Abstract:
The power system is a network made up of a generation, transmission and distribution system. The
distribution system reliability for electricity is one of the most criteria for determining how
effectively the power system can reliably distribute electricity to the load. Customers must receive
energy from distribution feeders consistently because the reliability of the electric power
distribution system is a primary concern for any electric power utility provider. Power utility
companies are implementing numerous techniques to deliver reliable power. This thesis evaluates
the Lefessa 15 kV distribution feeder, one of the feeders that distributes electric power to Jigjiga
City, for its reliability as a distribution feeder of electric power. Power interruption data on daily
basis for a period of two years on the feeder was collected and analyzed for the main causes of
interruptions wind, open section, tree contact, line loaded, maintenance and operational practices.
Based on the data collected, the exiting distribution system reliability indices System Average
Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI),
Average Service Availability Index (ASAI), Average Service unavailability Index (ASUI),
Expected energy not supplied (EENS), and Average energy not supplied (AENS) of the feeder
were calculated using analytical method and simulation. The obtained results are 365.5 f/customer.
yr, 548 hr/ customer. yr, 0.94 pu, 0.06 pu, 2,663 MW hr / yr, 25.362 MW hr / customer. yr and,
4,707,901.702 ETB per year loss due to power interruption respectively. The oneline diagram of
Lefessa feeder-15kV existing and future distribution systems was modeled without and with
reclosers, and solar PV distributed generations using ETAP 19.0.1 software and simulated
differently in five cases. The results showed that, the reliability indices of existing system are
beyond the Ethiopian standards and among all the cases of reliability improvement, the values of
reliability indices were significantly enhanced in case 5 (three reclosers and solar distribution
generator). SAIFI was reduced to 96.0840 f/customer interruptions per customer per year, SAIDI
was reduced to 144.9994 hr/ customer. yr, ASAI increased to 0.9834 pu, ASUI decrease to 0.01655
pu, EENS decrease to 721.670 MW hr / yr, and finally AENS decrease to 6.8730 MW hr /
customer. yr. In case 5 the utility can save revenue of 4,543,876.146 ETB/year. The installation of
reclosers in distribution lines and integration of solar PV distributed generations is proposed for
reliability improvement of the existing distribution system.