Power Engineering

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Browsing Power Engineering by Subject "AC Electrified railway"

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    Modeling and Simulation of Traction Power Supply System In the case of “Sebeta Substation”
    (AAU, 2017-06) Molalegn, Sisay; Kiros, Tesfaye (Mr.)
    Traction power supply system is an electrical power network used to receive power from three phase power transmission system and supply power for the train driving on the single-phase AC power supply system. It is composed of the traction substation, traction network, partition substation, switch substation and other components. In a railway traction power supply system, voltage variations, dynamic load characteristics and other types of supply changes, can influence the performance and movements of trains, the load in the electrical circuit are the trains/locomotives which are moving and demanding different levels of power according to their dynamic characteristics, operational mode and their speeds. Due to load variations, the 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. Power transfer problems have occurred frequently within large variations of loads. These issues are important in traction power supply system to ensure normal operation of the electric locomotives. Therefore, this thesis models and analyses the various force acting on the train using Davis equation for the train resistance regression coefficient for both freight and passenger locomotives. To minimize long calculation of the gradient force determination, this thesis considers a technique called equivalent gradient approximation. Sebeta to Indode traction power supply system and its general parameter such as catenary or the feeding line model, substation model, transmission line model and the load model of the system is modeled in this thesis,  Overall specific energy consumption, total running time and power consumption of passenger and freight train from Sebeta to Indode substation is determined.  The power flow of the modeled system investigated.  Substation voltage drop, catenary voltage drop, power consumption and power loss in the Sebeta substation and also their fault location is investigated. Generally, it is limited to modeling and simulation of Sebeta to Indode traction Substation. The modeling and simulation of AC traction power supply system, power flow and short circuit fault analysis from Sebeta to Indode substation is done using DIgSILENT/PowerFactory software. This thesis also verify the installed transformer capacity of 16 MVA at Sebeta substation is capable with the calculated capacity of 7.098MVA. Two cases are considered in this thesis work (for power flow solution) case one considers only two passenger trains occupied in the section with calculated power consumption of 3.22 MW at load side, from the load flow result the voltage drop is within the standard. In case two, one passenger train and one freight train are considered, load flow result shows that the voltage drop is between the standard at normal condition (at no fault condition). When fault occurred at Sebeta substation the train get power from Lebu section post through interrupter switch/load breaker. In this case the length becomes increased to supply power to the load, then the voltage drop becomes high, to minimize this voltage drop a compensator (shunt capacitor) at load voltage side with a 3.41MVAr is designed. The voltage drop for buses 8, 9 and 10 is improved from 2.63, 2.61 and 2.69kV to 2.1, 2.07 and 2.15kV respectively. After compensation the voltage at buses 6, 8, 9, 10 and 11 are improved from 0.917, 0.904, 0.905, 0.902 and 0.969 p.u to 0.936, 0.924, 0.925, 0.922 and 0.989 p.u, respectively. Also the total power loss for the modeled system is decreased from 0.6MW to 0.56 MW. Therefore, based on the result of this thesis work, it is recommended that the Ethiopian Railway Corporation has to consider compensator at Sebeta substation to enhance overall system power transfer capability, improving the network voltage and reduce voltage drop across the line in the system. Furthermore, a single line to ground and short circuit fault analysis for the modeled system is investigated. From the transient simulation result at bus 5, the maximum peak short circuit current for single line to ground fault is 2.747kA and for two phase short circuit fault current is 6.973kA. Therefore, this thesis deduce that the worst type of fault is the short circuit fault in the overhead contact system of the trains.