Power System Protection is the application of devices that monitor the power line currents and voltages (relays) and generate signals to de-energize fault sections of the power network by circuit breakers. Protective relaying is a vital part of any electric power system, protecting the system against a fault or other abnormal conditions. Protection Technologies of Ultra-High-Voltage AC Transmission Systems considers the latest research on UHV, UHV transmission line electromagnetic field, transmission line parameters, and tower structures, with a focus on protective relaying of UHV transmission systems. Countries are continuing to build UHV transmission systems on a large scale meaning attention has to be given to the possibility of network interconnection via high-voltage transmission systems. This book gives insights into protective relaying of UHV AC transmission systems and will shed light on the conundrum of protective relaying for the EHV systems as well as laying the technical foundation for the operation of UHV power systems. It elaborates on both traditional relaying and the application of new type current differential protection, distance protection and automatic reclosing, as well as protective schemes for transformers and reactors in UHV transmission systems. This book will serve as an important reference for technical personnel in network design and operation, as well as students and engineers in related engineering areas. Compares new advances and trends in Ultra-High-Voltage (UHV) transmission system from a global aspect Describes for the first time in a book 'UHV protection technologies' Evaluates conventional protection and novel protection principles in applied and verified global systems.