Electrified Railway Systems Research Articles

교류 전기철도 급전시스템을 위한 철도용 전기품질 보상장치의 제어방법

교류 전기철도 시스템은 비선형 단상 부하인 차량의 부하특성으로 인해 고조파 왜곡, 무효전력 발생, 3상 불평형과 같은 전기품질 문제를 가지고 있다. 이 같은 전기품질 문제는 철도 시스템뿐만 아니라 철도와 연계된 다른 건전한 계통에도 악영향을 미치게 된다. 따라서 본 논문에서는 이와 같은 전기철도 급전시스템의 전기품질 문제를 보상하기 위해 철도용 전기품질 보상장치(RPQC; railway power quality conditioner)를 적용하고, SRF(synchronous-reference-frame) 제어를 이용한 RPQC의 제어방법을 제안한다. 제안하는 제어방법을 통해 RPQC는 고조파 왜곡, 무효전력, 부하 불평형과 같은 전기품질 문제를 순시적으로 보상할 수 있으며, 시뮬레이션을 통해 이를 검증한다. 시뮬레이션 결과는 제안한 RPQC 제어방법의 타당성을 보여주고 있다.

Pantograph Arcing in Electrified Railways—Mechanism and Influence of Various Parameters—Part I: With DC Traction Power Supply

Pantograph arcing is a common phenomenon in electrified railway systems. This is also a source of broadband-conducted and radiated electromagnetic interference (EMI) for vehicle as well as traction power and signaling systems. In this paper and the companion paper, experimental analyses of pantograph arcing phenomena are presented for dc and ac feeding systems, respectively. Influences of different parameters on dc traction system, such as supply-voltage polarity, relative motion between pantograph and overhead contact wire, namely, forward motion along the track (longitudinal), and lateral sliding motion of the pantograph (zigzag) are presented here. From the voltage and current waveforms of the test runs, it is shown that pantograph arcing is a polarity-dependent phenomenon. For the positive-fed overhead traction system, where pantograph is cathode, the supply interruptions due to zigzag motion are comparatively less compared to negatively fed traction systems. As a result, the transients, due to pantograph arcing, are more frequent in negatively fed traction systems. It is found that the arc root movement along the electrode surfaces (pantograph-contact wire) is governed by the relative motion and polarity of the electrodes. The analyses presented in this paper also form a foundation to understand the pantograph arcing process and the corresponding influential parameters with the ac supply presented in the companion paper. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the EMI due to pantograph arcing in dc-fed traction systems.

고속전철에 의한 통신 선로에서의 유도전압 분석

본 논문에서는 고속전철 운행에 따라 인접 통신 선로에서 발생하는 유도전압을 국내 고시에 제시된 측정 회로에 따라 측정하고 유도전압의 특징을 분석하였다. 고속전철 선로와 2 km 병행하는 2개 루트의 시험용 통신선로를 구성하여 이격 거리, 병행 거리에 따른 유도전압을 측정 및 분석하고, 측정 회선 단말 접지 위치의 레일과의 거리에 따라 측정값에 대한 영향 여부를 검토하였다. 또한 1일간 시간에 따른 변화, 요일별 변화 등을 분석하였으며, 유도전압에 포함되어 있는 고조파 성분을 확인하였다. 이론과 같이 이격 거리에 따른 유도전압의 차이를 보였으며, 단말의 접지 위치는 측정값에 큰 영향을 주지 않음을 확인하였다. 또한 특정 시간대 및 특정 날짜에 상대적으로 큰 유도전압이 나타남을 확인하였다. This paper analyzed the induced voltages on a telecommunication line due to high-speed a.c. electrified railway system. The induced voltages were measured by domestic regulation, 2 test lines with 2 km length were installed near railway in parallel to compare the influence for distance from disturbing line. The analysis was made on the induced voltages with the distance from railway, line length, and the different earthing point, and also on the waveform and spectrum distributions. The statistical induced voltages for the time for a day and dates was analyzed.

A Method for Interfacing Lumped-Circuit Models and Transmission-Line System Models With Application to Railways

Transient analysis of lossy multiconductor transmission lines (MTLs) has been studied using the finite-difference time-domain (FDTD) method with lumped loads/devices connected at line terminations. In electrified railway networks, series and shunt devices (whose circuit models are derived either from experiments/borrowed off the shelf), e.g., transformers, converters, switchgear, signal equipments, etc., are found distributed along the MTL system. To simulate such railway systems involving both transmission lines (TLs) and lumped circuits, an interface technique between TL systems, which is solved using FDTD, and all the lumped circuits, which are solved using alternative transients program/electromagnetic transients program software (circuit solver), is proposed. This sufficiently accurate method is simple to apply as only instantaneous voltages and currents are transmitted between the stand-alone FDTD routine and circuit solver. Moreover, the user avoids coding complex circuit models within the FDTD, while at the same time, efficiently uses the potential of accurate frequency-dependent loss models (nonexistent in circuit software) coded in FDTD. The technique is applied on typical electrified railway systems to demonstrate how traction transformers, track circuits, and line interconnections affect the propagating voltages and currents. The method could be beneficial for transient protection and insulation coordination studies in electrified railway systems.

Vulnerability of European Rail Traffic Management System to Radiated Intentional EMI

In this paper, the vulnerability of the future electrified railway system in Europe from a high-power microwave (HPM) source is investigated. The scenario of in-band disturbances radiated toward a GSM-R antenna and damaging the connected communications system is evaluated for different classes of HPM sources and situations. The minimum realistic distances for the different HPM sources from the antenna to cause permanent damage is shown, and the severity of threat from the different sources is discussed.

Two-phase controlled compensator for alternating-current quality improvement of electrified railway systems

The technological development of electrified railway systems during recent decades has demanded higher and higher quality performances of the supply subsystem. For this purpose, the recourse to electronics and to automation techniques can represent the right way to secure a reliable and efficient electric supply to the railway. The paper summarises the general problems of quality in railway electrification and proposes a new configuration of traction substations for single-phase AC-supply railways, based on the use of a two-phase inverter with nonlinear and variable-structure control system. Such an advanced technical solution allows one to obtain full compensation of load unbalances, constant load voltage, satisfactory power factor and a remarkable reduction of both disturbances and nonlinear-load effects. Some numerical applications show the efficacy of the proposed controlled compensator in containing disturbances and power-parameter variations, as well as its high performances in terms of fast response time, accuracy in steady-state conditions and general low sensitivity to disturbances.

Optimal Impedance Termination of 25-kV Electrified Railway Systems for Improved Power Quality

Many single-phase 25-kV electrified railway systems today are loaded with conventional ac-dc thyristor-based locomotives, which draw current rich in harmonic content. The flow of this harmonic current through the feeder impedance can result in a distorted pantograph voltage waveform, which, in turn, can constrain the amount of power delivered to the locomotives. A possible solution to improve the supply quality is to connect a hybrid power-quality conditioner consisting of active and passive elements at the end of the traction feeder. However, if not appropriately designed, the installation of a power-quality conditioner can result in harmonic amplification at some points along the feeder. This paper now presents an analysis to study how the power-quality conditioner must function to implement an optimal impedance termination at the end of the feeder to achieve uniform harmonic suppression along the whole feeder length. The theoretical concepts presented have been confirmed in simulation and experimentally using a model traction system.

A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.

A Robust Multilevel Hybrid Compensation System for 25-kV Electrified Railway Applications

On many electrified railway systems with single-phase 25-kV industrial frequency supply, the power quality can be particularly poor when conventional thyristor based locomotives are operating, and this constrains the amount of power that can be delivered to the locomotives. This paper presents a hybrid shunt compensation system consisting of alternatively a cascaded or a reduced topology multilevel active power filter, and a low rating passive damping filter. The active power filter is controlled by a novel hysteresis current regulation strategy, and both mitigates low-order voltage harmonic distortion along the feeder and provides root mean squared voltage support. The passive filter damps harmonic resonances that are typical in such 25-kV traction systems. The results show that the filter system can significantly increase traction system power transfer capacity with only a relatively small capital investment, allowing older thyristor based locomotives and increased traffic levels to be supported without necessarily requiring a complete system upgrade. Simulation and experimental results are included showing the performance of the filter for both steady state and transient conditions.

On the influence of conductor heights and lossy ground in multi-conductor transmission lines for lightning interaction studies in railway overhead traction systems

Railway overhead traction system is a classic example of scattered conductor configuration, where tracks and other wires form multi-conductor transmission lines (MTLs) with large variation in conductor heights above ground and they are spread across regions having different soil conditions. Lightning transient analysis in such systems has not received much attention earlier. Here we analyze the influence of conductor heights and lossy ground on the induced voltages in a two conductor MTLs for the case of a direct lightning strike. For transient analysis, modified time domain transient ground impedance expressions having better early and late time behavior was used. The dependence of transient ground impedance on conductor heights and ground resistivity are presented and discussed. The early time transient ground impedances are unaffected by ground resistivity but their decaying nature is highly dominated by ground resistivity. It is found, if one of the conductors is close to ground (a rail) and if it is at large vertical distance from struck conductor (an auxiliary power line), then with increasing ground resistivity the peak induced voltages in the conductor close to ground initially increase, then decrease and finally tend to remain constant (within 100–10,000 Ω m). This phenomenon is opposite to that compared to conductors that are close to each other with minimum vertical separation (two auxiliary power lines), where the peak induced voltages increase with increasing ground resistivity. The study focuses mainly to access when a mutual coupling due to system geometry or due to ground losses becomes dominant in determining induced effects from lightning in MTLs, which could be an important contribution to the lightning interaction studies for electrified railway systems.

High-Performance Harmonic Extraction Algorithm for a 25 kV Traction Power Quality Conditioner

Many single-phase 25 kV electrified railway systems carry a large number of conventional thyristor-based locomotives, which draw current rich in harmonic content. A possible solution to mitigate this harmonic complication is to connect a power quality conditioner based on voltage detection at the end of the traction feeder. However, the performance of the installed power quality conditioner depends strongly on the accuracy and stability of the harmonic extraction algorithm used to generate the command harmonic current reference to be tracked by the inverter inner current control loop. A high performance, computationally efficient harmonic extraction algorithm is presented, implemented using delta-operator-based digital resonant filters for traction applications. Unlike most other extraction algorithms, the implementation of the algorithm presented does not require complex mathematical transformations, and therefore has a significantly faster computation speed and is suitable for single-phase traction applications. Also, through delta-operator-based implementation, the proposed algorithm exhibits improved accuracy and robustness over a wider range of operating conditions. The accuracy and robustness of the proposed algorithm have been verified by both simulation and experiment.

Voltage form factor control and reactive power compensation in a 25-kV electrified railway system using a shunt active filter based on voltage detection

AC railway traction systems are particularly susceptible to harmonic distortion. They are weak single-phase networks often loaded with severely distorting SCR-based locomotive drives which continually change their point of physical connection to the network. For a public distribution system the total harmonic distortion is a clear measure of supply quality. However, for a traction system the more important parameter is the voltage form factor, which is directly related to the maximum power a locomotive can deliver. To minimize this form factor, this paper proposes the use of a shunt active filter that minimizes the third, fifth, and seventh harmonic voltage components at the point of filter coupling. It is shown that the filter is effective in both compensating the pantograph voltage form factor, and providing reactive power to maintain the feeder voltage. The results are confirmed by detailed simulation using the EMTDC package.

Computer simulation and modeling in railway applications

An electrified railway system includes complex interconnections and interactions of several sub-systems. Computer simulation is the only viable means for system evaluation and analysis. This paper discusses the difficulties and requirements of effective simulation models for this specialized industrial application; and the development of a general-purpose multi-train simulator.

Control strategy of advanced 25 kV-50 Hz electrified railway systems

Technological innovation has been largely involved in the general modernisation of electrified railway systems in the last few decades. Better quality performances of supply and electrification subsystems are thus expected, which have until now made less recourse to electronic and automation techniques than other technological sections of the system. A method is proposed for compensating voltage and current unbalances in single-phase 25 kV-50 Hz railway power supply, based on a new configuration of the traction substation. Two Scott-connected transformers are coupled with an impressed voltage two-phase inverter, to obtain stabilisation of load voltages to rated values. Satisfactory power factor and reduction of network disturbances, as well as nonlinear load effects of the load, can also be reached. The full compensation of load unbalances and a substantial inherent protection against disturbances, even under changing conditions of power parameters, are obtained through a nonlinear control system, based on the variable structure system theory. Numerical simulations confirm the high performance of the compensation method with respect to fast response time, steady-state accuracy, and very low sensitivity to disturbances.

A tectonomagnetic effect detected in Central Italy

Significant variations in the absolute value of the geomagnetic field intensity related to tectonic events, as earthquakes and volcanic eruptions, have been observed in several cases. To detect such a tectonomagnetic effect related to seismic activity, a seismomagnetic network was installed by the Istituto Nazionale di Geofisica (ING) in the Abruzzi region (CentraI Italy), in July 1989. This area is being uplifting since the Pliocene. A logistic compromise between geophysical requirements and the electrified railway system tracks distribution led to the installation of five total magnetic field intensity data acquisition sites. From July 1989 to September 1992 geomagnetic intensity data were simultaneously recorded at all stations and compared to that recorded at the L'Aquila Observatory, located in the same area. A variation of about 10 nT in the absolute level of the geomagnetic field was measured at two stations located on the eastern side of the network. We suggest that the detected magnetic anomaly could resuIt from aseismic-changes in crustal stress during this time.

Comparison of physical and digital modelling techniques for a compensated railway system

Digital modelling systems are capable of providing highly accurate information about the systems which they describe. A disadvantage of such models is that, if there are flaws in the model representation or if certain features have been oversimplified or omitted, the results can be totally different from the behaviour of the real system. It is therefore always an advantage to be able to verify the accuracy of the model by an alternative technique. The digital CAD package, SABER, has been used for modelling the behaviour of 25 kV electrified railway systems. In order to validate the results of this package, comparative studies have been made using a physical simulator. The models for the physical simulator, although to some extent simplified, nevertheless include all the real and important aspects of the full scale equipment. The results given in this paper concern a 75 km railway system which includes static var compensators (SVCs) to enable the traction system to carry heavier train loads over longer distances than normal. The SVC includes thyristor controlled reactors (TCRs) which are controlled using a phase locked loop technique. The simulated results from the two modellingg systems are in good agreement.

AC train emergency fuzzy logic control using an event driven approach

The paper proposes a fast, versatile and easy-to-use technique for control of train despatch schedules in an electrified railway system for improving its performance following outage of a station transformer. Using the technique of event driven approach and fuzzy logic, it is shown how a set of performance indices which represent the requirements on passengers, headway, regularity, and electrical loading, are optimised during rescheduling following such outage. Without the proposed emergency control technique, the railway system under consideration exhibits unstable buildups of unserved passengers/transformer overloads. Such buildups severely restrict the system's capabilities to return to normal operation.

Paper 10: Design of Railway Rolling Stock for Heavy Urban Service

With a total fleet of 4250 railway cars, London Transport convey over 2 220 000 passengers each working day on a rail network of 236 route miles. More than half a million passengers alight at central London stations between 7 a.m. and 10 a.m., and the reverse flow takes place between 4.30 p.m. and 7 p.m. This concentrated demand presents a major problem. It can be shown than an electrified railway system can provide the most efficient and reliable means of rapidly conveying large numbers of people in dense urban areas. Various figures have been published and from these it can be demonstrated that a modern subway system can give a passenger-carrying capacity, under tolerable loading conditions, of between 25 000 and 30 000 per hour in each direction, or equivalent to 10 or 12 lanes of motorway in each direction. The actual capacity, however, will depend on a number of factors, many of which are dictated by the amount of foresight displayed by the original planners and contruction engineers of the line.