Power quality study and mitigation techniques: case study on Addis Centre distribution substation

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