Traction Network Research Articles

Резонансные явления в тяговой сети переменного тока

Резонансные явления в тяговой сети переменного тока

Simulation modeling balancing current in the traction network of a substation group

This article is devoted to assessing the transit of electricity from an external electrical power supply system through the traction network of a railway district that includes nine traction substations. Substation transformers has star-delta-11 connection. The paper presents a simulation model of the railway district implemented in the MATLAB/Simulink software package. Various options of loading the external power supply system are modeled including into account the symmetrical load of the external network and the single-phase load of traction substations. The values of the voltage difference on the traction windings of power transformers of adjacent substations that occurs at different loads, the balancing currents that this difference creates and real power losses in the inter-substation areas are calculated.

Ultracapacitor Energy Storage Systems based on Dynamic Setting and Coordinated Control for Urban Trains

The supply voltage of traction systems fluctuates frequently due to acceleration and braking during urban rail train running process. In order to achieve better performance for ultracapacitor energy storage systems, a bilateral ultracapacitor energy storage system structure is adopted, and a method based on dynamic setting and coordination is proposed, in which the charge and discharge voltage thresholds of ultracapacitors are dynamically set and the energy flows are coordinated controlled between the bilateral ultracapacitor energy storage systems. The simulation results show that the proposed control strategy can achieve good energy-saving effect and stabilize the traction network voltage under the premise of balanced use of the ultracapacitor energy storage systems.

Integrated configuration and control strategy of PV generation in railway traction power supply system

Recently, electric railways have experienced a rapid development with an increasing power demand. Due to the flexible installation at trackside land along railways, photovoltaic (PV) generation is suggested to extend to the traction power supply system (TPSS) in railway. Firstly, this paper proposes a three-phase integrated configuration for PV generation connected to two-phase traction network and on-site consumption of solar resource alongside railways. In this configuration, another inverse V/V transformer is used to maintain a balanced three-phase low voltage (LV) ac bus from two-phase traction network. It is more convenient to access more PV generation units. Then, in order to mitigate the negative sequence currents caused by electric trains, an individual phase current (IPC) control strategy for PV converters is developed for power quality improvement. It can not only supply the locomotive with asymmetrical currents but also feed back to the grid with symmetrical currents. All the implementation and calculations are conducted in the three-phase stationary reference frame without any sequence extracting and power compensations. Finally, simulation results are presented to validate the effectiveness of the proposed IPC control strategy.

Reduction of electric power losses by the reactive power compensation unit at the point of AC electric traction network sectioning

Changes of electric traction network with regulated and not-regulated reactive power compensation units (CU) are required due to switching on the reactive power static generators at the AC electric traction network sectioning points the specifying calculations of the reactive power. The method of calculation of power losses in the traction network with regulated and not-regulated cross capacity compensation units at the sectioning point was developed. The main positive effect of CU at the sectioning point is increasing of the carrying capacity of the railroad sections. However, calculation of CU effectiveness for reduction of electric power losses, as well as calculation of continuously controlled CU requires appropriate calculations. It is demonstrated that CU effectiveness at the sectioning points of reactive power compensation is reduced in connection with distribution of the draft load; CU regulation effectiveness is also reduced as a response to increase of the carrying capacity of the railroad section, which allows assessing the proposed calculation formulae. Presented examples of calculation for the actual baseline data demonstrate that full losses in the traction network (assumed as 100%) can be reduced by using of CU of the sectioning point up to 21% maximum with continuously controlled units and up to 13.4% with uncontrolled CU. As automatics of the reactive power static generator is designed for increasing the carrying capacity of the railroad, its operation frequently complies with the reactive power overcompensation regime when losses in the traction network are increased.

Construction of a method to protect a traction electric network against short­circuit currents, based on the new attribute

All types of relay protection are based on comparing the values for certain attributes under a system's normal and emergency operational modes. A new attribute for defining the emergency mode in a direct current traction electricity supply system has been proposed, namely, the speed of voltage drop in the feeder of a traction substation. It is known that at a short circuit in the traction network, its voltage is reduced. Its sharpest, almost linear, decrease is observed, first, at the first moment of the emergency transition process, and, second, at a short circuit site and at points near it. Therefore, the steepness of the front of such a reduction in a feeder voltage could become an attribute of short circuit. A given attribute makes it possible to determine the type of short circuit based on a distance from the power source. In addition, we have proposed the circuit solutions for implementing a system of protection based on this attribute. Three options for building such protection systems have been considered. A first option implies using a RC filter. A second variant employs a pulse transformer. A third option is to use a bridge scheme. Each scheme has its advantages and disadvantages; however, modern electronics and digital technology make it possible to implement any of them. In the future, this would facilitate the construction of a selective protection (in terms of distance) from short circuit. To this end, one needs to use as many protection kits as how many points along a traction line must be monitored. Such a system is also easily implemented by software using microprocessor equipment. The practical results from our study at a section of traction power supply of the Dnieper Railroad make it possible to assert that the proposed technique for determining short circuits is rather effective. It could be used as an additional (backup) system in general relay-protective hardware. That would improve the reliability of power supply systems for traction networks. Overall, the considered technique for determining short circuits could be used in any DC power system

Modelling and numerical solution of ungrounded DC rail traction system load flow using ladder circuit – part II: solution method

Accurate solution of dc ungrounded rail power system load flow requires detailed modelling of negative path components, resulting in large numbers of circuit nodes and branches. Such modelling complexity incurs heavy computational burden and potential ill numerical conditions when solved by nodal voltage equations. Part I of this study presented a ladder-circuit model for traction network between substations and a power flow formulation adopted from ac distribution load flow. Part II presents the solution algorithm that harnesses the ladder circuit models to achieve efficient load flow computation and numerical robustness for the entire dc traction system by sequentially solving for power flows of individual substations and wayside ladder circuits. The proposed algorithm requires computational burden linearly proportional to the number of substations, much less than those by nodal voltage equations. The computation results from two transit lines in Taiwan illustrate that the proposed algorithm accomplishes the objectives of computational proficiency, numerical robustness and versatility to train load models and various traction circuit configurations such as branch lines.

Modeling Effects of Stochastic Stray Currents from D.C. Traction on Corrosion Hazard of Buried Pipelines

The main problems discussed in the article concern the analysis of the phenomenon of stray currents generated by electric D.C. traction currents. These currents flow in the ground and, when they encounter an underground metal structure, can lead to the acceleration of electrochemical corrosion. There is a stochastic phenomenon that depends on many factors such as the position of the traction vehicle along the route or the current drawn by it from the traction network. The presented research concerns the use of probabilistic methods to analyze this phenomenon. The proposed algorithm allows determining the occurrence of electrochemical-pipeline corrosion risk for geometrically complex traction-pipeline systems, including many random variables and corrosion phenomena. The non-deterministic solution to such an interdisciplinary problem is an element of novelty.

DYMANIC CHATGING OF ELECTRIC BUSES - THE ELEMENT EMOBILITY IN PUBLIC TRANSPORTATION

Night charging and fast charging are currently the two most common systems for charging electric buses. Despite the fact that numerous trial installations were started, neither of these two systems has obtained unqualified approval of the users. The alternative is to charge vehicles in motion - dynamic charging which combines the advantages of trolleybus transport and of electric buses. One of the advantages is the reduction of risks associated with the electrification of urban transport. The investment in the construction of the traction network allows you to reduce the costs associated with the purchase and replacement of traction batteries, as well as increase the flexibility of the transport system. The article presents the financial benefits resulting from the use of a dynamic charging system.

Mechanism Analysis of Sympathetic Inrush in Traction Network Cascaded Transformers Based on Flux-Current Circuit Model

When electric multiple units (EMU) pass the neutral zone, the traction transformer may generate sympathetic inrush, which will cause a malfunction in the transformer differential protection. In order to study the mechanism of the sympathetic inrush of the cascaded traction transformer, the flux–current model of the transformer, line impedance, power system voltage source, and other loads was established. On the basis of the flux–current circuit model, the influence of different factors on the sympathetic inrush of the traction transformer was analyzed. The analysis results were verified by simulation. Research results show that the remanence, closing angle, line impedance, and load will affect the duration and amplitude of the sympathetic inrush.

Electromagnetic safety in points of overhead power lines and electrified railroads crossing

Traction networks of alternating current electrified railroads generate large electromagnetic fields with 50 Hz frequency. In points of overhead power lines (OPL) and electrified railroads crossing, traction network electromagnetic fields and overhead power lines interfere with each other, which can result in increase in intensities and appearance of the field complex spatial structure. To determine intensities of electrical and magnetic fields which are created in points of crossing, a procedure for intensities summing has been developed, which is based on fields intensities calculation with Fazonord software application, the fields corresponding to traction network and overhead power line mode. Modeling results indicated that intensities of traction network magnetic field are increased up to 13% by interference of 220 kV intensities power lines magnetic field, while at a regulated height of 1.8 m, magnetic field amplitude equals to 82 A/m. At the same time, OPL can increase traction field electrical field strength in the point of crossing by 66% while reaching 5.5 kV/m at 1.8 m height.

Low Frequency Oscillation Traceability and Suppression in Railway Electrification Systems

The low frequency oscillation (LFO) phenomenon has frequently occurred in railway electrification systems (RESs) and deteriorates the safety and reliability of RESs. This article proposes a simplified and analytical impedance model of the electric train and traction network interaction system (hereinafter train-network system) in the synchronous frame ( -dq ), which reveals that the dc-link voltage proportional-integral controller mainly brings the negative resistor to the d–d channel impedance of the train in the low frequency range. The in-depth stability analysis elaborates that the introduced negative resistor will lead the phase margin of eigenvalues of the impedance ratio matrix to be negative under some conditions and then causes the LFO issue. Moreover, case studies also illustrate that the narrower negative real-part area (NRA) caused by the negative resistor and the higher magnitude of the train impedance in the low frequency range can enhance the stability of the train-network system. Therefore, for suppressing the LFO, a proportion-derivation feedback of the current based on the analytical impedance model is then proposed to decrease the NRA and increase the magnitude of the train impedance at the same time in the low frequency range. Both simulation and experimental results validate the effectiveness and correctness of the theoretical analysis.

Defining energy indicators for detecting short circuits in a dc electric traction system

It has been proposed to use power losses as an additional energy parameter to complement basic energy indicators in determining the short circuit mode in a traction power grid. Three techniques have been reported to determine the transitional characteristics of an electrical network, which are based on methods of approximation, discrete electrical engineering, and spectral analysis. The need to construct these methods is predetermined by the non-stationarity and nonlinearity of electrical parameters for traction networks, which could form uncertainty in the moment of a short circuit occurrence.The input data to determine the energy characteristics and losses are the functions of transitional voltage and transitional current, measured at the clamps of the switchgear to which power conductors of the traction network are connected. Based on the experimental measurements and the reported methods, we have calculated basic energy parameters of the network, as well as losses, at different short circuits.Results of our calculations show that during short circuits in a traction network the quantitative values of energy indicators and unproductive losses make it possible to unambiguously assess the mode of network operation. The obtained results also make it possible to determine the actual load on protective switching devices at short circuits in a traction network.The proposed methods could be applied when developing computer models of traction networks in order to study them and perform engineering calculations. They could also be applied while designing new or reconstructing current DS traction networks, in order to more accurately substantiate design solutions. In addition, the proposed methods could be employed when constructing new or improving the existing samples of protective switching equipment

Mathematical Simulation of Electrical Interference of a 24-kV Direct-Current Traction Network on Adjacent Lines

A Simulink model has been developed of a dc traction power-supply system with voltages of 3 and 24 kV containing all links of traction network that need to be taken into account when analyzing the electromagnetic compatibility of 3- and 24-kV dc traction network with adjacent lines. The parameters of the links of this network are determined. The electrical interferences of a 3- and 24-kV dc traction power-supply system on adjacent lines was compared. The model makes it possible to determine the electromagnetic compatibility of a traction power-supply system with adjacent lines.

A Passivity-Based Control of Euler–Lagrange Model for Suppressing Voltage Low-Frequency Oscillation in High-Speed Railway

The traction network voltage low-frequency oscillation (LFO) in high-speed railways easily leads to the traction blockade of electric multiple units (EMUs), which seriously affects the normal operation of high-speed railways. A passivity-based control (PBC) strategy for single-phase EMUs rectifier is proposed in this paper. First, for the single-phase EMU rectifier, the Euler–Lagrange (EL) mathematical model in dq frame is built, which can realize the decoupling of active power and reactive power. Second, according to the unique characteristics of the rectifier, it is proven that the rectifier is strictly passive, which is the premise of PBC controller design. Third, using the deduced EL mathematical model and the passivity of rectifier, the PBC controller for the single-phase rectifier of EMUs is designed using the damping injecting method. Next, compared with dq current control and interconnection and damping assignment PBC (IDA-PBC), it can be verified that the PBC controller has better dynamic and static characteristics, and can significantly suppress the voltage LFO of traction network. In these strategies listed in this paper, using the PBC, the single-phase rectifier input current has minimal total harmonic distortion, and the dc-link voltage has minimal oscillation. Finally, the dSPACE semiphysical experiment platform of the cascade system of EMUs and traction network is built. Simulation results are validated by the dSPACE semiphysical experiments, which indicate that the PBC has the better inhibitory effect for LFO as compared with that of the IDA-PBC and dq current control in single-phase EMUs rectifier.

Research on electrified railway power router based on 81 level conversion technology

On the premise of realizing the application of renewable energy power generation in traction power supply system, aimed at the problems of power scheduling and operation cost in the traction network of 27.5 kV electrified railway, a kind of electrified railway energy router device based on 81 level conversion technology is proposed. The device adopts 81 level converter to realize the high voltage, high power quality and high power demand of grid-connected converter for electrified railway energy supply system. The energy dispatching mode of voltage-phase angle is adopted to ensure the normal power supply of electric locomotive and the voltage support of traction network. At last, the bidirectional converter of the energy storage unit realizes peak cutting and valley filling of energy and ensures the stability of renewable energy generation. Based on the theoretical study of the topology, technical principle, energy scheduling calculation and control strategy of the new electrified railway power router, the device was simulated and verified, and the effectiveness of the electrified railway power router technical solution was verified.

Digital computer protection of railway traction network

The article analyzes the existing system of protection of the traction network. Key aspects of its operation were analyzed. Innovative transition to a digital level of protection was described. Recommendations for further improvement based on the results of experimental operation, taking into account the use of monitoring and increasing the level of automation of the traction network feeder control system were provided.

An Approach to Suppress Low-Frequency Oscillation by Combining Extended State Observer With Model Predictive Control of EMUs Rectifier

Recently, low-frequency oscillation (LFO) occurs in electrified railways, which exhibits a synchronous periodic oscillation of about 2–7 Hz in the traction network and electric multiple units (EMUs). To suppress the LFO, an improved model predictive control (MPC) combining with extended state observer (ESO) is proposed. First, for the design of ESO, the changes of system parameters and the unmodeled item in vehicle mathematical model are extended to a new variable and then estimated to compensate the calculated control voltage in real time. Second, the observer stability is analyzed by obtaining the transfer function, and the appropriate gains of observer are chosen through the pole assignment technique. At last, by the combination of the predictive currents, the optimal control voltages can be obtained. The control performance among MPC, dq decoupling control, passivity-based control, and the proposed method is compared. In addition, the system robustness when system parameters change is discussed. At last, to further verify the effectiveness of the proposed method for suppressing LFO, an integrated dSPACE semi-physical experimental platform including eight simulated EMUs and an equivalent traction network is constructed. Simulation and experimental results show that the proposed method not only effectively suppresses LFO but also accelerates the response speed of traction line-side converter, reduces the distortion of grid-side and vehicle-side currents, and overcomes the disadvantages of MPC and dq decoupling control under the mismatching of system parameters.

Improving the methods of monitoring and automation and mathematical modelling of railway protection

Thee paper analyzes the electric traction network and its features. The article shows that the use of one type of protection creates dead zones. To ensure reliability of the protection system, along with the maximum pulse protection system, digital terminal should be used.

Research algorithms for the analysis of transient’s traction DC networks

Oscillograms make it possible to determine parameters of transient processes and analyze operation of protection systems. The article analyzes changes in current rates under various modes of operation of the traction network. When studying emergency processes, it is advisable to analyze disconnections of circuit breakers recorded by digital devices.