Railway Engineering

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Performance Analysis of Digital Subscriber Lines
(Addis Ababa University, 2003-12) Seife-Selassie, Abel; Ayele, Hailu (PhD)
In recent years, lots of emerging high-speed applications and networking requirements are calling for cost effective access network solutions. These applications are well driven in the high bandwidth transmission media of the backbone network. However, the last mile transmission media that uses the existing modems of maximum speed 64 kb/s, are failing under these high-speed requirements. Firstly, this problem was approached using the very high bandwidth fiber network but it was seen that present time and foreseeable future end user requirements are only within reach to a speed of 2 Mb/s unjustifying the involved high cost. The practical means followed is to use the widely installed copper based access network. It is the aim of this thesis to use standard techniques to investigate Asymmetric Digital subscriber Line, (ADSL). ADSL is a relatively new modem technology that provides high-speed data rates on the Plain Old Telephone Service (POTS) line. Efficient error control coding schemes and Discrete Multitone (DMT) modulation are the key mechanisms in ADSL. The objective of this work is to develop the software simulation modules for ADSL modem. In this thesis, DMT modulation is realized in an effort to demonstrate the end-to -end transmission of random generated bit streams through the twisted pair channel situated between the transmitter and receiver This simulation in done using a script code with MATLAB® Also largely described in this work are the physical properties of twisted pair channels and their frequency selective distortion. Moreover the high frequency behaviors of copper networks are highly varying among manufacturers. Accordingly twisted pair channel models are used using empirical or measured data. and Bit Error Rate (BER) is used as a measure of performance. The results of this work are performance measurement curves obtained from this end-to-end system simulation. These curves demonstrate the decreasing BER values against SNR agreeing with similar works of digital communications system simulation.
Enhanced Peak-to-Average Power Ratio Reduction Technique In 0fdm Communication Systems
(Addis Ababa University, 2007-06) Abera, Mengistu; Ayele, Hailu (PhD)
The Orthogonal Frequency Division Multiplexing (OFDM) is a strong candidate for the current and future wireless communications system due to its high data rates transmission capability and robustness against multi-path fading effects. A major drawback of OFDM is its high peak to average power ratio (PAPR). Since most practical transmission systems are peak power limited, the average transmit power should be reduced for linear operation over the full dynamic range, which degrades the received signal power. In this thesis we review the most popular OFDM PAPR-reduction techniques and demonstrate in detail that Selected Mapping (SLM) scheme is a particularly promising reduction technique. In a SLM system, an OFDM symbol is mapped to a set of independent but equivalent symbols and then the lowest-PAPR symbol is selected for transmission. The tradeoff for PAPR reduction in SLM is computational complexity as each mapping requires an additional inverse fast Fourier transform (IFFT) operation in the transmitter. An enhanced SLM method is proposed for computational complexity reduction. The proposed SLM scheme transforms an input symbol sequence into a set of OFDM signals by multiplying the phase sequences by the signal after a certain intermediate stage of inverse fast Fourier transform (IFFT). The enhanced SLM technique reduces computational complexity by 48% while it shows almost the same performance of PAPR reduction as that of the conventional SLM OFDM scheme.
Performance Comparison of Spatial Multiplexing and Spatial Diversity in Rate Adaptive Wireless MIMO Systems
(Addis Ababa University, 2007-06) Fikre, Zelalem; Ayele, Hailu (PhD)
Multiple antenna systems are known to provide spatial diversity and spatial multiplexing advantages in constructing a reliable and spectrally efficient communication link. In spatial diversity scheme the same message or replica of the same message is transmitted from the number of transmit antennas in such a way that at least one of transmitted messages reaches the receiver with out error. In this scheme the main objective is reduction in the probability of error. Unlike spatial diversity, in spatial multiplexing scheme different messages are transmitted from each of the transmit antennas so that the rate of data transfer between the transmitter and receiver is increased. As far as practical system is concerned it needs to have both advantages in order to have a high data rate link with low probability of error. In this thesis by adaptively varying the modulation order of the spatial diversity and spatial multiplexing systems both advantages are obtained for an application with a certain error rate performance requirement. The simulation result has shown that the spatial multiplexing system has a higher throughput at high SNR values as compared to the spatial diversity system. At low SNR values, it is the spatial diversity system that results in high throughput. The ML detection of spatial diversity system has less computational complexity as compared to ML detection spatial multiplexing scheme. Keywords: Spatial Diversity, Spatial Multiplexing, Maximum Likelihood Detection, Space Time Coding, D-Blast and V-Blast
Railway Timetable Stability Analysis: Case of Addis Ababa LRT
(Addis Ababa University, 2014) Asfaw, Workineh; Gulelat, Gatew (PhD)
Recently, railway traffic has increased considerably in the different parts of the world; moreover, it is expected that railway transportation will further grow for both passenger and freight transportation. These developments create needs to optimize both the utilization of the existing infrastructure and the coordination tasks inside the railway company. Specially, the process times at stations should be well monitored to deliver efficient services. Railway timetable is affected by several factors. The fact that makes the case more serious is that a disturbance encountered one train may propagate to the whole network unless a timetable that absorbs the fluctuation has been designed. This makes the railway timetable to be the heart of railway operation. Hence, the thesis at hand is aimed to develop stability analysis method which is used to design more stable timetable to handle the disturbances occurring to the railway network. In this research, both the interior and exterior factors that affect railway timetable stability were taken into account. In view of that, at the end of the research work, a model that is used to analyze trains timetable stability has been developed. The developed model is applicable to passengers’ railway network like Addis Ababa LRT.
Development of Service Quality Indicator for Ethiopian Freight Railways
(Addis Ababa University, 2014) Fasil, Tadele; Gulelat, Gatew (PhD)
In this study I try to develop the specific item of the rail freight transportation of quality indicator model which help to monitor, control and improve their service and competiveness. Indicator of quality for any service organization is the decisive factor to create the difference and obtain competitive advantage. The purpose of the study is making a model for rail freight quality indicator may give the true picture about the short comings in Railway freight service. The current article is to give a partial overview about experts/ specialist, importer/ exporter and Freight transportation organization (company) survey results. This survey, conducted in the form of a questionnaire, asked respondents to assign priority levels to forty four items considered to be important in maintaining the quality of transportation services. The questionnaire for survey was prepared after thorough deep Preliminary literature study. To this end, based on the result of the survey, I carried out a factor analysis and attempt to reduce the number of variables. The data obtained from the respondents are entered in the software SPSS sheet for calculating the descriptive statistics. The study is based on empirical research. Moreover the questionnaire-based survey proved that the following items are regarded as most important for freight transportation. Those determinants are identified are Safety of cargoes during transportation, Regularity of cargo arrival, Just-in-time delivery, Security of carriages, Proper maintenance of the cargos, Availability of cargo handling equipment at loading points. The findings are useful and applicable to most of railway country and the research findings may be applicable for a new constriction of Ethiopian freight railways. Those important quality indicators have emerged as an important framework in Ethiopia rail freight transportation management. This framework can help define, monitor and manage high quality freight transportation opportunities.
Distributive Train Track Communication System for Addis Ababa Light Railway
(Addis Ababa University, 2014-03) Lamesgnew, Yalemtsehay; Yalemzewud, Negash (PhD); Abi, Abate (Mr.)
Rail transport is an important mode of transport that can play significant role for economic development of a country. Especially, Electric system train driving technology has many advantages for environment protection and fuel consumption reduction. Train control system is a broad section in railway technology and has responsible for ensuring passenger’s safety and security during their journey. It also improves travel comfort, providing real time multimedia information and access to social networks in stations or in motion. Accident in railway technology is very series issue. So, maintaining safety is the first precondition for railway transport. To have safe operation in railway technology, train operators need to put in place an effective and reliable train-to-ground and train to train communication technology. On the other hand, the commercial wireless technologies have been evolving from voice centric 2G systems (e.g. GSM) with limited data transmission capabilities to 4G broadband multiservice systems (LTE). This Thesis addresses how the innovative commercial wireless technologies can enhance the safety and reliability of AA-LRT. It introduces the implementation of long term evolution (LTE) technology to Addis Ababa light railway. Each train communicates with their neighbor trains through modern communication system called LTE. The information like train speed, train distance and location of the train obtain from the speed capturing system and GPS technology. This information processed through Microcontroller and the system alert for the train pilot even it takes action on the braking system if necessary. The system decreases the need to construct additional track in the city and reduce the probability of train collision. In this scenario, this paper investigates capacity and quality of service improvement; energy efficiency, mobility, passenger’s safety and security and results obtained from simulations are presented.
Evaluation of Current Trends of High Speed Trains Brake System
(Addis Ababa University, 2014-04) Oumer, Mohammed; Demiss, Alemu (PhD); Tsegaye, Feleke (Mr.) Co-Advisor
The research aims reviewing currently available braking systems on different high speed trains which are found around the world and finally evaluates such systems using one of the Multicriteria decision making method TOPSIS. To do so various factors useful for evaluation were selected and utilized after examining different literatures. The result show that a significant importance of regenerative brake followed by rheostatic, eddy current E-P and magnetic track brakes. The result can help planners and engineers to conduct preliminary general assessments concerning the suitability of the five brake system, to develop tools for evaluation, to assess different brake system for a given high-speed train, and also helpful for anyone who engaged with train braking. The result obtained is satisfactory and currently 82.35% of high speed trains around the world use regenerative brake system.
Automatic Train Control Standard for Ethiopia
(Addis Ababa University, 2014-07) Sintayehu, Bezabih; Yalemzewd, Negash (PhD)
Railway transportation, which is needed in the achievement of effective development, is an efficient, cost-effective and it is environmental friendly transport system. In addition to the low railway network connectivity in Ethiopia like other developing countries, the available one is not modern; has low capacity and is insufficient to facilitate transit trade; and also Ethiopian railway transport has not standardized guidelines to design the control system. In this study an attempt is made to standardize guidelines for railway automatic train control system specifically standardization of equipments, interfaces, procedures of exchange of signals and transmission techniques for conventional (main) lines in Ethiopia. To achieve such objectives the research had a methodology of a task involving literature review discussion and comparison of different country standardization practice; and adaptation of the standards of the different countries according to the context of our country for railway system in Ethiopia. Standardization of guidelines for the automatic train system for Ethiopia context is done based on topography, economy of the country (cost of the control system), interoperability future development of the railway system of the country ,capacity of the control system ,level of safety , culture of the people and different literature reviews. In this automatic train control standard the research suggests two levels of train control system which are European Train Control System (ETCS) level 1 and Communication Based Train Control system (CBTC) according to the above parameters.
Multi-objective Optimization of Train Speed Profiles: The Case of Ayat to Megenagna Line of Addis Ababa Light Rail Transit
(Addis Ababa University, 2014-07) Tamirat, Gebremariam; Mengesha, Mamo (PhD)
The plan for the operation of trains on the Addis Ababa Light Rail Transit (AALRT) is based on a fixed interval of riding between stations. Fixed riding time between stations will have the effect of inefficient energy consumption by the trains. Furthermore, the transportation capacity of the network cannot be optimal. By properly managing the reference trajectories the trains use, it is possible to have optimum train operation with respect to energy consumption as well as network capacity. In this thesis, an optimization of train speed profiles is done. A multi-objective optimization problem has been formulated by making energy and time as the components of the two element objective vector function. A point mass model of the operation of trains has been developed by considering all the important force components acting on the train. The distance to travel between stations is discretized into 20 equal length elements where a two stage solution procedure has been applied to get to the final results. The first stage of the solution procedure is the application of a multi-objective genetic algorithm based optimization technique taking vector of riding modes as the decision variable. Using the developed algorithms for the calculation of cost functions for every type of riding mode, the MATLAB optimization toolbox determines a Pareto-optimal set of riding modes. The second stage of the solution process smoothes out the results found in the previous stage of the solution process without bringing about considerable change in the values of the cost functions. Different solutions for every section from Ayat station to Megenagna station are generated and they are essentially tradeoff solutions. It has been observed that the fastest ride between stations can be completed within a time of less than 3 minutes. This is equivalent to a 50% reduction in riding time over the plan. By shifting from the fastest to the slowest trajectories, it is possible to save up to 38.18% of energy, while 23.98% reduction in riding time can be achieved by preferring the fastest profiles over the slowest ones.
Capacity Analysis on Single and Double-Truck Lines
(AAU, 2014-07) Hewan, Getachew; Gulelat, Getaw (PhD)
Railway networks are complex technical systems. Investments in railway infrastructure are expensive and already constructed railway infrastructure is not easily adjusted or changed. Dimensioning and constructing railway lines and networks therefore require extensive knowledge of future operation and demand. However, experience shows that the traffic often develops differently than expected. This means that railway infrastructure has to be designed for flexibility, i.e. for different operational conditions. To achieve such flexibility, a deep knowledge of infrastructure, timetable and perturbation properties, as well as inter-correlations between these, is essential. This research has been investigate the impact of various operational changes on different level of heterogeneity to specify the potential use of operational changes to reduce delay in different scenarios especially for single- and double-track systems based on graphical calculation from time-space diagram and CN parametric model. The time-space diagram which is a simple but powerful graphical thinking tool has been used to mode the idealized existing operation. CN parametric model was used to investigate the impact of various operational changes on differing levels of heterogeneity on a hypothetical signalized, single-track rail line using delay as capacity metric unit. Changes considered included: adding sidings, increase in train headway, equalizing maximum speeds, increasing uniformity, removing dispatching priorities and the combination of the best ones. Since the railway transportation can have significant effects on mobility, economic development, environmental quality, government finance and the quality of life, this study did analyze that the change of each parameters would have great improvement for the idealized existing operation, the combination of specified alternatives, specially adding sidings did provide a great capacity increment for the particular subdivisions. Those results from this study has great significance for railway operational capacity problems specifically for single -track lines and provides insight into which aspects of train type heterogeneity have the greatest impact on delay and leads to investigate the potential use of different operational changes that may reduce this delay in Ethiopian, Addis Ababa-Djibouti rail line.
Rail Vehicle Cab Structural Dynamic Behavior under Collision and Improving its Crush Worthiness
(Addis Ababa University, 2014-07) Mesay, Diriba; Zewdu, Abdi (PhD); Tollossa, Deberie (Mr.) Co-Advisor
is now constructing a modern and reliable railway industry, consequently; one main problem of the Rail vehicle transportation industry is its accidents. This paper will attempt to develop a passive safety consideration for rail vehicle cab using computational methods for predicting the rail vehicle cab structural dynamic behavior under collision for enhancement in its crush worthiness. The rail vehicle cab structural dynamic behavior under collision analysis is done for light rail transit (LRT) vehicle cab, through finite element method (FEM) and it is one of the non-linear finite element problems as the vehicle cab structure is the assembly of multiple parts, diverse structural shape and is made of different materials. During crush, these parts experience high impact loads resulting in high stresses. Once these stresses exceed the material yield load and/or the buckling critical limit, the crashing structural components undergo large progressive elastic-plastic deformation and/or buckling. This system absorbs 4.5MJ kinetic energy in a progressive of 2.25m deformation length. The whole process occurs within very short time durations and this is simulated by non-linear FEM using ANSYS (LS-DYNA).
Train Scheduling of Addis Ababa Light Rail Transit System
(Addis Ababa University, 2014-07) Gebreaftse, Gebremichael; Yalemzewd, Negash (PhD)
Train scheduling is the process of timetabling and train assignment along a given train network. The key objective of this project is to design an efficient train scheduling of Addis Ababa Light Rail Transit system which minimizes passenger waiting time and operational costs without jeopardizing passenger safety. There are many approaches/techniques that are used to model and implement train scheduling especially for light rail transit systems that have many intermediate stations. In this thesis reviewing previous relevant literatures with a special attention paid to the light rail transit systems, quantitative analysis and simulation methods are being used. The scheduling is being generated using two separate rule-based systems that are off peak hours and peak hours. The main components of train scheduling such as trains, stations, routes are being described or specified with their constructive parameters. The mathematical model components proposed are being analyzed, and the extent that reflects real business practice is being presented. It was uncovered that the objective function which includes both the service level objective (minimizing passenger travel and waiting time) and the operational objective (minimizing the number of trains) especially for the Addis Ababa Light Rail Transit (AALRT) system as it is new in Ethiopia. Finally, this paper is focused on the constraints involved on the current system that can be used to generate an efficient train scheduling which is being modeled, solved the model, validated the model via simulation and verified the results in such a way that the schedule is made to be displayed at any station to show the trains allocated along that route with their arrival and departure times on the operating time of whole day to satisfy the desired service levels.
Analysis of Electromagnetic Emission from Contact lines of Light Rail Transit System
(Addis Ababa University, 2014-07) Tsegu, Worku; Getahun, Mekuria (PhD)
The implementation of Light Rail Transit System (LRTS) as an integrated form of public transportation, with the rail corridor running through city centers and connecting major commercial centers, presents a unique electromagnetic coupling scenario between sensitive installations and the dc magnetic field propagated from the LRTS. Magnetic fields created by a dc-electrified railway are a nuisance to the operation of a geomagnetic observatory and also disturb other electromagnetic studies and some researches were done using real operation measurements. Theoretical formulas and simulations that enable quantitative estimates of the magnetic effect of Addis Ababa LRT contact line including leakage currents in the ground are presented in this paper. The sliding contact between catenary and pantograph has to transfer a large amount of current and power to the locomotive reliably. Sometimes detachment and attachment occur between the contact wire and the pantograph. Arcing from the pantograph, a commonly observed phenomenon is known to be a major source of wideband electromagnetic emission which is more pronounced during the winter. Experience within the railway industry has shown that this source of Electromagnetic interference (EMI) and its characteristics need to be understood thoroughly for solving the associated EMI issues in the desired fashion. This thesis analyzes EMI generation from pantograph arcing, which is pantograph contact wire interaction, full loop of feeding line, which is substation, feeder line, train, return current and leakage current into the environment and ground. The methodology of the paper uses modeling of the system using mathematical modeling and simulates with MATLAB software. The result of this analysis is compared with the railway Electromagnetic Compatibility (EMC) standards and results with at 40m distance from center of track line out of the limit standard.
Effect of Change of Wheel-rail Contact Geometry on Contact Fatigue Stresses
(Addis Ababa University, 2014-08) Fikru, Bekele; Daniel, Tilahun (PhD); Habtamu, Tikubet (Mr.)
The general objective of this thesis is to analyze effect of change of wheel and rail profiles on contact fatigue stress using analytic and finite element softwares. The wheel rail contact condition is modeled assuming two general quadratic surfaces. The formulation in this study aims primarily at determination of stresses and fatigue parameters by varying contact geometry arising from variation in profile geometry. A change in surface geometry brings in a change in contact geometry and stresses. The theoretical models are based on the normal problem (Hertz theory) and the tangential problem (Kalker’s theory). Correspondingly, variations in the results in terms of principal stresses and fatigue parameters such as equivalent stresses, fatigue damage, and expected fatigue life with changes in wheel profile radii, wheel taper and rail profile radii are obtained. Comparisons of different profiles are taken place. Better profiles are suggested. Results obtained are expected to help understand the rail wheel configuration dependence on the stress deformation pattern and fatigue parameters. This may help an appropriate selection of wheel and rail profiles in the optimization process.
Harmonic Analysis of Addis Ababa Light Rail Transit Traction Converters
(AAU, 2014-08) Demissu, Legese; Mengesha, Mamo (PhD)
Traction power system is the main area of industrial sector where the application of power electronic technology is widely used. The uses of these devices create harmonics that cause a serious problem on the proper operation of the system. There have been different corrective methods proposed by different researchers. Among them, the AC side passive filters that provide low resistive path to eliminate the harmonics; and the active filter that produce harmonic currents in equal magnitude and 180 0 out of phase to suppress it, are the widely discussed ones. This thesis provides the harmonic analysis of Addis Ababa Light Rail Transit (LRT) traction system. The analysis is performed on the Lideta rectifier substation. The traction system is modelled using Matlab/Simulink environment. Based on the data obtained from Ethiopian Railway Corporation (ERC), simulation is carried out and compared with the IEEE standard limits. Taking into consideration the cost and simplicity of the operation, single tuned filters tuned at 11 th and 13 th harmonics and high pass filter adjusted for higher harmonics currents are designed for the AC side, and LC filter is proposed for the DC side of the system. The simulation result comes with significant reduction in harmonic distortion. The Total Harmonic Distortion (THD) is reduced to 0.80% for the current and to 0.33% for voltage, which is far below the 5% limits of IEEE standard. In addition to that the system power factor is improved from 0.77 to 0.99, which avoids the installation of power factor corrector.
Analysis of Gear Train Structure of Electric Traction Train Using Finite Element Method
(Addis Ababa University, 2014-08) Shuma, Michael; Demiss, Alemu (PhD)
gear trains are the critical components in a railway traction system as they transmit and withstand very high loads. Their primary function is to transmit power from one shaft to the other. In the railway traction system, there are several arrangements for the drives system. In this particular case the unit that takes power, from motor assembled to drives system through pinion on the shaft to the final spur or wheels by means of single stage or compound stage on the axle of the train, in such a way that power is transmitted. During the transmission of power from one shaft to another, for rail vehicles moving in high speed, torque is also transmitted. In this phenomenon, different kinds of stresses and deformations will occur on the structure of the gear train. FEM (Finite Element Method) is used to determine and analyze different kinds of stresses and deformations in the complex geometry. This thesis investigates the characteristics of gear trains under different kinds of loading, including bending and shear stresses, stresses due to vibration, contact stresses and deformations by FEM and proposes a better optimization for the gear units. Two or three spur gear trains with and without idler gears are modeled in both solid works and ANSYS work bench for drives system to distinguish the behaviors of the stresses and vibration for the system, and optimization will be proposed for the design of the gears. Then the result obtained will be compared with the analytical method. Contact stresses are also analyzed and compared with the current method which is known as Hertzian contact stress; if both value agree very well, FEM is then the accurate method to analyze the effect of the contact stress for the gear units in the drives system. American Gear Manufactures Association (AGMA) is used for stress analysis but it is limited and many assumptions to be taken into account. Lewis equation is also used to determine the bending stress. After different kinds of analysis, the parameters which may affect the overall efficiency of the system will be optimized, by proper treatment and design of the gear structure for the drives system. These treatments will also include improving tribological property of the gears, profile modification of the gear tooth and so on. Therefore, FEM will predict the different kinds of stresses and deformations on the gear train structures of electric traction train .
Customized Guideline for Designing Overhead Contact System for Ethiopian Railway: Case Study of Indode Station
(Addis Ababa University, 2014-08) Beyene, Aynabeba; Kumneger, Hussien (Mr.)
This thesis presents Overhead Contact Line System design for Indode station. Overhead Contact System (OCS) is an essential interface between fixed installation and moving energy consumer for electric railway. Its design depends on mechanical, electrical and environmental loads. Therefore proper design and standard of overhead contact line system for a particular environment according to specific service requirement is necessary. In this work detailed technical design of overhead contact system for Indode station as reference to review other overhead contact line system design in Ethiopia Railway is done. In this thesis first overhead contact system for electrified root is modeled based on bottom to top approach. Trolley and simple catenary of both semi and auto compensated Overhead Contact System is modeled. Traction impendence of overhead contact system especially double track of simple catenary equivalent impendence is determined. Then based on this model and meteorological data, maximum span length, critical span length, maximum sag height, and maximum anchoring length are derived and determined. From this determined parameter and site plan of Indode station, Overhead contact system plan is prepared according to planning rules and standard using Microsoft Visio. Finally main thesis work is summarized by preparing overhead contact system design manual for Ethiopia Railway.
Influence of Rail Vehicle Parameters on Lateral and Vertical Accelerations of a Passenger Rail Vehicle
(Addis Ababa University, 2014-08) Fiseha, Mengisteab; Zewdu, Abdi (PhD); Tolossa, Deberie (Mr.)
This paper presents parametric analysis study of the influence of rail vehicle parameters on vertical and lateral car body accelerations. Vehicle parameters such as bogie wheel base, primary and secondary suspension parameters, car body mass, car body yaw, pitch and roll mass moment of inertias have been studied by varying from - 25% to +25% of their original values. The analysis was conducted by modeling and simulating 41 DOF passenger rail vehicle using SIMPACK, multibody dynamics simulation software. The considered vehicle was a conventional rail vehicle with typical measured rail irregularities from SMPACK model data base. The parametric analysis results, in the human ride sensitivity frequency ranges i.e. 0.5-2Hz for lateral and 5-10Hz for vertical accelerations according to ISO 2631, showed that car body mass, car body pitch mass moment of inertia, secondary suspension vertical damping, secondary suspension vertical stiffness, primary suspension vertical damping, primary suspension vertical stiffness and wheel base were sensitive parameters influencing vertical car body acceleration. While lateral acceleration of the vehicle was influenced by car body mass, car body roll & yaw mass moment of inertias, and secondary suspension lateral stiffness & damping, primary suspension lateral stiffness & damping and wheelbase. The analysis was validated by comparing with experimental results. The study will give vital information to designers in optimization of rail vehicles.
Power Flow Analysis of Sebeta to Adama Railway Electrification power Line with Thyristor Controlled Series Compensator (TCSC)
(Addis Ababa University, 2014-08) Samuel, Biru; Kiros, Tesfaye (Mr.)
The Ethiopian Railway Corporation (ERC) is working hard to have modern railway system that uses the AC power supply system. Voltage drop in the feeding circuit differs substantially depending up on the train position, train current, number of train in the same power feeding section, track impendence etc. The minimum pantograph voltage for the train expected is to be 20kV, which is within the tolerable voltage fluctuation range of the overhead contact line. On the other hand, power transfer problems have occurred frequently within large variation of loads. These issues are important in traction power supply system to ensure normal operation of the electric locomotives. Considering these two problems this thesis work propose integration of Thyristor Control Series Compensator transmission system for improving traction network voltage and enhancing power transfer capability for double-track Sebeta-to-Adama section of Ethiopian Railway line. The necessary data and Electrical parameters are collected from the double-track Sebeta-to-Adama section of Ethiopian Railway line. Modeling and simulation of traction system have been performed using MATHLAB/SIMULINK. The plots after simulation of networks both with and without Thyristor control series capacitor has helped to analyze the power flow and traction voltage level. The overall power transfer capacity of the catenary line of the system is increased. This thesis work shows that the real power is enhanced from 11.9MW to 14.33MW (measured at the load side), which is 16.34% enhancement by using TCSC controlling of catenary line. Integration of TCSC has also advantages of improving the substation power factor, In this thesis it is shown that the power factor is improved from 0.94 to 0.99, at the same time it can be used as the load voltage improving device, As shown from result part of this thesis the load voltages of train one and train two are improved from 21.69kV to 25kV and 21.61kV to 25kV respectively. Based on these results it is recommended that Ethiopian Railway Corporation to consider integrating TCSC device for Sebeta to Adama railway line.
Design of Safety-Critical Wayside Train Control System
(Addis Ababa University, 2014-08) Jigsa, Tesfaye; Yalemzewd, Negash (PhD)
Due to the difficulty to analyze all failure modes of complex microprocessor based systems, it is risky to use those devices for a safety-critical Automatic Train Control system. A means to guarantee safety is a must in a microprocessor based train control systems. In this paper, the design and implementation of a safety-critical computing platform for real-time automatic train control system is presented. The input, output and interlocking logic controller module emulators are designed and implemented in software for the prototype based on a simplex processing configuration and its associated safety assurance scheme. The safety assurance method used is based on information redundancy which detects errors arising from faults in the software and hardware of the control system. A prototyping environment is also developed as an experimental test bed for design and performance evaluation of the system. Noisy random, data reference, symbol creation and timing errors were injected to the system to evaluate its performance. For the different classes of errors, the prototype control system provided safe decision to the railway plant. The results obtained indicate that the use of a simplex coded processor for the prototype control system was indeed reasonable to enforce safety. It was difficult to properly gauge the performance of the architecture with the current implementation, since it was implemented in software to provide a proof-of-concept to the adopted architecture. However, it serves as a solid foundation from which to develop future prototype designs. The prototype design represents an initial version of an architecture that is evolving from the wayside application to more advanced systems. Several design iterations are required to support advanced system functionality.

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