The utility company, EEP and EEU mission is to transmit, distribute and supply electricity inrnreliable and efficient manner. The problem facing electric power utilities is that the powerrndemand is increasingly but, power problem in distribution system occurs several times, due tornover loading, short circuit, improper allocated distribution transformers, poor maintenance,rnlimited protective devices. Therefore the substation need for more extensive justifications of thernsystem facilities, and improvements in production and use of electricity.rnThis thesis presents reliability assessment of the 132/15 kV transformer through five 15 kVrnoutgoing feeders. The 15 kV network is operated as radials and the total capacity of 132/15 kVrntransformer is 31.5 MVA supplying to five 15 kV outgoing feeders and the total connected loadrnto the 15 kV feeders between 14.5 and 19.5 MW. The distribution system consists of 45, 33, 15rnand 0.4 kV systems but the case study considered 15 and 0.4 kV outgoing feeders of therndistribution system with distributed generation providing support to the system adequacy andrnsecurity for reliability improvement. The distributed generation (DG) units considered for thisrnassessment are any possible DG units installed at optimal place and size at their site to therncustomers satisfactions. DG systems have received more attention recently due to their highrnoverall efficiency and increase in reliability. A composite system adequacy assessment, whichrnincludes the two main components of the power grid viz., generation and distribution, is donernusing Monte Carlo simulation. The analytical approach is system reliability using directrnnumerical solutions. The basic data and the topology used in the analysis are based on thernInstitution of Electrical and Electronics Engineers - Reliability Test System (IEEE-RTS) andrnIEEE-Reliability Bus bar Test System (IEEE-RBTS). Integrating DG units in 0.4 kV bus ofrndistribution system improve the overall system reliability indices SAIDI from 206.56 to 2.532,rnSAIFI form 188.8 to 1.9575, ASAI from 97.64% to 99.971%, ASUI from 2.36% to 0.0289%rnand also EENS, and EIC of the overall distribution system improved by 97.3%. Therefore a basernCotebe distribution system reliability index is very poor according to the reliability standards.rnKEY WORDS: Adequacy, DIgSILENT, ETAP, Distribution system, Expected Energy notrnsupplied, Expected Interruption cost, Failure rate, Forced outage, Indices, Interruptions,rnReliability, Security.rnM.Sc. Thesis by Amache Jara in Electrical Power Engineering, SECE AAiT Page iv