0885-8977 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TPWRD.2016.2615887, IEEE Transactions on Power Delivery 1 Abstract— Electromagnetic time reversal (EMTR) has been shown to be an efficient method for locating faults in AC and DC power grids. In the available literature, the back-propagation medium has been considered to have identical losses as the direct- time medium. However, the telegrapher’s equations describing the travelling wave propagation are time-reversal invariant if and only if inverted losses are considered in the back propagation phase. This paper presents an analysis of the impact of losses on the performance of the EMTR-based fault location method for power networks. In this respect, three back-propagation models are proposed, analyzed and compared. It is shown that a lossy back-propagation model, for which the wave equations are not rigorously time-reversal invariant, results in accurate fault locations. Finally, an EMTR fault location system based on the lossy back-propagation model and a fast electromagnetic transient simulation platform is developed and its performances validated. Index Terms— Fault location, electromagnetic time reversal, electromagnetic transients, telegrapher’s equations, transmission lines. I. INTRODUCTION The fault location problem has been extensively studied in the literature since 1950s [1] and numerous methods have been proposed. First, the subject was studied for transmission networks because of the importance of the fault location function in power systems operation and the difficulty of locating faults in meshed networks. Then, studies were extended to distribution networks as the power quality attracted an increased attention. The proposed fault location methods, in general, fall into two general categories (e.g., [2]): (i) phasor-based (using voltage and current phasors), or (ii) travelling wave-based methods. Using the voltage/current phasors at the line terminals is the most straightforward approach to estimate the fault location (e.g., [3], [4], [5], [6]). However, despite the straightforward solutions provided by the phasor-based fault location methods, their accuracy might be affected by the fault resistance, configuration of the line, load unbalance, and the presence of distributed generation [2]. To overcome the limitations associated with the phasor- based fault location methods, travelling wave-based methods have been increasingly investigated in the literature (e.g., [7], [8], [9], [10]). These methods rely on the analysis of the high- frequency components of the fault-originated transient signals which are rather uninfluenced by the fault impedance [11]. Despite the more precise fault location accuracy of the travelling wave-based methods compared to phasor-based methods, their accuracy might still be affected by the following factors [2]:  need of multiple observation points to avoid multiple solutions for the location of the fault.  requirement of a precise time stamping for methods requiring multiple synchronized metering stations.  loss of GPS signal impacting the fault location accuracy.  requirement for relatively sophisticated signal processing analysis To overcome the above-mentioned limitations associated with existing travelling wave-based fault location methods, an efficient fault location method based on the electromagnetic time reversal (EMTR) technique (e.g., [12], [13], [14]) has been proposed in [15]. It has been shown that telegrapher’s equations describing the travelling wave propagation along the transmission lines are time-reversal invariant. Therefore, EMTR process, which is an effective procedure in focusing electromagnetic waves, has been used to locate faults in various power network topologies including inhomogeneous networks. The EMTR method uses a straightforward procedure comprising three steps: (i) fault-originated transient signals are measured in a single observation point and then, time-reversed; (ii) a number of guessed fault locations (GFLs) is defined and for each GFL, the time-reversed signals are back-injected to the network back-propagation model and the Fault Current Signal Energy (FCSE) is calculated; (iii) according to the time reversal Assessment of the Influence of Losses on the Performance of the Electromagnetic Time Reversal Fault Location Method Reza Razzaghi, Member, IEEE, Gaspard Lugrin, Member, IEEE, Farhad Rachidi, Fellow IEEE, Mario Paolone, Senior Member, IEEE The authors are with the Electromagnetic Compatibility Laboratory (EMC) and Distributed Electrical Systems Laboratory (DESL) of the Swiss Federal Institute of Technology, Lausanne (EPFL), Switzerland, (e-mail: reza.razzaghi@epfl.ch, gaspard.lugrin@epfl.ch, farhad.rachidi@epfl.ch mario.paolone@epfl.ch).