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The aim of this project is to identify methods for improving the power transfer capacity of existing overhead power lines (OHL) with changes that require small modifications of the structure. These methods usually involve re-conductoring of the line with larger ‘traditional’, all aluminium alloy conductors (AAAC) or aluminium conductor steel reinforced (ACSR) or more technologically advanced high temperature low sag (HTLS) conductors. These options and their effects are investigated in this thesis by considering the overall OHL system and not only the conductor. Towards this end a holistic computational methodology has been developed to allow sag-ampacity-tension calculations considering electro-mechanical properties of arbitrary OHL systems. This methodology can be used for any aerial power line design to calculate the maximum sag, ampacity and losses developed under specified weather and operating conditions on flat and inclined terrain with common or novel conductors. Surveyed data of three OHL sections were used to verify the accuracy of the methodology. The results showed that the electrical calculations were in all cases very close to the measured values, and also that the sag prediction was correct and more accurate than the existing method of fixed temperature shift on two of the sections. Results are subsequently presented as illustrative applications of this methodology to show potential benefits from such a holistic perspective on the system. Firstly, the mechanical performance of conductors on a 33 kV wood pole OHL system is considered as a continuum and is divided into three main zones of sag which describe the system’s performance for different conductor sizes. Due to the complexity of OHL systems it was considered important to firstly examine the performance of the traditional AAAC and ACSR conductors on the structure and identify the influence of key parameters of the system (OHL strength, conductor strength, conductor weight etc.) on electrical and mechanical performance. This led to the conclusion that AAAC perform better on this particular system than the ACSR conductors due to their lighter design. Another comparison involved HTLS conductors which are known for their high improved performance at elevated operating temperatures (above 90 °C). Results indicated that the aluminium conductor composite core conductors (ACCC/TWs), which have also improved performance at normal operating temperatures, can allow voltage uprating of an existing 33 kV system up to 66 kV. Finally, performance analysis was performed for a 275 kV lattice tower OHL system, and it was found that the composite HTLS conductor types studied can double the ampacity of the lattice tower OHL. It was also found that conductor bundle configuration has better performance due to the reduction in weight and increase in strength. This allows larger conductor sizes on the same OHL structure, a conclusion which also identifies the importance of OHL structure strength on its overall performance.

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In contemporary power system studies, the optimal allocation and utilisation of Flexible AC Transmission System (FACTS) devices are imp0l1ant issues primarily due to their cost as well as their multifunctional capabilities. In this thesis, a depth literature review regarding the technical contribution of FACTS devices along with their allocation methods in power systems is presented. Four types of FACTS devices (Static Var compensator (SVC), Thyristor-Controlled Series Capacitor (TCSC), Thyristor-Controlled Voltage Regulator (TCVR), and Thyristor-Controlled Phase Shifting Transformer (TCPST)) are considered for optimal placement in a multi-machine power system to reduce the overall costs of power generation. The placement methodology simultaneously considers the cost of generated active and reactive powers and the cost of selected FACTS devices for a range of operating conditions. The annual Load Duration Curve (LDC) has been used in the selection of the operating conditions in order to make the proposed allocation beneficial over the year and to remove any bias in the device selection. Two global optimisation techniques: the Genetic Algorithm (GA) and a new method based on the Low Discrepancy Sequences (LOS), are employed to solve the allocation task. The Optimal Power Flow (OPF) is integrated into the proposed optimisation methods in order to solve for the cheapest generation dispatch. The Net Present Value( NPV) method is then utilised to assess the economic value of the solution. The NPV evaluation study includes a detail discussion of the uncel1ainties involved in the NPV main parameters. The system steady state propel1ies in terms of voltage profile and power transfer are investigated after the allocation of the devices in order to avoid any adverse effects of such allocations. The Voltage Security Margin (VSM) is used in the voltage profiles assessment which measures the relative voltage strength. In addition to the steady state performance assessment, the system dynamics has been examined as well after the placement of the devices in order to find out the devices impact on the system stability, both small signal and transient, as the contribution of such devices to damping the electromechanical oscillation represents a crucial benefit. In this assessment, a systematic explanation of the FACTS devices incorporation in the muItimachine power system is presented in addition to a method of coordinated tuning of the system damping controllers. Furthermore, an observability study is performed for the selection of the FACTS devices damping controllers input signals.

The thesis summarizes the results of the author's research performed over the last ten years, of which nine and a half, at the University of Manchester (formerly UMIST). It focuses on a set of 38 journal papers published over that period and highlights the authors major research contributions in two quite diverse areas, namely, power system dynamics and power quality. Though quite diverse, these areas are connected in the authors work by a common, underlying stream of probabilistic/stochastic modelling of uncertainties of events and system parameters.

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