Distributed generation (DG) is increasingly employed in modern utility grids to address the growing complexity and size of consumer energy demands. The obstacles associated with DG integration are related to the additive effect the DG has on the short circuit current characteristics of power systems during short circuit conditions. This thesis proposes a novel mitigation technique for synchronous machine based DG integration effects on existing radial fuse-recloser protection infrastructure. The mitigation method provides a comparative analysis of the utilization of resistive (R), inductive (L) and resonant (LC) type superconducting fault current limiters (FCLs) for prevention of excessive fault current contribution from DG sources. Within the frame of reference of this thesis is an interrogation into the effects of synchronous machine based DG sources, in conjunction with mitigation capabilities of FCL integration in the context of fuse-recloser coordination, recloser sensitivity and recloser directionality behavior during radial distribution short circuit conditions. For validation purposes, the proposed methods are demonstrated on a suburban test benchmark using the PSCAD/EMTDC program.

The gradual increase in global warming and environmental pollution has made low-carbon technologies an urgent need for the whole world. Superconducting technology, which is known for its extremely high conductivity and high power density, is capable enough to provide novel solutions, contributing to the future smart grid, thus aiding the power industry towards the realisation of a low-carbon and green planet. In recent decades, several industrial applications using superconducting technology have been developed. Of them, particularly in the power industry, a range of superconducting applications including superconducting magnetic energy storage (SMES), superconducting motors/generators, superconducting cables and superconducting fault current limiters (SFCLs) have been developed. Among them, SFCLs are one of the most promising and are successfully being implemented in power distribution networks. SFCLs exhibit low impedance during normal operation and gain considerable impedance under a fault condition, providing a new solution to the increasingly high fault current levels. However, most of the SFCL projects are limited to low-voltage and medium-voltage levels, there are very few successful operational trials of high voltage SFCLs. This thesis, for the first time, studies the comprehensive characteristics of solenoid type SFCLs based on second generation (2G) high temperature superconductors (HTS), which may be successfully implemented in power grids with high voltage levels. The main contributions of this work include three aspects: 1) proposing an innovative method for simulating the AC losses of the solenoid coils and an electro-magneto-thermal model for simulating the SFCL’s current limiting property; 2) comprehensive and in-depth comparison study concerning the application of the two types of non-inductive solenoid coils (braid type and non-intersecting type) in SFCLs both experimentally and numerically; and 3) the first and thorough discussion of the impact of different parameters such as pitch and radius of coils to the overall performance of braid type SFCLs and the validation of the braid type SFCL concept with a 220 V/300 A SFCL prototype. Based on these experimental and simulation works, the thesis provide strong guidance for the development of future non-inductive solenoid type SFCLs based on 2G HTS, which are promising for high voltage level power grid applications.

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The thesis begins with an introduction to transformer theory. The partial core transformer is then introduced and compared with a full core design. A brief introduction to superconductors and high temperature superconductors is then presented. High temperature superconducting fault current limiters are then examined and the advantage of a high temperature superconducting partial core transformer and fault current limiter as a single unit is highlighted. The reverse design model is discussed followed by the model parameters that are used in designing the high temperature superconducting partial core transformer. Partial core transformers with copper windings and high temperature superconductor windings at the University of Canterbury were then tested and the measured results compared with the results calculated from the reverse design model, to validate the model. The high temperature superconducting partial core transformer failed during an endurance run and the investigation of the failure is then presented. The results of the failure investigation prompted an alternative winding insulation design. A model to calculate the time at which the high temperature superconducting winding of the partial core transformer would melt at different currents was then built. The time was calculated to be used in the operation of the quench detection mechanism and it could also be used in choosing a circuit breaker with a known operating time. The design of the high temperature superconducting partial core transformer and fault current limiter is then presented. Design configurations with different core length and winding length are examined. The idea behind choosing the final design for the high temperature superconducting partial core transformer and fault current limiter is then discussed. The final design of the high temperature superconducting partial core transformer and fault current limiter is then presented. A new 7.5 kVA, 230-248 V high temperature superconducting partial core transformer and fault current limiter was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. A series of electrical tests were performed on the new device including open circuit, short circuit, resistive load, overload and fault ride through. These tests were performed to determine the operational characteristics of the new high temperature superconducting partial core transformer and fault current limiter. The measured results from the tests were compared with the calculated results. The fault ride through test results were then compared to a 15 kVA high temperature superconducting partial core transformer that was designed and built at the University of Canterbury. Since the resistive component of the silver matrix in Bi2223 high temperature superconductor plays a very little role in controlling the fault current, the current limited by the leakage reactance is compared between the two devices. The high temperature superconducting partial core transformer and fault current limiter was found to be 99.1% efficient at rated power with 5.7% regulation and fault current limiting ability of 500 % over the 15 kVA high temperature superconductor partial core transformer from University of Canterbury.