High Accuracy Measurement Device For Railways Applications
Creators: name: Signorino Davide
Publisher: name: Zenodo
Year: 2018

description: Considering the overall annual energy consumption of the European railway system, about 36.5 TWh, and the ambitious target of reducing CO2 railway transport emissions to 50% by 2030, it is clear that an efficient use of the energy in the railway system is mandatory. Considering also the recent European directives [1–3] that regulate railway networks in European Union (EU) law and allow open access operations on railway lines by companies other than those that own the rail infrastructure, accurate and reliable knowledge of the absorbed/exchanged energy between the train and the railway grid is essential. All the trains shall be equipped with an Energy Measurement Function (EMF), whose measurement accuracy has to be assessed and periodically reverified. Moreover, an accurate knowledge of the real-time power quality (PQ) is a valuable tool to foster the efficiency of the whole railway system by awarding the good power quality delivered and absorbed. The voltages supplied to trains are often distorted harmonically and subject to residual ripple from alternating current (AC) to direct current (DC) conversion; these distortions are typically much larger than those experienced on the usual electricity network. At the same time, the currents drawn by trains also contain high levels of harmonics, inter-harmonics, ripple and step changes in magnitude associated with train acceleration and raking. Arcing phenomena, generated by a bad pantograph-to-line contact quality, can further introduce transient distortions. Furthermore, the switching frequencies associated with IGBT train drives can resonate causing serious over-voltages, particularly in overhead line (catenary) systems. The combination of these effects means that accurate determination of real-time power consumption and cumulative energy (and efficiency) metering are significant challenges. Measurement systems and algorithms related to PQ in fixed installations (AC transmission/distribution grids) are currently available; however, these techniques<br> are not all directly applicable to railways, because the time frames of interest are different, the trains are mobile and the PQ phenomena are different. Meanwhile, the existing wide-area measurements on railways are limited to energy consumption with<br> a 300 second (5 minute) time quantization [4]. This provides enough information for particular train operating companies to be billed for energy use, but it provides very little useful data in terms of network management, efficiency assessment, condition monitoring, power quality and network stability. Moreover, PQ definitions for DC railway distribution systems are still an open research topic.<br> With respect to energy measurement on-board trains, the current European standard [3] gives requirements for current/voltage sensors and energy calculation function. In several parts, it adopts the requirement given for energy measurement for fixed<br> installation working at 50 Hz. This is a crucial point if we consider the dynamic effects (eg: catenary-pantograph contact) of a railway supply system. To improve the energy measuring systems more bandwidth is needed in order to analyze the described higher<br> frequency phenomena. All this let us perceive the necessity of a high performance measurement system, that have to collect and analyze railway typical quantities both onboard train and in substation. In order to do this, the first requirement of the system is the sampling synchronization of all the measurement devices to a common time reference. Therefore in this paper an embedded standalone measurement device, that can acquire various types of railway quantities (electrical and mechanical) synchronously to an absolute time reference, obtained by Global Positioning System (GPS) is presented. The proposed instrument has been conceived with flexibility in mind to be used for both substations and trains. It could be used to measure power and energy, to identify the PQ events affecting the power exchanged between the supply system and the rolling stock and to have input information to train eco-driving procedure implementation.