Electromagnetic Time Reversal: Theory, Application to Fault Location in Power Networks and Experimental Validation

The time-reversal invariance is readily described and universally embodied in most laws of nature, either in a strict or in a soft sense. Based on this underlying physical principle, time-reversal theory has been theoretically and experimentally studied in the field of acoustics first, and later introduced into electromagnetism, under the general denomination of Electromagnetic Time Reversal (EMTR). With the development of modern power system, especially represented by the technology of Smart Grids and Active Distribution Networks (ADNs), a reliable and efficient fault detection and location functionality is increasingly required to ensure the security and quality of supply. It has recently been shown that an EMTR-based fault location technique can provide superior performance with respect to existing techniques in terms of location accuracy and robustness against uncertainties. At the same time, several theoretical and technological challenges have to be addressed before such a technique can be used in real-world applications. The present work aims at addressing these challenges, which are summarized hereunder. Time reversal cavity applied to power networks. The concept of the time-reversal cavity was proposed by Cassereau and Fink for acoustic waves and later extended to electromagnetic waves. It is accepted that a time-reversal cavity is a theoretical concept and cannot be realized experimentally because it requires in principle an infinite number of transducers covering a closed surface around the medium to obtain information about all wavefronts propagating in all directions. Although this is true in a 3D situation, we believe that in the case of power networks in which waves are confined in a specific region of the space and propagate along the longitudinal direction of the lines (1D situation), such a time-reversal cavity is realizable. We propose to design, simulate, and experimentally validate such a cavity for the case of inhomogeneous power networks. Improving the performance of EMTR-based fault locating techniques. The currently-developed EMTR-based technique requires multiple simulations to identify the location of the fault. We will investigate possible ways of reducing the number of required simulation runs. Practical implementation of an EMTR-based fault locator. The EMTR-based method technologically requires the use of a hardware platform, such as a Field Programmable Gate Array (FPGA), capable of performing Electromagnetic Transient (EMT) simulations and post Digital Signal Processing (DSP). In order to address constraints of application in real-world power networks and robustness requirements, further improvement and optimization will be considered, namely, the determination of the minimum time-reversal window required to achieve a certain location accuracy, the development of a library of transmission lines and cables commonly used in power networks, analysis of the location error caused either by incomplete knowledge of the network, or other disturbances such as those originated by lightning, as well as limitations associated with the measurement. The final aim of the thesis is to further develop a fault location hardware platform integrating EMTR theory with numerous functionalities, like EMT simulations, DSP, interactive communication. Its performance will be verified by hardware-in-the-loop tests, and eventually by live tests in real power networks.