This research report is submitted as a partial fulfilment of the requirements for a Master of Science degree in Electrical Engineering (Power). / Thyristor Controlled Series Capacitors (TCSCs) are FACTS devices which incorporate power-electronic-based and other static controllers to enhance controllability and increase power transfer capability. This research investigated the possibility of applying TCSCs on the South African transmission network, in particular application on long transmission lines connecting bulk thermal generators in the northern part of South Africa to load centres located hundreds of kilometres elsewhere in the country. The investigation, conducted using PSS/E (a power system analysis software) demonstrated that application of TCSCs on this part of South African transmission network results in improved transient stability margins. The resulting improvement in transient stability is comparable to other transient stability enhancement options like addition of transmission lines, thus the use of TCSCs can be considered as an alternative. Further studies would be vital to understand the interaction between Power System Stabilizers (PSSs) and TCSCs in order to ensure proper tuning and interaction amongst the devices. / MT2017

M. Tech. Electrical Engineering. / Discusses energy as the basic necessity for the economic development of a country. Many functions necessary to present-day living grind to halt when the supply of energy stops. Energy exists in different forms in nature but the most important form is the electrical energy. Therefore, enhancing power flow in transmission systems is important for efficient power supply because a modern-day society requires a large amount of electrical energy for domestic, commercial and industrial purposes. Among the various means of enhancing power flow in transmission systems with the help of FACTS devices, this research work focussed on the aspect of improving the power system stability. Therefore, efficient supply of electric power to various customer load demands can be achieved when the future power system engineers and researchers carry out nonlinear modelling, bifurcation analysis and control of their system with FACTS devices such as TCSC for power system stability enhancement.

The power transfer capability of a transmission line is determined by the magnitude of the voltage at each end of the line, angle difference of these voltages and the impedance of the line. This impedance is mainly inductive. Traditionally, fixed series capacitor banks have been used for series compensation. However, due to instability problems associated with loading transmission line close to their thermal limits, researchers have looked at other alternatives to line compensation by static devices such as fixed series capacitors. Flexible AC Transmission Systems (FACTS) has allowed power utilities to use existing transmission line networks close to their thermal limits without compromising stability of the power system. A FACTS series compensator is capable of influencing the transmission of power in a transmission line by dynamic control of the series compensating reactance inserted in the line. There are several different devices under the FACTS family, however, in this thesis only the Thyristor-Controlled Series Capacitor (TCSC) was considered. A TCSC comprises a fixed capacitor in parallel with a thyristor-controlled reactor (TCR). By varying the firing angle ex:. of the thyristors, the TCSC can be made to act in variable inductive or capacitive reactance mode. The thesis' overall objective was to design a practical TCSC for use in a research laboratory for further research initiatives. This thesis looks at different issues that need to be considered when designing and rating a TCSC compensator. In particular, the thesis examines the effects of different sizes of TCSC components on the rating of the device, the effects of harmonics on the TCSC ratings, sizing of TCSC's variable reactance, and the response time of TCSC to a step change in the firing angle. A mathematical model of a TCSC in a single-machine infinite bus (SMIB) system was developed and subsequently used in the initial design of the TCSC. Studies that were done using mathematical model of the TCSC module confirmed the ability of the TCSC controller to dynamically control the capacitive compensating reactance in the transmission line. The thesis then describes the development of a laboratory-scale TCSC for research investigations. Measured results from the laboratory demonstrate the ability of the TCSC series compensator to provide rapid control of series reactance of a transmission line. A detailed mathematical model of the SMIB equipped with TCSC module was developed, using parameter values of the laboratory scale prototype, to investigate power oscillation damping. Time-domain simulation results are presented in this thesis to demonstrate its ability to damp power swings in an electrical network. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

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