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In recent decades, power systems worldwide have seen a significant increase in power electronic converters to facilitate the integration of renewable energy, e.g., solar and wind energy, and also for the transmission of electrical power between different areas, e.g., High-Voltage Direct Current (HVDC) links. Unlike Synchronous Generators (SGs), Converter-based Resources (CBRs) cannot generate high magnitude fault currents and their fault characteristics are dependent on implemented control strategies, which are governed by the associated grid codes. Those features of CBRs can pose severe challenges to the reliable operation of protection systems designed based on the fault characteristic of SGs. Two typical application scenarios with high penetrations of CBRs are investigated in this thesis, which includes the HVDC system connected to the transmission system and the low-voltage (LV) microgrid connected to the distribution system. In this thesis, the performance of distance protection is evaluated systematically using the Hardware-in-the-Loop (HIL) approach on two commercially available relays. Based on HIL test results and further supported by the theoretical analysis, it was found that the performance of the distance relay is compromised significantly after the connection of CBRs such as HVDC systems. The observed issues include the distance under/over-reach, incorrect faulted phase selection, problematic impedance measurement and oscillating impedance locus. A novel sequence component-based distance measuring element is proposed in this thesis to accurately reflect the fault distance and thus address the under/over-reach issue of the conventional impedance based distance algorithm, whose performance is verified by the simulation conducted using the Real-Time Digital Simulator (RTDS) under a wide range of system and fault conditions including varied fault types, fault resistances, fault positions, system fault levels and protected line length. Based on simulation results, the proposed algorithm can measure the fault distance accurately and trip faults within the time required by the GB grid code. Except for HVDC systems in the transmission system, significant amounts of inverter-interfaced distributed generators (IIDGs) are also connected to the distribution system, which poses severe challenges to the existing overcurrent protection relays because of the reduced fault contribution of IIDGs and the bi-directional power flow. Therefore, some solutions must be designed to protect the future distribution system. As an emerging type of distribution system, the microgrid, a compact network comprising generators, loads and storage devices, is selected in this thesis to investigate the protection challenges of the future distribution system and demonstrate the development of a new energy-based protection scheme. In normal conditions, a microgrid is typically connected to the main grid, i.e., grid-connected microgrid, but when severe disturbances occur, e.g., loss of major generation or faults, it can be safely disconnected from the main grid and run as an independent islanded system, i.e., islanded microgrid. This dual mode capability results in the dynamic variation of fault levels in different operating modes, where the fault level is reduced substantially in the islanded mode due to the loss of the fault infeed from the main network and the limited fault current contribution from IIDGs. Additionally, different fault responses of IIDGs in a microgrid, governed by embedded controllers of inverters, also increase the risk of protection failure. To address issues of fault level variation of two operating modes, reduced fault current infeed in the islanded mode, and non-uniform fault characteristics of CBRs, an energy-based protection scheme is designed in this thesis to protect LV microgrids, where the energy of high-frequency transients resulting from the reflections of travelling waves are extracted using the Maximal Overlap Discrete Wavelet Transform (MODWT) algorithm, and relays in microgrids are coordinated by a developed algorithm. The performance of the proposed protection algorithm is evaluated using a 400-V CIGRE benchmark microgrid implemented in MATLAB/SIMULINK. In summary, this thesis evaluates the challenges of conventional distance and overcurrent protection in transmission and distribution systems (i.e., microgrids) where high amounts of CBRs/IIDGs are expected. Solutions proposed in the literature are reviewed, along with a comprehensive discussion of their benefits and limitations. Additionally, a sequence components-based distance protection algorithm and a novel high-frequency transient-based protection scheme are developed in this thesis to protect transmission lines connected to CBRs and microgrids dominated by IIDGs.

This dissertation describes a system that analyses and summarises the operation of protection and provides backup protection functionality, using only voltage data from PMUs and wide-area communications infrastructure. The ability to rapidly identify the presence of faults, their locations and the presence of protection/circuit breaker failures, solely from voltage measurements, is the overarching contribution from this work. The scheme can operate in addition to existing backup schemes to provide a further, or alternative, relatively inexpensive, effective, simple, fast, wide-area backup protection to improve the resilience of power systems. Methods of power system model simplification for different types of fault have also been developed for establishing the capabilities and voltage thresholds of the scheme, and this simplification method is also claimed as a contribution arising from the work. It is shown how the system can operate for a wide range of fault levels, types and resistances - thereby addressing one of the key challenges for protection associated with concerns over protection in the context of reducing and more variable fault levels in future power systems. To validate the developed scheme, case studies assessing scheme performance in several scenarios are presented. Variations of fault resistance, time of fault occurrence, fault location, and fault levels are simulated in Matlab (Simscape Power Systems) using the well-established and accepted IEEE 14-bus network. Hardware in the loop tests are also conducted using an RTDS and actual PMU devices to test and validate the performance of the scheme and to demonstrate its ability to operate using actual hardware and in real time. Applicability of the developed system to large-scale power networks is also demonstrated. It is shown that the scheme is suited to interconnected power systems, and can operate with both reduced fault levels and for different types of faults with high resistances.