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    High voltage transmission system planning for a southern African regional grid
    (2022-09-29) Ndlela, Nomihla Wandile; Davidson, Innocent Ewaen
    It is proposed to use highly complex power system controllers to integrate African power grids into super-grids capable of accepting high levels of renewable energy penetration while maintaining power quality, active and reactive power flow, voltage, and power system stability. The proposed super-grid is built with ultra-high voltage direct current (UHVDC) and flexible AC transmission systems (FACTS), as well as dedicated AC and DC interconnectors with intelligent system applications, to create a Smart Integrated African Super-Grid. DC interconnectors will divide the continent's power grid into five substantial asynchronous portions (regions). Asynchronous segments will restrict AC fault propagation across segments while permitting power interchange between various regions of the super-grid, with minimal difficulties for grid code unification or harmonization of regular design regimes across the continent, as each segment retains its autonomy. A Smart African Integrated Electrical Power System Super-Grid powered by these technologies is critical to Africa's long-term economic growth and development; it is built on the foundation of green energy and harnesses over 200GW untapped potential of Africa's clean renewable hydro-electric, solar-PV, and wind power as part of a vast energy mix comprised of conventional and alternating energy resources. The proposed Super-Grid will power Africa's emerging economy and serve its 1.3 billion people by facilitating electricity trading and power exchange between regional power pools and countries. This study focuses on the development of the Southern African Power Pool (SAPP), into a robust Southern Africa regional grid (SARG), and prospects for a Smart Integrated African Super Grid. The Southern African countries have the potential to have a reliable, sustainable, and efficient electrical power grid; thus, the use of renewable energy is strongly encouraged, as is upgrading the existing AC grid, including encouraging power interconnections to exchange power more specifically for long-distance transmission networks when transmitting bulk power using High Voltage Direct Current (HVDC) and installing suitable FACTS controllers to maximize power transfer. Thus, the modernization of the traditional Power Grid into a Smart Grid will enable two-way digital communication technology by providing utilities with real-time, precise data on electricity demand, power outages, and quality of supply. This study develops a load flow model for a robust Southern African Regional Grid, and introduces a number of power interconnections for power exchange in the Southern African Regional Grid, to increase grid reliability, and reduce electrical losses. This load flow analysis was carried out using DIgSILENT PowerFactory. Results obtained from varying the load and observing the generator and transmission lines for different scenarios, using HVDC, and HVDC transmission links with FACTS controllers, are discussed and presented. This study is valuable as we seek to enable all SAPP countries to interchange power more efficiently, especially those who lack access to electricity
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    Modelling and fault ride-through control of grid supporting inverter-based microgrid
    (2021-03-02) Buraimoh, Elutunji; Davidson, Innocent Ewaen
    This thesis is focused on modeling and fault ride-through control, local load power delivery, and grid power exchange of power electronic interfaced Distributed Energy Resources (DERs) for grid supporting microgrids. Active and reactive power regulations are the requirements for a grid-supporting system operating as a current source, while frequency and voltage magnitude regulation in the grid-supporting system acting as a voltage source. Consequently, these are put into consideration as the primary control requirements for the inverter-based microgrid. To that end, two discrete-time models of a grid-feeding system and grid-forming system were developed to serve as controls for a single DER operating in grid-connected mode and islanded mode, respectively. Consequently, for the first set of mathematical models: grid feeding and grid forming were interfaced with a droop control to allow for parallel operation of additional DERs for power coordination within the microgrid for grid-connected and islanded operation. However, virtual impedance was incorporated into the grid-supporting system's droop control operating as a voltage source to emulate the link feeder's physical impedance to the main grid. Based on the developed grid supporting models, the microgrid primary control schemes effectively delivered power to the host grid and simultaneously contributed to the grid's frequency and voltage regulation. Furthermore, to ensure grid code compliance and ensure the microgrid provides ancillary services to the host grid, such as fault ride-through and reactive power compensation for voltage recovery, a novel technique is proposed in the microgrid's secondary control. The secondary control realizes the fault ride-through for the grid supporting system using a delay signal cancellation algorithm for negative sequence detection. The proposed control scheme actualizes grid code requirements by providing a secondary voltage control, which is active and more prominent in the transient period of faults without mode switching. The strategy's performance is further enhanced with an IGBT-Diodes switched AC reactor to improve the voltage and prevent the transient overcurrent in the microgrid during the grid fault. This ensures a continued supply of the microgrid's local sensitive load while meeting the grid code requirement. Similarly, the active power injection into the main grid is limited to maximize reactive power injection into the main network to support the grid voltage sag. The detection algorithm using the delayed signal cancellation algorithm is implemented to detect the instance of fault in 1.6% of the half-cycle under grid disturbance/fault to activate the proposed secondary control. This effectiveness and fault ride-through compliance of the developed control models were tested on an inverter-based microgrid system with an ideal voltage source DERs. Finally, to accommodate for the grid dynamics introduced to the DC link parameters of an ideal voltage source DER such as PV, the models were also implemented and assimilated for a solar PV sourced DER used with a grid supporting inverter-based microgrid. The injection of active power into the main grid is constrained by systematically shifting the MPPT operating point based on voltage sag depth to maximize reactive power injection to support the grid voltage sag. The strategy developed in the PV sourced system also ensured that the DC-link voltage and AC grid current raises are suppressed while meeting microgrid load requirements. The models' implementation, DER primary control, and proposed secondary control schemes are established through detailed time-domain simulation studies using MATLAB Simscape Electrical™ and Control System™.
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    Integrating the power transformer protection scheme to Telecontrol Terminal Unit (RTU)
    (2018-12) Madonsela, Bhekinkosi Pheneas; Davidson, Innocent Ewaen; Mulangu, T. C.
    Automated substations and distribution networks are key element of smart grid, however not all substations and distribution networks are automated to date due to the numerous reasons such as cost related to automation and scarcity of skilful workforce. With the drive to integrate renewable energy to the national smart grid, the advanced and innovative integrating methodologies need to be investigated. Automating the power system is the effort to improve power supply security, availability and reliability. Reliability is very important in substation automation systems and is achieved through real-time monitoring of the substation data. The interconnection of substation through substation automation devices is crucial because it provide the backup link to the network in case one substation fails. The utilities has developed a remarkable interest in substation automation due to the benefit its offers such as; reduction in maintenance and, operating cost and improved revenues due to stable power system networks. Substation automation is made up of four main functions that need to be fused together; protection, control, monitoring and, local and remote communications. There are numerous communication protocols available in the market for substation automation applications. However not all of them are utilized in the current application of smart grid.DNP3 and IEC61850 are the leading communication protocols currently. DNP3 has proved its technical advantages over the past few years in substation automation applications. On other hand IEC61850 was only published in 2003 and became more popular in substation around 2006; the standard is only fifteen years old. IEC61850 define the protocols such as; GOOSE, SMV, GSSE, GSE and MMS using its communication profiles. This research will investigate the possibilities of integrating DNP3 data point into IEC61850 data model. With this approach; the legacy substation shown in figure 1.1 will inherit the advantages of IEC61850 such as high speed data exchange, interoperability and interchangeability
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    Modeling and recognition of faults in smart distribution grid using maching intelligence technique
    (2018) Onaolapo, Adeniyi Kehinde; Akindeji, Timothy Kayode; Adetiba, Emmanuel
    Electrical power systems experience unforeseen faults attributable to diverse arbitrary reasons. Unanticipated failures occurring in power systems are to be prevented from propagating to other parts of the protective system to enhance economic efficacy of electric utilities and provide better service to energy consumers. Since most consumers are directly connected to power distribution networks, there is an increasing research efforts in distribution network fault recognition and fault-types identifications to solve the problem of outages due to faults. This study focuses on fault recognition and fault-types identification in electrical power distribution system based on the Design Science Research (DSR) approach. Diverse simulations of fault types at different locations were applied to the IEEE 13 Node Test Feeder to produce three phase currents and voltages as data set for this study. This was realized by modelling the IEEE 13-node benchmark test feeder in MATLAB-Simulink R2017a. In order to achieve intelligent fault recognition and fault-type identification, different Multi-layer Perceptron Artificial Neural Networks (MLP-ANN) models were designed and subsequently trained using the generated dataset with the Neural Network toolbox in MATLAB R2017a. The fault recognition task verifies if a fault occurs or not while the fault-types identification task determines the fault class as well as the faulty phase(s). Results obtained from the various MLP-ANN models were recorded and statistically analyzed. Acceptable performances were obtained for fault recognition with the 6-25-20-15-1 MLP-ANN architecture, for fault-types identification with the 6-40-4 MLP-ANN architecture and for fault location with the 6-30-15-5-4 MLP-ANN architecture. Given the result obtained in this study, MLP-ANN is adjudged suitable for intelligent fault recognition and fault-types identification in power distribution systems. The trained MLP-ANNs in this study could ultimately be incorporated in power distribution networks within South Africa and beyond in order to enhance energy customers’ satisfaction.