Abstract: The problem of electrical parameters identification in complex systems, and in particular in electric railway traction systems, is considered. Parameters are determined by an indirect approach: only the terminal variables (voltages and currents and, impedance and admittance, which can be readily calculated) are measured and the per-unit-length electrical parameters are determined using a Multiconductor Transmission Line model of the track section under test. It will be shown that some parameters cannot be measured directly, that they are not constant with frequency and that they may depend on other external conditions. An indirect method for parameters identification is proposed through an Adaptive Algorithm (AA), so that the calculated terminal variables match the measured ones. The AA is based on a Genetic Algorithm (GA) approach, with details on pattern generation (through mutation and recombination) and determination of the degree of fitness and, as a consequence, of matching and stop criteria. There is a general accordance with model previsions, within common variations of the most critical properties of the test track.
Abstract: Methods of measurement and data analysis are considered for the electromagnetic (e.m.) emissions of large power rotating machinery (in this paper a synchronous generator is considered as working example). The data recorded during two measurement campaigns are used to proof the analysis methods and to better describe the measurement procedures. Several important factors are considered: the reactive behavior of the field, site attenuation and antenna factor determination, the physical dimensions of the source of emissions and its impact on correction factor uncertainty, the e.m. environment and the ambient e.m. noise, practical factors (including safety distances, reproducible test conditions, etc.) that limit the choice of the measuring position and distance and determine measurement accuracy.
Abstract: An electric traction system supplied at 2x25 kV with Autotransformers (ATs) is considered. Conductors arrangement is that of the new European High Speed Railway Line (HSRL) under construction. The system is analysed with a validated Multiconductor Transmission Line (MTL) model with the aim of model simplification with reduction of the number of conductors and use of lumped circuit model. The scope is that of load flow and voltage stability problems, which may be large scale problems and benefit from model simplification and reduction of computational effort.
Abstract: An electric traction system supplied at 2x25 kV with autotransformers (ATs) is considered. The conductors’ arrangement is that of the new European High Speed Railway Line (HSRL) under construction: The overhead supply conductors in contact with the train pantograph are connected to a symmetrical circuit (the feeder) with the purpose of current balancing; the traction return current flows from the rolling stock axles back to the supply (i.e., substation) through the traction rails and additional return conductors. The test campaign carried on the Rome-Naples HSRL allowed the validation of the multiconductor transmission line model used for system analysis. Measurements were performed in normal system configuration (2x25 kV supply) and degraded configuration (1x25 kV with AT and feeder not operating). Metrological issues (accuracy and consistency) are detailed for the presented results.
Abstract: The industrial prototype of a superconducting magnetic energy storage (SMES), sized to deliver 1 MW for 1 s, was designed and constructed as the result of a research project, partly funded by the Italian Ministry of Education, University and Research. After successfully undergoing factory tests, the SMES was installed at the Elettra Synchrotron Light facility in Trieste-I and is there under commissioning and testing as protecting device from temporary voltage dips and interruptions, the most frequent grid malfunctions causing faults of the beam magnetic confinement system. The innovative part of the prototype, which also includes several sophisticated power electronics items, is a 2.6 MJ stored energy magnet, wound with a new low-losses Nb Ti cable, cooled by liquid helium at 4.2 K and adopting an electric insulation design solution to withstand 8 kV and obtain very close contact between coolant and coil. New design hybrid current leads, made of a resistive copper stage and a high temperature superconducting one, cooperate together with a set of three cryocoolers and a multi-shield cryostat to keep the helium loss amount negligible. Electrical insulation of the most critical components and the
quench detection system is extremely accurate, because the voltage at coil-ends rises up to 2.500 V. The experimental results obtained at Elettra during the beginning of the SMES commissioning phase are presented.
Abstract: The electrical behavior of the sample steel traction rails is analyzed, considering the resistance and internal inductance. Measurements are performed on a sample rail with a circulation of audiofrequency current (with frequency regulated on a wide frequency interval range of 1–100 kHz) superimposed on a dc supply current. The results complete the other measurement results obtained with a 50-Hz bias current; the resistance values are 30%–50% smaller, whereas the internal inductance is almost similar.
Abstract: Measurement results concerning rail-to-rail conductance are presented, based on two measurement campaigns performed in Italy at Rigutino (AR)and Anagni (FR)in spring/summer 2003. Rails in the two sites are isolated from the sleepers and the earth and the weather conditions were hot and dry, so the measured conductance values represent a lower bound. Results cover more than three frequency decades from 10 Hz to 10 kHz.
Abstract: The problem of determination of the accurate distribution of the return current in AT (autotransformer) electric traction systems (supplied at 2x25 kV) for High Speed Railways is considered. The path of the traction return current flowing from the rolling stock axles back to the supply (i.e., substation) is composed of the traction rails and additional earth potential conductors. The overhead supply conductors in contact with the train pantograph are connected to a symmetrical circuit (the feeder) with the purpose of current balancing. This arrangement and its influence on current to earth are considered: the return current divides among rails (as signalling disturbing current) and earth, depending on the value of the electric parameters of the system and the earth and on the circuit arrangement and on the relative position of system devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in AT electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters.
Abstract: An algorithm for voltage sag detection based on rectified voltage processing is presented and its performances are evaluated by means of simulated and real voltage waveforms (recorded at some low-voltage busbars and measured on a scaled prototype of a voltage support system). The algorithm is intended to detect voltage sag occurrence and to trigger the disconnection of the faulty supply network and subsequently the connection of a voltage support system. The algorithm is very convenient in terms of memory storage and computational requirements and may be implemented on low-cost platforms. The results show that the time for detection is very short and always less than a quarter of the supply voltage period.
Abstract: A comprehensive analysis of published experimental data and formulae for the determination of the electrical parameters of railway traction lines is performed. Several results from different authors are presented with particular attention to different assumptions and environmental conditions. Additional measurements were performed over the 5 Hz–200 kHz frequency range on a line section purposely prepared at La Spezia Railway Station (Italian State Railways). Theoretical formulae are considered and their validity is checked against experimental data. There is general accordance within common variations of the most critical parameters; calculations and measurements agree over the entire frequency range and are very accurate in the frequency range 50 Hz–50 kHz, where significant conducted disturbance lies.
Abstract: The electrical behavior of traction rails is considered. The values of resistance and internal inductance resulting from 80 years of literature are evaluated and compared; average values (with confidence intervals) are derived as a reference for further developments. The values are the results of direct measurements and information from practice and convention, so attention is given to measuring methods and to any simplifying assumption. The statistical properties of the published experimental results are evaluated as well as the correspondence with theoretical results.
Abstract: The superposition of the conducted interference produced by multiple electric traction vehicles into a track section is considered in the frequency range up to 20 kHz. The subject is
important not only for estimation of the disturbance produced by new rolling stock in plausible traffic conditions, but also for each railway operator to fix adequate limits for the return current of each unit. The analysis is performed on a reference ac single track line of overall 50-km length. First, the sources of interference are classified, with particular attention to the synchronization issue and phase displacement. Then, the railway line properties as the mean of conductive coupling are identified (attenuation and phase rotation versus frequency and length). Last, a preliminary attempt is made to derive summation rules for disturbance from different vehicles.
Abstract: The electrical behavior of sample steel traction rails is analyzed considering the resistance and the internal inductance. Measurements are performed on a sample rail with circulation of audiofrequency current superimposed on a 50-Hz supply current.
Abstract: A measurement campaign was carried out at Orte and S.Oreste dc substations along a high-speed trunk of the Italian railway lines. The results consist of H-field values measured at the two substations, inside the buildings (near the rectifier groups) and outside (in the area surrounding the high-voltage input line, the HV/MV transformers, and the rectifier transformers) for different load conditions during normal service. The goal of this work is to determine the H-field intensity at lowand medium frequency at dc railway substations. The measurement results are post-processed to extract statistical properties (namely, average values, dispersion, and distribution histograms). This information may contribute to updating and integrating standards regarding dc substation electromagnetic environment and specific immunity tests for housed equipment.
Abstract: This paper deals with the assessment of low-frequency magnetic-field emissions (MFE) in the engine-driver cab and the passengers’ compartments of rolling stock. For emissions’ measurement, an experimental setup is designed, involving a three-axial magnetic-field sensor mounted on an antenna positioner, and optically linked to the data-handling system. Measurement is accomplished in the time domain and allows one to retrieve digitized time series of the spatial components of the magnetic-flux density (MFD) vector, at specific points in the measurement volume. Worst case emissions are related to the train operating modes by referring to an experiment that includes acceleration from an initial stop, inertial motion, and braking up to a new stop. The nonstationary behavior of the most relevant MFD sinusoidal components is evidenced, and it is accounted in the spectral analysis by resorting to short-time Fourier transform based on a fixed-length time windows of proper duration. For safety assessment, a compliance check of MFE levels with exposure limits is proposed, based on the computation of an instantaneous safety parameter, obtained by extending requirements developed in the International Commission on Non-Ionizing Radiation Protection guidelines for the simpler case of multiple-frequency steady-state fields.
Abstract: An important element for the analysis of the electromagnetic conducted emissions in railway traction systems is
the line impedance Z at the pantograph terminals. Simplified expressions of Z are derived under various assumptions, and their validity is checked against an analytically derived reference expression. A sensitivity analysis of Z is performed with respect to some electrical parameters of the traction line. The influence of the substation impedance as a terminal condition for the traction line is considered for dc substations; several substation configurations (rated power and filter characteristics) in use in different countries are considered.
Abstract: The problem of the determination of the real distribution of the return current in electric railway traction systems is considered. One or more conductors (depending on the specific supply system) are purposely set up to carry the traction return current flowing from the rolling stock axles back to the supply (i.e., substation); yet, part of the return current flows through signalling conductors (disturbing current) and through the earth, depending on the value of the electric parameters of the system, on the circuit arrangement, and on the relative position of the supply, the rolling stock, and signalling devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in ac and dc electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters. The definition of the transfer function between the return current and the signalling circuit variables is an important element for the compatibility analysis between train detection systems, rolling stock and infrastructure, to promote the cross-acceptance of rolling stock in Europe and abroad.
Abstract: A general expression for the spectrum of the dc-link current of single- and three-phase voltage source inverters is presented to predict the amplitude and frequency of the harmonic components produced by balanced and unbalanced loads, defining positive, negative and zero sequence components. The computation is developed using the switching functions approach, relating the output voltage waveform to the absorbed dc-link current; so, the method may be applied also to measured waveforms, when no analytical expression is available. The method is extended also to the general case of non sinusoidal load currents. The spectrum of the dc-link current for several inverter modulations (deterministic and random modulations) is calculated and considerations on the harmonic distortion and dc-link filter requirements are presented.
Abstract: The problem of evaluation of the electromagnetic emissions from large power electrical rotating machinery is considered. The results of three measurement campaigns are reported: emissions are correlated with the operating conditions and the characteristics of the machine under test. The measured electric and magnetic field spectra are treated so that they may be used as a reference for preliminary evaluation on similar machines.
Abstract: Magnetic field measurements with a more than 6 decade dynamic range over a very extended frequency range are considered. This subject is getting nowadays more importance for compliance with the series of standards and regulations for human exposure to electromagnetic fields. ICNIRP and Video Display Terminal standards requirements in terms of field levels and bandwidth are translated into sensor specifications, which reveal to be very challenging. Furthermore, manufacturers’ information is sometimes poor and doesn’t allow easily engineers to design a fully compliant measuring equipment.
