Hybrid Active Power Filter Technique to Enhance Power Quality of Electric Railway Traction Substation (Case Study: Minilik Square Traction Substation NS27)
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Date
2020-11
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Addis Ababa University
Abstract
Addis Ababa Light Rail Transit (AALRT) is an electrified railway traction system with large
amount of harmonic currents being generated due to the nonlinear characteristics of rectifiers and
inverters devices and inject the harmonics back into the grid. This has caused serious impact on
the power supply network and resulted in power quality problems within the traction substation
that has led to multifunction of some system components. For the overall quality of railway
service, there should be reliable, efficient and safe power distribution systems by improving the
power quality. The power quality enhancement has been proposed by using hybrid active power
filter harmonic current compensation technique. This study presents theoretical and practical
aspects in improving the power quality of Minilik Square NS27 railway traction substation
network by reducing 11th and 13th harmonic currents using hybrid active power filter (HAPF).
Simulation studies of the Minilik Square NS27 railway traction substation network is carried out
using MATLAB Simulink in a discrete mode, variable step size with ode45 (Dormand-Prince)
solver.
The simulation results show that 11th order current harmonics is reduced from 26.99% to
3.75% while 13th order current harmonics is reduced from 11.05% to 4.38% at the point of
common coupling (PCC). Consequently, the total harmonic distortion (THD) of currents at PCC
is reduced from 88.19% to 80.55%. It is further noted that at primary side of the transformer 11th
order current harmonics is reduced from 17.99% to 1.55% while 13th order current harmonics is
reduced from 13.43% to 0.89%. Thus, the overall total harmonic distortion (THD) of currents is
reduced from 26.46% to 6.88% on the primary side of the transformer.
Furthermore, it is observed that the distortion power factor is also improved from 0.955 to
0.995 due to the reduction of 11th and 13th order harmonic currents. Therefore, the effective value
of fundamental current has been improved due to the reduction of 11th and 13th order harmonic
currents and consequently the corresponding active power in the traction network is also
improved.
Thus, the simulation results demonstrate the effectiveness of the proposed HAPF technique
for selective harmonic currents reduction and thereby power quality enhancement of Minilik
Square NS27 railway traction substation network of AALRT.
Description
Keywords
Hybrid active power filter, harmonic currents, electric traction, twelve pulse rectifier, six pulse rectifier