Distributed Measurement Methodology for System-Level Energy Assessment in Railway Applications
This article presents several lesser-known aspects of the difficulties involved in analyzing energy flows in complex systems such as DC railways, especially when energy recovery systems (ERSs) are present. In particular, it shows that quantifying energy savings based solely on local measurements taken on the recovery system is misleading and leads to significant overestimation. To address this issue, this article proposes a system-level methodology for assessing energy flows across an entire DC railway network. The approach is based on a distributed and time-synchronized measurement architecture, which allows for the simultaneous acquisition of voltage and current at all substations along the line. The proposed system was deployed in a measurement campaign conducted across an entire Madrid Metro line, where a reversible substation (RSS) was installed. To facilitate data analysis, a dedicated software tool has been developed that allows the visualization of all power flows of the entire system. The obtained experimental results revealed several unexpected and complex energy behaviors, including long-distance energy transfers between remote substations and nighttime circulating currents. A daily energy analysis carried out over two weeks across the entire line confirmed that the energy savings inferred from local measurements can be overestimated.