Degree Name

Doctor of Philosophy


School of Electrical, Computer and Telecommunications Engineering


This thesis addresses the topic of power system protection which its main objective is to keep the power system stable by isolating faulted section of electrical power system so that the rest of network can operate properly without any severe damage due to high fault current. To achieve this objective, protective relays measure electrical quantities and depending on their internal algorithm issue trip signals to circuit breakers that are designed to isolate faulty section from the rest of network.

With this in mind, recent development of renewable energy (RE) technologies has led to the erection of RE power plants with capacities in the order of several hundred megawatts. Increasing the penetration level of inverter-interfaced renewable energy power plants (IIREPP) negatively affect the performance of the protective relays in both transmission grids and DNs. On the other hand, power line faults have been recognised as one of the main causes of wildfires in Australia and across the world as legacy protection schemes cannot provide an efficient protection to prevent ignition of wildfires in such grids.

This thesis aims to develop a number of advanced power system protection tools and related strategies to ensure the secure and reliable operation of future transmission and distribution networks. At transmission level, challenges associated with FRT requirement of IIREPPs, which if not adequately addressed may adversely affect the correct operation of protection systems, have been analysed and investigated in this thesis. In this regard, the security of distance protection has been investigated in DCMC TLs during high penetration level of Inverter Based Resources (IBRs). Then, the performance of distance protection, fault detection and classification, directional relays, power swing blocking (PSB), and out-of-step tripping (OST) functions have been scrutinized. The advanced protection tools are then developed to enable transmission line (TL) protection relays to retain their security and dependability in transmission grids dominated by a high penetration level of IIREPPs.

The time-domain simulation including details modelling of the IIREPPs with FRT capability has been employed in this study, in which the detail model of doubly fed induction generator (DFIG)-based wind farms and full-scale converter-interfaced permanent magnet synchronous generator (PMSG) have been considered. The Thesis examines the unique fault response of the IIREPPs to identify the possible relay malfunction. Moreover, to reduce the risk of unstable power swing following the large disturbance nearby the synchronous generators, a new setting-free out-of-step (OOS) protection strategy is developed for synchronous generators (SGs).

At distribution level, power line faults have been recognized as one of the main causes of the wildfires in Australia and around the world. In this regard, rapid earth fault current limiter (REFCL) technology has been recognized as an efficient solution to be employed in resonant grounded distribution networks (RGDN) to reduce the risk of wildfire. The thesis has analysed the performance of the REFCL technology along with the limited fault current magnitude in RGDN in details. Further, the thesis has proposed a novel protection strategy for RGDNs with REFCL to detect and locate faults based on the local information at the relay location. The proposed protection scheme can be implemented through microprocessor-based relays which are commercially available, and hence can be practically realized. A novel overvoltage protection scheme based on the principle of the voltage clamping is developed to eliminate any transient overvoltage caused in DNs following the REFCL activation.

The developed strategies in the thesis combine to provide innovative solutions to enable modern power systems dominated by the IIREPPs and REFCL to have secure and reliable protection relaying during contingencies. The thesis contributes to the state-of-the-art of numerical protective relays and proposes methods to improve their operational performance in transmission as well as distribution grids dominated by high penetration levels of IIREPPs or with REFCL technology.

FoR codes (2020)

400803 Electrical energy generation (incl. renewables, excl. photovoltaics), 400805 Electrical energy transmission, networks and systems



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.