AC Traction Power Supply System Research Articles

Расчет полных сопротивлений тяговой сети систем электроснабжения 25 кВ и 2×25 кВ

Nowadays 25.7 thousand km of railway lines of the Russian Federation have been electrified using a single-phase alternating current system of industrial frequency with a voltage of 25 kV. Conditions of constant growth of cargo turnover explain the relevance of the issue of strengthening traction power supply systems, including alternating current, as well as shaping the direction of their further technical development. Thus, an urgent task is to develop a methodology for determining the parameters of 25 kV and 2ґ25 kV AC traction power supply systems, taking into account the use of reinforcing wires. The article discusses the methodology and sequence of calculating the resistance of traction network elements for the two specified systems, and presents the calculation results for the applied wire grades.

Utilisation of regenerative braking energy in adjacent power sections of railway systems

AbstractHuge regenerative braking (RB) energy is generated in the AC traction power supply system (TPSS) which is related to safe operation and comprehensive energy utilisation. For the RB energy utilisation, the authors propose a railway regenerative braking power conditioner (RBPC) with no energy storage system (ESS) integrated which is located at the end of the power sections between adjacent traction substations (TSSs). First, the RB characteristics are studied based on a large amount of measured data, and the load power states are classified according to the load powers of adjacent power sections. Then, the RB energy utilisation scheme, transferring the RB power to the adjacent power section where traction power exists, has been studied. Moreover, a dual closed‐loop control strategy for a back‐to‐back converter is adopted to achieve RB energy utilisation. Finally, a case study and an engineering application are carried out. The results have verified the feasibility of this method, which can illustrate that more than half of the RB energy can be mutually utilised in adjacent power sections.

A Novel Distance Protection Method for Out-of-Phase Faults of AC Traction Power Supply System

A Novel Distance Protection Method for Out-of-Phase Faults of AC Traction Power Supply System

Modeling and stability prediction for the static-power-converters interfaced flexible AC traction power supply system with power sharing scheme

The flexible traction power supply system (FTPSS) is a promising solution to solve the electric phase break and power quality problems existing in traditional traction power supply systems. To promote the balance of train power distribution among multiple substations, power sharing control is proposed by combining average power control and P-f and Q-V droops based on virtual power decoupling method. The active and reactive power is decoupled through introducing the impedance angle without knowing specific values of the line inductance and resistance. This system level control poses new challenges to the stability of the electric railway due to complex interactions between power electronic-based substations of the FTPSS. To address this issue, the frequency-domain model of the FTPSS with power sharing control is established. Then, the eigenvalue-based stability criterion is introduced to predict the stability of the interconnected system. In particular, to obtain how the power sharing control is sensitive to some controller/circuit parameters, a parameter-oriented stability analysis method is developed through assessing the influence of the key influential factors, including the time delay of wide-area communication, the controller parameters of the power sharing scheme, the circuit parameters, the length of the traction network and the train power requirement. The time-domain simulation and the downscaled prototype experiment are conducted to validate the effectiveness of the established model and the theoretical analysis. This lays the foundation for the design and stability analysis of the FTPSS.

DC Bias Suppression in Static Power Converter During Catenary Fault Handling for Railway Flexible AC Traction Power System

Flexible AC traction power supply system (FTPSS) has been a potential candidate for high-speed and heavy-haul railways. The catenary fault is a crucial issue in the FTPSS. Since the static power converters (SPCs) become the main source, SPC is required to switch between the voltage-frequency and the fault-current control modes, in order to achieve fault detection and rapid system recovery. However, inappropriate switching method may lead to violent change of instantaneous voltage. Therefore, serious DC bias of SPC output transformer may occur and excite severe overcurrent. It results in the tripping of SPCs and the failure of system recovery, and severely undermine the reliability of FTPSS. To address this issue, this paper analyzes and reveals the mechanism of this DC bias phenomenon. The voltage-time product imbalance during the mode switching process is the main cause of DC bias, and it is related to the voltage phase at the switching instants. Accordingly, a combined method of voltage waveform splicing and DC bias elimination control is proposed. Overcurrent can be avoided, and smooth control-mode switching and rapid system recovery can be achieved. Simulation and experimental results verify the validation of the proposed method.

Train-Network-HESS Integrated Optimization for Long-Distance AC Urban Rail Transit to Minimize the Comprehensive Cost

In order to solve the problem of the serious stray current existing in DC urban rail transit, and to improve the utilization rate of the regenerative braking energy (RBE) generated by locomotive, an AC traction power supply system (TPSS) for long-distance urban rail transit is proposed, in which the network power flow distribution is affected by the train trajectory, the parameters of network and hybrid energy storage system (HESS) configuration. For achieving the minimum comprehensive cost including the electricity cost and the life cycle cost (LCC) of HESS, this paper aims to develop a Train-Network-HESS integrated model to optimize network power flow distribution. The train trajectory is illustrated based on time-space conversion method and HESS control strategy is discussed to increase the utilization of the RBE. Furthermore, the optimized configuration of the AC TPSS for urban rail transit is obtained by the hybrid GA-PSO algorithm. Finally, the effectiveness of the proposed model is verified by detailed case studies and the comprehensive cost can be reduced up to 39.08% compared with conventional TPSS.

Simulation models and application options of electric power storage systems in traction power supply

Background: the determination of the energy indicators of the traction power supply system based on the train schedule in the conditions of operation of storage devices is based on the solution of a number of instantaneous schemes, each of which corresponds to the established operating mode. These methods require adaptation to account for non-linear characteristics or indicators, the value of which is associated with the retrospective of the change. In this regard, it is necessary to use calculation methods based on the solution of differential equations to solve problems related to the assessment of performance in transient or emergency modes, taking into account dynamic characteristics. Modeling the operation of storage devices in the traction power supply system allows you to evaluate the change in indicators depending on the parameters of the devices, traction load and circuit solutions for various topologies.
 Aim: to determine the structure of models of electric power storage devices in DC and AC traction power supply systems, to consider the results of calculating the main energy indicators, to determine ways to improve circuit solutions based on the identified features, to determine the technical requirements for electric power storage devices in traction power supply.
 Materials and Methods: to obtain the results, methods for solving differential equations corresponding to various variants of the topology of storage devices in traction power supply, implemented in the Matlab software package, are used.
 Results: the results obtained allow us to determine the structure of storage devices for traction power supply, evaluate models of devices for traction power supply of direct and alternating current, outline the prospects for further research in the field of circuit solutions and required device parameters.
 Conclusion: the results of the study allow models of electricity storage devices and technical solutions for their implementation aimed at introducing DC and AC traction power supply into the system.

Active Disturbance Rejection Control for Static Power Converters in Flexible AC Traction Power Supply Systems

Flexible traction power supply systems (FTPSSs) can solve problems in traditional systems and envision a promising future for rail transit power supply. The traction network voltage is determined by static power converters (SPCs), so the voltage control of SPCs is very important for the safe and stable operation of the system. The uncertainty of the train load, the power redistribution in the case of SPC disconnections from the network because of SPC internal faults, and the real-time cooperative control of multiple SPCs bring challenges to the voltage control of SPCs. Compared to classical error feedback control, active disturbance rejection control (ADRC) has better transient performance and immunity. An ADRC-based voltage-current dual-loop control strategy for SPCs is proposed in this paper. The equivalent block diagram and transfer function are deduced. The stability and immunity of the system are analyzed. Finally, the effectiveness and superiority of the proposed control strategy under different operating conditions are verified by simulation and experiment.

Unified Power Quality Management for Traction Substation Groups Connected to Weak Power Grids

In remote areas, weak power grids, fewer grid access points, and power quality (PQ) problems dominated by excessive voltage unbalance (VU) and lower power factor (PF) have been prominent obstacles in single-phase 25 kV AC traction power supply systems. To achieve a long-distance power supply with a high PQ, a traction substation group connected to a weak remote power grid is introduced, where the electrical structure is composed of multiple slave traction substations using single-phase traction transformers (TTs), a master traction substation (MTS) using a combination of TTs and a power flow controller (PFC) adopting a modular multilevel converter (MMC). Then, a unified mathematical model of the proposed system suitable for different TT wiring types revealing the effect of asymmetrical grids on the PFC is established. The negative sequence current (NSC) caused by multiple traction stations at the point of common coupling (PCC) and the PF can be improved effectively based on power conservation theory. In addition, to reduce the compensation capacity, an optimization compensation strategy is proposed. Finally, the effectiveness of the proposed algorithm is verified by simulation and a case study. The installed capacity of the PFC is 18.5% lower than that of traditional compensation.

Модель совместной работы системы тягового и внешнего электроснабжения

Purpose: To improve record accuracy of external power supply network influence on the operation of traction power supply systems of industrial frequency AC. The article shows that existing mathematical models of traction and external power supply joint operation have sounding limitations. These limitations almost exclude the possibility of their practical use. At the same time, when projecting a new electrification, it is required to choose the most efficient external power supply scheme. At the exploitation of existing electrified sections, the necessity arises to assess equalizing current value during repairs in external power supply networks and to adopt a decision on changing power supply and sectioning schemes. Corresponding model is required to solve these tasks. Methods: Analysis of existing mathematical models and computer programs for joint calculation for traction and external power supply networks. Development of three-phase PU-generator models on the basis of EMF source behind an inductive resistance, development of three-phase and single-phase load models. Results: The article presents a description of a mathematical model implied to study the joint operation of 25 kV AC traction power supply systems and 110-750 kV power supply systems. The principles of building the model of three-phase and single-phase PU-generators on EMF source basis behind inductive resistance as well as the models of three-phase and single-phase loads are considered. Based on the given mathematical expressions, a computer model has been developed that allows analyzing the joint operation of three-phase external power supply networks and single-phase traction ones. The model is implemented in MATLAB-Simulink software package. Using this computer model, the influence of power flows through 110–330 kV network of Karelenergo and “FSK EAS” Public Companies on equalizing currents in the traction network of Knyazhaya — Idel section of Oktyabrskaya railway was analyzed. Practical importance: The reliability raise for traction power supply system operation at the expense of precise calculation of equalizing currents. Energy loss reduction in a traction network in account of traction network optimal power supply scheme choice.

Traction Load Modeling and Parameter Identification Based on Improved Sparrow Search Algorithm

In this paper, a traction load model parameter identification method based on the improved sparrow search algorithm (ISSA) is proposed. According to the load characteristics of the AC traction power supply system under transient disturbance, the model structure of the traction load is equated to the composite load model structure of the static load shunt induction motor’s dynamic load. The traditional sparrow search algorithm is improved to enhance its accuracy and convergence. The generalization ability of the model was tested, and the accuracy of the proposed model was verified. Using the ISSA to determine the load model from the measured data, the results can verify the effectiveness of the ISSA for comprehensive load model parameter identification. Comparing the ISSA with the traditional SSA and PSO algorithms, it shows that the ISSA has better accuracy and convergence.

Ground Fault Analysis and Grounding Method of Static Power Converters in Flexible AC Traction Power Supply Systems

Flexible traction power supply system (FTPSS) can eliminate neutral sections of all catenaries and improve the poor power quality of railway substations. The static power converter (SPC) is the key equipment of FTPSS and its internal faults must be quickly identified and cleared with minimal impact on catenaries to ensure the safety and reliability. This article investigates the two-stage fault characteristics in FTPSS. Before blocking, overcurrent and voltage distortion may result in a wide range of abnormal power supply. After blocking, capacitor overvoltage becomes the primary problem threatening the safety of faulty SPC because of the energy feeding from other SPCs. Equivalent circuits are established and applied to various fault conditions. The most serious fault case can be found through the comparison, so the complicated large-scale simulation scanning can be avoided. A T-shaped grounding method is proposed to solve the problem of fault current and capacitor overvoltage. Based on the calculation and simulation results of several typical fault cases, the dimensioning criterion of grounding circuit is provided for reference. Moreover, a comprehensive scheme of grounding protection is designed to detect and isolate serious faults. The theoretical fault analysis and the proposed grounding method are verified by simulations and experiments.

Comparison of energy parameters of electric storage systems for DC and AC traction power supply systems

Introduction. The article discusses the energy parameters of electric power storage systems for DC and AC traction power supply systems. The purpose of the research is to evaluate the energy parameters of electric power storage systems located within the inter-substation zone boundaries of the AC traction power supply system at the 25 kV voltage.Materials and methods. The author used the methods of modeling, statistics and the experimental results processing. Moreover, the paper presented the parameter estimation of the energy accumulation system on the basis of the traction calculations for the AC rolling stock. In addition, the author made two variants of calculations — in the presence and the absence of the electric storage system. The researcher also made the simulation of the electric storage system for the voltage source connected to the sectioning post busbars.Results. Using the simulation modeling, the author presents active and reactive power graphs of the inter-substation zone boundaries in the active sectioning post operation conditions. Therefore, the article demonstrates the graph of the expected charge, the discharge depth calculations for the nominal energy capacity and the required charging features, which guarantee the charge restoration of the accumulation system to the initial level.Discussion and conclusion. The author offers the comparative assessment of the electric storage systems for the traction power supply with the DС voltage of 3 kV and the AC voltage of 25 kV. The research demonstrates the reducing potential of the nominal accumulation parameters.

Analysis of compensating devices efficiency in ac traction power supply systems

The article describes the main methods of reactive power compensation used in 27.5 kV AC traction power supply systems on the railways of the Russian Federation. The cases of installation of the longitudinal and transverse capacitive compensation devices at traction substation and sectiolizing post are considered in this paper. Based on experimental data their effectiveness has been analysed by comparing the main parameters of the traction power supply system before and after the installation of the compensating devices. The main effect in terms of power consumption reduction is achieved through application of reactive power cross-compensation devices. The results of the analysis show that the total electricity consumption in the researched area decreased by 23 % and the proportion of higher harmonic elements of voltage decreased by 15 %.

A Novel Co-Phase Power Supply System for Electrified Railway Based on V Type Connection Traction Transformer

Power quality and neutral section are two technical problems that hinder the development of electrified railway to high-speed and heavy railway. The co-phase power supply technology is one of the best ways to solve these two technical problems. At present, a V type connection traction transformer is widely used in a power frequency single-phase AC traction power supply system, especially in high-speed railway. In this paper, a new type of co-phase power supply system for electrified railway based on V type connection traction transformer is proposed. One single-phase winding in the V type connection traction transformer is used as main power supply channel, and three ports are used as compensation ports. Neutral section is no longer set with traction substation, and the train is continuously powered through. The independent single-phase Static Var Generators (SVGs) are used to compensate the three-phase imbalance caused by single-phase traction load. When necessary, the power factor can be improved at the same time. The principle, structure, control strategy, and capacity configuration of the technical scheme are analyzed in this paper, and the effectiveness of the scheme is verified by using the measured data of electrified railway. The advantage of this scheme lies in the universal applicability of the V type connection traction transformer, and the flexibility of the SVG device.

교류 급전시스템 실시간 시뮬레이션을 위한 고정설비 해석 모델 개발

본 논문에서는 교류 급전시스템을 구성하는 각종 전력설비의 동적 성능 시험을 위한 실시간 시뮬레이터의 모델링 방법과 그 결과를 제시하였다. 교류 급전시스템을 구성하는 주요 고정 설비, 즉 스코트변압기, 단권변압기 및 전차선로의 모델링을 제시하였다. 각 설비들의 회로 구성을 분석하여, 실시간 시뮬레이터의 단상 설비 라이브러리를 조합하는 방법으로 회로 모델링을 하였다. 또한, 각 설비의 특성을 나타내는 파라미터를 얻기 위하여, 스코트 변압기와 단권변압기는 형식시험 성적서를 활용하였고, 전차선로는 현장 측정을 통하여 자기 임피던스 및 선간 어드미턴스를 얻었다.

Algorithm for calculating the rail-ground potential in heavy load conditions

Increased freight turnover on railway transport inevitably leads to increased traction current in DC and AC traction power supply systems. The increase in traction current is already causing problems related to the normal operation of the 25 kV AC traction power supply systems. One of the adverse consequences of the increased traction currents is the increased rail-to-ground potential. This has already caused a number of accidents and related traffic interruptions on the Far Eastern Railway of Russia and other railway sections powered with alternating current. The study considers the problem of increased rail-to-ground potentials and provides basic formulae for calculating the wave parameters of the rail network and rail-to-ground potentials. Various methods are given for calculating rail-to-ground potentials for a 25 kV AC traction power supply system. Since in an alternating current system, expressions for calculating the potential are functions of a complex variable, the calculation of such expressions requires the use of special programs. Adaptation of existing methods to modern software and computing systems allows you to optimize and significantly speed up the process of calculating the “rail-to-ground” potentials, either considering the use of certain potential-reducing measures or not. A calculation method includes an algorithm developed for calculating the rail-to-ground potentials in the 25 kV AC traction power supply system for an inter-substation zone of any length with any number of electric locomotives within the zone.

Fault Analysis of the Gautrain 2 × 25 kV AC Traction Power Supply System Using Disturbance Fault Records and On-Site Testing

A typical 2 × 25 kV traction power supply system consists of both primary and secondary equipment housed in control rooms, and the traction overhead wiring (OHW) that runs between the substations. The substation secondary equipment consists of the protection and control intelligent electronic devices (IEDs) known as relays. Each section of the OHW between the substations is protected by a set of two relays at both ends of a line for impedance protection and their backup relays. At substations facing the sections at the end of the line, where there is no other substation on the other end, usually the overcurrent and earth fault protection is used. At the substations, there are disturbance fault recorders installed or relays equipped with a capability to record and store disturbance fault records. An analysis of these fault records makes a significant contribution to the efficient running of a traction system such as the Gautrain rapid rail system. A combination of the analysis of the faults that occur in the OHW as recorded and stored in the relays as well as the performance of the IEDs and the protection settings using the on-site tests are a subject of this article.

Перспектива внедрения системы тягового электроснабжения переменного тока с опорами контактной сети, не заземленными на рельс

Objective: To study the problems and possible solutions in the introduction of an alternating current traction power supply system with catenary supports without rail grounding. Methods: To solve the set tasks, we used the statements and methods of the theory of power supply, experimental planning, mathematical and system analysis, and the theory of electrical measurements. In the experimental studies, the Trans-AURA Emergency Process Recorder and the Tektronix TDS 2014 Digital Oscilloscope were used, and the Aura2000 and MS Excel 2010 software products were used to process the experiment results. Results: The basic requirements for the AC traction power supply system grounding are presented. The flaws of the traditional grounding system of the catenary supports on the rail network are revealed. Two possible directions are described, which allow eliminating issues during the operation of the AC traction power supply system. The first direction requires the introduction of an additional stage into the traction network protection system, which makes it possible to identify short circuits through a high rail-to-earth resistance. The second suggests the need to revise the relay protection system itself, which includes changing the approach to grounding the catenary structures, the methodology for calculating the relay protection settings, a more detailed analysis of electrical safety conditions, etc. An equation has been formulated to determine support-groupto-earth resistance taking into account the group grounding cable and the existing requirements for ensuring the sensitivity of the main protection means, which allows ensuring reliable operation of feeders’ relay protection. The results of experimental tests of electrical safety conditions and electromagnetic influence are presented. The tasks are identified being the essential prerequisite to the widespread introduction of a system with supports without rail network grounding. Practical importance: The developed methodology for selecting the protection settings will make it possible to operate the AC catenary system without the supports’ rail grounding, as well as introduce the proposed additions to the instructions for grounding traction power supply devices at “Russian Railways”

A Co-Phase Traction Power Supply System Based on Asymmetric Three-Leg Hybrid Power Quality Conditioner

Single-phase 25kV AC traction power supply system (TPSS) is widely used for electric power feeders in high-speed rail. Modern locomotives draw a large amount of unbalanced, inductive power from two phases of the grid through the traction transformer and lead to severe problems of voltage unbalance and reactive power existence. These problems are mitigated in the promising co-phase TPSS with the equipment of Railway Power Conditioner (RPC) or Hybrid Power Quality Conditioner (HPQC), in which HPQC can operate with a lower voltage and cost. However, HPQC installation involves the adoption of a bulky and expensive coupling transformer. In this paper, a co-phase TPSS employing asymmetric back-to-back modular multilevel converter (MMC) is proposed and it is named asymmetric three-leg hybrid HPQC (ATHPQC). Through the simulation verifications in this research work, the proposed design can effectively remove the additional and costly step-down coupling transformer, which is required by symmetric HPQC. For comprehensiveness of the ATHPQC design, internal circulating current modeling and analysis are investigated. Control system is implemented, including external compensating current control, internal balancing control and PWM module. ATHPQC is a promising alternative TPSS for next-generation high-speed rail.