Monitoring a DC train supplied by a reversible substation

European energy policy has been supporting a gradual shift towards an efficient energy management in order to reduce the railway transport emissions by 50 % within 2030. One of the most promising solutions to reduce emissions is the recovery of braking energy: it is possible to convert kinetic energy back to the electrical form and reinject it back to the grid. Currently, because of the unidirectional nature of the substation, the receptivity of the supply network is limited and only a small part of the traction energy is sent back to the catenary. The remaining part is usually wasted on the train braking rheostats. In this scenario, new installations of reversible substations in DC railway systems, can improve energy savings. In this paper, in order to evaluate the impact of this innovative technology, a preliminary analysis of the data acquired during a measurement campaign conducted jointly with Metro de Madrid (train and substation owner) and HitachiRail (train manufacturer) is presented. Energy exchanged between train and supply line and real-time power quality events survey can be valuable tools to make an estimation of the impact of the reversible substation.