This thesis investigates the use of flexible AC transmission systems (FACTS) and voltage source converter (VSC) high-voltage direct current (HVDC) transmission systems for improving the power transfer capability of the Libyan internal tie-line between east and west, for a secure, reliable and efficient operation of this power corridor. Mathematical-based analysis supported by numerical-based analysis, which employs NEPLAN power system analysis tool, are carried out to investigate the steady state and dynamic behaviour of the power system. Different FACTS technologies, including variable impedance based and converter-based shunt and series FACTS devices, are studied during steady-state and transient operating conditions to evaluate the capabilities, control systems and weaknesses in these technologies. The investigations focus on the common types of shunt and series FACTS including: the static VAr compensator, static synchronous compensator, and thyristor controlled series compensator. A challenge in this thesis is to find an efficient method to allocate and size FACTS devices, to ensure maximum utilization of the tie-line considering technical constraints including:; voltage rise at a point of voltage collapse, equipment terminal voltage and subsynchronous resonance risk. For the VSC-HVDC system, a mathematical model that calculates power flow throughout the HVDC link and at both AC sides is confirmed as an efficient steady-state model facilitating estimation of reactive power requirements at the converter terminal and at the point of common coupling. This model can be used to estimate the optimal converter rating based on the system strengthens at both sides. Further modelling and analysis investigates the operation of a hybrid AC/DC system. Multi-tasking control systems for voltage source converter HVDC systems are used to facilitate operation of the hybrid AC/DC system during normal and emergency operating conditions. The controllers include: frequency control in the case of an unsynchronized connection and power management control necessary to balance the power flow during an emergency, in additional to the primary control of the AC and DC voltages, and active and reactive powers. Well-known and referenced two areas Kundur test system with a weak tie-line, which suffers from a limited power transfer capability between the operating areas, is used throughout the analysis. the tie-line between two regions in the Kundur test system is investigated when incorporating different FACTS technologies and a VSC-HVDC system. Based on the introduced approaches and models the benefits and challenges of these technologies in the Libyan internal tie-line are explored. The research shows that the power transfer capability of the tie-line can be improved by shunt and to a lesser extent, by series compensation. Comparison between FACTS devices and VSC-HVDC indicates, apart from the cost, VSC-HVDC transmission may be the better option for Libyan internal tie-line improvement, especially in the near future, when secure and reliable interconnected power system is required.

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The growing issue of power-grid congestion and a global increase in disturbances have emphasized the need to enhance electrical power networks using Wide Area Monitoring, Protection, and Control (WAMPAC). This is a cost-effective solution for improving power system planning and operation. In addition to these existing issues, the Great Britain (GB) power system is facing significant changes, in terms of both power transmission technology and the nature of the generation mix, that will cause the operation of the future GB power system to become more unpredictable and complex. Therefore, developing a WAMPAC system will be essential to enhance the stability and optimise the operation of the future GB power system. The main objectives of the research presented in this thesis are to design a GB WAMPAC system and develop solutions to overcome the challenges that will be involved in the initial stage of the GB WAMPAC project. As Synchronized Measurement Technology (SMT) is the most essential element and enabler of WAMPAC, this thesis first provides a study of SMT and its applications. This study also reviews the state of the art of these SMT applications, and worldwide experience with the operation of WAMPAC in terms of system architecture, communication technologies and data management. After the basic study of WAMPAC, this thesis presents a new methodology for designing a roadmap that will ensure the future GB WAMPAC system will be developed in a logical and economic manner. This methodology takes into account the international experience with WAMPAC project management and the practical challenges faced in the future GB power system. With this new methodology, the GB strategies for the development of WAMPAC are devised. Two major SMT applications are then developed that can form main parts of the proposed future GB WAMPAC system. These applications are developed to enhance the small signal stability of the future GB power system.1. Wide Area Inter-area Oscillation Monitoring using Newton Type Algorithm.2. Wide Area Inter-area Oscillation Control using Power Electronic Devices. Finally, the operation of a proposed GB WAMPAC system is demonstrated using the DIgSILENT software package. The proposed real time applications are tested and evaluated using dynamic simulations of a full GB power system model. In addition, some key factors that will influence the operation of the future GB WAMPAC system will be analyzed and discussed.

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The development of an advanced outdoor valve requires coordinated research in the areas of light-triggered self-protecting thyristors, light triggering systems, insulation, cooling and mechanical design aspects. This thesis addresses the first two areas primarily, with a conceptual discussion of the remainder. Using the experience gained from evaluation of a prototype thyristor and computer IKdelling of turn-on behaviour, a light-triggered thyristor with immunity to damage from weak optical triggering and dv/dt triggering was designed, manufactured and evaluated. The optical turn-on process was investigated by measuring currents and voltages in the gate structure during turn-on, and this yielded insights not obtained through conventional measurement techniques. The mechanism by which the thyristor was immune to weak triggering damage is explained, and techniques for optimising the design of the gate structure are proposed. The most significant achievement, however, was the first demonstration of the feasibility of self-protection against forward recovery failure onditions. Furthermore, this was achieved without the need for complex structures or high levels of irradiation. The perfomance of the devices was limited by the inrush capability of the Zones, but it is believed that this can be improved by conventional means. A light triggering system was developed using sem~conductor lasers, and this incorporated several improvements over prior art In terms of optical performance and flexibility.

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