For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer (AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profile for both power supply configuration on the basis of BS EN 50163:2004 international standard.

Clean energy, system planning, Traction power supply, Voltage profile, Autotransformer.

Introduction

Nowadays, the development of railway infrastructure shows a rebirth in many countries including Ethiopia after a long period of recession. This revival of the railway is mainly due to the new trend of clean energy production and consumption. As a consequence, the expansion of a traction power supply system is growing massively – without it, only the weaker and less energy efficient steam and diesel locomotives could be used [1]. An accurate power supply system analysis offers important information for planning, operation and design. Almost in all traction power supply system analysis or study, the widely adopted trend and cost-effective mechanism is simulation. In [2], widespread applications which deal with many railway power feeding system simulators were discussed.

In this study, a different approach, using MATLAB, is developed. Several alternative analysis methods are used for designing the electrical scheme of the power supply system for electrified railways [3]. Selection of an appropriate supply system is always very dependent on the railway system objectives. Many studies show that direct linking of the feeding transformer to the overhead catenary system and the rails at each substation is relatively simple and economical. Nevertheless, there are some drawbacks to this arrangement such as high impedance of feeders with high losses, high rail-to-earth voltage and the interference to neighboring communication circuits [2] [4]. Moreover, the autotransformer feeding configuration has many advantages and solves many disadvantages of the direct feeding system. The addition of autotransformer at every 8-15 km intervals improves the voltage performance along the traction line and increases the substation coverage up to 50-100 km [4]. The electromagnetic interference in an AT system is normally much lower compared with direct feeding (1 × 25 kV) system [5]. In addition, for high power locomotives and high-speed trains, direct feeding system is out of choice because most countries are replacing the existing (1 × 25 kV) system with autotransformer fed supply system (2 × 25 kV) [6]. In this paper, analysis, modeling and simulation of autotransformer traction power supply system are presented and a comparative analysis with a direct power supply system in terms of voltage profile along the traction network is performed.

Longitudinal force acting on the train

Modeling of traction power supply system

Simulation results and discussion

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