**1. Introduction**

Tramway systems are more and more di ffused today, in order to limit environmental impact from transportation field. However, their electrical feeding substations show significant margin for improvements by introduction of new features, to improve their technical characteristics.

Firstly, feeding system solutions typically do not allow the reversibility of power fluxes from electrical feeding substations (ESSs). Therefore, the braking energy can be recovered only by other trains running, when available to do that (e.g., during acceleration or constant speed phases). As deeply investigated in [1–4], if some storage capability is used, the amount of the energy to recover can be significantly enhanced.

Another option typically considered in the literature is the use of bidirectional feeding substations without any storage capability, as described in [5]. However, we must consider that in this case the amount of the recoverable energy is slightly reduced, since losses increase due to the high distances to be covered. Additionally, the absence of storage capability does not help in improving the system reliability, and the overall cost of the system is very high due to its complexity.

If non-reversible feeding substations equipped with storage are considered, the authors already did the calculation of the energy saving derived from introduction of some stationary storage systems on an existing tramway, through a simulation tool specifically developed in Modelica language, which include the electrical network, the vehicles, and the driver [6]. This tool has been validated through the experimental measurements collected from an existing tramway and outputs crosschecked

also with results given by di fferent tools, in di fferent case studies [7]. Once developed and properly set, the tool has allowed to demonstrate, from the evaluation of the annual demand of electricity from electrical feeding substations (ESSs), the cost-e ffectiveness due the introduction of a limited number of storage systems, allowing a payback time shorter with respect to the useful plant life [8,9]. However, it can be of interest to analyze if the number of installed storages can further increase with respect to what already studied, up to the installation of one storage for each electrical feeding substation (ESS), in order to increase the system reliability and to guarantee adequate levels of redundancy in the case of failure of one or more electrical feeding substations (ESSs). Additionally, when they are installed on each substation, they can also reduce the size of the transformers, since they are able to sustain peaks of power requested by the di fferent trains on track. These aspects will be widely analyzed in this paper.

Additionally, the extensive campaign of measurements also has shown the high amount of losses caused by the transformers linked to the MV network. Starting from this, a deep analysis about component technologies inside each electrical feeding substation (ESS) was carried out. In particular, utilization of the amorphous core transformer (AMT) was considered, by designing a customized version for the considered application, in order to improve e fficiency and thus verifying how much losses can be reduced.

This paper therefore shows how to systematically improve the electrical feeding substations (ESSs) from the point of view of the electrical energy utilization, moving from the improvement of the transformer technology and of the solutions regarding stationary storage systems, within a cost-e ffectiveness perspective.
