Power Distribution System Failure and Vulnerability Analysis in Ethiopia Case Study : Kotebe Distribution System

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa University


Distribution systems are usually the main areas where power outages occur. Electric power interruptions in the capital city of Ethiopia,i.e. Addis Ababa, are usual problems. Even there are situations that electric power interruption occurs several times a day. This thesis tries to identify the causes of power interruptions for the Kotebe distribution system and the vulnerability of the existing components. It is a componentbased failure analysis on a selected feeder of the distribution system. It is selected considering the total annual frequency of interruptions for each feeder of the distribution system. Feeder 6 of the Kotebe substation is the most frequently interrupted line. The existing conditions of the components on the feeder are inspected. Distribution poles, conductors, insulators, transformers, protection and other auxiliary devices are the inspected components. The probable effect of the most frequent causes of interruptions identified in the distribution on the poor distribution components is studied. Interruption during operation and maintenance is the common cause identified in the distribution. But this is through the order of the maintenance workers of the utility. Sudden faults are usually due to weather influences. It accounts for 48.66% of the total known faults excluding interruption due to operation. The vulnerability to failure of the existing distribution poles is identified through modelling the distribution poles, gravitational force of tilted poles and weather influence by COMSOL software. Decay depth of wooden poles considering the selected area weather condition is studied using TimberLife software, and its effect for failure is simulated using COMSOL. Poles will deflect upto 3.050 and 1.7490 with and without considering decay depth at the worst condition of a certain weather influence, respectively. Poles resilience condition is also identified by analyzing deflection and stress on their surface. Many of the existing distribution transformers are working overloaded. The loss of life of distribution transformers and their vulnerability is studied using the IEEE standard (C57.19-1995) guidelines. The hot spot temperature, ageing acceleration factor, and percent loss of life of each transformer are calculated. 83 of 157 transformers are expected to sustain below the IEEE standard expected life (i.e., 20.55 years). The effect of lightning considering soil resistivity of the area is also studied by modelling the feeder 6 of Kotebe distribution system using Matlab/Simulink. Metal Oxide Varistor(MOV) Surge arresters with grounding resistance above 25Ω would have higher surge magnitude that could damage the transformers and surge arresters.



Distribution components, Distribution system, Failure analysis, Loss of life of transformer, Resilience, Soil resistivity, Vulnerability