YISHAK KIFLE2026-03-092016-04-27https://etd.hu.edu.et/handle/123456789/1182Electricity is produced and delivered to customers through generation, transmission and distribution systems. A stable and reliable electric power supply system serve customer loads without interruptions. Distribution systems deliver power from bulk power systems to customers. Distribution reliability primarily relates to equipment outages and customer interruptions. This thesis work attempts to thoroughly identify causes for power interruptions and customer dissatisfaction and discusses the design, reliability and operation and maintenance of Hawassa feeder 10 distribution networks. With recent advances in technology, utilities expect to see increasing amounts of distributed generation (DG) on the distribution systems. Reliability worth is very important in power system planning and operation. Having a DG ensures reliability improvement and may be used to increase the reliability worth. This research presents the study of a radial distribution system and the impact of placing renewable energy DG (PV, Wind) and battery energy storage in order to increase the reliability worth. The reliability improvement is measured by different reliability indices that include SAIDI, CAIDI, EENS and ASAI. The analyzed and calculated distribution reliability indices values have been compared with standard benchmark values and comparison clearly indicates that Hawassa feeder 10 distribution systems is extremely unreliable. The values for SAIDI, SAIFI, CAIDI and ASAI are 240 minutes/year, 1.5 interruptions/customer, 123 minutes/year and 99.91% respectively in a USA standard, whereas the corresponding values for the existing distribution system of Hawassa feeder 10 are 5129.002 minutes/year, 47.5205 interruptions/customer, 107.94 minutes/year and 99.02% respectively. also unavailability of energy per year is 93.706mwh. The thesis also evaluates reliability of distribution networks, including islanded micro grid cases, is presented. The network includes two types of distributed energy resources solar photovoltaic (PV), wind turbine (WT) and energy storage as back up. These distributed generators contribute to supply part of the load during grid-connected mode, but supply the high densely loaded area Arbegona load during islanded micro grid operation. The studies performed are supported with the Power Management System Software ETAP and MATLAB CODED for power output of renewable energy source.enThesis