Traction Transformer Research Articles

A Power Electronic Traction Transformer Model for a New Medium Voltage DC Electric Railway

All state-of-the-art Power Electronic Traction transformers (PETT) were developed for the existent Medium Voltage (MV) AC Electric Railway Systems (ERS). This work, however, presents a ...

Improvement of External and Traction Power Supply System’s Efficiency by Normalizing the Schemes

The article deals with improvement off the efficiency of external and traction power supply systems using for example indicators of traction substations for a real electric transmission line segment of a traction network of 25 kV. The analysis of the functioning of a real section of electrified railways with traction substations, two of which are connected according to the "feeding" scheme is providing in the article. The currents in the wind-ings of traction transformers are calculate for these substations. The proportion of the currents values of the most loaded winding to the two less loaded is 2: 1. The coefficient asymmetry of currents of transformer wind-ings operating on existing traction substations is equal to 1. The results prove a significant currents asymmetry of transformers windings and phases of electric transmission lines which leads to an increasing voltage unbal-ance. New schemes for connecting traction substations for the considered section of electrified railways have been developed in order to improve the quality indicators of electrical energy. New connection schemes for three traction substations, determined according to the requirements for connecting to the external and trac-tion power supply system are presents in the article. The calculation for new schemes of connecting traction substations, similar to the previously considered option, has been performed. The values of winding currents, power transmission line phases and coefficient asymmetry were obtained for new substation connection schemes. The proposed schemes for connecting traction substations provide a decrease in the coefficient asym-metry of the winding currents from 1 to 0.5 and a decrease in the current modulus in the most loaded windings by 1.5 times. New schemes for connecting traction substations reduce the currents of the most loaded windings and phases of the power transmission line, as well as the asymmetry of currents, which ensures an improvement in the efficiency of the external and traction power supply systems of the real traction network.

Running Status Diagnosis of Onboard Traction Transformers Based on Kernel Principal Component Analysis and Fuzzy Clustering

The onboard traction transformer is a critical equipment of high-speed trains, its running state directly affects the safety and stability of a train’s operation. Given the complexity of the running condition of the onboard traction transformer, this paper proposes a running state diagnosis algorithm based on kernel principal component analysis (KPCA) and fuzzy clustering. To fully extract the status information of the onboard traction transformer, the aging characteristics of insulating oil and main insulation are analyzed under different running mileage as the first step. Thereby, to eliminate the signal redundancy, the status feature set of the onboard traction transformer is analyzed by KPCA combined with the characteristic quantities of the traditional dissolved gas analysis (DGA), and the eigenvalues with the contribution rate of over 95% are used as new eigenvectors. Finally, a status diagnosis model is established by using fuzzy clustering analysis, considering the limitations of fault data of onboard traction transformer. The results from field collected data show that the proposed method is effective in diagnosing the running status of the onboard traction transformer.

Analysis on Differential Protection Sensitivity of Traction Transformers Based on Different Conversion Modes

With the rapid development of high-speed rail technology in China, the traction transformers of various types have been used more and more extensively. The differential protection of traction transformers has different differential conversion modes [1-2] which are different in their sensitivities. In this paper, taking the YNV traction transformer as an example, by comparing the sensitivities of two different common differential conversion modes and through analysis, it shows that the sensitivities of differential protection are slightly different. The sensitivities of differential protections based on different principles depend on the retention degree of differential current to the positive sequence, negative sequence and zero sequence components in the internal fault current. The sensitivity of phase current minus zero sequence differential is the highest when single-phase grounded, which completely retains all the sequence components in the internal fault current. The sensitivity of interphase differential protection is the highest when interphase fault occurs. The widely used phase current differential and phase current minus zero sequence differential do not reflect the zero-sequence component of internal fault current, which provides the basis for field fault analysis and setting.

An Estimation Method for Real-Time Thermal Capacity of Traction Transformers Under Unbalanced Loads

Real-time thermal capacity estimation is not only part of prognostics and health management but also determines the dynamic loading capability of the traction transformer. The hot-spot temperature (HST) is the vital parameter for real-time thermal capacity estimation. In high-speed railway, the unbalanced loads of the two phases of the traction transformer cause unbalanced winding losses and therefore affect the top-oil temperature and further influence the HST in each phase. In order to explore the dynamic thermal performance of the transformer under unbalanced load (current), a thermal model for calculating the HST was proposed incorporating thermal interaction between two power supply phases. This model treats the winding loss of each phase independently, considering the temperature dependence of winding ohmic losses and eddy current losses. A thermal circuit topology is presented with independent phase windings sharing the same top-oil temperature, where an improved heat transfer correlation is used to account for the nonlinear thermal convection. The proposed model is verified by the factory temperature rise tests and field operation data for the same batch of transformers.

Gas-in-oil analysis and evaluation criteria for synthetic esters in offshore and traction transformers

It is generally recognized that dissolved gas analysis (DGA) is a powerful tool in the diagnosis of insulating liquid filled power equipment. There exist numerous evaluating schemes for the mineral oil filled equipment, nevertheless, the experiences show that a fine tuning and revision of the schemes is required for equipment filled with synthetic esters.

SiC-Based Power Electronic Traction Transformer (PETT) for 3 kV DC Rail Traction

The design of rolling stock plays a key role in the attractiveness of the rail transport. Train design must strictly meet the requirements of rail operators to ensure high quality and cost-effective services. Semiconductor power devices made from silicon carbide (SiC) have reached a level of technology enabling their widespread use in traction power converters. SiC transistors offering energy savings, quieter operation, improved reliability and reduced maintenance costs have become the choice for the next-generation railway power converters and are quickly replacing the IGBT technology which has been used for decades. The paper describes the design and development of a novel SiC-based DC power electronic traction transformer (PETT) intended for electric multiple units (EMUs) operated in 3 kV DC rail traction. The details related to the 0.5 MVA peak power medium voltage prototype, including the electrical design of the main building blocks are presented in the first part of the paper. The second part deals with the implementation of the developed SiC-based DC PETT into a regional train operating on a 3 kV DC traction system. The experimental results obtained during the testing are presented to demonstrate the performance of the developed 3 kV DC PETT prototype.

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.

Experimental Studies on the Estimated Life of Oil-Immersed Insulation Paper in Traction Transformers

Traction transformers are one of the most important equipment in the traction power supply system. Thermal aging of transformer insulation system determines its reliable life. To achieve an estimation of the insulation life of traction power transformers operated under real load condition, the effects of traction loads on the thermal aging of oil-paper insulation in traction transformers were investigated. First, the design principles for the accelerated thermal aging experiment were studied and proposed by considering magnitude (i.e., load rate) and frequency (i.e. spare time and lasting time) of the traction load. Then, an experimental system was established in the laboratory to conduct extensive accelerated thermal aging experiments, in which the traction loads were mimicked by using positive temperature coefficient (PTC) heating plates and a programmable logic controller (PLC). Finally, the experimental results were analyzed and discussed to reveal the effects of traction load on the thermal aging of oil-paper insulation in traction transformers.

Fault Diagnosis of Traction Transformer Based on Bayesian Network

As the core equipment of a traction power supply system, the traction transformer is very important to ensure the safe and reliable operation of the system. At present, the three-ratio method is mainly used to distinguish transformer faults, whereas such a method has some defects, such as insufficient coding and over-general fault classification. At the same time, on-site maintenance personnel make an empirical judgment based on various test data, which is subjective and uncertain to a certain extent. For cases with multiple abnormal data and relatively complex conditions, on-site personnel often need to discuss and even dismantle the transformer to identify the fault, which is time-consuming and costly. In order to improve the effect of fault diagnosis for traction transformer, this paper uses Bayesian network to correlate the cause and effect of various tests and faults. By combining the results of field tests, the fault is diagnosed by the causal probability of the Bayesian network, rather than relying on the exception that occurred in a single experiment to judge its fault. The diagnosis results are more accurate and objective by using the Bayesian network. In this paper, the frequent test anomalies of the traction transformer are taken into account in the network, so that the network can more comprehensively analyze the operation situation of the traction transformer and judge the type of fault. According to field situations, based on the existing set of symptoms of the Bayesian network fault diagnosis, this paper further considers the insulation resistance, dielectric loss tangent value, oil and gas, power frequency voltage, and leakage current. By combining the association rules algorithm and the experience of the field operators, the cause–effect relationship of test data and the conditional probability parameters of the network are obtained. Then, the Bayesian network is constructed and used for traction transformer fault diagnosis. The case study shows that the four types of fault diagnosed using the Bayesian network model proposed in this paper are consistent with the fault types inspected by on-site operators, which shows promising engineering application prospects.

Two-Phase Short Circuit in the Power Grid Powered by a Transformer with a Y/Δ-11 Winding Connection

The article describes main provisions and relations for calculating short-circuit currents and phase currents in a three-phase traction transformer with a star-triangle-11 connection of windings, which feeds two single-phase loads in AC traction networks with a nominal voltage of 25 kilovolts. These transformers provide power to the enterprises of the agro-industrial complex located along the railway line. (Research purpose) The research purpose is in substantiating theoretical equations for digital intelligent relay protection in two-phase short circuits. (Materials and methods) It was found that since the sum of instantaneous currents in each phase is zero, each phase of the transformer works independently. We found that this significantly simplifies the task of analyzing processes with a two-phase short circuit. In this case, the problem of calculating short-circuit currents in the traction network can be simplified by reducing it to the calculation of an ordinary electric circuit with three unknown currents. (Results and discussion) The article describes equations for calculating short-circuit resistances for one phase of the transformer when connecting the secondary winding as a star or a triangle. The currents in the phases of the transformer winding at short circuit for the star-triangle-11 and star-star-with-ground schemes are compared. It was found that when calculating short-circuit currents, there is no need to convert the secondary winding of the traction transformer from a triangle to a star. (Conclusions) It was found that the results of the research can be used in the transition of relay protection systems from electromagnetic relays to modern high-speed digital devices, which will increase the operational reliability of power supply systems for traction and non-traction power consumers.

A Method for Diagnosing the State of Insulation Paper in Traction Transformer Based on FDS Test and CS-DQ Algorithm

Traction transformer is vital equipment in high-speed railway. Insulation status decides its safety and reliability, and the frequency-domain dielectric spectrum (FDS) test is one of the most effective methods reflecting the changing of insulation status. For field applications, the following problems should be addressed: 1) how to obtain the result of paper insulation from the combined result of the oil–paper insulation system and 2) how to discriminate the defects of insulation paper between aging and damp. In this article, the first problem was transferred to a nonlinear equation set, and a cuckoo search algorithm optimized by the differential evolution algorithm and the quadratic interpolation (QI) method (CS-DQ algorithm) was proposed to solve it. Then, the insulation states were discriminated by establishing a multiclass least-squares support vector machine (LS-SVM) model, in which the CS-DQ algorithm was also used. Finally, a diagnostic approach for the insulation paper in the traction transformer was proposed. The results in the laboratory show that the pure result of insulation paper can be obtained, and the insulation states can be discriminated effectively by using the proposed approach. Meanwhile, the proposed CS-DQ algorithm has a better performance than the conventional CS algorithm. The results of field testing also verify the proposed approach.

Increasing Power Supply Efficiency for “Two Wire-Rail” Line Consumers

The article is devoted to the problem of non-traction consumers power supply of AC railways. The low efficiency of energy transfer is caused by the design of a non-traction power supply line. The absence of bilateral power is typical for non-traction network 27,5 kV which consist of “two wire-rail” lines. This line is outdated technology, which does not correspond to modern requirements on the power quality, but used on AC railways with three-phase traction transformers. The purpose of the article is to investigate the methods of power supply improvements for non-traction consumers in terms of voltage unbalance, harmonic distortions and energy losses. Connection of the phasing device to delta winding traction transformer for bilateral supplying non-traction customers from network 27,5 kV is suggested in the article. The implementation of a method to increase the efficiency of electricity transmission in the non-traction network power supply allows to reduce power losses from 720 MWh / year to 441 MWh / year, the voltage unbalance from 1,9% to 1,3% and the total harmonic distortion from 8 % to 6 % respectively. Additionally, investment attractiveness of the decision was evaluated. Keywords: non-traction customers, two wire-rail line, phase coordinates, AC railway, power quality

Компьютерная модель тягового трансформатора электровоза переменного тока серии «O’Z-ELR»

Компьютерная модель тягового трансформатора электровоза переменного тока серии «O’Z-ELR»

Modelling and control of a novel AT-fed co-phase traction power supply system for electrified railway

A large unbalanced current injected into the power gird and the neutral sections at the exits of traction substations have been the outstanding obstacles in conventional single-phase 25 kV AC traction power supply systems (TPSS). In order to meet the requirements of high-speed and heavy haul transportation systems, a novel autotransformer (AT)-fed co-phase TPSS is proposed, which can provide continuous power for the trains with high power quality (PQ). In this research, the electrical configuration of the new TPSS is presented, which is structured with Vx-connection traction transformer (TT) and power flow controller (PFC) adopting the modular multilevel converter (MMC) topology. Furthermore, the mathematic model of the novel system is built. The unbalanced current and the reactive power caused by traction load can be compensated effectively based on power balance principle. Moreover, a hierarchical control strategy is designed including upper optimized PQ compensation algorithm and low-layer PFC control, which can coordinate dynamic characteristics between different working patterns. Finally, the validity of the control method and the performance of the system are demonstrated by case studies. The results indicate that compared to the conventional co-phase TPSS, the proposed co-phase TPSS is able to reduce the compensation capacity by up to 59%.

Research on Optimal Nonperiodic Inspection Strategy for Traction Power Supply Equipment of Urban Rail Transit Considering the Influence of Traction Impact Load

The inspection and maintenance work of traction power supply equipment (TPSE) is growing heavy with the construction and operation of a large number of urban rail transits (URTs). In order to improve the existing regular preventive maintenance mode and implement a “high-efficiency with low-cost” maintenance strategy, this article proposes an optimal nonperiodic inspection decision-making method for TPSE of URT considering the influence of impact load. First, the comprehensive degradation model of TPSE is established based on the linear Wiener process and the compound Poisson process. Second, the nonperiodic inspection model of TPSE in a single-maintenance period is established by introducing inspection planning functions for three types of degradation processes. With the lowest operating cost per unit time as the decision goal, the optimal maintenance plan is, thus, achieved. Finally, the proposed decision-making method is applied to the benchmark data taken from a URT administration in China related to a dry-type traction transformer in five years. The results show that the proposed method can help formulate efficient inspection strategies with the optimal cost. In addition, sensitivity analysis reflects the influence of different parameters on the optimization results, which helps to identify which parameter exerts the largest influence.

A preventive opportunistic maintenance method for railway traction power supply system based on equipment reliability

Conventional maintenance mode for the traction power supply system (TPSS) is to perform scheduled regular maintenance activities for power supply equipment, while such maintenance mode may result in undue maintenance tasks and low efficiency due to different degradation processes of different sorts of equipment. To address this problem, this paper introduces a preventive opportunistic maintenance (POM) method for TPSS based on equipment reliability. Firstly, a POM model is established by considering the equipment reliability degradation process based on Weibull distribution. Then, by considering the total power outage time in the planned operation cycle of TPSS as the optimization objective, the optimal maintenance scheme of TPSS is formulated by iterative method of maintenance strategies. The proposed method is verified by introducing practical maintenance strategies and fault record data of the traction transformer, circuit breaker and disconnector in an actual TPSS of a railway administration. Results show that the presented method can make full use of the existing fault data to develop a POM scheme for TPSS. It can improve maintenance efficiency and reduce power outage time, providing guidance to formulate scientific maintenance strategies for TPSS.

An Equivalent Scheme for Calculating Short-Circuit Currents in a Traction Power Supply System with Two-Way Power Supply

The cause of a methodological error in the calculations of short-circuit currents as exemplified in the power supply of a traction network with two-way supply has been shown. It is to be noted that, in an actual power supply circuit, two adjacent traction substations are connected along the 110 (220)-kV lines by mutual resistance, whereas there is no such connection in the designed arrangement. On the basis of the designed scheme, a new equivalent circuit is formed, in which the resulting traction power circuit remains unchanged. The transformation of the initial circuit has enabled removing the error and calculating the short-circuit voltages in the traction network explicitly. Replacement of a symmetric three-phase external power supply system and a traction transformer with an equivalent single-phase circuit when calculating two-phase short-circuit currents in the traction network is shown to be viable. The validity of replacement of a symmetrical three-phase network for a single-phase one has been proved both by transformation of the three-phase equivalent circuit and by means of the equivalent generator method. It is established that, despite the difference in phase resistances of substations with Y/Δ and Y/Y transformer connection circuits, equations for determination of two-phase short-circuit currents prove to be the same.

899 Retrieval Number: D1560029420/2020©BEIESP DOI: 10.35940/ijitee.D1560.039520 Journal Website: www.ijitee.org Published By: Blue Eyes Intelligence Engineering & Sciences Publication Rooftop Solar and Wind Power Based Hybrid Energy Storage System for AC Railway Traction

The conventional AC/DC Railway Traction Systems are undergoing number of improvements. Thanks to modern technologies such as Renewable Energy Systems (RES), Energy Storage Systems (ESS) and Hybrid Energy Storage Systems (HESS). At present the traction transformers cater electric supply to traction motors and auxiliary loads which may not be adequate enough to meet demands. Furthermore in the event of failure of traction supply, the alternative source of supply is required. This papers suggests a noval method of feeding auxiliary loads through the integration of RES and ESS. Solar and Wind power are vital renewable energy sources. The pros and cons of proposed method are also discussed in this paper.

AC Loss Calculation on a 6.5 MVA/25 kV HTS Traction Transformer With Hybrid Winding Structure

HTS wire cost is a critical factor for successful commercialization of HTS traction transformer technology. Wire cost might be minimized without significantly increasing AC loss by introducing a hybrid winding structure: the end-part of the windings is wound with high-cost high- I c wires; the central-part of the windings is wound with low-cost low -I c wires. We report AC loss simulation results on HTS windings with both HV and LV windings wound with REBCO wires. The 2D axisymmetric FEM simulation was carried out using H -formulation. The HV windings are wound with 4 mm-wide wires and LV windings are wound with 8/5 (eight 5 mm – wide strands) Roebel cables. Both HV and LV windings have a hybrid structure in order to reduce the wire cost. Flux diverters are placed at the end of the windings to reduce AC loss. Significant HTS wire cost reduction could be achieved without compromising AC loss by using hybrid windings. This may help commercialize HTS traction transformer technology.