Newsletter December 2025
High-Resolution and Synchronized Measurement System for Metro de Madrid DC Traction Network
The University of Campania “Luigi Vanvitelli” and INRiM – Istituto Nazionale di Ricerca Metrologica in close collaboration with Metro de Madrid, has deployed a distributed, high-resolution measurement system across five consecutive substations on the final segment of Metro de Madrid’s Line 10.
This installation establishes a sophisticated platform for the in-depth analysis of electrical phenomena within the DC traction power network, enabling holistic analysis of power flows and accurate energy balancing within the complex operating environment of a modern DC traction power system, incorporating innovative elements such as reversible substations or energy recuperators.
The project encompasses the substations located at Tres Olivos, Las Tablas, La Moraleja, Baunatal, and Hospital Infanta Sofia, which execute the essential function of converting the Medium Voltage (MV) AC supply (15 kV) into the DC traction voltage (3 kV). Five independent monitoring units were deployed to capture raw electrical samples at a significantly high frequency (50 kHz), allowing for comprehensive broadband frequency spectrum analysis across the monitored segment. In four of the five locations, the systems acquire the DC voltage and two DC currents that delineate the bi-directional power flow towards adjacent sections and traction loads.
The substation at La Moraleja features an expanded system configuration due to the presence of an Energy Recovery System designed to re-inject regenerative braking power into the MV AC grid. At this specific point, the system not only measures the standard DC parameters but also acquires the DC current absorbed by the Energy Recovery System. In this substation, for the specific aim of efficiency evaluation of energy conversion in both directions, an additional measuring system was installed by researchers from FFII – LCOE that acquires all three-phase AC voltages and currents on the MV side and also line DC voltage and current.
A critical technological feature of this distributed setup is the utilisation of the LTE network to establish a single, unified time base across all measurement units. This synchronisation is paramount, ensuring that all data acquisitions along the entire line segment are simultaneous, a fundamental requirement for executing advanced analytical functions. The high-fidelity, synchronous data generated by this installation will be leveraged to perform crucial Power Flow Analysis, detailed Spectral Analysis of power quality, and accurate Energy Balance Studies on this complex network, providing invaluable insights into operational optimisation and energy efficiency within modern railway infrastructure.
Metrology’s crucial role in the e-TRENY project: Advancing the Efficiency of Metro Substations
Metrology, through its precise calibration and enhanced accuracy of sensing equipment, is delivering the high-quality data required to pinpoint inefficiencies, optimise control strategies, and introduce condition-based maintenance within substation systems.
As part of the e-TRENY project, a dedicated measurement was carried out in Germany during May and June 2025. This campaign focused on monitoring both the efficiency and power quality of the AC/AC power transformer, the AC/DC power converter, and the charge–discharge DC electric energy storage system—all integral elements of a non-conventional, bi-directional metro substation.
To guarantee reliable and accurate data, reference standards such as wideband voltage transformers, Rogowski coils, fibre optic current sensors, Hall effect current sensors, and power analysers were meticulously calibrated at National Metrology Institutes. These instruments were then deployed on-site, ensuring precise assessment of the overall substation power efficiency, as well as a closer look at the performance of each component.
Preliminary analysis is promising: in most scenarios, the substation system’s efficiency aligns with its design targets. Currently, our team is performing an even deeper dive—analysing efficiency across a variety of operational conditions and power levels, during both charging and discharging phases, and investigating the uncertainties involved in efficiency measurements.
If you are interested in learning more about this project or have any questions regarding measurement challenges, we invite you to reach out for further discussion. Please contact Wei Zhao (wzhao@vsl.nl) or Domenico Giordano (d.giordano@inrim.it).
Advancing On-Site Calibration with Fibre-Optic Current Sensors
On-site calibration poses unique challenges compared to laboratory environments. Fibre-Optic Current Sensors (FOCS) offer a versatile solution for DC, AC, and even pulsed current measurements, delivering several key advantages: High accuracy at the 0.2% level, Wide dynamic range from hundreds of amperes to mega-amperes, Immunity to electromagnetic interference, and Galvanic isolation between high-voltage components and low-voltage measurement systems. These features make FOCS particularly suited for on-site applications where precision and safety are paramount.
Although FOCS technology is increasingly used for monitoring electricity grids, its role as a traceable reference standard in metrological applications—especially for on-site calibration—remains underexplored in published literature. Further research and validation by National Metrology Institutes (NMIs) are essential before these systems can be widely adopted as reference instruments in the field. Laboratory calibration and cross-institutional comparisons are critical steps toward ensuring reliability and traceability under real-world conditions.
As part of the EU 22NRM04 e-TRENY project, a strong collaboration has been established among consortium partners and NIM. Two FOCS units were calibrated in NMI laboratories and subsequently deployed for an on-site measurement in Germany. Preliminary results indicate that FOCS measurements deliver significantly lower noise and a broader dynamic range. This work deepens our understanding of the metrological characteristics of FOCS and supports their wider adoption for on-site calibration.
If you would like to learn more about this project or discuss measurement challenges, please feel free to contact: Wei Zhao (wzhao@vsl.nl) or Domenico Giordano (d.giordano@inrim.it).
