Study of Reliability of Power Distribution System and Improvement Options

Abstract

Unreliable electric power distribution reduces power consumption, affects daily activity and drags the modern lifestyle. It impacts societal development and individuals’ income. Basically, a power distribution reliability has been a major challenge in Awash7 kilo city. The existing substation has encountered frequent power interruptions problems. The interruptions are caused mainly by the short circuit (SC) and earth fault (EF). There are also planned outages for operation and maintenance purpose. The substation’s System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI) are 414.0 interruptions per customer per year and 319.67 hours per customer per year, respectively. The substation is not reliable by the standard of Ethiopian Electric Agency (EEA) which set SAIFI is equal to 20 interruptions per customer per year and SAIDI which is around 25 hours per customer per year. This reliability gap calls for searching for effective methods for improving the reliability of the distribution system. Thus, the objective of the study is to assess the reliability of the existing distribution system and suggest solutions for reliability improvement in heuristic techniques. To limit the scope of the study, 15 kV Awash7 kilo city feeder of the substation has chosen for reliability improvement measures and also predict the reliability analysis for the future. The historical outage interruption data of years 2015/16-2017/18 G.C has been used as a base year. The study has evaluated four different mitigation scenarios have been assessed using the heuristic method to improve the system reliability. From the mitigation scenarios with the lowest SAIDI, SAIFI and Expected Energy Not Supplied (EENS) at a reasonable cost has been selected. The simulation results have been done with the help of Electrical Transient Analysis Program (ETAP 12.6) software. The result of this thesis work reveals that the reliability of the system has been improved significantly by implementing reliability improvement solutions that are justified economically. The researcher identifies scenario four as the optimum one as comparing the power reliability improvement and the cost. Hence, the overall reliability of Awash7 kilo city feeder has been improved significantly by 86%, 85.4% and 92.94% for SAIFI, SAIDI, and EENS respectively as compared with the existing system. The economic analysis shows that the selected solution results in a cost saving of 556,615.9686 ETB per year from the unsold energy of one feeder only with three years payback period investment. Satisfaction of the society has been considered as a priceless benefit as well.