An Investigation of Power System Reliability Problem in Distribution Network (The Case of Bale Robe Town Distribution Sub Station)

Abstract

A power system is a system which requires high reliability and power quality due to high system infrastructure investment and failure cost. Even though the reliable and quality electric power supply is essential to modern society, the extensive use of electricity is led to a high sensitivity to power failures. More than 85% of all customer interruptions occur due to failures in the distribution system. Based on the results of this thesis, the reliability of the Bale Robe town power distribution system does not meet the requirements set by the Ethiopian Electric Agency (EEA). As per the thesis result analysis, the average frequency of interruptions per customer per year (int/cust/yr.) of Bale Robe town at the current feeders for Goba, Agerfa, Sinana, Madda Walabu University (MWU) and Gasera is found to be 259 int/cust/yr., 253 int/cust/yr., 217 int/cust/yr., 3 int/cust/yr. and 557 int/cust/yr. respectively. In connection, the average duration of interruptions (hr/cust/yr) of Goba, Agerfa, Sinana, MWU and Gasera feeders were found to be 175.56 hr./cust/yr., 209.92 hr./cust/yr., 230.90 hr./cust/yr., 1.1 hr./cust/yr. and 1011.8 hr./cust/yr. respectively. In this regard, it can be seen that a Bale Robe town distribution system reliability violates the requirements set by EEA in which System Average Interruption Frequency Index (SAIFI) is supposed to be below 20 and System Average Interruption Duration Index (SAIDI) is below 25 hr./cust/yr. This interruption indexes are also validated against other countries requirements. In addition, the thesis models the power distribution system network under the case study and carries out its analysis with brief discussions. Furthermore, the reliability indices improvement techniques reliability for the proper protection coordination was recommended. Mainly, the distribution system network planning and its design are done in the thesis work in order to minimize and improve the indices so that the effect on customers connected to the feeders can be minimized. Finally, by implementing the developed model using ETAP software, the overall reliability of the first three feeders of the Goba, Agerfa and Sinana power distributions were improved by 99.5%, 71.75% and 47.4% for SAIFI, SAIDI and ENS respectively.