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.