This paper describes the measurement system used to monitor the energy dissipated in the braking rheostat resistors on board a locomotive operating in a DC rail system. The aim of the activity is the accurate estimation of the energy, nowadays wasted, that could be recovered thanks to the implementation of the smart grid paradigm in the DC railway system. To provide metrological reliability to the measured wasted energy, a preliminary identification and estimation of the uncertainty is provided. The target uncertainty of the measurements is 1 %.
Main topics will be: 1) Accurate and traceable measurement of energy consumed by trains: mise en pratique of the “metrology control” to comply with the technical standards required for interoperability 2) Power quality in railway systems: what, where and how to measure? 3) Energy efficiency: how much energy can be recovered by electric braking? how much energy can be saved by eco-driving?
In AC electrified railways there is a significant exchange of power at fundamental and harmonics in quite dynamic conditions. Harmonic patterns of AC rolling stock and railway networks are analysed in terms of active and nonactive power flow, relating it to the characteristic of the network and to operating conditions, synthesized in the fundamental current intensity and speed. The work shows that correlation and clustering can separate distortion terms of internal and external origin also without a priori information. The use of harmonic power terms (product of voltage and current components) shows improved robustness with respect to the analysis of the voltage and current components alone.
In DC electrified railways pantograph electric arcs represent not only a disturbance, but the step change of the pantograph voltage affects power losses directly and indirectly. The available line voltage is reduced if the train is in traction condition, the arc itself is characterized by ohmic power losses, and the triggered oscillating transient responses are characterized by a net power loss. In addition, if arc occurs during braking the arc voltage suddenly increases the pantograph voltage and may interfere with the dissipative braking chopper, reducing the recovered energy. This work presents the model and analysis of these phenomena with experimental results for arcs measured on a 3 kV dc line in traction and braking conditions.
An electric arc is an example of a transient event that is quite common in electrified transportation systems as by-product of the current collection mechanism. As a broadband transient, an electric arc excites a wide range of (often oscillatory) responses related to the substation and onboard filters, as well as the line resonances and anti-resonances. Similarly do the charging of onboard filter and other related inrush events. This work considers the electrical characteristics of these transients and of the excited responses in order to define their typical spectral signatures in DC railways and take them into account concerning their impact on Power Quality measurements and the measurements of instruments deployed onboard.
In electrified railways, harmonic active power terms can be significant in the order of the uncertainty required by the EN 50463-2 standard for power and energy measurements in railways. Nonactive power terms (encompassing reactive and distortion harmonic terms) are much more significant than the sole fundamental reactive power. This work considers the implementation of the EN 50463-2 energy measurement function, including the criteria for the significance of the measured and calculated terms, and it carries out a Monte Carlo analysis to assess the impact of harmonic power terms on the measured energy and its uncertainty.
Power quality (PQ) phenomena characterizing the voltage and current signals of railway electricity networks differ from those present in transmission and distribution electricity grids. Presently, there are no standardized procedures focused on PQ measurement techniques explicitly for railway applications. This paper evaluates whether the standard power quality measurement algorithms used in monitoring 50 Hz electrical grids are sufficient for an accurate evaluation and classification of PQ parameters of voltage dips, swells and interruptions present in 25 kV AC railways. An algorithm is presented to better characterize different types of interruption, distinguishing between causes due to network configuration or by other factors. For voltage dips and swells it is also shown that a smaller window size (less than 1 cycle) produces a more accurate estimate of the disturbance magnitude and duration. The two methods are verified against recorded signals of pantograph voltage and current. Recommendations are therefore provided for PQ measurement algorithms for AC railways.
This paper focuses on the electric circuit model of the railway supply system and locomotive to analyze the conducted effects of arc events at the sliding contact. The characterization of the arc voltage waveform is backed up by an intense preliminary laboratory activity. The comparison between simulated and measured pantograph voltage and current shows which electric parameters are relevant to identify the characteristic dynamic responses of the system, to use as electric signature of arc events.
A non-negligible amount of active power is carried also by harmonic (or, in general, spectral) terms, especially for highly distorted systems, such as electrified ac railways. The paper considers the distribution and correlation of these spectral active power terms, including train operating conditions, and gives criteria to select and group harmonic power terms. Several processing and display techniques are used to this aim: scatter histograms for joint probability, correlation coefficients, V-I maps. Results are shown and discussed for the Swiss 15 kV 16.7 Hz railway, using measured pantograph voltage and current quantities.
Highly dynamic and distorting loads like electrified trains have complex power flow schemes, with active power not exclusively assigned to the fundamental (either dc or ac). The estimate of energy consumption shall thus cover the most relevant power spectral terms, in order to adequately track and quantify the active power flow. This work investigates the dynamic behaviour of two distortion power indexes calculated with the pantograph quantities, voltage and current, using experimental recordings performed over some European railway networks (3 kV dc, 2x25 kV 50 Hz and 15 kV 16.7 Hz). The results show the relevance of a reduced set of components and the strong correlation with train operating conditions. The relevance is significant for ac systems, and in particular 16.7 Hz systems.
The electrical arc occurring in the sliding contact between the supply contact line and the current collector (pantograph) of an electrical locomotive is a fast transient phenomenon able to degrade progressively the line-to-pantograph contact quality and, consequently, the continuity of operation. In order to increase the energy efficiency of the railway system, an inexpensive solution is constituted by the detection of the arc event by the analysis of voltage and current measurements already available on-board train. An essential activity to reach this objective is to set up a reliable electrical model of the railway system in which the arc events originate. To this end, this paper presents a combination of experimental and simulation analysis for the development of an electrical model of a direct current (dc) 3 kV railway system, which is aimed at better understanding the propagation of conducted effects generated by arc events. First, a laboratory experimental activity is carried out to investigate the electrical dynamic characteristics of the arc in a controlled environment. Then, a model of the dc railway system is derived and validated by using the experimental data collected in a measurement campaign on-board train. Finally, a sensitivity analysis of the main model parameters is carried out.
The recordings of the pantograph voltage and current waveforms across Italian and French high speed railway lines (both Autotransformer 2x25 kV 50 Hz systems) are analyzed to estimate some Power Quality indexes: harmonic spectra, harmonic distortion, displacement factor and fundamental component, in various rolling stock operating conditions. These indexes, that define the electrical interface between the rolling stock and the power supply, are all relevant in order to assess both the impact of the rolling stock on the network and the suitability of the latter to ensure agreed performances (electrical interoperability).
The dc voltage fluctuation (sometimes referred to as ripple) is considered for the pantograph voltage on dc railways. Some indexes and processing techniques are considered to evaluate steady state and transient phenomena: Ripple Index based on time and frequency domain expressions, DFT and wavelet analysis. Copyright © 2011 by the International Measurement Confederation (IMEKO) All rights reserved.
The pantograph voltage and current waveforms recorded across the Italian and French high speed railway lines (both Autotransformer 2×25 kV 50 Hz systems) are analyzed to estimate some Power Quality indexes: harmonic spectra, harmonic distortion, displacement factor and fundamental component, in various load conditions. These indexes, that define the electrical interface between the rolling stock and the power supply, are all required by the technical standards for interoperability.