Electric Railway Systems Research Articles

An Improved Q-Axis Current Control to Mitigate the Low-Frequency Oscillation in a Single-Phase Grid-Connected Converter System

An electric railway system is a typical single-phase grid-connected converter system, and the low-frequency oscillation (LFO) phenomenon in electric railway systems has been widely reported around the world. Previous research has indicated that the LFO is a small-signal instability issue caused by impedance mismatching between the traction network system and electric trains. Therefore, this paper proposes an improved q-axis current control method to reshape the train’s impedance. The proposed method can be implemented easily by relating a reverse q-axis reactive current directly to the reference of the q-axis current under the dq current decoupled control. Moreover, considering the additional q-axis reactive current control, a small-signal impedance model of a train–network system is built. The impedance-based analysis results indicate that the proposed q-axis reactive current feedback control can increase the magnitude of the train’s impedance, which is beneficial to enhancing the system’s stability. Finally, this paper employs experimental results to verify the effectiveness of the proposed method.

Distribution of Currents in 2 × 25 kV Electric Railway Systems under Normal Conditions

This article shows a detailed analysis of the distribution of currents in 2 × 25 kV electric railway systems under normal conditions. The network equations are clearly formulated in a way that enables the presentation of a novel simplified analytical solution as well as the traditional numerical solution of the equation set. The simplified analytical solution is obtained when the transformer impedances are neglected, and under these conditions: (a) the distributions of currents are analytically deduced for cases with only one train; (b) the distribution of currents among autotransformers and between catenary and feeder can be easily understood, as well as the effect of the train position on the distribution of currents; and (c) the superposition method is applied for cases with multiple trains in order to clearly explain the distribution of currents from the results with only one train. On the other hand, the network equations are also numerically solved, including autotransformer impedances, and it is shown that their effect is very low, especially because these impedances are typically small. Therefore, the proposed analytical method is a good tool to obtain an easy and approximate solution for the distribution of currents in these systems, as well as an excellent tool to facilitate the understanding of that distribution.

Improvement of the Electrical Performance of Outdoor Porcelain Insulators by Utilization of a Novel Nano-TiO2 Coating for Application in Railway Electrification Systems

The present study aimed to develop the electrical performance of outdoor insulators using a nano-TiO2 coating for railway electrification systems. The prototype design of porcelain insulators with normal coatings and using a nano-TiO2 coating is based on IEC 60815-1. The first test was performed to measure the low-frequency flashover AC voltage under both dry and wet conditions. In addition, the other test was conducted to measure the lightning impulse critical-flashover voltage at positive and negative polarity under dry-normal and wet-contaminated conditions. X-ray diffraction (X-RD) and Scanning electron microscopy (SEM) were used to examine the micro surface and show that the nano-TiO2 coating was adhered to the surface of the outdoor porcelain insulator and exists in an amorphous state. Additionally, it was observed and discovered that scattered nano-TiO2 strengthens the glassy matrix and creates a sturdy barrier that causes flashover voltage to be reduced under conditions of high dielectric strength. Nanostructured ceramic formulations outperform ordinary porcelain in terms of breakdown voltage strength, particularly for the insulators’ low-frequency flashover performances under dry and wet test conditions. However, a significant change in the lightning impulse critical-flashover voltage characteristics is observed and is not much better when adding the nano-TiO2 coating to the porcelain insulators.

A Train Scheduling for Energy Optimization: Tehran Metro System as a Case Study

Energy efficiency is one of the main issues in designing and operating different electrical systems. Energy-saving in electrical railway systems is an important concern due to the high amount of used energy. In order to find optimum energy consumption, different methodologies shall be examined. In addition, various affecting factors should be determined, and suitable solutions should be adopted. This paper illustrates that proper train scheduling is one of the effective approaches to optimize the system energy. Accordingly, comprehensive modeling is proposed considering different affecting factors such as the slope of different lines, the speed limits in each section, the time limit between the arrivals of trains to each station, and different modes of operation such as motoring and braking. Using the proposed model, an optimization problem with the objective function of energy-saving is solved. To evaluate the effectiveness of the proposed method, the proposed scheduling scheme is applied to Line 2 of Tehran Urban & Suburban Railway Operation Company. Based on the results, using the proposed scheme causes a 3.2% energy-saving compared to the existing train movement schedule in the same line. The proposed train movement scheduling program is proceeding to the last verification steps and will be used as a part of Tehran Metro navigation system in the near future.

Assessment of Energy Requirement of a Proposed Electric Railway System in Southern Sri Lanka

The SLEMA Journal is published by the Sri Lanka Energy Managers Association (SLEMA). Published twice a year since 1984, the SLEMA Journal carries research papers, articles, reviews and news about the status and new developments in the energy sector of Sri Lanka.

Data-Driven Low-Frequency Oscillation Event Detection Strategy for Railway Electrification Networks

Low-frequency oscillations (LFO) occur in railway electrification systems due to the incorporation of new trains with switching converters. As a result, the increased harmonic content can cause catenary stability problems under certain conditions. Most of the research published on this topic to date is focused on modelling the event and analysing it using frequency spectrums. However, in recent years, due to the new technologies linked to Big Data (BD) and data mining (DM), a new opportunity to study and detect LFO events by means of machine-learning (ML) methods has emerged. Trains continuously collect data from the most important catenary variables, which offers new resources for analysing this type of event. Therefore, this article presents the design and implementation of a data-driven LFO event detection strategy for AC railway network scenarios. Compared to previous investigations, a new approach to analyse and detect LFO events, based on field data and ML, is presented. To obtain the most appropriate detection approach for the context of this application, on the one hand, this investigation includes a comparison of machine-learning algorithms (support vector machine, logistic regression, random forest, k-nearest neighbours, naïve Bayes) which have been trained with real field data. On the other hand, an analysis of key parameters and features to optimize event detection is also included. Thus, the most significant result of this work is the high metric values of the solution, reaching values above 97% in accuracy and 93% in F-1 score with the random forest algorithm. In addition, the applicability and training of data-driven methods with real field data are demonstrated. This automatic detection strategy can help with speeding up and improving LFO detection tasks that used to be performed manually. Finally, it is worth mentioning that this research has been structured based on the CRISP-DM methodology, established as the de facto approach for industrial DM projects.

활선 상태 전기적 특성 평가를 위한 이상 상태모니터링 적용방안 검토

Recently, various technologies for safety inspecting of electrical equipment such as energy storage system and contact line related with cu based conductor were studied. This paper were analysis quantitative evaluation technologies to determine the arc flash characteristics with abnormal state through the non-contact state. In particular, in order to analyze the characteristics of voltage, current and UV light according to arc flash, the test results of the arc flash simulator analyzed and presented. Various studies are being conducted on the characteristics of voltage, current, and arc light according to the occurrence of arc flash defects and it was analyzed that additional research need to can be used for defects detection in small-scale systems connected with storage devices such as ESS and electric railway systems and life expectancy systems.

Medium‐voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

Medium‐voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

Comprehensive Control of Reflux Safety Parameters Based on Flexible Grounding Scheme in DC Railway Electrification System

Currently, the excessive rail potential (RP) and stray current (SC) are disasters to the safety of equipment and staff in dc railway electrification system (dc RES). However, abnormal increase of RP and SC still exists and the coupling relationship between RP and SC with the complex grounding scheme has not been clarified. In this article, a flexible grounding scheme (FGS) is proposed to realize the comprehensive control of RP and SC with dynamic operation of multitrain. By establishing the simulation model of dc RES with FGS, the coupling mechanism of the abnormal increase between RP and SC is clarified. In order to prove the effectiveness of FGS, simulation results of dc RES with ungrounded scheme, over voltage protection device (OVPD) grounded scheme and FGS are compared. Field tests of reflux safety parameter (RSP) are carried out in Hefei Metro Line 2 with different grounding resistance. Simulations and field tests show that coupling effect between RP and SC at multiple stations is obvious, and FGS can realize the comprehensive control of RP and SC effectively.

A Study on the Vibration Characteristics and Damage Mechanism of Pantograph Strips in a Railway Electrification System

This paper presents the vibration characteristics of a pantograph–catenary interaction in a rigid catenary system. Both computational simulation and laboratory tests are carried out to evaluate the frequency contents of pantograph strips. Based on the observation that irregular wear is characterized by the consistency between the pantograph strips’ wear pattern and the mode shape of their dominant modal frequencies, it is deducted that resonance occurs at the pantograph strip and the contact wire interface in the high frequency range. By applying damping treatment to the pantograph strip, and hence improving its damping property, a reduction of 7 dB in the total vibration level at the sliding contact can be achieved, as verified through field tests. It is also found that the worse the initial condition of the pantograph–catenary system, the more prominent the damping effects on the control of high-frequency vibration for irregular wear problems.

Technology Trend of Lightning Protection Measures in Railway Electrical Systems

Technology Trend of Lightning Protection Measures in Railway Electrical Systems

A Survey on Automatic Inspections of Overhead Contact Lines by Computer Vision

Automatic inspections of overhead contact lines (OCLs) are developed to implement anomaly detection during normal operation. It is an essential prerequisite for efficient maintenance of railway electrification system. This paper presents a comprehensive survey on the inspections of OCLs with an emphasis on computer vision technology, which has developed rapidly due to its ability to understand images. Our survey begins with a brief introduction on anomalies in OCL inspections and generic procedures of computer vision inspection for anomaly detection. Subsequently, for detecting deviations of parameters and defective components during OCL inspections, the existing techniques involving stereo vision and object vision, especially convolution neural networks are described in detail from two aspects: measurement of OCL parameters and identification of OCL conditions. Some interference factors in OCL inspection are analyzed. Actual cases of the inspections are also briefly shown. Challenges and suggestions for further research on OCL inspection are drawn toward the end of the paper.

Optimal linearized operation of electric railway system in the presence of flexible renewable sources and switchable capacitor banks considering supply and demand sides’ uncertainties

The electric train (ET) is a great energy consumer in an electrical network, which regenerates a high amount of energy into the grid at the braking moment. Therefore, in this paper, the optimal operation of the electric railway system is proposed considering renewable sources, hybrid storage systems (battery and ultracapacitor units), switchable capacitor banks, and regenerative braking energy of ET at the same time to attain a favorable economic, environmental and operational condition. Renewable sources reduce operating costs and environmental pollution. The storage system is utilized as a flexible source along with renewable generations. The ultracapacitor stores the ET braking energy, and the capacitor bank regulates the voltage. The scheme minimizes the expected network operating cost, while the AC optimal power flow and other technical limits are considered. This problem is nonlinear, and a linearized approximation formulation is implemented to achieve a unique optimal solution with the best and minimum computation time. The unscented transformation method is used to model uncertainties of load, ETs’ energy consumption, and renewable energies. Finally, by evaluating the numerical results, it is illustrated that the efficiency of the proposed method simultaneously improves the economic, environmental, and operational features of the network.

Simultaneous DC Railway Power System Analysis Method Using Model-Based TPS

This paper focuses on the development of a model-based train performance simulation with the practical train operation data using MATLAB Simulink. The developed program uses input operation data of a DC 1500 V metro line. And the simultaneous and multi-rate simulation for DC metro was performed to interface train schedule data with actual railway electrification system and vehicle. In the simulation, the voltage and power measured at each substation are provided during the traction, coasting and breaking mode. From this study, railroad vehicle load can be virtually modeled in the system internally and contribute to verifying new parts of the overall railway electrification systems.

Harmonic mitigation of AC electric railway power feeding system by using single-tuned passive filters

Harmonic is an important factor affecting the quality of the power transmission system. caused by non-linear loads and power conversion devices. In this research, several train simulation samples of the city line Airport Rail Link (ARL) electric train were used to simulate the effects of harmonics on the power electric substation (ESS) by calculating the Total Harmonic Distortion of voltage (THDv) and current (THDi). Then compared with IEEE519-2014 standards to indicate the quality of power found that THDi 35th–50th exceeds the standard. In addition, the comparison of the harmonic reduction effect of the sample train from the single tuned passive filter designs of 3rd, 5th, 7th, and 11th showed that the 11th filter was able to keep the THD within the standard.

High-Frequency Damping Analysis and Compensation Method Above Half PWM Sampling Frequency for Train Grid-Connected Converter

There are serious harmonic overvoltage phenomena in the electric railway system caused by the high-frequency resonance or instability issues, which is rooted in the region not only below, but also above half the PWM sampling frequency. To effectively evaluate the high-frequency admittance of train and further suppress the harmful high-frequency instability issue, a multi-frequency averaging model combining sampling sideband components is developed. Compared with the single-frequency model, the multi-frequency model is more accurate in the region near sampling frequency. After simplification, it is found that the time delay of digital control system is the cause of high-frequency negative damping. However, the time delay may make the traditional virtual impedance method fail in the high-frequency domain. Therefore, a virtual-impedance-controller (VIC) with variable damping characteristic is proposed to reshape the train admittance. The proposed VIC has the same structure as PID control. The detailed design method is given to offset the influence of time delay. The multiple high-frequency negative damping regions of train can be eliminated simultaneously by using multiple parallel VICs. The proposed method is applicable when changing the switching frequency. Hardware-in-the-loop test and low-power physical experiments validate the effectiveness of the proposed VIC strategy.

Low Frequency Stability of AC Railway Traction Power Systems: Analysis of the Influence of Traction Unit Parameters

Dynamic interactions between AC railway electrification systems and traction unit power converters can result in low frequency oscillation (LFO) of the contact-line voltage amplitude, which can lead to a power outage of the traction substation and the shutdown of train traffic. Several system parameters can influence the low frequency stability of the railway traction power system, including contact-line length and traction unit parameters such as transformer leakage inductance, DC-link capacitance, control bandwidths and synchronization systems. This paper focuses on the influence of these parameters on the LFO. The methodology is based on a frequency-domain analysis. Nyquist and Bode diagrams are used to determine the stability limit. The validation of the method is performed through the use of time-domain simulations.

Smart soft open point to synergically improve the energy efficiencies of the interconnected electrical railways with the low voltage grids

This paper presents a novel smart soft open point (sSOP) that interconnects railway electrification system to the local low voltage (LV) distribution grid to provide additional flexibility and controllability for both networks. The proposed sSOP builds on the concept of soft open points, adding an energy storage system and embedding a rail and grid (R + G) energy management system to enable the energy transfer between the two networks at different average power levels. The smartness of the proposed soft open point is realised in the integration of an energy storage system to act as an energy buffer between these two networks of different dynamics. The paper demonstrates that the proposed sSOP improves the braking efficiency of trains and increase the local use of renewable energy through employing an integrated simulation platform between a railway and smart grid simulators that takes into account the trains' timetables as well as the daily variation of the grid loads and renewable energy generation. The results show that an appropriate design and control of the sSOP enables the recuperation of most of the braking energy available from the railway and that energy is enough to mainly supply the local power distribution grid, thereby effectively implementing the concept of smart grids.

Study on Rail Electrification Systems and their Harmonic Distortion Issues

Due to the harmonics insertion from of the asymmetric electric engine, particularly high / elevated / sizable trains, torque ripple and chromatic resonant difficulties have been commonly documented in railway electrification systems (RESs). We investigated the imbalance and switching frequency caused by a neighborhood transmission system, as well as their effects and mitigation policies, in this work. The varying levels of deformation in the supplying program's input characteristics can present a hazard to the propulsion loads. The many

Calculation algorithm and method for optimizing electricity consumption for the railway traction system

Abstract This article presents a calculation algorithm for establishing the electricity demand consumed by the railway electric traction system on a railway section, as well as methods for lowering power consumption and cost. In order to conceive the calculation algorithm, the following variables are taken into account: the number of trains in circulation on the section, the slope of the section, the train speed and the speed restrictions. For factors that substantially increase electricity consumption, but can be controlled, optimal values are computed using specific equations in the MATLAB program. The optimal values are implemented using the train’s timetable or a railway control system (SCADA). A decrease in power consumption of 5% can be expected with this method.