Browsing by Author "Getahun, Mekuria (PhD)"

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    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.
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    Electromagnetic Radiation from Cable Harnesses on board Addis Ababa LRT
    (Addis Ababa University, 2016-03) Zenawi, Gebremichael; Getahun, Mekuria (PhD)
    Electromagnetic Compatibility (EMC) is becoming the main concern of many industries. One aspect of EMC is limited Electromagnetic (EM) radiation from the source. In order for a given device, equipment or system not to cause Electromagnetic Interference (EMI), its radiation level must not exceed some regulatory limits accepted worldwide. This thesis researches electromagnetic radiation from cable harnesses on board Light Rail Transit (LRT) trams. Main target of the research is to compute high-frequency (HF) and low-frequency (LF) Electromagnetic Field (EMF) inside and outside the LRT tramcar and assess them against known standard limits. HF and LF fields have different nature in generating interference to a system. As a result, separate consideration of these fields was important. Radiation level mainly depends on physical and electrical parameters of a given structure. To adhere to this basic principle, the study was conducted by collecting data about electrical value and geometrical positioning of cables on board Addis Ababa (AA) LRT trams. After collecting all relevant data, equivalent three-dimensional (3D) model was developed for electromagnetic simulation with the help of software. CST Studio Suite is mainly used for numerical computation of electric and magnetic fields in both LF and HF ranges. The results obtained from software simulations were compared with standard regulatory limits. The limits are taken from International Commission on Non-Ionizing Radiation Protection (ICNIRP) for static magnetic fields, and Institute of Electrical and Electronics Engineers (IEEE) for static electric fields. IEEE sets 5 kV/m as exposure limit for general public and 20 kV/m for controlled environment. The ICNIRP limits on static magnetic fields have many varieties depending on the exposure characteristic (ceiling value, continuous exposure, and medical device). For Radio Frequency Interference (RFI), regulatory limits of Federal Communications Commission (FCC) are adopted. Field distributions inside and near the tramcar vary spatially. In this thesis, more focus was given to internal floor of the tramcar and outside levels of the track. On smaller portion of the floor, near the cab side, static magnetic field distribution exceeding the limit for medical devices (0.5 mT) was observed; it reached 12 mT. However, the place with such phenomenon was very limited, and the other exposure characteristics (ceiling value and continuous exposure) were never exceeded around the floor. Static electric field distribution around the floor of the tramcar was far below the corresponding regulatory limit, too. 5 kV/m was taken as assessment limit, and all field values were below it. Coming to RF EM radiation, the limits varied over subrange of the frequencies. EM simulation of a structural model was conducted, and the radiation levels were below the limits in both vertical and horizontal polarization.
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    Power Line Communication Based Real Time Train Tracking System for Addis Ababa Light Rail Transit
    (Addis Ababa University, 2015-04) Solomon, Firew; Getahun, Mekuria (PhD)
    In railway traffics the low friction between wheel and rail causes long braking distances, normally much longer than the driver‟s sight distance, i.e. if the driver starts the braking when he discovers a problem on the track it is too late to stop the train. The conclusion will be that the railway traffic can not only rely on the driver for the traffic safety, there must also be a signaling or even an automatic surveyor system, which can supervise the positions of different trains along the track and organize the traffic. Having the traffics information on the track helps to avoid situations of conflict and those that might be potentially unsafe. There are different train detection systems in service worldwide. Track circuit, Axle counter and GPS are the most prevailed approaches. The first two types provide the information that whether the section is occupied or not. They don‟t provide the information “where exactly the train is?” Beside Axle counter has huge installation cost and maintenance cost. Regarding GPS, since it is using satellites to determine the location of the train and the accuracy is dependent on the no of satellites tracked, the error spread is variable. In addition to this it doesn‟t operate in tunnels like we have for A.A LRT (Addis Ababa Light Rail Transit) track, from St. George church to Atikilit tera. Not only these but also since the satellites are administered by third party, the operation is totally out of the control of the railway company. With this research, Power line based real-time train tracking system is proposed for A.A LRT. It has an advantage of providing continuous distance information, low capital cost, low maintenance cost and under a full control of Railway Company. Since it uses the power line communication, the channel is secured since the train is on the track and the overhead contact system exists. Beside of the train detection software is developed to display visually the train movement according to the distance information obtained. The system can also extend to broadcasting the information obtained via a possible communication means (GSM-R) to control center or other trains on the track. This increases the movement confidence of the trains since the driver operates with the knowledge of distance, direction and speed of trains at the back and front that helps a lot for efficient use of the track.