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