Year

2018

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering

Abstract

Fault current levels are rising across electrical grids globally as grid infrastructure ages, energy demand increases and energy sources become increasingly decentralised. Utility operators have mitigated the problem through use of conventional approaches such as network splitting and grid impedance increases. However, these approaches lead to loss of supply redundancy and an increase in generation losses. The ideal solution is a system with minimal operating impedance, cost and energy consumption. Its reaction to grid-faults must be instantaneous and fail-safe, inserting a level of impedance that significantly limits the fault current, then instantaneously returns to its low impedance state once the fault has been extinguished. Numerous technologies have been developed that meet most of these requirements, though none entirely meets all.

Superconducting Fault Current Limiters (FCLs) are one solution that has been proposed. Saturated Core FCLs are typically a variant of these, in which a Superconducting Magnet system is used to magnetically bias the devices steel core(s) around which coils carrying the grid load current are positioned. Further development of Saturated Core FCLs is the subject of the research presented in this thesis. The main disadvantages of devices in this technology class are the physical size and weight of the devices at distribution and transmission voltage levels, along with the cost of the superconducting magnet systems used to bias the core steel.

New configurations of Open Core Fault Current Limiters, that eliminate the requirement for much of the core steel in higher voltage applications, were developed, characterised and optimised in this work. Novel magnetic arrangements of the AC and DC magnetic systems were developed to inherently protect the Superconducting DC bias coils, such that the requirement for expensive and complex electrical and magnetic protection systems could be reduced. New FCL arrangements providing significantly improved fault and impedance characteristics were developed. Total DC bias requirement was reduced to such an extent that much of the complex and expensive superconducting material and magnet ancillary systems could be eliminated.

The investigative, research and technical developments made in Saturated Core FCL technology presented in this thesis, offer significant contribution to fundamental knowledge in the field. Numerous FCL devices designed around the principles and functional understanding developed in this work were manufactured and installed in Utility grids as demonstration projects. Implementation of further developments made in this work, leading to superior FCL performance, cost and reliability, are being incorporated in commercialisation projects ongoing in the area.

FoR codes (2008)

0906 ELECTRICAL AND ELECTRONIC ENGINEERING, 0913 MECHANICAL ENGINEERING, 0915 INTERDISCIPLINARY ENGINEERING

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.