Reliability Assessment and Enhancement of Wolkite City Distribution Substation

Abstract

Reliability analysis is a main aspect of power system planning, design, and operation. In a country like Ethiopia, which is growing fast, ensuring power system reliability should be given better attention since energy is the main engine for any form of development. Unreliable power distribution reduces user power consumption, affects daily activity, and drags modern lifestyles. It impacts societal development and individuals’ income. Reliability has been a major challenge in Wolkite city. The existing distribution network of Wolkite city has encountered frequent power interruptions. The interruptions are caused mainly by short circuits (SC) and earth fault (EF). In Wolkite, customers have faced frequent interruptions and utility has taken a long time to clear the faults. Hence, we have to solve these problems. Thus, the objective of this study is to assess the reliability of the current distribution system and suggest solutions for reliability improvement. Wolkite substation of South Western district, which has a high rate of interruption, is selected as a case study area. Wolkite substation’s reliability is assessed based on the data collected about the overall nature of the existing Wolkite city distribution system for three years period of substation monthly fault summary report. To limit the scope of the study, Wolkite Line 1 15 kV is chosen for reliability improvement measures. Wolkite Line 1 15 kV has a System Average Interruption Duration Index (SAIDI) of 144.0286 hours/customer/year and System Average Interruption Frequency Index (SAIFI) of 425.6461 interruption/customer/year. The reliability index values of Wolkite Line 1 15 kV indicate that the system is not reliable based on the standard of the Ethiopian Electric Authority (EEA) which set System Average Interruption Frequency Index (SAIFI) = 20 interruption/customer/year and System Average Interruption Duration Index (SAIDI) = 25 hours/customer/year. Wolkite city distribution network reconfiguration capacity is enhanced by designing lateral using insertion of auto-reclose and switching technique that can supply the feeder during contingencies. It’s simulated in Electrical Transient and Analysis Program Software (ETAPS 16.0.0). The system reliability improvement by each new device is also calculated. Power restoration is boosted by integrating these devices. On average, the System Average Interruption Duration Index (SAIDI) of 11.459 hours/customer/year, System Average Interruption Frequency Index (SAIFI) of 49.94 interruption/customer/year, Expected Energy Not Supplied (EENS) of 92.4%, and Average System Availability Index (ASAI) of 99.87% have been achieved for network reconfiguration at various fault points.