DISTRIBUTION SYSTEM RELIABILITY ASSESSMENT AND ENHANCEMENT BY USING TIE SWITCHES AND SECTIONALIZER’S (CASE STUDY: BULE HORA DISTRIBUTION SYSTEM)

Abstract

The majority of outage events experienced by customers are due to electrical distribution failures. Increasing distribution network reliability is a necessity in order to reduce interruption events Unreliable electric power distribution affects daily activity and drags the modern lifestyle. Basically, Power Distribution Reliability has been a major challenge in Bule hora city. The interruptions are caused mainly by the short circuit (SC) and earth fault (EF). Bule hora substation’s System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI) are 341.46 interruptions per customer per year and 666.82 hours per customer per year, respectively. Bule hora substation is not reliable by the standard of Ethiopian Electric Agency (EEA) which has set SAIFI as equal to 20 interruptions per customer per year and SAIDI which is around 25 hours per customer per year. 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 Bule hora city feeder of the substation has been chosen for reliability enhancement measures. The historical outage interruption data of years 2009-2011 E.C has been used as a base year. The study has evaluated four different mitigation cases to improve the system reliability. From the mitigation cases 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 16.0) software. The result of this thesis work reveals that the reliability of the system has been improved significantly by assessing reliability enhancement solutions that are justified economically and technically. Hence, the overall reliability of Bule hora city feeder indices SAIFI by 83.23%, SAIDI by 89.48% and EENS by 97.51%, have been improved as compared with the existing system for the simulated best option. The economic analysis shows that the selected solution results in a cost saving of 2,105,530.3 ETB per year from the unsold energy of one feeder only with 1.48 payback period investment. Satisfaction of the society has been considered as a priceless benefit as well