Power quality analysis in 25 kV 50 Hz AC railway system networks

Railway electricity networks are characterised by different power quality (PQ) phenomena from those of transmission and distribution electricity grids Trains are mobile and continuously interact with overhead contact line and other trains, exchanging power during acceleration, coasting and notably during regenerative braking This producer consumer behaviour of the locomotive with the rest of the system deteriorates the PQ of the railway grid

Power quality measurement and active harmonic power in 25 kV 50 Hz AC railway systems

Railway electrical networks rated at 25 kV 50 Hz are characterised by significant levels of voltage and current harmonics. These frequency components are also time varying in nature due to the movement of trains and changing operational modes. Processing techniques used to evaluate harmonic results, although standardised, are not explicitly designed for railway applications, and the smoothing effect that the standard aggregation algorithms have on the measured results is significant. This paper analyses the application accuracy of standardised power quality (PQ) measurement algorithms, when used to measure and evaluate harmonics in railway electrical networks. A shorter aggregation time interval is proposed for railway power quality measurement instruments, which offers more accurate estimated results and improved tracking of time varying phenomena. Harmonic active power present in railway electrical networks is also evaluated in order to quantify the impact it has on the energy accumulated by electrical energy meters installed on-board trains. Analysis performed on 12 train journeys shows significant levels of non-fundamental active power developed for short periods of time. As an energy meter will inadvertently absorb the financial cost of non-fundamental energy produced by other trains or other external power flows, results are provided to support recommendations for future standards to measure only fundamental frequency energy within train energy measurement meters

Review of PMU algorithms suitable for real-time operation with digital sampled value data

Phasor Measurement Unit (PMU) instruments are continuously evolving to reflect the needs of electrical grids for enhanced and more accurate monitoring of the AC signal parameters, and to contribute towards optimization of real-time control tasks. In turn, enhanced monitoring can contribute to a more stable and reliable power supply. PMU standards are also being updated to reflect the latest performance requirements PMUs and new technological developments. As described in standard IEC/IEEE 60255-118-1, a PMU may receive streams of timestamped digital samples using the IEC 61850-9-2 Sample Values (SV) protocol, instead of traditional analog signals. This means that the signal conditioning and sampling parts can be located at a different location from the computational unit. This approach requires remote processing, so additional time delay is introduced that affects the reporting latency of the PMU. Therefore, not all the PMU algorithms presented in the literature will be valid candidates to operate with SV data and at the same time comply with reporting latency requirements. To address this issue, the paper presents a literature review of PMU algorithms, to identify algorithms which are suitable for real-time operation with the SV data protocol. Among many proposed PMU algorithms, only a few of them can estimate synchrophasor, frequency, and rate of change of frequency (ROCOF) on a sample per sample basis. Recommendations on selecting PMU algorithms for hardware implementation that complies with SV data has been also provided

Pantograph arc location estimation using resonant frequencies in DC railway power systems

Pantograph arcing in electrified railway systems not only reduces the power collection quality of a locomotive but can also damage pantograph strips and overhead lines (OHLs). Most research detects pantograph-to-OHL arcs based on onboard voltage/current measurements, pantograph cameras, and so on. The use of onboard voltage/current data, though being cost-effective, rarely reflects arc locations along OHLs. This article develops an arc positioning method, which matches the position-dependent resonant frequency (RF) of an OHL with the RF extracted from voltage measurements in a pantograph arc event. A particular 20-km DC railway line supplied by two substations is first modelled in MATLAB/Simulink, with the model effectiveness being assessed based on voltage measurements in an arc event. Then, the OHL-related RFs estimated by the model are validated by the Tableau formula and discussed alongside impacts on RFs based on line models, locomotive locations, and line lengths. These evaluations permit the generation of an RF curve that links OHL-related RFs with arc locations. The arc positioning method is tested based on the pantograph arc events presumed at various positions along the 20-km line, showing errors within 0.2 km at certain locations. The ability to determine arc locations will permit periodic inspections to be performed on the determined line sections

Images of Research : Towards Sustainable and Safe Aviation

Electric arc faults (high-power discharge of electricity between conductors) can develop in any electrical system. Generating heat, these faults can trigger dangerous electrical fires. In our quest to develop greener transport, we are studying the occurrence of these faults in direct current (DC) systems, aiming to assist industry in the safer development of aircraft electrification and robust protection technologies

Accurate measurement of energy dissipated in braking rheostats in DC railway systems

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 %

Control architecture for smart digital node providing hybrid AC/DC supply

STRATA project develops a fully new digitally enabled concept for increasing the intelligence of distribution transformers and for enabling them to serve as local service nodes for different stakeholders. The project is building multiple prototypes for the new unit as well as the control system around it. This paper focuses on the architecture work taken for the concept to allow proper information exchange and controllability across different use cases and stakeholders under different conditions. The paper discusses the high-level architecture as well as the functional dimensions of defined use cases. Practical examples from different setups are presented, complemented with first experiences and ideas for future work to be undertaken

Analysis and development of power quality metrics for railway electric networks

Ensuring acceptable levels of power quality (PQ) in electrified railway networks has become crucial due to the increased utilisation of power electronics within locomotives and power grids. There is a lack of clear analysis and standardised procedures focusing on PQ measurement techniques explicitly for railway applications, and therefore a need to develop appropriate PQ measurement methods and indices. This thesis addresses this gap through review and analysis of PQ phenomena and measurement methods applicable to AC railway signals. Recommendations of methods for rail PQ instruments are provided, including newly developed techniques to detect unique disturbances in AC and DC railway networks. A new measurement technique to identify voltage interruptions at locomotive terminals resulting from network re-configuration has been developed. It allows distinguishing these disturbances from voltage interruptions caused by faults in the system or failure of equipment, thereby improving event identification and classification. A half-cycle measurement interval, in contrast to the one-cycle approach proposed by the IEC 61000-4-30 standard for voltage dips and swells evaluation in grid applications, has been analysed and developed for improved detection and classification of short-time voltage events, allowing an enhanced correlation of their impact on rail assets, and supporting network planning and new standards for rail PQ instruments. It is shown that a new aggregation time interval equal to 50 cycles for 50 Hz signals is required to improve the accuracy of voltage and current harmonics measurements by rail PQ instruments. Due to improved tracking of the time-varying frequency components, a better estimation of harmonic emission levels in 25 kV 50 Hz rail systems has been proven, leading to improved health condition monitoring of the network assets. A novel and cost-effective method for detecting electric arcing phenomenon between Chapter 0. Abstract the pantograph and overhead contact line (OCL) of 3 kV DC railway networks has been developed. Information extracted about the geographical localisation of the arc enables predictive maintenance of the entire pantograph-catenary system, thereby reducing operational costs and improving the safety and reliability of DC rail networks. In summary, this work has addressed the need for focused analysis of unique railway PQ phenomena, has developed and proven the effectiveness of new tools for rail PQ monitoring, and has established a new foundation for health and condition monitoring in rail electrical systems.Ensuring acceptable levels of power quality (PQ) in electrified railway networks has become crucial due to the increased utilisation of power electronics within locomotives and power grids. There is a lack of clear analysis and standardised procedures focusing on PQ measurement techniques explicitly for railway applications, and therefore a need to develop appropriate PQ measurement methods and indices. This thesis addresses this gap through review and analysis of PQ phenomena and measurement methods applicable to AC railway signals. Recommendations of methods for rail PQ instruments are provided, including newly developed techniques to detect unique disturbances in AC and DC railway networks. A new measurement technique to identify voltage interruptions at locomotive terminals resulting from network re-configuration has been developed. It allows distinguishing these disturbances from voltage interruptions caused by faults in the system or failure of equipment, thereby improving event identification and classification. A half-cycle measurement interval, in contrast to the one-cycle approach proposed by the IEC 61000-4-30 standard for voltage dips and swells evaluation in grid applications, has been analysed and developed for improved detection and classification of short-time voltage events, allowing an enhanced correlation of their impact on rail assets, and supporting network planning and new standards for rail PQ instruments. It is shown that a new aggregation time interval equal to 50 cycles for 50 Hz signals is required to improve the accuracy of voltage and current harmonics measurements by rail PQ instruments. Due to improved tracking of the time-varying frequency components, a better estimation of harmonic emission levels in 25 kV 50 Hz rail systems has been proven, leading to improved health condition monitoring of the network assets. A novel and cost-effective method for detecting electric arcing phenomenon between Chapter 0. Abstract the pantograph and overhead contact line (OCL) of 3 kV DC railway networks has been developed. Information extracted about the geographical localisation of the arc enables predictive maintenance of the entire pantograph-catenary system, thereby reducing operational costs and improving the safety and reliability of DC rail networks. In summary, this work has addressed the need for focused analysis of unique railway PQ phenomena, has developed and proven the effectiveness of new tools for rail PQ monitoring, and has established a new foundation for health and condition monitoring in rail electrical systems

A novel arc detection method for DC railway systems

Electric arcing due to contact interruption between the pantograph and the overhead contact line in electrified railway networks is an important and unwanted phenomenon. Arcing events are short-term power quality disturbances that produce significant electromagnetic disturbances both conducted and radiated as well as increased degradation on contact wire and contact strip of the pantograph. Early-stage detection can prevent further deterioration of the current collection quality, reduce excessive wear in the pantograph-catenary system, and mitigate failure of the pantograph contact strip. This paper presents a novel arc detection method for DC railway networks. The method quantifies the rate-of-change of the instantaneous phase of the oscillating pantograph current signal during an arc occurrence through the Hilbert transform. Application of the method to practical pantograph current data measurements, demonstrates that phase derivative is a useful parameter for detecting and localizing significant power quality disturbances due to electric arcs during both coasting and regenerative braking phases of a running locomotive. The detected number of arcs may be used to calculate the distribution of the arcs per kilometre as an alternative estimation of the current collection quality index and consequently used to assess the pantograph-catenary system performance. The detected arc number may also contribute to lowering predictive maintenance costs of pantograph-catenary inspections works as these can be performed only at determined sections of the line extracted by using arcing time locations and speed profiles of the locomotive

Power Quality Event Analysis in 25 kV 50 Hz AC Railway System Networks

open5siPower quality phenomena characterizing the voltage and current signals of railway electricity networks differ from those present in transmission and distribution electricity grids. There are no standardized procedures yet focused on PQ measurement techniques explicitly for railway applications. This paper evaluates whether the standard power quality measurement algorithms used in monitoring 50Hz 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 when caused by network configuration and 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 magnitudes and duration. The two methods are verified against some recorded signals of pantograph voltage and current. Recommendations are finally provided for PQ measurement algorithms for AC railways.openYljon Seferi ; Paul Clarkson ; Steven M. Blair ; Andrea Mariscotti ; Brian G. StewartSeferi, Yljon; Clarkson, Paul; Blair, Steven M.; Mariscotti, Andrea; Stewart, Brian G