critical in supporting Africa 's sustained economic growth and development; established on the cornerstone of renewable energy and utilizing over 200GW enormous potential of Africa's clean and renewable hydroelectric, photovoltaic and wind power as a portion of a vast energy mix made of traditional and complementary energy resources.Item A review of LCC-HVDC and VSC-HVDC technologies and applications(EEEIC International Publishing, 2016) Oni, Oluwafemi Emmanuel; Mbangula, Kamati I.; Davidson, Innocent EweanHigh Voltage Direct Current (HVDC) systems has been an alternative method of transmitting electric power from one location to another with some inherent advantages over AC transmission systems. The efficiency and rated power carrying capacity of direct current transmission lines highly depends on the converter used in transforming the current from one form to another (AC to DC and vice versa). A well configured converter reduces harmonics, increases power transfer capabilities, and reliability in that it offers high tolerance to fault along the line. Different HVDC converter topologies have been proposed, built and utilised all over the world. The two dominant types are the line commutated converter LCC and the voltage source converter VSC. This review paper evaluates these two types of converters, their operational characteristics, power rating capability, control capability and losses. The balance of the paper addresses their applications, advantages, limitations and latest developments with these technologies.Item Harmonic distortion of LCC-HVDC and VSC-HVDC link in Eskom's Cahora Bassa HVDC Scheme(IEEE, 2016-11) Oni, Oluwafemi E.; Davidson, Innocent EwaenCahora Bassa, a thyristors based HVDC link transmits 1,920 MW of power from hydropower plant located in Zambezi river, north of Mozambique to Johannesburg, South Africa. This HVDC converter suffer few deficiency in its high level of harmonics distortion that transferred into its AC side of the transmission network couple with persistence rate of commutation failure. AC and DC filters with rugged controller are often used to minimize this effect but are limited in some aspect. Modern converter technology used for different HVDC links reduces harmonics content level, increases power transfer capabilities, enhances network stability and finally reduced the rate of commutation failure. This paper therefore investigate the level of harmonic distortion in line commutated converter used in Cahora Bassa link and thus proffer a suitable solution with the use of VSC-HVDC link. Current waveform characteristics and latest developments was also addressed. Simulation analysis was carried out using DigSILENT PowerFactory.Item Dynamic voltage stability studies using a modified IEEE 30-Bus system(IEEE, 2016) Oni, Oluwafemi E.; Davidson, Innocent Ewaen; Mbangula, Kamati N. I.Power System stability is an essential study in the planning and operation of an efficient, economic, reliable and secure electric power system because it encompasses all the facet of power systems operations, from planning, to conceptual design stages of the project as well as during the systems operating life span. This paper presents different scenario of power system stability studies on a modified IEEE 30-bus system which is subjected to different faults conditions. A scenario whereby the longest high voltage alternating current (HVAC) line is replaced with a high voltage direct current (HVDC) line was implemented. The results obtained show that the HVDC line enhances system stability more compared to the contemporary HVAC line. Dynamic analysis using RMS simulation tool was used on DigSILENT PowerFactory.Item A review of LCC-HVDC and VSC-HVDC technologies and applications(IEEE, 2016) Oni, Oluwafemi E.; Davidson, Innocent E.; Mbangula, Kamati N.I.High Voltage Direct Current (HVDC) systems has been an alternative method of transmitting electric power from one location to another with some inherent advantages over AC transmission systems. The efficiency and rated power carrying capacity of direct current transmission lines highly depends on the converter used in transforming the current from one form to another (AC to DC and vice versa). A well configured converter reduces harmonics, increases power transfer capabilities, and reliability in that it offers high tolerance to fault along the line. Different HVDC converter topologies have been proposed, built and utilised all over the world. The two dominant types are the line commutated converter LCC and the voltage source converter VSC. This review paper evaluates these two types of converters, their operational characteristics, power rating capability, control capability and losses. The balance of the paper addresses their applications, advantages, limitations and latest developments with these technologies.