Harmonic Analysis in 25kV AC Railway Electrification system: The case of the proposed Ethiopian Railway System

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Date

2014-08-05

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AAU

Abstract

Electrical locomotives generate harmonic currents in railway power-supply system. Which in turn produce continuous distortion of current and voltage waveform in the supply network. This distortion gives adverse effect in traction power-supply system such as overheating, vibration and torque reduction of rotating machines, additional losses of lines and transformers, interference with communication systems, malfunctions of protection relays, measuring instrument error, etc. Therefore, the distortion in voltage and current waveform at various points in the traction system should be quantified and analyzed according to international standards such as IEEE 519-1999. This thesis focuses on studying voltage and current distortion in the supply system due to harmonics injected by locomotive with diode rectifier. The system considered under study for harmonics analysis is a proposed Ethiopian single-phase 25KV AC electrification system. Major components of the electric traction system are modeled for harmonic study using MATLAB/SIMPOWER system. Added to this, mathematical model of supply network to quantify voltage distortion at different bus analytically is developed. The systems without harmonic filter have been simulated to investigate the harmonic levels for different operating conditions. Accordingly, the simulation result at PCC for train at full load reveals that a THD of 11.26% for voltage and a THD of 37.15% for current in worst scenario. This is large as compere to the limit set by IEEE 519-1999.Therefore, a passive harmonic LC filter is designed to filter out the noticeable harmonics in the system. As the result, it was found that THD of 3.13% for voltage and THD of 3.15% for current waveform, which are below IEEE 519 standard, limits. This shows power quality and EMC improvement of the traction power supply system.

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Keywords

Electric Traction System, Power Quality, modeling, harmonic distortion, harmonic mitigation, passive filter

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