Publications

Characterization and Application of Fiber-Optic Current Sensors for On-site Calibration

 Abstract—Fiber-optic current sensors (FOCS) have significant potential as traceable references in metrological applications, yet their widespread adoption remains limited. Laboratory calibration and comparison are essential for establishing traceability and reliability under real-world conditions. This paper presents the operating principle of self-developed FOCSs and evaluates key performance metrics. It reports the first comparison among National Metrology Institutes (NMIs) for calibration and performance assessment of FOCSs, covering stability, accuracy, linearity, temperature dependence, and frequency response. The results demonstrate that self-developed FOCSs achieve an accuracy of 0.1 %, linearity of 0.03 % up to 4 kA at room temperature, and an error variation of less than 0.2 % across the temperature range −10 °C to 60 °C. The wideband FOCS exhibits a bandwidth exceeding 120 kHz. Furthermore, FOCSs were deployed for current measurements in a medium-voltage substation and compared against Hall-effect current sensors under operational conditions. Findings confirm that FOCSs meet performance requirements in practical environments, offering excellent repeatability and traceability for on-site calibration and highlighting their unique value in metrological applications.

Measurement Dataset from All Traction Substations of Madrid Metro Line 10B, Including a Reversible Substation

Impact of Temperature on Nonlinearity of Voltage Transformers in Harmonics Measurement

The aim of the study here presented is to evaluate how temperature variations affect the metrological performance of inductive voltage transformers (VTs) in harmonic measurements. The analysis specifically targets the harmonics up to 1 kHz, where measurements using VTs can be challenging due to their nonlinear behavior. In fact, recent scientific literature has evidenced that when a VT operates under distorted conditions, the harmonics at its secondary side are not simply a scaled version of those injected. Instead, they are a combination of the injected harmonics and the spurious ones generated by the iron core due to its B–H curve. This phenomenon has been investigated in laboratory under controlled conditions, and the specific techniques have been proposed to compensate for it. However, no studies have analyzed the impact of temperature variation on this phenomenon and, consequently, on the introduced errors. This article addresses this open issue through experimental activities on two different VTs using a high-accuracy reference setup. Results show that, for different temperatures, the measured VT harmonic errors can differ up to an order of magnitude, indicating that this influence quantity cannot be neglected.

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.

Energy Analysis of a Metro Train

For over a decade, Europe has focused on greening public transport, with modern railways playing a key role to reduce pollution and transport emissions because it is characterized by a relatively low ratio between energy consumption and transport capacity. However, DC railways waste a significant amount of energy regenerated with dynamic braking. Despite the evident importance of the presented topic, there is a lack of experimental knowledge in technical and scientific literature about the amount of energy and the power levels that are involved in the described mechanism though this is fundamental information for the design of the storage system. This paper presents some experimental results of an energy analysis of a metro train

Energy Recovering in DC Railway Systems

For over a decade, Europe has focused on greening public transport, with modern railwaysplaying a key role to reduce pollution and transport emissions because it is characterizedby a relatively low ratio between energy consumption and transport capacity. However,DC railways waste a significant amount of the energy regenerated with dynamic braking.The adoption of an energy storage system can greatly improve this situation by increasingenergy saving. This paper explores this issue starting from experimental data recordedduring the monitoring of a railway traction unit in commercial service on different tracks.The energy flows during braking in real conditions has been analyzed, quantifying theamount of energy that can be recovered by adopting an energy storage system placed onboard trains or in railway stations.

Traceability for AC Ripple Over DC Current

Direct current (dc) is experiencing a new renaissance. The consolidated high-voltage direct current (HVdc), together with new medium voltage direct current (MVdc), and low-voltage direct current (LVdc) are more and more present in research and development projects. One of the relevant topics, associated with the usage of dc, is the ac ripple that unavoidably accompanies the dc signals. The interest in the measurement of this quantity is linked with the determination of the performance of dc energy meters for billing purposes. The on-line power quality (PQ) analysis, the verification of the capabilities of the filtering systems, and the accurate determination of losses associated with the transmission, distribution, and conversion of the electric energy by dc systems require accurate determination of the ac ripple. National metrology institutes (NMIs) provide traceability only for pure ac or pure dc current signals. To guarantee a high-quality standard for such measurements, the article proposes a novel methodology, named ALFO, for the traceable calibration of measuring systems with signals composed by dc with superimposed ac ripple. The calibration setup is based on a decoupling transformer (DeT) which has been specifically designed by a numerical tool. A detailed analysis and quantification of the systematic errors affecting the measurement and of uncertainty budget have been performed. The setup can calibrate current measuring systems up to 100 A (dc) with ac ripple up to 1% of the dc in the frequency range 300 Hz–150 kHz. Preliminary evaluation of the standard uncertainty, performed at maximum 40 A dc and 1 A ac up to 250μA /A in the range of 300 Hz–150 kHz.

Estimation of Railway Line Impedance at Low Frequency UsingOnboard Measurements Only

Setup for the calibration of current measuring systems under DC signals affected by ripple