Publications

21/01/2025

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

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14/11/2024

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.

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19/09/2024

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.

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30/07/2024

Estimation of Railway Line Impedance at Low Frequency UsingOnboard Measurements Only

Estimating line impedance is relevant in transmission and distribution networks, in particular for planning and control. The large number of deployed PMUs has fostered the use of passive indirect methods based on network model identification. Electrified railways are a particular example of a distribution network, with moving highly dynamic loads, that would benefit from
line impedance information for energy efficiency and optimization purposes, but for which many of the methods used in industrial applications cannot be directly applied. The estimate is carried out onboard using a passive method in a single-point perspective, suitable for implementation with energy metering onboard equipment. A comparison of two methods is carried out based on the non-linear least mean squares (LMS) optimization of an over-determined system of equations and on the auto- and cross-spectra of the pantograph voltage and current. The methods are checked preliminarily with a simulated synthetic network, showing good accuracy, within 5%. They are then applied to measured data over a 20-minute run over the Swiss 16.7 Hz railway network. Both methods are suitable to track network impedance in real-time during the train journey; but with suitable checks on the significance of the pantograph current and on the values of the coefficient of determination, the LMS method seems more reliable with predictable behaviour.

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16/04/2024

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

In recent years, the adoption of DC technology in power systems is attracting renewed interest from the technical scientific side not only in traditional high-voltage applications (HVDC) which allow more efficient transmission of large quantities of energy over large distances but also in low-voltage DC networks (LVDC), which allow for more efficient and sustainable integration of renewable energy sources and battery storage systems. An obstacle to its widespread diffusion is the lack of traceable reference systems able to evaluate the performance of energy meters for billing purposes in operating conditions characterized by DC with AC components (up to hundreds of kHz). The present work proposes a methodology to calibrate current measuring systems experiencing DC with AC ripple providing the metrological traceability for this combined signal. The developed and tested archetype, here presented, proves the feasibility of the methodology.

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