Abstract:
Distribution systems deliver power from bulk power systems to customers. A stable and reliable
electric power supply system serve customer loads without interruptions. Electric power system
interruption in Addis Center (ADC) distribution substation is becoming a day to day
phenomenon, even there are time that electric power interruption occurs several times a day at
ADC distribution substation systems.
Currently power quality problem is an issue to the end user. As a result, many of the residential,
commercial and industries in our country faced with the problem of power quality, having
various causes. In this thesis the study of power quality problems of ADC distribution substation
and its mitigation techniques will be study. The study focuses on evaluating and identifying the
major power quality problems of the ADC distribution substation as per IEEE standards.
The data required for the study is collected from the ADC using model–8335 Power Quality
Analyzer and from recorded data. Based on the data have been recorded, oscillatory transient that
reaches two times as much the standard voltage, voltage sags which is less than 90% of the RMS
voltage, sustained power interruptions for 4-5 hrs. Per week, voltage unbalance of 2.4% and
current distortions of (THDI
) value that reach 25.10%.
The collected data have been analyzed and simulations are done using MATLAB/SIMULINK
model to show the effectiveness of mitigation techniques. In this thesis pre-insertion resistor and
inductor are used to mitigate the problem of oscillatory transient and the result indicates that the
transient voltage reduced from 25kV to 15kV. For the problem of voltage sag, dynamic voltage
restorer is as a solution and the results shows that the device restores the voltage for the three
phases from 13.02kV, 13.025kV, and 13.026 kV, respectively to 15kV. Third order high-pass
filters that are 5th and 7th harmonic filters are designed and simulated for the mitigation of
harmonic distortion and the filters are filtered out the harmonics and reduces the THDI value
from 25.10% to 3.05%. D-STATCOM system is also designed and simulated as a solution to
harmonic distortion from 33.93 to 3.93 and for the problem of voltage unbalance redistribution
of single phase loads equally among the three phases is taken as a mitigation technique
