Methods and instruments for stray current verification in DC rapid transit and railway systems

Modern electrified transportation systems feature increasing installed power and performance and correspondingly stray current phenomena and corrosion are receiving more attention in terms of contractual specifications and request of final validation of proposed solutions, as well as a maintenance program that can actively tackle stray current issues. The problem is complex for the system physical extension, difficult measurement conditions and variability of electrical parameters. This work considers validation of stray current protection performance, in terms of track voltage, track leakage and collected current, and impressed potential on structures along the right-ofway. The exemplification of the specifications of a hypothetical instrument and setup support the discussion

Self and mutual capacitance of conductors in air and lossy earth with application to electrified railways

The problem of a closed-form accurate determination of self and mutual capaci- tance of conductors in air and earth is considered: the application is the complete modeling of a railway line including buried conductors. The Generalized Potential Method (GPM) is presented and analyzed with regard to conditions of validity and solution methods. The accuracy of the GPM is evaluated solving some reference cases using the Complex Image Method and a commercial Finite Element Method simulator, comparing the model results with experimental data, and including the sensitivity on soil conductivity and permittivity, distance of conductors from the air\u2013earth interface and frequency

Harmonic and Supraharmonic Emissions of Plug-In Electric Vehicle Chargers

open1noElectric vehicle (EV) charging represents a relevant electric load with a rapid evolution in terms of number, power rating and distortion, in particular, considering the connection to the low-voltage public grid: available short-circuit power may be limited and particularly susceptible loads may co-exist in the same grid portion. Standards can partially address the problem cover-ing only the harmonic interval, but they necessitate significant extension and improvement in the supraharmonic range. In addition, EV chargers have been observed to violate in some scenarios the applicable harmonic limits, so that the mechanisms of emission and distortion should be better understood and evaluated, including phenomena of mutual influence between EV chargers and with pre-existing grid distortion. Although models can help simulate large-scale scenarios in terms of fundamental frequency phenomena, such as power flow, voltage fluctuation and imbalance, sub-stantial and reliable information can come from experimental results, providing measured harmonic and supraharmonic emissions, accompanied by details on loads mix, grid characteristics and EV charger operating conditions. This work thus defines the applicable constraints in terms of limits and compatibility levels for public and light industrial low-voltage grids, discusses the available experimental results and datasets, analyzing the typical distortion behavior and providing indication of sources of information for further studies.openMariscotti, AndreaMariscotti, Andre

Non-Intrusive Load Monitoring Applied to AC Railways

Non-intrusive load monitoring takes place in residential and industrial contexts to disaggregate and identify loads connected to a distribution grid. This work studies the applicability and effectiveness for AC railways, considering the highly dynamic behavior of rolling stock as an electric load, immersed in varying contexts of moving loads. Both voltage–current diagrams and harmonic spectra were considered for identification and extraction of features relevant to classification and clustering. Principal components were extracted, approaching the problem using principal component analysis (PCA) and partial least square regression (PLSR). Clustering methods were then discussed, verifying separability performance and applicability to the railway context, checking the performance by means of the balanced accuracy index. Based on more than one hundred measured spectra, PLSR has been confirmed with superior performance and lower complexity. Independent verification based on dispersion and correlation were used to spot relevant spectrum components to use as clustering features and confirm the PLSR outcome

Relevance of Harmonic Active Power Terms for Energy Consumption in Some Railway Systems

Active power is not carried solely by the fundamental component (either dc or ac) especially for highly distorted systems, as electrified railways. The paper proposes two indexes and a preliminary assessment of the relevance of harmonic active power terms. Results are shown for three major railway systems architectures (3 kV dc, 2x25 kV 50 Hz and 15 kV 16.7 Hz) using experimental pantograph voltage and current. Harmonic power terms are relevant for the estimate of energy consumption especially for ac systems rather than dc, with some significant situations especially for 16.7 Hz systems

Impact of rail impedance intrinsic variability on railway system operation, EMC and safety

Running rails in electrified transportation systems are the interface element for several phenomena related to system performance, electromagnetic compatibility and safety: useful voltage at rolling stock, short circuit current, induced voltage, stray current, and track circuit operation. This work presents the physical and mathematical groundings of rail electrical parameters (dc and ac resistance, ac internal and external inductance) and experimental results available in the literature, discussing variability and reliability for each interface. The results consist thus of the identification of the relevant rails longitudinal electrical parameters, the presentation of a set of reliable experimental values, and the discussion of the best approach to manage their variability and uncertainty

Track insulation verification and measurement

Methods for the measurement of track insulation are reviewed pointing out minimum necessary conditions and practical aspects, as well as consistency and repeatability of results. Track configuration, need of electrical sectioning and use of external electrodes or conductive structure are key parameters to determine suitable methods

A magnetic field probe for hostile environments

Peer Reviewe

Electrical Characteristics of Pantograph Arcs in DC Railways: Infrastructure Influence

Electric arcs are an unavoidable by-product of current collection by sliding contact in electrified transportation systems. Electric arcs are transient phenomena with implications for PQ measurements and wearing estimation and prevention of the sliding contact and catenary. Besides being heavily influenced by mechanical characteristics and material properties, their electrical characterization encompasses spectral properties and the influence of train and traction line circuits and relative position of infrastructure elements. This paper identifies the influence of such electrical and system characteristics onto the spectral signature of electric arcs for DC railways

Energy Efficiency Improvement with Reversible Substations for Electrified Transportation Systems

More and more often overall energy efficiency of an electrified transportation system appears as a target of new constructions, sometimes with incomplete definitions of performance indexes to assess that target has been reached. A worked out example is based on the introduction of reversible substations. Reversible substations are a method to improve energy efficiency, whose application in an existing system can be progressive and does not require large traffic intensity to be effective. Their effectiveness depends on some system parameters (nominal catenary voltage in particular). A simulation model fed with experimental data from a line section of Metro de Madrid is used to demonstrate the operation and optimization of reversible substations